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Search Results (525)

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23 pages, 3989 KiB  
Review
Progress and Trends in Research on Soil Nitrogen Leaching: A Bibliometric Analysis from 2003 to 2023
by Getong Liu, Jiajun Sun, Chenfeng Liu, Huading Shi, Yang Fei, Chen Wang, Guilong Zhang and Hongjie Wang
Sustainability 2025, 17(1), 339; https://doi.org/10.3390/su17010339 - 5 Jan 2025
Viewed by 369
Abstract
An in-depth discussion on the research progress and trends in soil nitrogen leaching is essential for the development of agricultural sustainability. However, not enough attention has been paid to the progress and future trends of soil nitrogen leaching research. Using software such as [...] Read more.
An in-depth discussion on the research progress and trends in soil nitrogen leaching is essential for the development of agricultural sustainability. However, not enough attention has been paid to the progress and future trends of soil nitrogen leaching research. Using software such as VOSviewer and CiteSpace, bibliometric analyses of a total of 2767 documents in the Web of Science Core Collection were conducted; the documents considered were published over the last 20 years (2003–2023). The results are as follows: (1) The research output on soil nitrogen leaching has been increasing steadily, showing a single-discipline dominance in agronomy, but a trend of multidisciplinary cross-research has gradually begun to emerge in recent years. (2) There has been close cooperation between authors, countries, and institutions; the main cooperation includes research on modelling and management, and research related to nitrogen management practices and soil types has a high international profile. (3) The research components at the heart of soil nitrogen leaching are nitrogen cycling in soils, soil properties, water environments and crops, greenhouse gas formation and emissions, and agronomic management practices and the research hotspot has gradually changed to applied research. (4) Increasing the considerations of management measures, deepening the related research on soil microorganisms, and constructing a complete evaluation system constitute the main future research directions. This study can provide valuable references for the sustainable development of agriculture. Full article
(This article belongs to the Section Sustainable Agriculture)
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<p>Bibliometric search, screening, and analysis processes.</p>
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<p>Annual publication volume in the field of soil nitrogen leaching.</p>
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<p>Trends in publications in different research areas.</p>
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<p>Annual publishing trends of top 5 countries.</p>
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<p>Cooperation between different countries in the field of soil nitrogen leaching. Each node represents a country, and the size of the node is proportional to the amount of publishing carried out by the country. The color of the nodes represents the intensity of cooperation in the country, with red representing a high intensity of cooperation and yellow representing a low intensity of cooperation. The lines between the nodes indicate cooperation between countries, with thicker lines and darker colors indicating closer cooperation.</p>
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<p>Collaborative clustering of core authors in soil nitrogen leaching studies. Each node represents an author; the size of the node is proportional to the author’s publication volume; the closely connected nodes are in the same circle, indicating the same cluster.</p>
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<p>Cooperation between different institutions in the field of soil nitrogen leaching. Each node represents an institution, and the size of the node is proportional to the amount of publishing carried out by the institution. The color of the nodes represents the intensity of cooperation in the institution, with red representing a high intensity of cooperation and yellow representing a low intensity of cooperation. The lines between the nodes indicate cooperation between institutions, with thicker lines and darker colors indicating closer cooperation.</p>
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<p>The map of the co-occurrence network of keywords; each node represents a keyword; the size of the node is proportional to the frequency of occurrence of the keyword; the closely connected nodes are in the same circle, indicating the same cluster.</p>
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<p>Soil leaching nitrogen keyword burst map, with light blue representing years in which the keyword did not appear, blue representing years in which the keyword began to appear, and red representing years in which the keyword burst.</p>
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21 pages, 19289 KiB  
Article
Soil–Plant Carbon Pool Variations Subjected to Agricultural Drainage in Xingkai Lake Wetlands
by Wei Wang, Lianxi Sheng, Xiaofei Yu, Jingyao Zhang, Pengcheng Su and Yuanchun Zou
Water 2025, 17(1), 125; https://doi.org/10.3390/w17010125 - 5 Jan 2025
Viewed by 322
Abstract
This study examines the responses of soil organic carbon (SOC) pools and their components to agricultural water drainage in paddy fields, with a focus on the wetland–paddy field ecotone of Xingkai Lake, a transboundary lake shared by China and Russia. Field investigations targeted [...] Read more.
This study examines the responses of soil organic carbon (SOC) pools and their components to agricultural water drainage in paddy fields, with a focus on the wetland–paddy field ecotone of Xingkai Lake, a transboundary lake shared by China and Russia. Field investigations targeted three representative wetland vegetation types: Glyceria spiculosa (G), Phragmites australis (P), and Typha orientalis (T), across drainage durations ranging from 0 to over 50 years. SOC fractions, including light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), dissolved organic carbon (DOC), and microbial biomass carbon (MBC), were systematically analyzed. The results revealed that SOC components in T and P wetlands steadily increased with drainage duration, whereas those in G wetlands exhibited a fluctuating pattern. SOC dynamics were primarily driven by LFOC, while MBC displayed species-specific variations. Correlation analyses and structural equation modeling (SEM) demonstrated that soil physicochemical properties, such as total nitrogen and moisture content, exerted a stronger influence on SOC fractions than microbial biomass. Overall, water drawdown significantly altered SOC dynamics, with distinct responses observed across vegetation types and wetland ages. This study provides critical data and theoretical insights for optimizing carbon sequestration and hydrological management in wetland–paddy field systems. Full article
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<p>(<b>a</b>) represents the sampling diagram; (<b>b</b>) represents the workflow diagram.</p>
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<p>Comparison of wetland water and farmland drainage sources. COD<sub>Mn</sub>′, BOD<sub>5</sub>′, Fe<sup>3</sup>⁺′, Fe<sup>2</sup>⁺′, TN′, and TP′ correspond to agricultural drainage water, whereas COD<sub>Mn</sub>, BOD<sub>5</sub>, Fe<sup>3</sup>⁺, Fe<sup>2</sup>⁺, TN, and TP refer to wetland surface water. The plots B, C, D, E, and F in the figure represent the wetland drainage sources and the farmland drainage sources discharging into these plots, respectively.</p>
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<p>Changes in plant biomass under different years of water withdrawal. (<b>a</b>) Soil associated with <span class="html-italic">Glyceria spiculose</span>; (<b>b</b>) soil associated with <span class="html-italic">Phragmites australis</span>; (<b>c</b>) soil associated with <span class="html-italic">Typha orientalis</span>.</p>
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<p>Changes in physical and chemical properties under different years of water withdrawal. (<b>a</b>) Soil associated with G; (<b>b</b>) soil associated with P; (<b>c</b>) soil associated with T; (<b>d</b>) the water content of the soil of G; (<b>e</b>) the water content of the soil of P; (<b>f</b>) the water content of the soil of T. TP represents the total amount of all phosphorus forms in the soil, including inorganic phosphorus and organic phosphorus, and serves as an important indicator of soil phosphorus reserves. AP, on the other hand, refers to the forms of phosphorus that plants can directly absorb and utilize, including water-soluble phosphorus and weakly adsorbed phosphorus.</p>
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<p>Changes in organic carbon composition under different years of water withdrawal. (<b>a</b>) Soil associated with G; (<b>b</b>) soil associated with P; (<b>c</b>) soil associated with T; (<b>d</b>) dissolved organic carbon in the soil of G; (<b>e</b>) dissolved organic carbon in the soil of P; (<b>f</b>) dissolved organic carbon in the soil of T.</p>
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<p>Changes in microbial biomass under different years of water withdrawal. (<b>a</b>) Soil associated with G; (<b>b</b>) soil associated with P; (<b>c</b>) soil associated with T.</p>
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<p>Changes in total soil iron and available iron under different years of water withdrawal. (<b>a</b>) Soil associated with G; (<b>b</b>) soil associated with P; (<b>c</b>) soil associated with T.</p>
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<p>The correlation coefficients among the parameters. Statistical significance is denoted as *** <span class="html-italic">p</span> &lt; 0.001, ** <span class="html-italic">p</span> &lt; 0.01, and * <span class="html-italic">p</span> &lt; 0.05. Red represents a positive correlation, and blue represents a negative correlation. The intensity of the color corresponds to the strength of the significance, with darker shades indicating stronger significance. (<b>a</b>) Soil associated with G; (<b>b</b>) soil associated with P; (<b>c</b>) soil associated with T.</p>
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<p>The correlation coefficients among the parameters. Statistical significance is denoted as *** <span class="html-italic">p</span> &lt; 0.001, ** <span class="html-italic">p</span> &lt; 0.01, and * <span class="html-italic">p</span> &lt; 0.05. Red represents a positive correlation, and blue represents a negative correlation. The intensity of the color corresponds to the strength of the significance, with darker shades indicating stronger significance. (<b>a</b>) Soil associated with G; (<b>b</b>) soil associated with P; (<b>c</b>) soil associated with T.</p>
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<p>The path coefficient and significance test results of the PLS-SEM. (<b>a</b>) The path coefficients and significance testing results of PLS-SEM with G; (<b>b</b>) the path coefficients and significance testing results of PLS-SEM with P; (<b>c</b>) the path coefficients and significance testing results of PLS-SEM with T. Pathway significance is indicated as *** <span class="html-italic">p</span> &lt; 0.001, ** <span class="html-italic">p</span> &lt; 0.01, and * <span class="html-italic">p</span> &lt; 0.05. Bold solid arrows denote significant correlations, whereas red dashed arrows represent non-significant correlations.</p>
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24 pages, 4223 KiB  
Article
Spatial Changes in Soil Nutrients in Tea Gardens from the Perspective of South-to-North Tea Migration: A Case Study of Shangluo City
by Ziqi Shang, Jichang Han, Yonghua Zhao, Ziru Niu and Tingyu Zhang
Land 2025, 14(1), 74; https://doi.org/10.3390/land14010074 - 2 Jan 2025
Viewed by 310
Abstract
[Objective] This study focused on the primary tea-producing regions of Shangluo City (ranging from 108°34′20″ E to 111°1′25″ E and 33°2′30″ N to 34°24′40″ N), which include Shangnan County, Zhen’an County, Zhashui County, Danfeng County, and Shanyang County. The aim was to explore [...] Read more.
[Objective] This study focused on the primary tea-producing regions of Shangluo City (ranging from 108°34′20″ E to 111°1′25″ E and 33°2′30″ N to 34°24′40″ N), which include Shangnan County, Zhen’an County, Zhashui County, Danfeng County, and Shanyang County. The aim was to explore the characteristics and influencing factors of soil nutrient content variation across different tea gardens in the area. The study involved an analysis of various soil nutrient indicators and an investigation of their correlations to assess the nutrient status of tea gardens in Shangluo City. [Method] A total of 228 soil samples from these tea gardens were quantitatively analyzed for pH, soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP), available potassium (AK), as well as clay, silt, and sand content. Additionally, the soil texture was qualitatively analyzed. Statistical methods including analysis of variance (ANOVA), correlation analysis, principal component analysis (PCA), and regression analysis were performed using SPSS software to examine the relationships between soil nutrients and texture in relation to altitude, latitude, and fertility status. [Results] The results indicated that the pH of tea garden soils in Shangluo City was relatively stable, ranging from 4.3 to 7.6, with the mean of 5.9 and a coefficient of variation of 11.0%. The soil organic matter (SOM) content varied from 7.491 to 81.783 g/kg, exhibiting a moderate variability with a coefficient of variation of 38.75%. The mean values for total nitrogen (TN), available nitrogen (AN), total phosphorus (TP), available phosphorus (AP), total potassium (TK), available potassium (AK), clay, silt, and sand were 1.53 g/kg, 213 mg/kg, 0.85 g/kg, 49.1 mg/kg, 5.5 g/kg, 110 mg/kg, 3.99, 44.89, and 51.11, respectively. AN and AP displayed higher coefficients of variation at 57% and 120.1%, respectively. Significant differences in pH, SOM, TN, TP, TK, silt, and sand were observed at varying elevations, while TN, TP, TK, clay, silt, and sand varied significantly across different latitudes. Principal component analysis (PCA) results revealed that altitude had four principal components with eigenvalues greater than 1, accounting for 71.366% of the total variance, whereas latitude exhibited five principal components with eigenvalues exceeding 1, explaining 76.304% of the total variance. Regression analysis indicated that altitude exerted a stronger influence on soil indicators, as demonstrated by a well-fitting model (Model 4), where the coefficients of principal components 1, 3, and 4 were positive, while that of principal component 2 was negative. In contrast, latitude influenced soil indicators most effectively in Model 3, where the coefficient of principal component 5 was positive, and the coefficients of principal components 1 and 4 were negative. [Conclusions] The variation in soil nutrients and pH in the tea gardens of Shangluo City is closely associated with altitude and latitude. Notably, there is no discernible trend of pH acidification. Therefore, tea garden management should prioritize the rational application of soil nutrients at varying altitudes and focus on enhancing soil texture at different latitudes to adapt to the diverse soil characteristics under these conditions, thereby promoting sustainable development in tea gardens. Full article
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<p>Overview of Shangluo City and distribution map of tea garden sampling points. (<b>a</b>) Location of the study area. (<b>b</b>) Kernel density map of sampling points in Shangluo City. (<b>c</b>) Altitude distribution map of tea garden sampling points in Shangluo City.</p>
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<p>Statistics of soil texture distribution at tea garden sampling points in Shangluo City.</p>
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<p>Statistics on the distribution of soil texture at different altitudes.</p>
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<p>Statistics on the distribution of soil texture in different latitudes.</p>
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<p>The correlation analysis chart between soil nutrients and soil texture. (<b>a</b>) The correlation between soil nutrients and soil texture with altitude. (<b>b</b>) The correlation between soil nutrients and soil texture with latitude.</p>
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<p>Correlation analysis between altitude and soil fertility factors.</p>
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<p>Correlation analysis between latitude and soil fertility factors.</p>
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<p>Principal component gravel map of altitude.</p>
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<p>Principal component gravel plot at latitude.</p>
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21 pages, 4044 KiB  
Article
The Effect of Soil Tillage Systems on the Soil Microbial and Enzymatic Properties Under Soybean (Glycine max L. Merrill) Cultivation—Implications for Sustainable Soil Management
by Jacek Długosz, Bożena Dębska and Anna Piotrowska-Długosz
Sustainability 2024, 16(24), 11140; https://doi.org/10.3390/su162411140 - 19 Dec 2024
Viewed by 479
Abstract
Reducing soil tillage with the application of catch-crop green mass as a mulch is a conservation practice that is used in agriculture to improve soil ecosystem functioning. Such a cultivation method enhances soil organic matter quantity and quality through the improvement of soil [...] Read more.
Reducing soil tillage with the application of catch-crop green mass as a mulch is a conservation practice that is used in agriculture to improve soil ecosystem functioning. Such a cultivation method enhances soil organic matter quantity and quality through the improvement of soil biological activity and nutrient availability, while reducing soil disturbance. Therefore, a three-year field experiment was conducted in the years 2017–2019 to evaluate the effect of three tillage methods (TMs) (conventional, CT; reduced, RT; and strip tillage, ST) on soil microbial and specific enzyme properties (microbial C and N content, the activity of dehydrogenases—DHA, the rate of fluorescein sodium salt hydrolysis—FDAH, CMC-cellulase—Cel and β-glucosidase—Glu) and certain basic soil properties. The study was performed in a field; it was a one-factor experiment that was carried out in a randomized block design. The soil samples were collected from the upper soil layer five times a year: in April (before the sowing of soybean), May, June, August and September (before soybean harvesting). The tillage methods or sampling dates used had no significant effect on the organic carbon and total nitrogen levels. Most of the C-related properties (the content of microbial biomass and the C-cycling enzymatic activity such as Cel and Glu) and microbial activity bioindicators (DHA activity, FDAH rate) revealed significant seasonal changes, whereby each variable was affected in a different order (e.g., the Cel activity was significantly higher in April and September than in other months—22%, while the DHA activity was significantly higher in June and August compared to other months—18%). RT significantly increased the enzymatic activity as compared to CT and ST, and the difference was between 8 and 33% (with a mean of 18%). The exception was the β-glucosidase activity as determined in 2019, which was significantly higher in the case of CT (1.02 mg pNP kg−1 h−1) and ST than in RT (0.705 mg pNP kg−1 h−1). However, the explanation for such phenomenon could not possibly be based on the available data. Our results suggested that the response of the enzyme activities toward the same factor may be due to the inherent variability in enzyme response associated with the spatial variability in soil properties as well as the properties of the enzyme itself and changes in the periodic occurrence of its substrates in the soil. Generally, the reduced tillage combined with plant residues return could be recommended for enhancing soil health and quality by improving its microbial and enzymatic features. The findings above suggest that a reduced tillage system is an important component of soil management in sustainable agriculture. Full article
(This article belongs to the Special Issue Sustainable Environmental Analysis of Soil and Water)
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<p>Climatograms presenting meteorological conditions in the study area: (<b>a</b>) 2017, (<b>b</b>) 2018 and (<b>c</b>) 2019. IV—April, V—May, VI—June, VII—July, VIII—August, IX—September, 1—the 1st decade, 2—the 2nd decade, 3—the 3rd decade.</p>
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<p>Block diagram of the soil properties determined in the laboratory. TOC—total organic carbon, DOC—dissolved organic carbon, Nt—total nitrogen, DNt—dissolved nitrogen, DHA—dehydrogenase, FDAH—rate of fluorescein sodium salt hydrolysis, Cel—CMC-cellulase, Glu—β-glucosidase.</p>
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<p>The content of microbial biomass carbon (MBC) (<b>a</b>,<b>b</b>) and nitrogen (MBN) (<b>c</b>,<b>d</b>) depending on the tillage system and sampling dates; mean values (±SE) (mg kg<sup>−1</sup>). CT—conventional tillage, RT—reduced tillage, ST—strip tillage. IV—April, V—May, VI—June, VIII—August, IX—September. Different capital letters indicate significant differences (<span class="html-italic">p</span> &lt; 0.05) between tillage systems within the same year. Different small letters indicate significant differences (<span class="html-italic">p</span> &lt; 0.05) between the sampling months within the same tillage system.</p>
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<p>Principal component analysis derived from the studied soil properties; (<b>a</b>) plot of the first two principal components (PC) for the assessed soil variables; TOC—total organic carbon, Nt—total nitrogen, DHA—dehydrogenase, FDAH—fluorescein sodium salt hydrolysis, Cel—cellulase, Glu—β-glucosidase, DOC—dissolved organic carbon, DNt—dissolved nitrogen, MBC—microbial biomass carbon, MBN—microbial biomass nitrogen, (<b>b</b>) principal component analysis of the properties determined in the individual study years (2017, 2018, 2019); CT—conventional tillage, RT—reduced tillage, ST—strip tillage.</p>
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22 pages, 2533 KiB  
Article
The Sources of Nutrients for the Growing Ear of Winter Wheat in the Critical Cereal Window
by Witold Grzebisz, Witold Szczepaniak, Katarzyna Przygocka-Cyna, Maria Biber and Tomasz Spiżewski
Agronomy 2024, 14(12), 3018; https://doi.org/10.3390/agronomy14123018 - 18 Dec 2024
Viewed by 349
Abstract
The process of winter bread wheat (WW) nutrient management in the Critical Cereal Window (CCW) has a decisive impact on yield component formation and, consequently, the grain yield (GY) and grain protein content (GPC). This hypothesis was verified in a single-factor field experiment [...] Read more.
The process of winter bread wheat (WW) nutrient management in the Critical Cereal Window (CCW) has a decisive impact on yield component formation and, consequently, the grain yield (GY) and grain protein content (GPC). This hypothesis was verified in a single-factor field experiment carried out in the 2013/2014, 2014/2015, and 2015/2016 seasons. It consisted of seven nitrogen-fertilized variants: 0, 40, 80, 120, 160, 200, and 240 kg N ha−1. The mass of nutrients in ears was determined in the full flowering stage. The mass balance of nutrients (N, P, K, Mg, Ca, Fe, Mn, Zn, and Cu) was determined in leaves and stems. These sets of data were first used to calculate the soil nutrient uptake and then to predict the GY and GPC. Three nutrients, i.e., N, Ca, and Mg, were the main predictors of ear biomass. The set of ear nutrients significantly predicting GY and GE consisted of Ca, P, and Zn. Overall, this indirectly indicates a balanced N status for the ear. A positive nutrient balance in leaves, indicating their remobilization, was found for N, P, Fe, Zn, and Cu. Negative values, indicating a net nutrient accumulation in the non-ear organs of WW, were found for the remaining nutrients. The greatest impact on the GY and its components was observed for the balance of Mg and P but not N. The predictive worth of the nutrient balance for stems was much lower. The GPC, regardless of the type of indicator, depended solely on the N balance. Meanwhile, the main nutrient sources of N and Fe in ears were leaves and stems due to their uptake from the soil. For Cu, the primary source was soil, completed by its remobilization from leaves. For the remaining nutrients examined, the key source for the ear was soil, which was completed by remobilization from leaves and stems. Mg and Ca differed from other nutrients because their source for ears was exclusively soil. They were invested by WW in the ears and non-ear organs, mainly in the stems. The effective use of the yield potential of WW and other cereals requires insight into the nutritional status of the canopy at the beginning of the booting stage. This knowledge is necessary to develop an effective N management strategy and to correct and possibly apply fertilizers to improve both the yield and the GPC. Full article
(This article belongs to the Section Soil and Plant Nutrition)
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<p>Winter wheat in the full flowering phase—the layered structure of ears in the canopy. [Photo by Witold Grzebisz].</p>
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<p>The daily mean air temperature and precipitation at the Smolice Experimental Station during the study.</p>
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<p>The redistribution of nutrients taken up by winter wheat plants from the soil in the CCW. Legend: *, **—nutrient source, kg ha<sup>−1</sup>, macronutrients, micronutrients, respectively; LE—leaves; ST—stems, SOIL—soil.</p>
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<p>Percentage of individual nutrient sources in the ear of winter wheat in the full flowering phase. Legend: *—nutrient share; LE—leaves; ST—stems, SOIL—soil.</p>
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<p>The redistribution of nutrients taken up by winter wheat in the CCW between its organs during full flowering, 2014. * The percentage redistribution based on the amount of a given nutrient in the ears. Legend: LE—leaves, ST—stems, SOIL—soil nutrient sources.</p>
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<p>The redistribution of nutrients taken up by winter wheat in the CCW between its organs during full flowering, 2015. * The percentage redistribution based on the amount of a given nutrient in the ears. Legend: LE—leaves, ST—stems, SOIL—soil nutrient sources.</p>
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<p>The redistribution of nutrients taken up by winter wheat in the CCW between its organs during full flowering, 2016. * The percentage redistribution based on the amount of a given nutrient in the ears. Legend: LE—leaves, ST—stems, SOIL—soil nutrient sources.</p>
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16 pages, 1394 KiB  
Article
Effects of Seven-Year-Optimized Irrigation and Nitrogen Management on Dynamics of Soil Organic Nitrogen Fractions, Soil Properties, and Crop Growth in Greenhouse Production
by Jianshuo Shi, Longgang Jiang, Liying Wang, Chengzhang Wang, Ruonan Li, Lijia Pan, Tianyuan Jia, Shenglin Hou and Zhou Jia
Agriculture 2024, 14(12), 2319; https://doi.org/10.3390/agriculture14122319 - 17 Dec 2024
Viewed by 443
Abstract
Exploring the temporal evolution dynamics of different soil organic nitrogen (N) components under different water–N management practices is a useful approach to accurately assessing N supply and soil fertility. This information can provide a scientific basis for precise water and N management methods [...] Read more.
Exploring the temporal evolution dynamics of different soil organic nitrogen (N) components under different water–N management practices is a useful approach to accurately assessing N supply and soil fertility. This information can provide a scientific basis for precise water and N management methods for greenhouse vegetable production. The objective of this study was to investigate the effects of optimized irrigation and nitrogen management on the dynamics of soil organic nitrogen fractions, soil properties, and crop growth. This research was conducted from 2017 to 2023 in a greenhouse vegetable field in North China. Four treatments were applied: (1) high chemical N application with furrow irrigation (farmers’ practice, FP); (2) no chemical N application with drip irrigation (DN0); (3) 50% N of FP with drip irrigation (DN1); and (4) 75% N of FP with drip irrigation (DN2). The volume in drip irrigation is 70% of that in furrow irrigation. The results showed that in 2023 (after seven years of field trials), compared with FP, the soil organic carbon (SOC), total N, and water use efficiency of the DN1 and DN2 treatments increased by 15.9%, 11.4%, and 11.3% and 7.7%, 47.2% and 44.6%, respectively. However, there was no significant difference in the total crop yield except in the DN0 treatment. Soil organic N was mostly in the form of acid-hydrolyzed N (AHN). After seven years of optimized irrigation and N management, the DN1 treatment significantly increased the content of ammonium N (AN) and amino sugar N (ASN) in AHN compared with the FP treatment. The results of further analysis demonstrated that SOC was the main factor in regulating AHN and non-hydrolyzable N (NHN), while the main regulatory factors for amino acid N (AAN) and ASN in the AHN component were dry biomass and water use efficiency, respectively. From a time scale perspective, optimization of the water and N scheduling, especially in DN1 (reducing the total irrigation volume by 30% and the amount of N applied by 50%), is crucial for the sustainable improvement of soil fertility and the maintenance of vegetable production. Full article
(This article belongs to the Section Agricultural Soils)
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<p>TN (<b>a</b>), SOC (<b>b</b>), C/N (<b>c</b>), NO<sub>3</sub><sup>−</sup>-N (<b>d</b>), pH (<b>e</b>), and EC (<b>f</b>) under various irrigation and N application rates in 2017, 2019, 2021, and 2023. Different lowercase letters mean significant differences among treatments in the same year, and different uppercase letters mean significant differences among different years of the same treatment (<span class="html-italic">p</span> &lt; 0.05). Vertical bars represent standard error of mean. DN0: no chemical N application with drip irrigation; DN1: 50% N of FP with drip irrigation; DN2: 75% N of FP with drip irrigation. TN: soil total N; SOC: soil organic carbon; C/N: the ratio of soil organic C to soil total N; NO<sub>3</sub><sup>−</sup>-N: nitrate nitrogen; pH: soil pH; EC: soil electrical conductivity.</p>
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<p>AN content (<b>a</b>), AAN content (<b>b</b>), ASN content (<b>c</b>), UN content (<b>d</b>), AHN content (<b>e</b>), and NHN content (<b>f</b>) under various irrigation and N application rates in 2017, 2019, 2021, and 2023. Different lowercase letters mean significant differences among treatments in the same year, and different uppercase letters mean significant differences among different years of the same treatment (<span class="html-italic">p</span> &lt; 0.05). Vertical bars represent standard error of mean. DN0: no chemical N application with drip irrigation; DN1: 50% N of FP with drip irrigation; DN2: 75% N of FP with drip irrigation. AN: ammonium N; AAN: amino acid N; ASN: amino sugar N; UN: hydrolyzable unknown N; AHN: acid hydrolyzed N; NHN: non-hydrolyzable N.</p>
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<p>Percentage of soil organic N fraction contents in TN in (<b>a</b>) 2017, (<b>b</b>) 2019, (<b>c</b>) 2021, and (<b>d</b>) 2023 under various irrigation and N application rates. AN: ammonium N; AAN: amino acid N; ASN: amino sugar N; UN: hydrolyzable unknown N; NHN: non-hydrolyzable N. DN0: no chemical N application with drip irrigation; DN1: 50% N of FP with drip irrigation; DN2: 75% N of FP with drip irrigation.</p>
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<p>The relative importance drivers of AN (<b>a</b>), AAN (<b>b</b>), UN (<b>c</b>), ASN (<b>d</b>), AHN (<b>e</b>), and NHN (<b>f</b>). The vertical bars represent 95% confidence intervals. SOC: soil organic carbon; TP: soil total phosphorus; EC: soil electrical conductivity; TK: soil total potassium; TDM: total dry biomass; AK: soil available potassium; TY: total yield; NO<sub>3</sub><sup>−</sup>-N: nitrate nitrogen; annual WUE: annual water use efficiency.</p>
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17 pages, 3872 KiB  
Article
Impact of Land Use Types on Soil Physico-Chemical Properties, Microbial Communities, and Their Fungistatic Effects
by Giuseppina Iacomino, Mohamed Idbella, Salvatore Gaglione, Ahmed M. Abd-ElGawad and Giuliano Bonanomi
Soil Syst. 2024, 8(4), 131; https://doi.org/10.3390/soilsystems8040131 - 16 Dec 2024
Viewed by 1036
Abstract
Soilborne plant pathogens significantly impact agroecosystem productivity, emphasizing the need for effective control methods to ensure sustainable agriculture. Soil fungistasis, the soil’s ability to inhibit fungal spore germination under optimal conditions, is pivotal for biological control. This study explores soil fungistasis variability across [...] Read more.
Soilborne plant pathogens significantly impact agroecosystem productivity, emphasizing the need for effective control methods to ensure sustainable agriculture. Soil fungistasis, the soil’s ability to inhibit fungal spore germination under optimal conditions, is pivotal for biological control. This study explores soil fungistasis variability across land-use intensities, spanning deciduous and evergreen forests, grasslands, shrublands, and horticultural cultivations in both open fields and greenhouses. Soil characterization encompassed organic matter, pH, total nitrogen, C/N ratio, key cations (Ca2+, Mg2+, K+, Na+), enzymatic activities, microbial biomass, and soil microbiota analyzed through high-throughput sequencing of 16s rRNA genes. Fungistasis was evaluated against the pathogenic fungi Botrytis cinerea and the beneficial microbe Trichoderma harzianum. Fungistasis exhibited similar trends across the two fungi. Specifically, the application of glucose to soil temporarily annulled soil fungistasis for both B. cinerea and T. harzianum. In fact, a substantial fungal growth, i.e., fungistasis relief, was observed immediately (48 h) after the pulse application with glucose. In all cases, the fungistasis relief was proportional to the glucose application rate, i.e., fungal growth was higher when the concentration of glucose was higher. However, the intensity of fungistasis relief largely varied across soil types. Our principal component analysis (PCA) demonstrated that the growth of both Trichoderma and Botrytis fungi was positively and significantly correlated with organic carbon content, total nitrogen, iron, magnesium, calcium, and sodium while negatively correlated with fluorescein diacetate (FDA) hydrolysis. Additionally, bacterial diversity and composition across different ecosystems exhibited a positive correlation with FDA hydrolysis and a negative correlation with phosphoric anhydride and soil pH. Analysis of bacterial microbiomes revealed significant differences along the land use intensity gradient, with higher fungistasis in soils dominated by Pseudoarthrobacter. Soils under intensive horticultural cultivation exhibited a prevalence of Acidobacteria and Cyanobacteria, along with reduced fungistasis. This study sheds light on soil fungistasis variability in diverse ecosystems, underscoring the roles of soil texture rather than soil organic matter and microbial biomass to explain the variability of fungistasis across landscapes. Full article
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<p>Images of the selected ecosystems across a climatic and land use intensity gradient in terms of organic amendment input, synthetic fertilizers, and pesticide application in the Campania Region (Southern Italy). All pictures by Giuliano Bonanomi.</p>
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<p>Box plots illustrating the variation in species richness (<b>A</b>) and the Shannon diversity index (<b>B</b>) for bacterial communities across the ecosystem soils. The boxes represent the interquartile range (IQR), with the lower and upper bounds indicating the 25th and 75th percentiles, respectively. The horizontal line within each box marks the median, while the whiskers extend to the range of data within 1.5 times the IQR. Different letters indicate significant differences (<span class="html-italic">p</span> &lt; 0.05). (<b>C</b>) Non-metric multidimensional scaling (NMDS) plots depict bacterial community composition in the different soils. The MDS axis1 and MDS axis2 correspond to the two axes of the two-dimensional ordination space, with each point representing a replicate sample. The stress level, shown on each plot, indicates how well the distances between objects are preserved (values closer to 0 indicate a better representation of the data in the ordination space). The <span class="html-italic">p</span>- and F-values represent the results of the PERMANOVA test conducted with 999 permutations on the bacterial data. (<b>D</b>) Bar charts display the relative abundance of bacterial phyla in the different soils.</p>
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<p>Heatmap showing the relative abundance of the 100 most frequent Amplicon Sequence Variants in the bacterial community in the soil of each ecosystem. The grouping of variables is based on Whittaker’s association index.</p>
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<p>Fungal growth of <span class="html-italic">B. cinerea</span> conidia (expressed as a percentage compared to the control (0%)) on soil watery extracts from the selected ecosystems during a 168 h incubation period that followed a single application of glucose at four application rates (0.10%, 0.30%, 1%, and 3%). Values are averages ± standard deviation.</p>
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<p>Fungal growth of <span class="html-italic">T. harzianum</span> conidia (expressed as a percentage compared to the control (0%)) on soil watery extracts from the selected ecosystems during a 168 h incubation period that followed a single application of glucose at four application rates (0.10%, 0.30%, 1%, and 3%). Values are averages ± standard deviation.</p>
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<p>Principal component analysis (PCA) based on soil physico-chemical characteristics (<b>A</b>) and SIMPER resulting taxa (<b>B</b>) as variables. Microbial biomass, fungal growth, and bacterial diversity and composition were fitted as factors with significance &lt;0.05 onto the ordination.</p>
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20 pages, 12596 KiB  
Article
Spectral Data-Driven Prediction of Soil Properties Using LSTM-CNN-Attention Model
by Yiqiang Liu, Luming Shen, Xinghui Zhu, Yangfan Xie and Shaofang He
Appl. Sci. 2024, 14(24), 11687; https://doi.org/10.3390/app142411687 - 14 Dec 2024
Viewed by 684
Abstract
Accurate prediction of soil properties is essential for sustainable land management and precision agriculture. This study presents an LSTM-CNN-Attention model that integrates temporal and spatial feature extraction with attention mechanisms to improve predictive accuracy. Utilizing the LUCAS soil dataset, the model analyzes spectral [...] Read more.
Accurate prediction of soil properties is essential for sustainable land management and precision agriculture. This study presents an LSTM-CNN-Attention model that integrates temporal and spatial feature extraction with attention mechanisms to improve predictive accuracy. Utilizing the LUCAS soil dataset, the model analyzes spectral data to estimate key soil properties, including organic carbon (OC), nitrogen (N), calcium carbonate (CaCO3), and pH (in H2O). The Long Short-Term Memory (LSTM) component captures temporal dependencies, the Convolutional Neural Network (CNN) extracts spatial features, and the attention mechanism highlights critical information within the data. Experimental results show that the proposed model achieves excellent prediction performance, with coefficient of determination (R2) values of 0.949 (OC), 0.916 (N), 0.943 (CaCO3), and 0.926 (pH), along with corresponding ratio of percent deviation (RPD) values of 3.940, 3.737, 5.377, and 3.352. Both R2 and RPD values exceed those of traditional machine learning models, such as partial least squares regression (PLSR), support vector machine regression (SVR), and random forest (RF), as well as deep learning models like CNN-LSTM and Gated Recurrent Unit (GRU). Additionally, the proposed model outperforms S-AlexNet in effectively capturing temporal and spatial patterns. These findings emphasize the potential of the proposed model to significantly enhance the accuracy and reliability of soil property predictions by capturing both temporal and spatial patterns effectively. Full article
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<p>Sampling points of European Union.</p>
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<p>Initial absorbance spectra and preprocessed spectral curves for mineral soil samples from the LUCAS 2015 topsoil database: (<b>a</b>) shows the original spectra, and (<b>b</b>) displays the preprocessed spectra. Both figures present the 5th, 16th, 50th, 84th, and 95th percentiles to illustrate the variability within the dataset.</p>
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<p>Diagram of the LSTM model structure featuring the forget gate, input gate, and output gate.</p>
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<p>Self-attention mechanism.</p>
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<p>The framework of the proposed LSTM-CNN-Attention model.</p>
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<p>The flowchart of soil property prediction with the LSTM-CNN-Attention method.</p>
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<p>KDE plots of soil properties for the total dataset, training set, and test set: (<b>a</b>) OC, (<b>b</b>) N, (<b>c</b>) CaCO<sub>3</sub>, and (<b>d</b>) pH(H<sub>2</sub>O).</p>
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<p>KDE plots of PCA-transformed spectral data for the total dataset, training set, and test set: (<b>a</b>) PC1 and (<b>b</b>) PC2.</p>
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<p>Actual vs. predicted values of the proposed framework: (<b>a</b>) OC, (<b>b</b>) N, (<b>c</b>) CaCO<sub>3</sub>, and (<b>d</b>) pH(H<sub>2</sub>O).</p>
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<p>Residual comparison: (<b>a</b>) OC, (<b>b</b>) N, (<b>c</b>) CaCO<sub>3</sub>, and (<b>d</b>) pH(H<sub>2</sub>O).</p>
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<p>Line charts of (<b>a</b>) R<sup>2</sup> and (<b>b</b>) RPD for the proposed and other models.</p>
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16 pages, 5717 KiB  
Article
Effects of Different Fertilization Treatments on Leaf Litter Quality in a Plantation in Heilongjiang Province, China
by Siqi Sun, Yangjing Gao, Kuo Zhou, Luping Jiang, Xiaoting Liu and Xiyang Zhao
Forests 2024, 15(12), 2193; https://doi.org/10.3390/f15122193 - 12 Dec 2024
Viewed by 481
Abstract
Litter decomposition is a highly complex physical and biochemical process that plays a crucial role in promoting energy transformation in forest ecosystems. This study examines the impact of different concentrations of nitrogen and compound fertilizers on the quality of litter in a plantation [...] Read more.
Litter decomposition is a highly complex physical and biochemical process that plays a crucial role in promoting energy transformation in forest ecosystems. This study examines the impact of different concentrations of nitrogen and compound fertilizers on the quality of litter in a plantation of Populus euramericana ‘N3016’ × Populus ussuriensis. The major components and elemental contents of litter from different decomposition layers (the undecomposed layer and semidecomposed layer) were analyzed across various months. Overall, the application of nitrogen fertilizer or compound fertilizer did not significantly alter the cellulose, lignin, or potassium (K) contents of the litter in the different decomposition layers. Nitrogen fertilizer increased the average content of undecomposed layer (U-layer) nitrogen (N) and phosphorus (P) by 0.220% and 0.009%, respectively. Compound fertilizer increased the average content of U-layer nitrogen (N) by 0.055%. These findings suggest that while fertilization can increase the initial N and P contents in litter to some extent, it has a minimal overall impact on litter quality. Future research should be focused on the effects of climatic conditions, soil properties, soil fauna, and microbial activity on litter decomposition. Full article
(This article belongs to the Section Forest Soil)
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<p>Nitrogen deposition and decomposition material cycle of leaf litter.</p>
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<p>Dynamic changes of lignin content under nitrogen fertilizer treatments in leaf litter. CTRL (control group), L-N (low concentration nitrogen fertilizer), M-N (medium concentration nitrogen fertilizer), H-N (high concentration nitrogen fertilizer). Letters (A, B) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>Dynamic changes of lignin content under compound fertilizer treatments in leaf litter. CTRL (control group), L-C (low concentration compound fertilizer), M-C (medium concentration compound fertilizer), H-C (high concentration compound fertilizer). Letters (A, B) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>Dynamic changes of cellulose content under nitrogen fertilizer treatments in leaf litter. CTRL (control group), L-N (low concentration nitrogen fertilizer), M-N (medium concentration nitrogen fertilizer), H-N (high concentration nitrogen fertilizer). Letters (A, B) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>Dynamic changes of cellulose content under compound fertilizer treatments in leaf litter. CTRL (control group), L-C (low concentration compound fertilizer), M-C (medium concentration compound fertilizer), H-C (high concentration compound fertilizer). Letters (A–C) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>Dynamic changes of nutrient element content in undecomposed layer under nitrogen fertilizer treatments. N content (<b>A</b>), P content (<b>B</b>), K content (<b>C</b>). CTRL (Control group), L-N (Low concentration nitrogen fertilizer), M-N (medium concentration nitrogen fertilizer), H-N (High concentration nitrogen fertilizer). Letters (a–d) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>Dynamic changes of nutrient element content in semidecomposed layer under nitrogen fertilizer treatments. N content (<b>A</b>), P content (<b>B</b>), K content (<b>C</b>). CTRL (Control group), L-N (Low concentration nitrogen fertilizer), M-N (medium concentration nitrogen fertilizer), H-N (High concentration nitrogen fertilizer). Letters (a–d) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>Dynamic changes of nutrient element content in undecomposed layer under compound fertilizer treatments. N content (<b>A</b>), P content (<b>B</b>), K content (<b>C</b>). CTRL (control group), L-C (low concentration compound fertilizer), M-C (medium concentration compound fertilizer), H-C (high concentration compound fertilizer). Letters (a–c) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>Dynamic changes of nutrient element content in semidecomposed layer under compound fertilizer treatments. N content (<b>A</b>), P content (<b>B</b>), K content (<b>C</b>). CTRL (Control group), L-C (Low concentration compound fertilizer), M-C (medium concentration compound fertilizer), H-C (High concentration compound fertilizer). Letters (a–c) different between the same group differ statistically (<span class="html-italic">p</span> &lt; 0.05).</p>
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<p>PCA of leaf litter quality under different fertilization treatments in May (<b>A</b>), June (<b>B</b>), September (<b>C</b>), and November (<b>D</b>).</p>
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11 pages, 1311 KiB  
Article
Influence of Annual Ryegrass (Lolium multiflorum) as Cover Crop on Soil Water Dynamics in Fragipan Soils of Southern Illinois, USA
by Amitava Chatterjee, Dana L. Dinnes, Daniel C. Olk and Peter L. O’Brien
Soil Syst. 2024, 8(4), 126; https://doi.org/10.3390/soilsystems8040126 - 3 Dec 2024
Viewed by 625
Abstract
Fragipans are dense subsurface soil layers that severely restrict root penetration and water movement. The presence of shallow fragipan horizons limits row crop production. We hypothesized that the roots of cover crop might improve soil physiochemical properties and biological activity, facilitating drainage and [...] Read more.
Fragipans are dense subsurface soil layers that severely restrict root penetration and water movement. The presence of shallow fragipan horizons limits row crop production. We hypothesized that the roots of cover crop might improve soil physiochemical properties and biological activity, facilitating drainage and increasing effective soil depth for greater long-term soil water storage. To evaluate annual ryegrass as one component of a cover crop (CC) mix for promoting the characteristics and distribution of soil water, on-farm studies were conducted at Marion and Springerton in southern Illinois, USA. Soil samples were collected at 15 cm increments to 60 cm (Marion) and 90 cm (Springerton) depths during the fall of 2022. Both sites had low total soil carbon and nitrogen contents and acidic soil pH (≤6.4). A soil water retention curve was fitted using the van Genuchten equation. At Springerton, the CC treatment increased saturated (thetaS) and residual (thetaR) soil water contents above those of the no cover crop (NCC) at the 60–75 cm and 75–90 cm depths. Changes in volumetric soil water content were measured using a multi-depth soil water sensor for the Springerton site during late July to early August of the soybean growing phase of 2022; NCC had higher soil water than CC within the 0–15 cm depth, but CC had higher soil water than NCC at the 30–45 cm depth. These findings indicate that cover crop mix has the potential to improve soil water movement for soils with restrictive subsoil horizon, possibly through reducing the soil hydraulic gradient between the surface and restrictive subsurface soil layers. Full article
(This article belongs to the Special Issue Land Use and Management on Soil Properties and Processes)
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<p>(<b>a</b>) Location of two growers’ fields, Marion and Springerton in southern Illinois, (<b>b</b>) schematic diagram of soil profile of two dominant soil series, ‘Bluford’ and ‘Rend’ found at Springerton and Marion and sites, respectively, and (<b>c</b>) daily high and low air temperatures (°C) and precipitation (cm) during 2022 growing season in Carbondale, Illinois.</p>
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<p>(<b>a</b>) Changes in volumetric soil moisture content (cm<sup>3</sup> cm<sup>−3</sup>), (<b>b</b>) comparison of drydown time (days), and (<b>c</b>) changes in soil water storage (cm) with (CC) and without (NCC) annual ryegrass as cover crop during 2022 (soybean growing phase) at Springerton, Illinois.</p>
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21 pages, 7317 KiB  
Article
Black Soil Quality After 19 Years of Continuous Conservation Tillage
by Chengyuan Zhang, Jianye Li, Francisco Alberto Sosa, Qiang Chen and Xingyi Zhang
Agronomy 2024, 14(12), 2859; https://doi.org/10.3390/agronomy14122859 - 29 Nov 2024
Viewed by 435
Abstract
Conservation tillage is a practice adopted worldwide to prevent soil degradation. Although there have been many studies on the impact of conservation tillage on soil quality, most studies on cultivated land in the black soil region of Northeast China are based on the [...] Read more.
Conservation tillage is a practice adopted worldwide to prevent soil degradation. Although there have been many studies on the impact of conservation tillage on soil quality, most studies on cultivated land in the black soil region of Northeast China are based on the physical and chemical indicators of soil. In addition, the experiment time is generally short, so there is a lack of information about long-term conservation tillage from the perspective of the physical, chemical, and biological integration of soil. A comparative analysis of the physical, chemical, and biological characteristics of soil was conducted under no-till (NT) with straw mulching and conventional tillage (CT) treatments after 19 years of field experiments. By using membership functions to normalize and render all the indicators dimensionless, and calculating the weight of each indicator through principal component analysis, the comprehensive index of soil quality can be calculated as a weighted summation. The results indicate that NT had no significant effect on soil bulk density at a soil depth of 0–20 cm. NT increased the field water-holding capacity of the 0–5 cm layer, reduced the total porosity of the 5–10 cm soil layer, and decreased the non-capillary porosity of the 0–20 cm soil layer. Compared to CT, NT significantly increased the organic carbon content of the soil in the 0–5 cm layer, comprehensively improved the total nutrient content of the soil, and significantly increased the contents of ammonium nitrogen, nitrate-nitrogen, and available phosphorus in the soil. It also significantly improved the total phosphorus content in the 5–20 cm soil layer. NT improved the microbial carbon and nitrogen content of the soil, significantly enhanced the microbial nitrogen content in the 0–5 and 5–10 cm soil layers, and reduced the bacterial species diversity in the 5–10 cm soil layer. However, the soil enzyme activities showed no significant differences between different treatments. Under the NT treatment, the evaluation of soil quality indicators, such as mean weight diameter, field water-holding capacity, non-capillary porosity, microbial biomass nitrogen, total nutrients, and available nutrients, was relatively successful. Based on the weight calculation, the organic carbon, catalase activity, fungal richness, and bacterial diversity indicators are the most important of the 22 soil quality indicators. In terms of the comprehensive index of soil fertility quality, NT increased the soil quality comprehensive index by 34.2% compared to CT. Long-term conservation tillage improved the physical, chemical, and biological properties of the soil, which significantly enhanced the quality of the black soil. Full article
(This article belongs to the Section Farming Sustainability)
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<p>Differences in soil bulk density (<b>a</b>), field water-holding capacity (<b>b</b>), total porosity (<b>c</b>), and non-capillary porosity (<b>d</b>) between NT and CT. Different lowercase letters indicate a significant difference between the same soil layer under different tillage treatments (<span class="html-italic">p</span> &lt; 0.05). n.s., no significant differences (<span class="html-italic">p</span> &gt; 0.05); CT, conventional tillage; NT, no-till with straw mulching.</p>
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<p>Differences in soil organic carbon (<b>a</b>), total nitrogen (<b>b</b>), total phosphorus (<b>c</b>), and total potassium (<b>d</b>) carbon and nitrogen ratios (<b>e</b>) between long-term NT and CT. Different lowercase letters indicate a significant difference between the same soil layer under different tillage methods (<span class="html-italic">p</span> &lt; 0.05). n.s., no significant differences (<span class="html-italic">p</span> &gt; 0.05); CT, conventional tillage; NT, no-till with straw mulching.</p>
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<p>Differences in the soil’s ammonium nitrogen (<b>a</b>), nitrate-nitrogen (<b>b</b>), and available phosphorus (<b>c</b>) between long-term NT and CT. Different lowercase letters indicate a significant difference between the same soil layer under different tillage methods (<span class="html-italic">p</span> &lt; 0.05). n.s., no significant differences (<span class="html-italic">p</span> &gt; 0.05); CT, conventional tillage; NT, no-till with straw mulching.</p>
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<p>Differences in soil catalase (<b>a</b>), alkaline phosphatase (<b>b</b>), sucrase (<b>c</b>), and urease (<b>d</b>) activities between long-term NT and CT. n.s., no significant differences (<span class="html-italic">p</span> &gt; 0.05); CT, conventional tillage; NT, no-till with straw mulching.</p>
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<p>Differences in the soil’s microbial biomass carbon (<b>a</b>) and microbial biomass nitrogen (<b>b</b>) between long-term NT and CT. Different lowercase letters indicate a significant difference between the same soil layer under different tillage methods (<span class="html-italic">p</span> &lt; 0.05). n.s., no significant differences (<span class="html-italic">p</span> &gt; 0.05); CT, conventional tillage; NT, no-till with straw mulching.</p>
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<p>Radar charts of 0–5 cm (<b>a</b>), 5–10 cm (<b>b</b>), and 10–20 cm (<b>c</b>) membership values of each soil index. CT, conventional tillage; NT, no-till with straw mulching.</p>
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<p>Radar charts of 0–20 cm membership values of each soil index. CT, conventional tillage; NT, no-till with straw mulching.</p>
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19 pages, 3266 KiB  
Article
Soil and Microbial Biomass Response to Land-Use Changes in the Loess Plateau
by Zhandong Pan, Xuemei Cai, Liqun Cai, Bo Dong, Fasih Ullah Haider, Yongming Bo, Zhaozhao Hu, Anqi Li and Qin Xue
Sustainability 2024, 16(23), 10496; https://doi.org/10.3390/su162310496 - 29 Nov 2024
Viewed by 582
Abstract
Vegetation restoration is a critical strategy for addressing ecosystem degradation globally. However, understanding the specific impacts of land-use changes, particularly the conversion of farmland to forestland and grassland, on soil nutrients and microbial biomass in the Loess Plateau remains limited and requires further [...] Read more.
Vegetation restoration is a critical strategy for addressing ecosystem degradation globally. However, understanding the specific impacts of land-use changes, particularly the conversion of farmland to forestland and grassland, on soil nutrients and microbial biomass in the Loess Plateau remains limited and requires further evaluation. Therefore, this study was conducted to explore how these conversions affect soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and microbial biomass components under various land-use patterns. We studied the SOC, TN, TP, soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP) content and their ratios under six land-use patterns (Farmland (FL), Abandoned cropland (ACL), Natural grassland (NG), Alfalfa grassland (Medicago sativa L. (MS)), Spruce forestland (Picea asperata Mast. (PA)) and Cypress forestland (Platycladus orientalis (L.) Franco (PO))). The conversion of FL to grassland and forestland significantly increased C:N and C:P by 9.82~64.12%, 10.57~126.05%, and 51.44~113.40%, 22.10~116.09%, respectively. The conversion of FL to ACL reduced the C:N and C:P by 5.34~13.57% and 1.51~7.55%, respectively. The conversion of FL to NG can increase soil N:P. The conversion of FL to grassland and forestland increased soil MBC, MBN, and MBP by −31.54~84.48%, −48.39~1533.93%, −46.55~173.85%, and −34.96~17.13%, 68.72~432.14%, −38.39~318.46%, respectively. However, the MBC, MBN, and MBP contents in the soil converted from FL to ACL varied from −28.21~11.95%, 11.17~531.25%, and −82.64~70.77%, respectively. Soil SOC, TN, TP, available potassium (AK), pH, and soil bulk density (BD) are the main factors causing microbial biomass differences. These results indicate that converting farmland into forestland and grassland can improve soil nutrient structure and increase soil microbial biomass and carbon accumulation. The results of this study provide theoretical support for the scientific management of regional land. Full article
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<p>The geographical location map of the study area (Anjiagou, Dingxi, China). (<b>a</b>) China map, (<b>b</b>) Loess Plateau area (enlarged area of the highlighted part in (<b>a</b>)), (<b>c</b>) Dingxi city (enlarged area of the highlighted part in (<b>b</b>)).</p>
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<p>Stoichiometric characteristics of soil carbon, nitrogen and phosphorus under different land use patterns ((<b>a</b>):C:N, (<b>b</b>):C:P, and (<b>c</b>):N:P) at various soil depths. Note: The bar represents standard error. Different letters indicate significant (<span class="html-italic">p</span> &lt; 0.05) differences among different land use patterns. 0–10 cm soil depth = 0–10; 10–30 cm soil depth = 10–30; 30–50 cm soil depth = 30–50; Farmland = FL; Abandoned cropland = ACL; Natural grassland = NG; Alfalfa grassland = MS; Spruce forestland = PA; Cypress forestland = PO; Carbon = C; Nitrogen = N; and Phosphorus = P.</p>
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<p>Contents of soil microbial biomass carbon, nitrogen and phosphorus under different land-use patterns ((<b>a</b>): MBC, (<b>b</b>): MBN, and (<b>c</b>): MBP) at various soil depths. Note: The bar represents standard error. Different letters indicate significant (<span class="html-italic">p</span> &lt; 0.05) differences among different land-use treatments. 0–10 cm soil depth = 0–10; 10–30 cm soil depth = 10–30; 30–50 cm soil depth = 30–50; Farmland = FL; Abandoned cropland = ACL; Natural grassland = NG; Alfalfa grassland = MS; Spruce forestland = PA; Cypress forestland = PO; Soil microbial biomass carbon = MBC; Microbial biomass nitrogen = MBN; and Microbial biomass phosphorus = MBP.</p>
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<p>Correlation between soil microbial biomass carbon, nitrogen, phosphorus, and soil physicochemical factors. Note: * and ** in the figure, respectively, indicate <span class="html-italic">p</span> ≤ 0.05, and <span class="html-italic">p</span> ≤ 0.01. Soil microbial biomass carbon = MBC; microbial biomass nitrogen = MBN; microbial biomass phosphorus = MBP; total nitrogen = TN; total phosphorous = TP; total potassium = TK; available phosphorous = AP; available potassium = AK; bulk density = BD; soil water content = SWC; carbon = C; nitrogen = N; and phosphorous = P.</p>
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<p>Redundancy analysis of soil microbial biomass carbon, nitrogen, phosphorus, and soil physicochemical factors. Note: Soil microbial biomass carbon = MBC; microbial biomass nitrogen = MBN; microbial biomass phosphorus = MBP; total nitrogen = TN; total phosphorous = TP; total potassium = TK; available phosphorous = AP; available potassium = AK; bulk density = BD; soil water content = SWC; carbon = C; nitrogen = N; and phosphorous = P.</p>
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15 pages, 2197 KiB  
Article
Effects of Diverse Crop Rotation Sequences on Rice Growth, Yield, and Soil Properties: A Field Study in Gewu Station
by Ruiping Yang, Yu Shen, Xiangyi Kong, Baoming Ge, Xiaoping Sun and Mingchang Cao
Plants 2024, 13(23), 3273; https://doi.org/10.3390/plants13233273 - 21 Nov 2024
Viewed by 738
Abstract
This long-term field study conducted in Yancheng, China, evaluated the effects of diverse crop rotation sequences on rice growth, yield, and soil properties. Six rotation treatments were implemented from 2016 to 2023 as follows: rice–wheat (control), rice–rape, rice–hairy vetch, rice–barley, rice–faba bean, and [...] Read more.
This long-term field study conducted in Yancheng, China, evaluated the effects of diverse crop rotation sequences on rice growth, yield, and soil properties. Six rotation treatments were implemented from 2016 to 2023 as follows: rice–wheat (control), rice–rape, rice–hairy vetch, rice–barley, rice–faba bean, and rice–winter fallow. Rice growth parameters, yield components, biomass accumulation, and soil properties were measured. Results showed that legume-based rotations, particularly rice–faba bean and rice–hairy vetch, significantly improved rice growth and yield compared to the rice–wheat control. The rice–faba bean rotation increased yield by 19.1% to 8.73 t/ha compared to 7.33 t/ha for the control, while rice–hairy vetch increased yield by 11.9% to 8.20 t/ha. These rotations also demonstrated higher biomass production efficiency, with increases of 33.33% and 25.00%, respectively, in spring crop biomass. Soil nutrients improvements were observed, particularly in available nitrogen, potassium, and electrical conductivity. Legume-based rotations increased the available nitrogen by up to 35.9% compared to the control. The study highlights the potential of diversified crop rotations, especially those incorporating legumes, to enhance rice productivity and soil health in subtropical regions. These findings have important implications for developing sustainable and resilient rice-based cropping systems to address challenges of food security and environmental sustainability in the face of climate change and resource constraints. Full article
(This article belongs to the Special Issue Effects of Conservation Tillage on Crop Cultivation and Production)
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<p>Schematic diagram of six crop rotation sequences implemented at Gewu Field Experimental Station from 2016 to 2023. (<b>A</b>) the rotation process information as seasons change. S1: Rice–wheat (control); S2: Rice–rape; S3: Rice–hairy vetch; S4: Rice–barley; S5: Rice–faba bean; S6: Rice–winter fallow. Rice was cultivated in spring across all treatments, while the specified crops or fallow were implemented in autumn; (<b>B</b>) spring and autumn cropping rotations; and (<b>C</b>) process activities in the crop rotations. (Note, RI, rice; WH, wheat; BA, barley; RA, rape; FB, faba bean; and HV, hairy vetch).</p>
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<p>Effects of different rotation patterns on rice growth indexes. (<b>A</b>) Plant height (cm); (<b>B</b>) Stem diameter (cm); (<b>C</b>) Effective tiller number per plant; and (<b>D</b>) Actual panicle number per plant. (Note, RW: Rice–wheat (control); RO: Rice–rape; RV: Rice–hairy vetch; RB: Rice–faba bean; RF: Rice–barley; and RS: Rice–fallow. The significance between the different treatments at <span class="html-italic">p</span> &lt; 0.05 is indicated with different letters while the error bars show the standard error of three biological replicates (n = 3)).</p>
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<p>Effects of different rotation patterns on rice yield. (<b>A</b>) Single panicle weight (g); (<b>B</b>) Grain number per panicle; (<b>C</b>) Single plant weight (g); and (<b>D</b>) Rice yield (t/ha). (Note, RW: Rice–wheat (control); RO: Rice–rape; RV: Rice–hairy vetch; RB: Rice–faba bean; RF: Rice–barley; and RS: Rice–fallow. The significance between the different treatments at <span class="html-italic">p</span> &lt; 0.05 is indicated with different letters while the error bars show the standard error of three biological replicates (n = 3)).</p>
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<p>Effects of different rotation patterns on crop biomass. (<b>A</b>) Spring crop biomass (t/ha); and (<b>B</b>) Rice plant biomass at harvest (t/ha). (Note: Treatment abbreviations: RW: Rice–wheat (control); RO: Rice–rape; RV: Rice–hairy vetch; RB: Rice–faba bean; RF: Rice–barley; RS: Rice–fallow. Different letters above bars indicate significant differences between treatments at <span class="html-italic">p</span> &lt; 0.05. Error bars represent standard error of three biological replicates (n = 3)).</p>
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<p>Effects of different rotation patterns on soil properties (0–15 cm depth). (<b>A</b>) soil pH in spring; (<b>B</b>) soil pH in autumn; (<b>C</b>) soil electrical conductivity (mS/cm) in spring; (<b>D</b>) soil electrical conductivity (mS/cm) in autumn; (<b>E</b>) soil available nitrogen (mg/kg) in spring; (<b>F</b>) soil available nitrogen (mg/kg) in autumn; (<b>G</b>) soil available phosphorus (mg/kg) in spring; (<b>H</b>) soil available phosphorus (mg/kg) in autumn; (<b>I</b>) soil available potassium (mg/kg) in spring; and (<b>J</b>) soil available potassium (mg/kg) in autumn. (Note: Treatment abbreviations: RW: Rice–wheat (control); RO: Rice–rape; RV: Rice–hairy vetch; RB: Rice–faba bean; RF: Rice–barley; RS: Rice–fallow. Different letters above bars indicate significant differences between treatments at <span class="html-italic">p</span> &lt; 0.05. Error bars represent standard error of three biological replicates (n = 3). Soil samples were collected before rice planting in spring and after rice harvest in autumn).</p>
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17 pages, 8272 KiB  
Article
Retention Levels and Years-After-Harvesting Influence over Soil Microbial Activity and Biomass in Southern Patagonian Forests
by Santiago Toledo, Guillermo Martínez Pastur, Julián Rodríguez-Souilla and Pablo L. Peri
Land 2024, 13(11), 1963; https://doi.org/10.3390/land13111963 - 20 Nov 2024
Viewed by 736
Abstract
Variable retention harvesting (VRH) was designed for timber purposes and biodiversity conservation in natural forests. This system was globally tested, but few studies are related to soil microbial components. The objective was to evaluate different retention types (aggregated and dispersed retention) considering different [...] Read more.
Variable retention harvesting (VRH) was designed for timber purposes and biodiversity conservation in natural forests. This system was globally tested, but few studies are related to soil microbial components. The objective was to evaluate different retention types (aggregated and dispersed retention) considering different years-after-harvesting (6, 9, 16 YAH) on soil microbial community attributes compared with unmanaged primary forests (PF) in Nothofagus pumilio forests of Tierra del Fuego (Argentina). This study also evaluated the influence of climate, soil, and understory vegetation. Results showed that aggregated retention increased microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and soil basal respiration (SBR) compared to dispersed retention, but with similar values than PF. However, harvested areas decreased MBC/MBN values compared with PF. The results showed an overall decrease in microbial biomass and activity in 9 YAH stands, with a positive recovery at 16 YAH. Soil pH, mean annual temperature, and understory vegetation cover showed a positive relationship with MBC, MBN, and SBR. The recovery after 16 YAH reached to different microbial communities. Therefore, the maintenance of retention components in managed stands for longer periods is needed. The results highlight some advantages of VRH as a tool for conservation of forest-dwelling soil microorganisms, including microbial biomass and activity. Full article
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<p>(<b>A</b>) Study area in the gradient of <span class="html-italic">N. pumilio</span> forests distribution (green) in Tierra del Fuego (Argentina). (<b>B</b>) Satellite image showing variable retention harvesting design in Los Cerros ranch (AR = aggregated retention, DR = dispersed retention, PF = unmanaged primary forests). (<b>C</b>) Diagram of the experimental design and soil sampling points (stars) at each forest stand (AR = blue circles, DR = red area, PF = green area).</p>
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<p>Principal components analyses (PCA) including microbial variables (MBC = microbial biomass carbon, MBN = microbial biomass nitrogen, SBR = soil basal respiration, MBC/MBN ratio, qCO<sub>2</sub> = metabolic quotient), climate and topographic variables (MAP = mean annual precipitation, MAT = mean annual temperature, elevation), soil characteristics (soil pH, SOC = soil organic carbon, N = soil nitrogen, P = soil phosphorus) and understory vegetation variables (species richness, understory vegetation biomass, advance regeneration, dominant height, recruitment, initial regeneration, forest growth, bare soil, tree density) in <span class="html-italic">N. pumilio</span> forests of Tierra del Fuego. (<b>A</b>) Forest treatments including primary unmanaged forests (PF, green), aggregated retention (AR, blue), and dispersed retention (DR, red). (<b>B</b>) Years-after-harvesting including 6 YAH (white), 9 YAH (gray), and 16 YAH stands (black). The ellipses indicate clustering of treatments: green for PF and 16 YAH, red for DR and 9 YAH, and blue for AR and 6 YAH.</p>
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<p>Relationships among soil microbial biomass and soil activity variables in <span class="html-italic">N. pumilio</span> forests of Tierra del Fuego. (<b>A</b>) Microbial biomass carbon (MBC) and soil organic carbon (SOC), (<b>B</b>) MBC and soil pH, (<b>C</b>) MBC and soil nitrogen (N), (<b>D</b>) microbial biomass nitrogen (MBN) and SOC, (<b>E</b>) MBN and soil pH, (<b>F</b>) MBN and soil N, (<b>G</b>) soil basal respiration (SBR) and SOC, (<b>H</b>) SBR and soil pH, and (<b>I</b>) SBR and soil N. Dots were classified as primary unmanaged forests (green), aggregated retention (blue) and dispersed retention (red) considering different years-after-harvesting (6 = triangles, 9 = squares, 16 = circles). Lines showed a linear regression, where r<sup>2</sup> = adjusted parameter, and <span class="html-italic">p</span> = probability.</p>
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<p>Relationships among soil microbial biomass and activity and climatic variables in <span class="html-italic">N. pumilio</span> forests of Tierra del Fuego. (<b>A</b>) Microbial biomass carbon (MBC) and mean annual temperature (MAT), (<b>B</b>) MBC and elevation, (<b>C</b>) MBC and mean annual precipitation (MAP), (<b>D</b>) microbial biomass nitrogen (MBN) and MAT, (<b>E</b>) MBN and elevation, (<b>F</b>) MBN and MAP, (<b>G</b>) soil basal respiration (SBR) and MAT, (<b>H</b>) SBR and elevation, and (<b>I</b>) SBR and MAP. Dots were classified as primary unmanaged forests (green), aggregated retention (blue) and dispersed retention (red) considering different years-after-harvesting (6 = triangles, 9 = squares, 16 = circles). Lines showed the linear regression, where r<sup>2</sup> = adjusted parameter, and <span class="html-italic">p</span> = probability.</p>
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<p>Relationships among soil microbial biomass and activity and vegetation variables in <span class="html-italic">N. pumilio</span> forests of Tierra del Fuego. (<b>A</b>) Microbial biomass carbon (MBC) and species richness, (<b>B</b>) MBC and vegetation cover, (<b>C</b>) MBC and forest growth, (<b>D</b>) microbial biomass nitrogen (MBN) and species richness, (<b>E</b>) MBN and understory vegetation cover, (<b>F</b>) MBN and forest growth, (<b>G</b>) soil basal respiration (SBR) and species richness, (<b>H</b>) SBR and understory vegetation cover, and (<b>I</b>) SBR and forest growth. Dots were classified as primary unmanaged forests (green), aggregated retention (blue), and dispersed retention (red) considering different years-after-harvesting (6 = triangles, 9 = squares, 16 = circles). Lines showed the linear regression, where r<sup>2</sup> = adjusted parameter, and <span class="html-italic">p</span> = probability.</p>
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<p>Principal components analyses (PCA) including microbial variables (MBC = microbial biomass carbon, MBN = microbial biomass nitrogen, SBR = soil basal respiration, MBC/MBN ratio, qCO<sub>2</sub> = metabolic quotient), climate and topographic variables (MAP = mean annual precipitation, MAT = mean annual temperature, elevation), soil characteristics (soil pH, SOC = soil organic carbon, N = soil nitrogen, P = soil phosphorus) and understory vegetation variables (species richness, understory vegetation biomass, advanced regeneration, dominant height, recruitment, initial regeneration, forest growth, bare soil, tree density) in <span class="html-italic">N. pumilio</span> forests of Tierra del Fuego. (<b>A</b>) Forest treatments including primary unmanaged forests (PF, green), aggregated retention (AR, blue) and dispersed retention (DR, red), and (<b>B</b>) Years-after-harvesting including 6 YAH (white), 9 YAH (gray), and 16 YAH (black).</p>
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<p>Relationships among MBC/MBN ratio and soil variables, climatic variables, and vegetation variables in <span class="html-italic">N. pumilio</span> forests of Tierra del Fuego. (<b>A</b>) MBC/MBN and soil organic carbon (SOC), (<b>B</b>) MBC/MBN and soil pH, (<b>C</b>) MBC/MBN and soil nitrogen (N), (<b>D</b>) MBC/MBN and mean annual temperature (MAT), (<b>E</b>) MBC/MBN and elevation, (<b>F</b>) MBC/MBN and mean annual precipitation (MAP), (<b>G</b>) MBC/MBN and species richness, (<b>H</b>) MBC/MBN and understory vegetation cover, and (<b>I</b>) MBC/MBN and forests growth. Dots were classified as primary unmanaged forests (green), aggregated retention (blue) and dispersed retention (red) considering different years-after-harvesting (6 = triangles, 9 = squares, 16 = circles). Lines showed the linear regression, where r<sup>2</sup> = adjusted parameter, and <span class="html-italic">p</span> = probability.</p>
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17 pages, 6741 KiB  
Article
Comprehensive Assessment of the Correlation Between Ancient Tea Garden Soil Chemical Properties and Tea Quality
by Houqiao Wang, Wenxia Yuan, Qiaomei Wang, Yuxin Xia, Wang Chun, Haoran Li, Guochen Peng, Wei Huang and Baijuan Wang
Horticulturae 2024, 10(11), 1207; https://doi.org/10.3390/horticulturae10111207 - 15 Nov 2024
Viewed by 637
Abstract
Understanding the correlation between soil chemical properties and tea quality is essential for the comprehensive management of ancient tea gardens. However, the specific links between these factors in ancient tea gardens remain underexplored. This study analyzes the soil chemical properties of four distinct [...] Read more.
Understanding the correlation between soil chemical properties and tea quality is essential for the comprehensive management of ancient tea gardens. However, the specific links between these factors in ancient tea gardens remain underexplored. This study analyzes the soil chemical properties of four distinct research regions in Nanhua County to explore their effects on key chemical components in ancient tea garden teas, providing a scientific basis for improving the quality of ancient tea garden teas through soil management. Employing high performance liquid chromatography (HPLC) and inductively coupled plasma mass spectrometry (ICP-MS), the chemical components of tea and the chemical properties of the soil were meticulously quantified. Following these measurements, the integrated fertility index (IFI) and the potential ecological risk index (PERI) were evaluated and correlation analysis was conducted. The results revealed that ancient tea garden tea quality is closely linked to soil chemical properties. Soil’s total nitrogen (TN), total sulfur (TS), and available potassium (AK) negatively correlate with tea’s catechin gallate (CG) component and AK also with polyphenols. Most other soil properties show positive correlations with tea components. The research also evaluated soil heavy metals’ IFI and PERI. IFI varied significantly among regions. Hg’s high pollution index indicates ecological risks; Cd in Xiaochun (XC) region poses a moderate risk. PERI suggests moderate risk for XC and Banpo (BP), with other areas classified as low risk. Implementing reasonable fertilization and soil amelioration measures to enhance soil fertility and ensure adequate supply of key nutrients will improve the quality of ancient tea gardens. At the same time, soil management measures should effectively control heavy metal pollution to ensure the quality and safety of tea products. Insights from this study are crucial for optimizing soil management in ancient tea gardens, potentially improving tea quality and sustainability. Full article
(This article belongs to the Special Issue Tea Tree: Cultivation, Breeding and Their Processing Innovation)
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<p>Representative ancient tea trees from four regions. In (<b>a</b>): represents the typical tea tree of the CLZ research region; In (<b>b</b>): represents the typical tea tree of the BP research region; In (<b>c</b>): represents the typical tea tree of the XC research region; In (<b>d</b>): represents the typical tea tree of the GLT research region.</p>
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<p>Analysis of the components of epicatechin distribution in four research regions. Note: ECG-epicatechin gallate. In (<b>a</b>): Percentage stacked bar chart of catechin composition; In (<b>b</b>): Radar chart of catechin composition.</p>
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<p>Box plots of ten soil properties at four research regions. In (<b>a</b>): Box plot of soil pH distribution in four research regions; In (<b>b</b>): Box plot of Soil Organic Matter distribution in four research regions; In (<b>c</b>): Box plot of soil Total Nitrogen distribution in four research regions; In (<b>d</b>): Box plot of soil Total Phosphorus distribution in four research regions; In (<b>e</b>): Box plot of soil Total Potassium distribution in four research regions; In (<b>f</b>): Box plot of soil Alkali-hydrolyzable nitrogen distribution in four research regions; In (<b>g</b>): Box plot of soil Available Phosphorus distribution in four research regions; In (<b>h</b>): Box plot of soil Available Potassium distribution in four research regions; In (<b>i</b>): Box plot of soil Cation Exchange Capacity distribution in four research regions; In (<b>j</b>): Box plot of soil Total Sulfur distribution in four research regions; In (<b>k</b>): Box plot of soil Exchanged magnesium distribution in four research regions; In (<b>l</b>): Box plot of soil Fluoride distribution in four research regions.</p>
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<p>The linear correlation between individual soil fertility indicators and the comprehensive IFI. In (<b>a</b>): Linear correlation between soil pH and Integrated fertility index in four research regions; In (<b>b</b>): Linear correlation between Soil Organic Matter and Integrated fertility index in four research regions; In (<b>c</b>): Linear correlation between Total Nitrogen and Integrated fertility index in four research regions; In (<b>d</b>): Linear correlation between Total Phosphorus and Integrated fertility index in four research regions; In (<b>e</b>): Linear correlation between Total Potassium and Integrated fertility index in four research regions; In (<b>f</b>): Linear correlation between Alkali-hydrolyzable nitrogen and Integrated fertility index in four research regions; In (<b>g</b>): Linear correlation between Available Phosphorus and Integrated fertility index in four research regions; In (<b>h</b>): Linear correlation between Available Potassium and Integrated fertility index in four research regions; In (<b>i</b>): Linear correlation between Cation Exchange Capacity and Integrated fertility index in four research regions; In (<b>j</b>): Linear correlation between Total Sulfur and Integrated fertility index in four research regions.</p>
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<p>Heavy metal element distribution analysis of four research regions soil layers including topsoil (0–20 cm, top) and subsoil (20–40 cm, sub). Soil heavy metal elements included As, Cu, Hg, Cd, Cr, Ni, Pb, and Zn. Note: Significant differences are indicated by different letters at the 0.05 level. In (<b>a</b>): Heavy metal As content in the 0–20cm and 20–40cm soil layers of four regions; In (<b>b</b>): Heavy metal Cd content in the 0–20cm and 20–40cm soil layers of four regions; In (<b>c</b>): Heavy metal Cu content in the 0–20cm and 20–40cm soil layers of four regions; In (<b>d</b>): Heavy metal Hg content in the 0–20cm and 20–40cm soil layers of four regions; In (<b>e</b>): Heavy metal Cr content in the 0–20cm and 20–40cm soil layers of four regions; In (<b>f</b>): Heavy metal Ni content in the 0–20cm and 20–40cm soil layers of four regions; In (<b>g</b>): Heavy metal Pb content in the 0–20cm and 20–40cm soil layers of four regions; In (<b>h</b>): Heavy metal Zn content in the 0–20cm and 20–40cm soil layers of four regions.</p>
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<p>PCA of soil properties and tea quality parameters across different soil layers. In (<b>a</b>): Principal component analysis of soil chemical properties and tea quality parameters in the 0–20 cm layer across four research regions; In (<b>b</b>): Principal component analysis of soil chemical properties and tea quality parameters in the 20–40 cm layer across four research regions.</p>
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