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To understand the effects of different stover mulching amounts in no-tillage on soil carbon and nitrogen contents and enzyme activities, finding a stover mulching amount which can meet the requirement of soil carbon and nitrogen accumulation while maximizing economic benefits, we conducted a long-term conservation tillage field experiment since 2007 in Mollisols area of Northeast China. We analyzed soil carbon and nitrogen contents, enzyme activities and economic benefits under conventional tillage (Control, CT), no-tillage without stover mulching (NT 0 ), no-tillage with 33% stover mulching (NT 33 ), no-tillage with 67% stover mulching (NT 67 ), and no-tillage with 100% stover mulching (NT 100 ) before planting in May 2020. The results showed that compared with CT, NT 0 did not affect soil organic carbon (SOC) and total nitrogen (TN) contents, but increased soil organic carbon recalcitrance and decreased the availability of dissolved organic nitrogen (DON) and ammonium nitrogen. Compared with NT 0 , no-tillage with stover mulching significantly increased SOC contents in 0-10 cm layer and increased with the amounts of stover. In addition, NT 67 and NT 100 significantly increased SOC stocks, facilitating the accumulation of soil organic matter. The effects of different stover mulching amounts on soil nitrogen content in 0-10 cm layer were different. Specifically, NT 33 increased DON content and DON/TN, NT 67 increased DON content, while NT 100 increased TN content. Compared with CT, NT 0 decreased peroxidase (POD) activity in 0-10 cm layer. Compared with NT 0 , NT 33 increased β-glucosidase (βG), cellobiase (CB), 1,4-β-N-acetylglucosaminidase (NAG), polyphenol oxidase (PPO) and POD activities, while NT 67 only increased CB, NAG and POD activities in 0-10 cm soil layer, both alleviated microbial nutrient limitation. NT 100 increased PPO activity in 10-20 cm layer. NT 33 increased carbon conversion efficiency of stover compared with NT 100 , and had the highest economic benefit. In all, no-tillage with 33% stover mulching was the optimal strategy, which could promote nutrient circulation, boost stover utilization efficiency, improve the quality of Mollisols, and maximize guaranteed income.

Scientific evaluating ecosystem service value (ESV) of cover crop cultivation system can provide important guidance for the construction of conservation tillage pattern in Northeast China. Based on empirical analysis and the theory of ecosystem service value, we calculated the ESVs of intercropping maize with gramineous cover crop ryegrass and with leguminous cover crops, alfalfa and hairy vetch, with maize monoculture as the control. The ESVs included product supply, gas regulation, nutrient cycling, and soil and water conservation. Results showed that ESVs of cover crop-maize intercropping were higher than those of maize monoculture. Nutrient cycling value was the highest, followed by product supply value, accounting for 67.3% and 29.3% of total ESV, respectively. The nutrient cycling value of cover crop-maize intercropping was higher than that of maize monoculture. The product supply value of alfalfa-maize and hairy vetch-maize were 18.7% and 21.0% higher than that of ryegrass-maize, respectively. Cover crops had the potential to increase the value of gas regulation services, but had little impact on the value of soil and water conservation. Considering the ESVs, intercropping maize with leguminous cover crops would have the greatest benefits.

To investigate the effects of no-tillage and different amounts of stover mulch on soil microbial community composition and their residues, we set up a field experiment of different amounts of stover mulch under no-tillage on the long-term maize conservation tillage station located in the Mollisols area of Northeast China (built in 2007), including without stover mulch (NT0), 1/3 stover mulch (NT1/3), 2/3 stover mulch (NT2/3) and full stover mulch (NT3/3), and the conservation tillage (plowing without stover mulch, CT) as control. We analyzed phospholipid fatty acid, amino sugar biomarker and soil physicochemical properties at different soil layers (0-5 cm, 5-10 cm, 10-20 cm). The results showed that compared to CT, no-tillage without stover mulch (NT0) did not affect soil organic carbon (SOC), total nitrogen (TN), dissolved organic carbon and nitrogen (DOC, DON), water content, microbial community and their residue. The main effects of no-tillage and stover mulch were found in the topsoil. Specifically, the NT1/3, NT2/3 and NT3/3 significantly increased SOC content by 27.2%, 34.1% and 35.6%, respectively, phospholipid fatty acid content was significantly increased under NT2/3 and NT3/3 by 39.2% and 65.0%, respectively, and NT3/3 significantly increased the content of microbial residue-amino sugar by 47.2% in the depth of 0-5 cm compared with CT. The variations in soil properties and microbial community induced by no-tillage and different amounts stover mulch decreased with soil depth, with almost no difference in the 5-20 cm soil layer. SOC, TN, DOC, DON, and water content were the main factors influencing the composition of the microbial community and the accumulation of microbial residue. Microbial biomass was positively correlated with microbial residue, particularly fungal residue. In conclusion, all stover mulch treatments promoted SOC accumulation to different degrees. When there is sufficient stover, it is advisable to opt for no-tillage with full stover mulch, as it is most conducive to the increases of soil microbial biomass, microbial residue and SOC. In case when the amount of stover is inadequate, however, no-tillage with 2/3 stover mulch can still improve soil microbial biomass and SOC content. This study would provide practical guidance for stover management in conservation tillage and sustainable agricultural development in the Mollisols area of Northeast China.

Clarifying the differences of maize yield and its stability under long-term no-tillage with different stover mulching amounts can provide theoretical and technical supports for establishing and evaluating long-term conservation tillage pattern and promoting grain production. Based on a long-term conservation tillage field experiment in the mollisol area of Northeast China since 2007, we analyzed the interannual variation, variation coefficient and stability of maize yield during 2013 and 2019 across five treatments, i.e ., no-tillage stover-free mulching (NT 0 ), no-tillage with 33% stover mulching (NT 33 ), no-tillage with 67% stover mulching (NT 67 ) and no-tillage with 100% stover mulching (NT 100 ), with the traditional ridge cropping (RT) as the control. The results showed that compared with RT, long-term no-tillage with stover mulching treatments could increase maize yield. NT 100 had the highest increasing rate of 11.4%, followed by NT 67 and NT 0 , with the increasing rate of 11.0% and 10.4%, respectively. Maize yield exhibited a nonlinear relationship with the amount of stover mulch. The variation coefficient of maize yield under multi-year no-tillage with different stover mulching could be sorted as NT 67 100 33 0 , and the yield sustainability index was NT 67 >NT 0 >NT 100 >RT>NT 33 , indicating that NT 67 treatment could significantly reduce the interannual fluctuation of maize yield and had better sustainability of yield. No-tillage stover mulching significantly increased soil total carbon and total nitrogen contents, which were significantly positively correlated with maize yield. In conclusion, compared with traditional tillage, no-tillage stover mulching could increase maize yield and soil carbon and nitrogen contents. Appropriate stover mulching (NT 67 )had the potential to improve the stability and sustainability of maize yield.

Agricultural tillage practices significantly affect the structure and function of soil micro-bial community, as well as its control over soil carbon cycling. Conservation tillage practice based on no-tillage and crop straw returning is an important measure to improve soil carbon sequestration and fertility, in which soil microorganisms play a key role. Although many previous studies focus on the structure and function of microbial communities under conservation tillage, our overall understanding of soil microbial responses at community level upon conservation tillage is still lacking, due to the complexity of the soil, environmental factors and the different selections of microbial research methods. Furthermore, previous studies paid more attention to the role of soil microorganisms as decomposers and the contribution of plant-derived carbon to the formation of soil carbon pool, but ignored the contribution of microbial-derived carbon to the formation and stability of soil carbon pool. We summarized the paradigm shift in soil organic matter formation and stability theories, reviewed the research methods of soil microbial community, focused on the effects of conservation tillage on soil microbial biomass, community diversity and composition, carbon metabolism, as well as microbial-derived carbon storage, and proposed suggestions for future study, aiming to provide support for future studies regarding microbial responses and its control over soil carbon dynamics in agroecosystem.

We examined carbon chemical composition and stability along soil depth (topsoil 0-5 cm, mid-soil 20-40 cm, and deep soil 60-100 cm) in a no-tillage (NT) agricultural system with various amount of corn stover as mulch for 8 years, including 0 (NT 0 ), 33% (NT 33 ), 67% (NT 67 ) and 100% (NT 100 ), in Northeast China, using mid-infrared spectroscopy. The results showed that, relative to NT 0 , the treatments of NT 33 and NT 100 increased polysaccharide content of the top layer and mid-layer soils, the former decreased topsoil carbon component diversity, while the latter maintained soil carbon stability of three soil layers. NT 67 increased carbon stability at the deep layer soil. Our results demonstrated that if corn stover resources were sufficient, NT with 100% corn stover mulch could both be beneficial to carbon availability at 0-40 cm soil layer and stability of the whole soil profile. The nonlinear relationship between the amount of corn stover mulch and the mid-infrared spectral characteristics of the soil called for further research on the microbial-control mechanism over soil carbon cycling under different amounts of corn stover mulch.

Cover crops are grown in temporal and spatial gaps of agricultural production to reduce or avoid soil exposure. As it can protect farmland soil from wind erosion, water erosion and human disturbance, planting cover crops is considered as a new type of conservation tillage practice. Here, we briefly introduced the planting management of cover crops, including crop species, planting modes, and the returning to farmland after their termination, which could provide a reference for efficiently planting cover crops at large scale during the fallow period. Based on domestic and foreign studies, we summarized the benefits of cover crops on agroecosystem, including cash crops, soil quality, weed control, greenhouse gas emission, and soil microbes. Our review illustrated their importance in improving soil quality and achieving sustainable agricultural development, despite the limitation of cover crops, including unobvious benefits in the short-term and the reduction of crop yield caused by improper management.

We investigated the fire impacts on nutrients in litter and soil, and their C:N:P stoichio-metry in forests of Great Xing'an Mountains. The studied sites differed in their burning year (post-fire 4, 14, 40, 70 years and unburned within 120 years) and had different topographic locations (sloped land and flat land). The results showed that there were significant differences in stoichio-metry characteristics of C, N, P for both litter and soil with different burning years. No significant fluctuation was observed for the litter C content, while the contents of litter N and P increased with the increasing post-fire recovery years. In specific, we found the contents of litter N and P decreased at post-fire 4 and 14 years and nearly recovered to the control level at 40 years after fire. Additionally, C:N and C:P ratios of litter decreased, but N:P ratio of litter increased following post-fire recovery time. The contents of C, N, P and their ratios (C:N, C:P and N:P) in soil decreased with soil depth. Soil C content exhibited an increasing trend following post-fire recovery time and was significantly higher than the control at post-fire 70 years in sloped land, but no significant difference in the flat land. Significant interactive effects between fire history and slope were observed in soil P content and C:P ratio. Soil P content was higher than the control at post-fire 4 years in sloped land, but was higher than the control at post-fire 40 years in flat land. The C:P ratio recovered to the control level at post-fire 14 years in sloped land, and there was no significant diffe-rence in flat land. Redundancy analysis showed that slope effect played a more vital role than fire history effect in soil organic layer, while fire history effect was the most important factor for the varia-tion of soil nutrients in soil mineral layer. In our study, nutrients of litter and soil were lower than the control level at post-fire 4 and 14 years. The quality of litter and soil was improved with accele-rated plant growth and litter decomposition following post-fire recovery time and recovered to the pre-fire level at post-fire 40 years, reaching a steady status.