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Soil organic carbon (SOC) transformation is susceptible to tillage practices. Conservation tillage is known to optimize soil structure, improve microbial community diversity and increase SOC storage. However, how soil aggregate distribution and microbial community structure and function within aggregates affect SOC transformation under long‐term conservation tillage remains unclear. In this study, SOC mineralization dynamics were studied in situ and under laboratory conditions to examine the mechanisms by which C functional genes within soil aggregates of different sizes (i.e., mega‐, macro‐, and micro‐aggregates) influence SOC mineralization under long‐term tillage (i.e., zero, chisel, and plow tillage) in a dryland. The results indicated that in the winter wheat and summer maize rotation cropping system, SOC‐derived CO2‐C emissions were 143.99 and 133.29 g CO2‐C m−2 h−1 lower under chisel and zero tillage than that under plow tillage, respectively. Moreover, after 180 days of laboratory incubation, SOC mineralization in micro‐ and macro‐aggregates was 1.98 and 1.63 mg CO2‐C g−1 d−1 higher than that in mega‐aggregates, respectively. The aggregate‐associated differential modules of bacterial co‐occurring networks may be directly governed by bacterial community diversity and composition, which might play critical roles in driving SOC mineralization in response to different tillage intensities. Moreover, aggregate‐associated functional genes involved in labile and recalcitrant C compositions, which were determined by shotgun metagenomic sequencing, were associated with SOC mineralization and were significantly affected by the legacy effect of tillage intensity and aggregate size. Particularly, partial least squares path modeling revealed that genes involved in simple sugar metabolism exerted significantly positive effects on SOC mineralization, except for the effects of tillage intensity and aggregate size. Overall, this study showed that decreased abundances of labile C decomposition‐related functional genes within aggregates and community composition changes, as elucidated by the differences in bacterial network modules, under conservation tillage inhibit SOC mineralization. These findings may help in the development of adaptive soil tillage strategies for reducing carbon emissions in agroecosystems. [ABSTRACT FROM AUTHOR]

Tracking photosynthesized carbon (C) allocation into different C pools is crucial for management of C sequestration, especially in agroecosystems. However, the effects of long–term tillage management on allocation and dynamics of recently fixed C in the crop–soil–atmosphere system have been rarely investigated under dryland conditions. Using in–situ 13CO 2 repeat labeling, this study quantified the photosynthesized C input to soil, and assessed the responses of allocation dynamics, microbial utilization, and aggregate protection of newly fixed C in three long–term (>10y) tillage practices (no–till, chisel–till, and plow–till) in a dryland wheat cropping system. Regardless of tillage practice, the 13C included into the shoots, roots, soil respiration, rhizosphere, and bulk soils accounted for 46–64%, 4.6–6.0%, 17–38%, 6.4–11.7%, and 2.8–7.2%, respectively, of added 13C over a 35–d chase period. Owing to relatively low plant biomass, compared to plow–till, long–term no–till and chisel–till on average lowered plant 13C fixation and its allocation in rhizosphere soil by 17% and 11%, and 21% and 15%, respectively. Nevertheless, the 13C relocated to bulk soil was significantly higher under both no–till (0.24 g m−2) and chisel–till (0.22 g m−2) than that under plow–till (0.18 g m−2) over the chase period. This could be partially attributed to the decreased allocation of belowground 13C to root–derived CO 2 releases and the increased C retention in both macroaggregates and microaggregates in conservation tillage plots. Moreover, the reduced microbial utilization of new C in rhizosphere soil, as indicated by the low 13C amount in microbial biomass, may further facilitate new C accumulation in bulk soil under reduced tillage. Our findings suggest that despite low photosynthetically–fixed C input to belowground pools during the early growth stages, soils under long–term conservation tillage, in particular no–till, can have a distinct efficiency advantage in soil carbon sequestration by enhancing photosynthesized C preservation in soil aggregates and decreasing new C loss from root–derived CO 2 release in the dryland wheat–soil system. • In–situ 13C labeling was used to assess newly assimilated C allocation in crop–soil system. • Long–term conservation tillage significantly affected C allocation and microbial use in the belowground system. • Both no–till and chisel–till increased C retention in macroaggregates and microaggregates. • Conservation tillage improved new C sequestration efficiency in dryland cropping system. [ABSTRACT FROM AUTHOR]

Reducing greenhouse gas emissions and loss of soil fertility, while ensuring stable yield, is crucial to achieving "Carbon Peak" and "Carbon Neutrality" in grain production but is different to achieve. In this study, we aimed to understand the effects of conservation tillage on the yield, GHG emissions, soil carbon and nitrogen sequestration, and net ecosystem economic benefit (NEEB) to promote the transformation of tillage methods in the Loess Plateau, China, based the continuous application (>11 yr) of conservation tillage. Four-year observations showed that zero tillage and chisel plough tillage obviously reduced N 2 O and CO 2 emissions but greatly increased CH 4 uptake relative to plow tillage. Furthermore, the coupling relationship between CO 2 and N 2 O fluxes was weakly antagonistic during the winter wheat growing season, whereas there was a strong synergistic coupling between these fluxes during the summer maize growing season. An antagonistic coupling relationship appeared between CH 4 and N 2 O fluxes, whereas CO 2 and CH 4 fluxes appeared to be randomly related. Importantly, when carbon (C) emission reached 17.5 Mg C ha−1yr−1, and nitrogen (N) emission reached 7.8 kg N ha−1yr−1, the soil changed from a C sink to C source; when C emission reached 17.3 Mg C ha−1yr−1, and N emission reached 6.8 kg N ha−1yr−1, the soil changed from a N sink to N source. Considering yield gains, agricultural activity costs, and global warming potential costs together, chisel plough tillage significantly increased NEEB by 19.87%. Together, the advantages of long-term chisel plough tillage can reduce greenhouse gases emissions and increase NEEB while achieving soil carbon and nitrogen sequestration. Therefore, chisel plough tillage practice has both economic and environmental benefits. • Conservation tillage increased soil C and N sequestration in wheat-maize multiple cropping soils. • Conservation tillage reduced soil CO 2 and N 2 O emissions, while increased CH 4 uptake. • The CO 2 and N 2 O fluxes show an antagonistic or synergistic coupling relationship. • The coupling of GHG fluxes are the main triggers for sequestration of soil SOC and TN. • CPT practice significantly increased NEEB by reducing the GWP costs. [ABSTRACT FROM AUTHOR]

Soil bacterial communities are important soil regulators in agroecosystems. However, few studies have investigated the influences of integrated agricultural management practices on farmland soil bacterial community diversity and assembly processes. In this study, we assessed the impact of crop species (maize and soybean), tillage practice (chisel plow tillage, CPT; zero tillage, ZT; plow tillage, PT), rhizosphere effect (rhizosphere and bulk soils), and their interactions on the soil bacterial communities in Loess Plateau farmlands. Conservation tillage significantly increased soil moisture (SM), clay and sand fractions, and carbon and nitrogen levels; whereas silt fraction and pH decreased. Rhizosphere effect significantly improved soil texture and decreased SM, pH, total nitrogen, and nitrate nitrogen. Soybean cultivation significantly increased SM, silt fraction, and pH; while clay fraction decreased. Additionally, the rhizosphere effect decreased the competition among rhizosphere bacterial communities (edges: rhizosphere = 926, bulk = 1095; density: rhizosphere = 0.157, bulk = 0.184) and increased the structural complexity of the community network (modularity: rhizosphere = 0.857, bulk = 0.556); moreover, conservation tillage and soybean cultivation increased community network complexity (modularity: CPT = 0.879, ZT = 0.742, PT = 0.495; maize = 0.525, soybean = 0.888). Although the phylogenetic clustering of rhizosphere bacterial communities caused by the rhizosphere effect was lower than that of bulk soil bacterial communities (2.13%), it had no significant influence on rhizosphere or bulk soil bacterial community assembly, and deterministic processes dominated the formation of soil bacterial community structure. In conclusion, clarifying the variations in soil bacterial communities under integrated agricultural management practices can help predict trends in soil bacterial community function which can, in turn, effectively guide biological management decision-making in farming operations. Our findings may provide additional insights into the underground processes in farmland and facilitate the development of conservation farming operations as sustainable agricultural practices. • Tillage practices and rhizosphere effect markedly altered soil properties. • CPT, ZT, and soybean cultivation simplified soil bacterial community networks. • Deterministic processes dominated most bacterial community assembly processes. • Crop selection process enhanced rhizobacterial phylogenetic clustering effects. [ABSTRACT FROM AUTHOR]

Root-associated bacteria are studied under a single agricultural measure, but the responses of rhizosphere bacterial communities toward agricultural management, in an arid agroecosystem, are unclear. Here, we evaluated the effects of tillage practice, crop rotation pattern, and crop development on rhizobacteria in a field experiment in the dryland region of northern China. Three tillage [chisel plow tillage (conservation), zero tillage (conservation), and plow tillage (conventional)] practices and two crop rotation (maize–wheat rotation and soybean–wheat rotation) patterns were been combined to assess changes in rhizosphere bacterial communities during wheat development. Our results showed that conservation tillage practices had considerable effects on soil physicochemical properties compared with conventional tillage, thus changing the rhizosphere microenvironment. Spearman's correlation analysis also indicated that soil physicochemical properties were closely related to the relationships among the rhizosphere bacterial communities and taxa. Furthermore, the composition and α-diversity of the rhizosphere bacterial communities were substantially affected by the crop growth stage and tillage practices; however, the legacy effect of the previous crop had different effects on the rhizosphere bacterial communities owing to the short period of implementing crop rotation. The phylogenetic diversity and taxonomic composition of rhizosphere bacterial communities were mainly explained by the crop growth stage and tillage practice, respectively. Additionally, conservation tillage practices and soybean–wheat rotation pattern both delayed rhizobacteria successions. Co-occurrence networks also showed that the differential modules among the rhizosphere bacterial communities decreased with wheat development, whereas the soybean–wheat rotation pattern increased their degree of co-occurrence. The differences in taxonomic compositions and phylogenetic diversities of the rhizosphere bacterial communities may affect their potential functions and alter crop growth and development. • Integrated agricultural management practices altered wheat rhizobacteria. • Integrated agricultural management practices altered turnover rate of rhizobacteria. • The differential modules among rhizobacteria communities had a decreasing trend. • There was a higher degree of co-occurrence in the soybean–wheat rotation pattern. [ABSTRACT FROM AUTHOR]

• CPT and ZT improved farmland soil properties in China's Loess Plateau. • CPT and ZT changed the diversity and composition of rhizobacterial communities. • CPT had the potential to increase the total biomasses and N accumulations of crop. • Crop species had weaker effects on rhizobacteria than those of tillage practices. • Rhizosphere bacterial communities were weakly correlated with crop development. Conservation tillage, that is, reduced or zero tillage, can change the soil ecological environment and rhizosphere bacterial communities. Here, we investigated temporal variations in rhizosphere bacterial communities during crop development and their relationships with crop growth characteristics under three tillage practices (Plow tillage (PT), chisel plough tillage (CPT), and zero tillage (ZT)) in maize and soybean fields on the Loess Plateau of China. Conservation tillage (CPT and ZT) practices significantly increased the contents of soil moisture (3.62–13.13%), soil organic carbon (29.19–39.67%), and nitrogen (38.69–60.23%) and decreased soil pH (1.15–3.76%). The overall responses of rhizosphere bacterial community composition to tillage practice and phenological period were taxonomically consistent across maize and soybean fields, and changes were predominantly observed in the relative abundances of dominant bacterial phyla. Co-occurrence network analysis indicated that the average connectivity degree among 16S operational taxonomic units was higher under PT (38.92% and 73.60%) practice than under CPT and ZT practices. CPT practice tended to increase the total biomass and nitrogen accumulation of maize and soybean compared with PT practice, whereas ZT practice significantly (P < 0.05) decreased them. Partial least squares path modeling analysis showed that temporal variations in the rhizosphere bacterial communities (explained variations in maize and soybean fields were 94.7% and 92.7%, respectively) were regulated by tillage practices and phenological periods, and partly explained the changes in growth dynamics of maize and soybean (0.161 and 0.031, respectively). Overall, CPT practice could improve the soil ecological environment and promote crop growth in the China's Loess Plateau. Therefore, we recommend that CPT practice should be adopted in semi-arid agricultural areas to improve the potential relationships between the underground and aboveground in agroecosystems. [ABSTRACT FROM AUTHOR]

Fertilized agricultural soils can be a major source of soil nitrous oxide (N 2 O) emissions to the atmosphere. Conservative soil management may have the ability to reduce N 2 O emissions through affecting a number of N-cycling-related soil biophysical properties. Using in situ N 2 O measurements combined with the techniques of quantitative polymerase chain reaction (qPCR), amplicon sequencing, and metagenomic sequencing, we aimed to understand the effects of long-term (>10 y) conservation tillage (i.e., zero- and chisel-till vs. conventional plow-till) on soil N 2 O production and associated microbial guilds following inorganic N fertilizer application in maize. Between 2017 and 2019, continuous in situ measurements of N 2 O fluxes indicated that both zero- and chisel-till significantly lowered cumulative emissions within the growing season, compared to plow-till, mainly through shortening the duration and reducing the magnitude of post-fertilization emission events. Conservative soil management, in particular zero-till, consistently increased the Shannon diversity index of bacterial community over the growing season, compared with plow-till. High-frequency qPCR analyses further revealed a clear tillage-induced niche differentiation between nosZI- and nosZII- N 2 O reducers, as evidenced by the dominant gene abundance of nosZII compared to nosZI in the conservation tillage soil, which eventually probably contributed to the transformation of N 2 O to N 2. Moreover, compared to plow-till, zero-till significantly decreased gene abundances involved in N 2 O production including the nirS , nirK , and narG genes, but increased abundances of N 2 O reduction genes such as nosZ during peak N 2 O emissions. Critically, the abundances of detected species involved in denitrification, such as Deltaproteobacteria_bacterium spp. and Alphaproteobacteria_bacterium spp. were clearly inhibited by zero-till. Overall, the reduced soil N 2 O emissions under reduced tillage positively and strongly depended on the nosZI -to- nosZII ratio, while increased emissions due to conventional tillage were positively associated with intensified denitrification. Such improvements in understanding of the responses of N-cycling gene abundances to tillage intensity can certainly help in the development of updated soil management practices and adaptative N application strategies to reduce reactive N emissions in agricultural ecosystems. • Conservation tillage shortened the duration and lowered the magnitude of post-fertilization N 2 O emissions. • nosZI , and nosZII genes suggested a tillage-induced niche differentiation among N 2 O reducers. • Conservation tillage decreased abundance of genes involved in N 2 O production. • The reduced N 2 O emissions were mainly attributed to the low nosZI -to- nosZII ratio. • Intensified denitrification resulted in higher emissions of N 2 O under conventional tillage soil. [ABSTRACT FROM AUTHOR]

Conservation tillage has been recommended as one of the effective soil management practices for mitigating the negative environmental effects of synthetic ammonia application and hence achieving cleaner agricultural production. However, information about how long-term conservation tillage affects agroecosystem nitrogen balance in dryland winter wheat-summer maize cropping is limited. Based on a long-term (>9 yr) field tillage experiment and in-situ observation, we assessed the effects of different tillage practices (i.e., chisel plough tillage (CPT), zero tillage (ZT), and conventional ploughing tillage (PT)) on soil nitrogen balance and crop productivity in the 2016–2017 and 2017–2018 growing seasons. Each tillage practice was exposed to a local widely adopted N application rate (240 kg ha−1 yr−1) in both seasons. Our results indicated that, compared with PT, CPT and ZT significantly (P < 0.05) reduced N 2 O emissions by 39.7% (2.8 kg N ha−1 yr−1) and 55.3% (3.9 kg N ha−1 yr−1), and N leaching by 52.3% (11.8 kg N ha−1 yr −1) and 147.7% (33.3 kg N ha−1 yr−1) across the two growing seasons, respectively. CPT significantly enhanced crop aboveground N uptake by 4.0%, and increased the annual crop yield by 5.9–8.1% (0.8–1.2 t ha−1 yr−1). Although CPT and ZT enhanced NH 3 volatilization by 46.7% (14.6 kg N ha−1 yr−1) and 84.3% (26.3 kg N ha−1 yr−1), the total N losses under CPT and ZT were decreased on an average by 7.4% and 22.4%, respectively. Overall, CPT and ZT significantly increased the accumulation of soil total nitrogen in the 0–100 cm layer by 34.8 and 54.1 kg N ha−1 yr−1, respectively. Taking N inputs and outputs together, CPT achieved a lower N surplus mainly due to increased crop N harvest and reduced N losses including gaseous emissions and hydrological leaching. Our findings suggest that long-term chisel plough tillage in dryland agroecosystems could serve as a promising soil management practice in increasing crop productivity and maintaining sustainability through enhancing N removal from crop biomass and decreasing N losses via N 2 O emission and nitrate-N leaching. Image 1 • CPT practice significantly increased grain yields and grain N harvested. • CPT and ZT significantly reduced the loss of N 2 O, NO 3 − leaching and straw N removal. • Conservation tillage in drylands should mitigate risk of NH 3 volatilization. • Accumulation of soil total N in 0–100 cm layer remained increasingly in CPT and ZT. • The CPT is a promising tillage practice for achieving cleaner production. [ABSTRACT FROM AUTHOR]