Abstract:The aim of this study was to explore the long-term effects of biochar on improving soil fertility in farmland in the northern Xinjiang irrigation area. A three-year field trial with three treatments: no biochar application (B0), low biochar application (10 thm-2, B1), and high biochar application (20 thm-2, B2), was conducted to systematically analyze the effects of biochar on soil aggregate carbon and nitrogen components, enzyme activities, and microbial community structure. The results showed that when the biochar application rate was 10 t·hm-2, it exhibited the optimal soil improvement effect. Specifically, the organic carbon content in aggregates larger than 2 mm and smaller than 0.25 mm demonstrated an upward trend with the application of biochar. Among them, in the aggregates larger than 2 mm, the organic carbon content in treatment B1 was significantly increased by 44.05% compared to treatment B0. In the aggregates smaller than 0.25 mm, the organic carbon content initially increased and then decreased with the application of biochar, reaching the maximum in B1. Also, the total nitrogen content in aggregates larger than 2 mm first increased and then decreased with the application of biochar, reaching the highest level in B1. Furthermore, the findings indicated that the application of biochar increased the microbial biomass carbon and nitrogen in aggregates larger than 2 mm and in the range of 2~0.25 mm, while reducing the microbial biomass nitrogen in aggregates smaller than 0.25 mm. Meanwhile, the urease activity in all three types of aggregates showed an upward trend with the application of biochar. Under the three aggregate conditions, compared to B0, B1 increased the activity of urease by 14.53%, 5.43%, and 1.08%, respectively. In addition, catalase activity was highest under the B1 condition, increasing by 10.64%, 21.43%, and 23.4% compared to B0, respectively. Although sucrase activity slightly decreased, it still remained at a relatively high level, ensuring the supply of carbon sources. The application of biochar significantly enhanced the α-diversity (Shannon and Chao1 indices) of the soil bacterial community. This promoting effect was strengthened as the aggregate particle size decreased. Moreover, under the application rate of 10 t·hm-2 (B1), the improvement effect was relatively balanced. In contrast, the impact of biochar on the α-diversity of fungi was relatively weak. The Shannon index only increased slightly, and the Chao1 index showed no significant change, indicating that the fungal community was less sensitive to the application of biochar compared to the bacterial community. Under the conditions of this study, applying 10 t·hm-2 of biochar (B1) can increase the content of carbon and nitrogen components in soil aggregates of wheat fields while enhancing the abundance of beneficial microbial communities.

Abstract:【Objective】Litter quality is a key factor regulating the intensity and direction of the soil priming effect. However, it remains unclear whether inputs of litter from different organs of the same plant or litter with different carbon to nitrogen ratios (C/N) from the same organ differentially impact soil priming effect, as well as the underlying mechanisms.【Method】To address this gap, 13C-labeled seedlings of Phoebe bournei were used as study materials. Through fertilized and non-fertilized treatments, leaf, stem, and root tissues with low and high C/N ratios were obtained to investigate the effects of litter inputs with different C/N ratios on soil priming. Soil microbial biomass, enzyme activity, and soil available nitrogen contents (NH4+-N and NO3--N) were measured concurrently to elucidate the underlying mechanisms.【Result】After 180 days of incubation, the addition of high and low C/N ratio leaf litter and low C/N ratio root litter inhibited the mineralization of soil organic carbon (SOC) by about 11.09%, 9.05% and 8.07%, respectively, inducing a significant negative priming effect. However, the other treatments did not cause significant priming effects. The influence of different C/N ratios in the same organ of Phoebe bournei on soil priming effect was primarily observed within the first 8 days of incubation, with high C/N ratio litter inducing a stronger negative priming effect than low C/N ratio litter. The reason is that high C/N ratio litter input caused microbial nitrogen (N) immobilization, reducing soil available N content, which led to N limitation and suppressed microbial activity, thereby decreasing SOC decomposition. In the later stages of incubation, the effects of different C/N ratio litter on soil microbial biomass carbon and carbon metabolism-related enzyme activities were not significant, so the influence of C/N ratio on soil priming gradually diminished. Among different plant organs, leaf litter induced a stronger negative priming effect than root litter. Specifically, the negative priming effect induced by leaf addition weakened over time, while root addition continuously induced a negative priming effect. Stem addition caused a priming effect that fluctuated between positive and negative, but the cumulative effect offset, resulting in no significant change in SOC decomposition.【Conclusion】The impact of Phoebe bournei litter input on soil priming effect varied significantly among organs, whereas the influence of litter C/N ratio on soil priming effect was mainly concentrated in the early stages of litter decomposition. The main mechanism by which leaf litter induced a negative priming effect was through reducing soil available nitrogen, which inhibited microbial activity, thereby decreasing SOC decomposition. In contrast, the negative priming effect induced by low C/N ratio roots was because their high lignin content and low bioavailability, causing C limitation for microorganisms during decomposition, leading to reduced SOC decomposition.

Abstract:【Objective】 Soil acidification is a prominent issue in the typical black soil region of the northern Songnen Plain, which hinders the sustainable development of regional agriculture. Thus, exploring the characteristics of soil pH, exchangeable acidity, and their influencing factors in the cultivated soils of the typical black soil region can provide a scientific basis for the zoning and classification of soil acidification improvement measures. 【Method】 In this study, surface soils of cultivated land in Bei""an City and Wudalianchi City, Heilongjiang Province, were taken as the research object. Soil samples from 119 soil sites were collected to determine soil acidity and related soil properties, while data on relevant environmental and anthropogenic factors were collected. Pearson correlation analysis and random forest model were used, combined with the theory of soil acid-base buffering, to explore the main controlling factors affecting the spatial variation of soil pH, exchangeable H⁺, and exchangeable Al³⁺ contents. 【Result】 The results showed that the surface soils of cultivated land in the study area were dominated by strongly acidic and acidic soils. The spatial variability of soil pH was low, while the spatial variability of soil exchangeable acid content was high. There were no significant differences in soil pH and exchangeable acidity contents between dark brown soils, black soils, marsh soils, and meadow soils. Pearson correlation analysis indicated that soil pH was extremely significantly and positively correlated with the contents of exchangeable Ca²⁺ and Mg²⁺, clay fractions, and mean annual temperature, and significantly negatively correlated with soil organic matter content, silt content, aluminum saturation, mean annual precipitation, and elevation. Soil exchangeable H⁺ and Al³⁺ contents were extremely significantly and positively correlated with soil organic matter content, silt content, aluminum saturation, mean annual precipitation, and elevation, and extremely significantly and negatively correlated with the contents of exchangeable Ca²⁺ and Mg²⁺, clay fractions, and mean annual temperature. The random forest model showed that the 15 influencing factors explained 84.38% and 71.61% of the variations in soil pH and exchangeable acids, respectively. Among these factors, soil factors contributed the most (65.67% and 56.19%), followed by environmental factors such as annual average precipitation (18.57% and 13.87%), whereas the contribution of anthropogenic factors was negligible with respect to the spatial variation of soil pH and exchangeable acid (0.14% and 1.55%). 【Conclusion】 The typical black soil region in northern Songnen Plain has a high acid buffering capacity due to its high base saturation and abundant feldspar minerals, which is significantly different from the soil in typical red soil regions. The main controlling factors for the spatial variation of soil acidity are soil exchangeable base ions (Ca²⁺ and Mg²⁺) contents, aluminum saturation, and annual average precipitation.

Abstract:【Objective】High soil penetration resistance (PR) limits global crop growth and sustainable agricultural productivity. Heavy soil texture, low soil organic matter, and low topsoil water content during summer significantly increase PR under a subtropical monsoon climate in southern China. However, the specific mechanisms controlling these processes remain elusive. Thus, the objectives were to investigate the applicability of various penetration resistance characteristic models in red soils with different parent materials and identify key influencing factors, and assess the ameliorative effects of mechanical- and bio-tillage on PR in Ultisols. 【Methods】This study investigated four red soils derived from different parent materials in China’s humid subtropical climate, including granitic (GS), Quaternary red clayey (CS), argillaceous shale (AS), and red sandstone red soil (SS). Key parameters measured included soil PR, water content (SWC), bulk density (), organic matter (SOM) and texture. We evaluated the performance of five PR models (soil water content model, soil matric potential model, soil water content and bulk density model, soil matric potential and bulk density model, and saturated stress model) and identified their influencing factors in red soils, assessed the ameliorative effects of mechanical- and bio-tillage on PR in Ultisols, and determined the PR threshold for four red soils using the least limiting water range. 【Results】Among the five characteristic models of soil PR, the saturated stress model provided a better fit (lower SSE and higher R²) for the four red soils, followed by the soil water content model, the soil water content and bulk density model, and the soil matric potential model. PR in red soils increased with decreasing water content, exhibiting a sharp increase once the water content fell below a critical value (~ 0.32 cm³·cm-³). The PR of low bulk density soils (1.3 g· cm-³) experienced a sharp increase at low water contents, whereas that of high bulk density soils (1.5 g·cm-³) showed a dramatic increase at high water contents. Soil texture (clay content) was a primary factor influencing PR of different parent material red soils, while SOM had negligible effects. When the soil water content was 0.25 cm³·cm-³, mechanical tillage (deep tillage with 30 cm ploughing depth) reduced PR by ~1 034 kPa in the 0~40 cm depth compared to control treatment (no-tillage), whereas bio-tillage achieved a reduction of ~785 kPa in the same depth and reduced PR (~1 500 kPa) in the subsoil. The critical PR thresholds of the four red soils exceeded 2 500 kPa, and thresholds for clayey red soils were higher than those for sandy red soils. 【Conclusion】The saturated stress model proved highly effective for predicting red soil PR in of southern China. SWC,  and texture played the primary factors influencing PR across different parent material red soils, with clayey red soils (CS and AS) exhibiting higher PR thresholds than sandy red soils (GS and SS). This research provides a scientific basis for identifying the occurrence of seasonal drought and rationally selecting tillage practices for drought prevention in subtropical red soil regions of China through the lens of soil penetration resistance.

Abstract:【Objective】Green manure cultivation in orchards plays a positive role in improving soil physicochemical properties, such as soil structure, and in reducing soil erosion. However, the mechanisms by which green manures mitigate soil erosion in sloping orchard systems remain unclear. 【Method】This study was conducted using runoff plots in a citrus orchard to systematically monitor runoff and sediment yield under natural rainfall conditions in plots planted with ryegrass (Lolium perenne), hairy vetch (Vicia villosa), and white clover (Trifolium repens), compared with bare tilled (bare soil) control plots. The effects of green manure plant characteristics, stem thickness, plant height, root length, and vegetation cover, on soil structural properties (porosity, bulk density, average infiltration rate) and organic matter content, as well as their relationships with runoff and sediment production, were analyzed. 【Result】The results showed that (1) Green manure plant traits significantly improved from initial to peak flowering. Hairy vetch exhibited the greatest plant height and root length, ryegrass had the optimal stem thickness, and white clover achieved the highest vegetation cover. (2) Soil bulk density and porosity were closely correlated with green manure root length: more developed root systems were associated with lower bulk density and higher porosity (P < 0.05). At peak flowering, green manure plots showed a significant decrease in bulk density and notable increases in porosity and average infiltration rate compared to the seedling stage, whereas the bare tilled control exhibited opposite trends. Organic matter content increased in all plots from seedling to peak flowering, but the smallest increase occurred in the bare control. Among treatments, hairy vetch showed the greatest reduction in bulk density (–8.69%) and the largest increases in porosity (+8.22%) and organic matter (+45.88%). Also, ryegrass demonstrated the best infiltration performance, followed by white clover. (3) Root length exerted strong influences on subsurface flow (effect strength = 0.66) and sediment yield (0.71), while plant height and vegetation cover primarily affected surface runoff (0.62) and sediment yield (0.61) by dissipating rainfall energy and resisting overland flow. Over a full annual cycle, including growth, residue decomposition, and tillage periods, the average runoff and sediment yields followed the order: bare tillage > hairy vetch > white clover > ryegrass, clearly indicating the superior overall erosion control by ryegrass. Although the hairy vetch plots recorded the lowest sediment concentration in runoff, temporal analysis revealed distinct performance patterns. Specifically, white clover was most effective in reducing runoff and sediment during the early growth stages (seedling/initial flowering) due to its rapid establishment, whereas ryegrass performed best during peak flowering, decomposition, and the non-growing season, owing to its persistent biomass and robust root system. 【Conclusion】Intercropping ryegrass and white clover in sloping citrus orchards provides the most effective control of soil and water loss. These findings provide theoretical support for the strategic mixing and temporal scheduling of green manure species, tailored to specific ecological functions in different agroecological zones.

Abstract:【Objective】 Land-use change is a primary driver of soil structure alteration and nutrient cycling in ecosystems. In subtropical hilly areas of China, which are ecologically fragile and experience significant land-use pressure, understanding the interplay between soil physical structure and biogeochemical cycles is crucial for sustainable land management. The stability of soil aggregates and the ecological stoichiometry of nutrients serve as critical indicators for evaluating ecological restoration and soil quality. Thus, this study aims to elucidate the mechanism by which typical land use practices in subtropical hilly areas influence nutrient variations through alterations in the distribution characteristics of soil aggregates. 【Method】 We examined soils from three representative land use types (forestland, tea garden, and cultivated land) in Yingshan County, Hubei Province. Key stability indices, including the mean weight diameter (MWD), geometric mean diameter (GMD), soil erodibility (K), and fractal dimension (D), were calculated. Utilizing both stoichiometric methods and multivariate statistical models, we analyzed the relationship between aggregate stability levels and the distribution patterns of soil organic carbon, total nitrogen, and total phosphorus. 【Result】 The results revealed that: (1) The content of >5 mm aggregates in forestland soils was 3.43 and 1.58 times higher than that in tea garden and cultivated land, respectively. Both the mean weight diameter (MWD) and geometric mean diameter (GMD) followed the order: forestland > cultivated land > tea garden. The tea garden soil exhibited the highest erodibility (K) value and fractal dimension (D) value. (2) The soil organic carbon content in forest land was significantly higher than in other plots, reaching 10.22 g·kg?1. Total nitrogen content followed the order of forest land > tea garden > cultivated land, while total phosphorus content exhibited the opposite trend. Both C:P and N:P ratios were highest in forestland soils, followed by cultivated land and tea garden. (3) Aggregate characteristics were significantly correlated with nutrient indicators (P < 0.05), with the macroaggregates (> 5 mm) playing a major role in shaping C:P and N:P ratios. Also, the partial least squares path modeling (PLS-PM) showed good fit (goodness-of-fit > 0.61) and the path coefficients indicated that the influence pathways of aggregate particle size on nutrient stoichiometric ratios varied under different land use types, with the direct effect being most pronounced in forested areas. 【Conclusion】 This study illustrates that changes in land use significantly affect the relationship between soil structure and nutrient cycling. Forestland, which experiences minimal disturbance, encourages the creation of stable macroaggregates. This process enhances long-term nutrient sequestration and maintains a balanced stoichiometric environment. On the other hand, intensive management practices in tea gardens and cultivated lands can disrupt aggregate stability. This disturbance leads to structural degradation and a notable stoichiometric imbalance. Therefore, it is crucial to preserve forestland and implement sustainable soil practices in managed lands. This approach will significantly improve soil quality and promote ecological sustainability in subtropical hilly areas.

Abstract:【Objective】Intensive orchard management in semi-arid regions has caused soil quality degradation and declining ecosystems’ multifunctionality, thereby threatening production sustainability. While green manure mulching shows promise for sustainable orchard management, the mechanistic impact on soil quality and ecosystem multifunctionality remain unclear.【Method】This study investigated the impact of four green manure mulching treatments- no mulching, gramineae monoculture (ryegrass, Lolium perenne L.), legume monoculture (white clover, Trifolium repens L.), legume-gramineae mixture (1:1) on soil quality and ecosystem multifunctionality in semi-arid orchards.【Result】The results revealed that green manure mulching substantially enhanced soil quality, with legume monoculture showing superior performance (89.0% and 88.5% increases versus grass and mixed systems, respectively). All treatments stimulated soil enzyme activities and alleviated microbial limitations (carbon: 5.8%-8.6%; nitrogen: 5.0%-14.7%), collectively increasing ecosystem multifunctionality by 87.4%-100.2%.【Conclusion】This study reveals that green manure mulching effectively enhances soil ecosystem multifunctionality in semi-arid orchards, with legume-based systems (monoculture or mixed) recommended for implementation.

Abstract:Straw incorporation poses a persistent challenge while remaining fundamental to soil fertility management in modern Chinese agriculture. However, traditional straw incorporation methods are characterized by slow decomposition, inefficient soil organic matter enhancement, and significant yield reduction. To combat these drawbacks, we proposed and developed straw pelletization technology as a novel alternative for efficient straw utilization over 14 years, providing a novel solution for land conservation and intensive utilization. This review synthesized the research progress in straw pelletization and incorporation, with the aim of providing a theoretical foundation and technical guidance for its high-quality development. This review commenced with a retrospective analysis of the conceptual foundation of straw pelletization and incorporation, which involves secondary crushing and pelletizing of straw to simultaneously tackle decomposition and field incorporation challenges. Subsequently, based on previous practices, the study delineated ten major advantages, such as markedly increased incorporation rates, rapid soil organic carbon sequestration, and stable yield improvements. It also identifies three salient scientific questions, the mechanism of accelerated decomposition, carbon turnover processes, and carbon sequestration thresholds, while envisioning the application potential of pelletized straw returning in intensive agriculture, organic agriculture, medium- and low-yield fields, and reserve croplands. Finally, to bridge the gap in large-scale and widespread adoption, two essential supporting measures were proposed: the optimization and widespread deployment of integrated straw crushing and pelletizing machinery, and the establishment and development of a straw pellet trading platform. In summary, straw pelletization and incorporation enable the simultaneous improvement of soil fertility and crop yield, thereby supporting the national strategies of the Two Stores (storing grain in the land and through technology) and the Dual Carbon (Carbon Peak and Carbon Neutrality).

Abstract:Abstract: 【Objective】 Optimizing nitrogen management of the farmland is critical to achieve the strategy of reducing fertilizer input and improving efficiency, as well as advance the agricultural green development. This study aims to explore the spatio-temporal variations of soil total nitrogen (TN) and nitrogen use efficiency (NUE) in typical county of cinnamon soil region over the past four decades, which can provide the scientific basis for enhancing farmland nitrogen management. 【Method】 Based on the farmland soil properties (soil nutrients, etc.) in Shouyang County, Shanxi Province in 1983, 2010, and 2023, and the agricultural production statistical data (planting area, crop yields, fertilizer types and application rates, livestock breeding quantity, etc.) from 1980 to 2023, classical statistics and geostatistics were employed to analyze the spatiotemporal dynamics of TN. The farmland nitrogen balance model was used to estimate nitrogen use efficiency (NUE) and nitrogen surplus. Random-forest analysis was applied to identify the key factors that affected the variations of TN. 【Result】 From 1983 to 2023, the farmland TN content in Shouyang County increased significantly, rising from 0.66 g·kg-1 to 1.02 g·kg-1. The most notable increase in TN occurred in Pingtou Town, Yinlingzhi Town, and the eastern part of Chaoyang Town. Over the past four decades, the NUE showed a pattern of first decreasing and then increasing, which declined from 48.63% in the 1980s to 33.08% in the 2000s and subsequently rose to 43.75% in the 2010s. Spatially, the farmland NUE value ranged from 30.66% to 50.99% among various regions during the 1980s to 2000s, which showed no significant difference. While in the 2010s, the NUE in the northern region (45.52%) was significantly higher than that in the central (36.84%) and southern regions (36.80%). The Random-forest analysis identified that soil organic carbon and nitrogen fertilizer amount were the key influencing factors to the changes of TN, with the relative importance of 33.95% and 10.57%, respectively. Currently, the farmland NUE and nitrogen surplus in Shouyang County were 45.78% and 97.2 kg·hm-2, respectively, which were still outside the optimal nitrogen management level. The northern region exhibited a relatively high NUE but a substantial nitrogen surplus, while Jingshang Town and Xiluo Town in the southern region recorded extremely low NUE and high nitrogen surplus. 【Conclusion】 Overall, although the farmland nitrogen management in Shouyang County has been improved over the past four decades, it still falls short of the optimal level. It is recommended that the entire Shouyang County, especially the Jiechou Town in the northern region, the Chaoyang Town in the central region, and the Jingshang Town and Xiluo Town in the southern region should prioritize rational nitrogen fertilizer amount to enhance farmland NUE, reduce nitrogen surplus, and ultimately achieve the optimal nitrogen management level.

Abstract:【Objective】The application of organic fertilizers in agricultural soils increases the density of earthworms. However, it remains unclear how earthworms change the fate of soil nitrogen under different fertilizer applications. 【Method】Using a pot experiment, the present study explores the effects of earthworms on soil nitrogen utilization, loss, and nitrogen transformation processes under the application of chemical (urea) and organic (compost) fertilizers. 【Result】The results showed that earthworms significantly increased the fresh weight of plants and the amount of nitrogen uptake by plants by 12.14% and 15.24% under chemical fertilizers and 18.38% and 37.28% under organic fertilizers, respectively. Earthworms significantly increased the cumulative soil N?O emissions and the cumulative soil ammonia volatilization only under the application of chemical fertilizers. There was no significant difference in nitrogen leaching loss between the treatment with and without earthworms. Overall, earthworms increased the nitrogen loss by 6.31 and 1.69 mg·pot?1 under the application of chemical and organic fertilizers, respectively. Also, earthworms significantly increased the ratio of the total nitrogen utilization by plants to the total nitrogen loss under the application of organic fertilizers, but no significant difference was found under the application of chemical fertilizers. The soil nitrogen primary transformation rate model showed that earthworms affected more nitrogen transformation processes under the application of organic fertilizers than under the application of chemical fertilizers, significantly increasing the total primary nitrogen mineralization rate of the soil. 【Conclusion】Regardless of the type of fertilizer applied, earthworms played a dual role in promoting plant nitrogen utilization and increasing nitrogen loss. However, considering the ratio of nitrogen utilization to loss, the application of organic fertilizers provided a more conducive environment for achieving the beneficial effects of earthworms in the soil nitrogen cycle.