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Delineating management zones (MZs) is considered one of the most important steps towards precision nitrogen (N) management, as MZs are required to optimize N inputs and improve environmental health. However, no reports have fully explored the optimization of regional MZs related to policymaking to achieve long-term Sustainable Development Goals. This study developed a new sustainable environmental index (SEI) by integrating the Euclidean distance after feature normalization, spatial autocorrelation, and expert knowledge. The SEI was then used to delineate MZs in the main wheat-producing provinces of China using the fuzzy C-mean clustering. The results showed that compared to the two data-driven-based methods (Random Forest- and all variables-based methods), the SEI-based method performed the best and identified 9 MZs in terms of practical production and spatial distribution of zones. Further analysis indicated that the dominant drivers of MZ delineation showed strong spatial heterogeneity and high input uncertainty. Climatic factors explained 15.6% of the yield variability, while both soil factors and topographic factors individually accounted for 10.2% of the variability. The similar spatial characteristics of input uncertainty were found to be consistent across various MZs, with a high level of uncertainty ranging from 0.7 on a scale of 0 to 1. Finally, this study provided potentially valuable suggestions for policymakers and farmers, as well as possible directions for further N management. Overall, the proposed methodological framework on regional MZs has important implications for precision N management, providing a new perspective for intensive sustainable development. [ABSTRACT FROM AUTHOR]

Agriculture faces great challenges to ensure global food security by increasing yields while reducing environmental costs. Here we address this challenge by conducting a total of 153 site-year field experiments covering the main agro-ecological areas for rice, wheat and maize production in China. A set of integrated soil-crop system management practices based on a modern understanding of crop ecophysiology and soil biogeochemistry increases average yields for rice, wheat and maize from 7.2 million grams per hectare (Mg ha−1), 7.2 Mg ha−1 and 10.5 Mg ha−1 to 8.5 Mg ha−1, 8.9 Mg ha−1 and 14.2 Mg ha−1, respectively, without any increase in nitrogen fertilizer. Model simulation and life-cycle assessment show that reactive nitrogen losses and greenhouse gas emissions are reduced substantially by integrated soil-crop system management. If farmers in China could achieve average grain yields equivalent to 80% of this treatment by 2030, over the same planting area as in 2012, total production of rice, wheat and maize in China would be more than enough to meet the demand for direct human consumption and a substantially increased demand for animal feed, while decreasing the environmental costs of intensive agriculture. [ABSTRACT FROM AUTHOR]

Abstract: The challenges facing agriculture in China are probably more severe than ever before. We have developed an integrated technology system in which the focus is on achieving both high crop productivity and high resource use efficiency (“double high” technology system) to ensure food security and environmental sustainability. The components comprise (1) significantly increased grain-yield through high-yield crop management, i.e. an optimal cropping system design and management well adapted to climate conditions; (2) greatly increased nutrient-use efficiency through root/rhizosphere management to optimize the nutrient supply intensity and composition in the root zone to maximize root/rhizosphere efficiency; (3) improved soil quality to ensure long-term food security by managing soil organic matter and eliminating soil physical, chemical and biological constrains and (4) enhanced agricultural sustainability through resource and environment management by increasing resource use efficiency, reducing nutrient losses and greenhouse gas emissions and minimizing negative ecological footprints. In our work in major agricultural regions of China, this system has been successfully tested and demonstrated through well-organized farmer associations, enterprises with improved products and government extension networks. The new “double high” concept has the potential to become an effective agricultural development path to ensure food security and improve environmental quality, especially in China and other rapidly developing economies where agricultural intensification must achieve and must be transformed from low-efficiency systems to achieving high yields with high resource use efficiency. [Copyright &y& Elsevier]

Abstract: In the last three decades there has been a major shift in China''s agriculture with the conversion from cereal fields to vegetable production, however little is known about the impact of this land use change on labile soil carbon and microbial community structure. We conducted a study to characterize dissolved organic carbon (DOC) and soil microbial community by comparing greenhouse vegetable fields with contrasting management intensity and adjacent cereal fields (wheat–maize rotation) in Shouguang and Quzhou in North China. Compared with cereal fields, greenhouse vegetable cultivation increased soil organic carbon (SOC) and total nitrogen (TN), while it decreased the soil pH, particularly at the high-intensity site. The DOC concentration was significantly higher in greenhouse vegetable fields than in cereal fields, whereas DOC composition differed between greenhouse vegetable fields and cereal fields only at high management intensity. Chemical fractionation indicated that DOC from greenhouse vegetable fields with high management intensity was less decomposed than DOC from cereal fields, because the percentage of hydrophobic acid (HOA) as DOC was higher in vegetable fields. Vegetable production significantly changed the microbial community structure in comparison to cereal fields: high-intensity management increased total bacteria, G (+) bacteria and fungi, while low-intensity decreased fungi and increased bacteria-to-fungi ratio. The main factor affecting microbial community structure was soil pH in this study, accounting for 24% of the differences. [Copyright &y& Elsevier]

In recent years, agricultural growth in China has accelerated remarkably, but most of this growth has been driven by increased yield per unit area rather than by expansion of the cultivated area. Looking towards 2030, to meet the demand for grain and to feed a growing population on the available arable land, it is suggested that annual crop production should be increased to around 580 Mt and that yield should increase by at least 2% annually. Crop production will become more difficult with climate change, resource scarcity (e.g. land, water, energy, and nutrients) and environmental degradation (e.g. declining soil quality, increased greenhouse gas emissions, and surface water eutrophication). To pursue the fastest and most practical route to improved yield, the near-term strategy is application and extension of existing agricultural technologies. This would lead to substantial improvement in crop and soil management practices, which are currently suboptimal. Two pivotal components are required if we are to follow new trajectories. First, the disciplines of soil management and agronomy need to be given increased emphasis in research and teaching, as part of a grand food security challenge. Second, continued genetic improvement in crop varieties will be vital. However, our view is that the biggest gains from improved technology will come most immediately from combinations of improved crops and improved agronomical practices. The objectives of this paper are to summarize the historical trend of crop production in China and to examine the main constraints to the further increase of crop productivity. The paper provides a perspective on the challenge faced by science and technology in agriculture which must be met both in terms of increased crop productivity but also in increased resource use efficiency and the protection of environmental quality. [ABSTRACT FROM PUBLISHER]

Yield gap (Yg) analysis is useful to map the scope for sustainable intensification of agriculture, but explaining and quantifying the underlying causes of yield gaps remains a considerable challenge. The objective of this study was to decompose maize yield gaps under different nitrogen (N) application rates and soil quality conditions across irrigated and rainfed cropping systems in China. A comprehensive database consisting of 5228 on-farm trials located in three major maize production regions of China was used for this purpose. The on-farm trials contained detailed information for four different treatments: fertilizer omission (control), optimal N rate (optimal N), 50% of optimal N rate (low N) and 150% of optimal N rate (high N). These were combined with biophysical and yield potential data from the Global Yield Gap Atlas (http://yieldgap.org). An analytical framework integrating stochastic frontier analysis and principles of production ecology was applied to decompose the overall maize yield gap into components of efficiency (and respective management and soil quality effects, Yg-M and Yg-S), resource (Yg-R), and technology Yg (Yg-T). The potential yield (Yp) of irrigated maize averaged 14.5 Mg/ha in Northeast China (NE) and 11.9 Mg/ha for North China Plain (NCP), and the water-limited potential yield (Yw) of rainfed maize averaged 12.0 Mg/ha in NE and 10.5 Mg/ha in Southwest China (SW), respectively. Maize yield gaps were highly variable across N treatments and cropping systems and ranged between 27–56% of Yp or Yw. Larger absolute yield gaps were observed in irrigated cropping systems in NE (4.8–8.1 Mg/ha) than in NCP (3.8–6.1 Mg/ha) and in rainfed cropping systems in NE (3.6–6.7 Mg/ha) and SW (2.8–5.9 Mg/ha). The components of the yield gap differed in size across cropping systems and N treatments. Yg-T was fairly small and consistent across N treatments ranging between 7.0% and 12.0% of Yp for irrigated maize and only ca. 2.0% of Yw for rainfed maize in NE. Yg-R was strongly associated with the N treatment explaining between 16.0–26.0% of Yp (or Yw) for control and low N treatments and being close to negligible for the optimal and high N treatments. Yg-M due to inefficient crop management accounted for 6.0–14.0% of Yp (or Yw) across cropping systems and N treatments, which is equivalent to 0.7–1.8 Mg/ha. The Yg-S explained the largest proportion of the total yield gap, especially in trials with low and medium soil quality levels, accounting for 11.0–24.0% of Yp or Yw (1.3–3.1 Mg/ha). The Yg-S was linked to partly manageable soil properties, such as low soil organic matter contents and low available P and/or K. This study is one of the first to incorporate the effects of soil quality in yield gap analysis and provides a basis to target management practices that can improve soil quality and N use efficiency while narrowing maize yield gaps in China. [ABSTRACT FROM AUTHOR]

• Maize-based organic amendments were examined after seven years of annual application. • All organic amendments increased SOM in bulk soil and all physical fractions. • Biochar exerted the strongest positive effect on SOC contents and thermal stability. • The majority of the accumulated C and N occurred in the silt + clay fractions. Application of organic amendments and N fertilizer can affect C and N sequestration, however, the degree to which diverse organic amendments and optimal N fertilization for matching demand for high crop productivity contributes to soil organic matter (SOM) of Cambisol in the North China Plain is not fully known. The objective was to evaluate the combined effects of annual maize straw-derived organic amendments (straw, manure, compost, biogas residue, or biochar) and in-season mineral N fertilizer amendment on soil organic carbon (SOC) and total N (TN) accumulation and thermal stability in bulk soils and physically isolated soil aggregate fractions in a long-term field experiment on the North China Plain. Application of organic amendments either alone or with N increased the proportion of macroaggregates (+62 to 137 %), aggregate mean weight diameter (+50 to 106 %), SOC (+38 to 206 %) and TN (+13 to 52 %) contents in bulk soil. The organic amendments and N fertilizer additions also increased SOC and TN contents in each of the isolated fractions: macroaggregates (+119 to 851 % for SOC, +109 to 237 % for TN) and microaggregates (+42 to 192 % for SOC and +30 to 145 % for TN), total fine particulate organic matter (T fPOM, +143 to 891 % for T fPOM-SOC, +129 to 549 % for T fPOM-TN) and total silt + clay within aggregates (53–139 % for SOC and 20–106 % for TN). Biochar resulted in the largest increase in SOC contents and improved soil aggregation without N fertilization, but fertilization greatly decreased these responses. The majority of the accumulated C and N occurred in the total silt + clay fractions, making up 50–90 % of total SOC and 79–96 % of total TN. Total fine POM and total silt + clay within aggregates contributed to 40–78 % and 10–56 % of SOC, 28–60 % and 37–71 % of TN increase between soil with and without organic amendments. Our results suggested that C and N retained in T fPOM and silt + clay fractions within aggregates were important mechanisms for C and N stabilization. Substitution of annual above-ground litter with biochar with or without mineral N fertilizer was the most effective way for SOM build up and stabilization under a wheat/maize system in the North China Plain, while manure, compost and biogas residue resulted in little to no increases of SOM in bulk soils and physically isolated aggregate fractions compared to straw amendment. Besides the effects of each amendment type on SOC, the different recovery rates of the various amendments, which determines the total quantity of each amendment that can be produced, should be taken into consideration in decisions about maize residue management at the regional scale in the North China Plain. [ABSTRACT FROM AUTHOR]

The semi-arid grasslands in northern China are subjected to accelerating land use change due to population growth and food demand. Considerable uncertainty exists on annual methane (CH 4 ) fluxes of different land uses because most measurements have only been conducted during the growing season. Using static chamber – gas chromatographic technique, we quantified and characterized annual CH 4 fluxes (from 2012 to 2015) from four land uses common in an agro-pastoral ecotone of northern China: summer-grazed grassland (SumGrazed), winter-grazed grassland (WinGrazed), ungrazed grassland since 1997 (Ungrazed) and oat cropland (OatCrop). The soil at all land uses functioned exclusively as a sink for atmospheric CH 4 through the entire three years. Annual CH 4 uptake rates averaged 1.42, 2.36, 1.12 and 2.57 kg C ha −1 yr −1 for SumGrazed, WinGrazed, Ungrazed and OatCrop, respectively, during 2012–2015. Compared to Ungrazed, OatCrop and WinGrazed increased annual CH 4 uptake by 129 and 111%, respectively. Non-growing season (October–April) contributed 28–43% of the annual CH 4 uptake at all land uses. Across all four land uses, annual cumulative CH 4 uptake decreased with increasing soil water-filled pore space (WFPS) explaining 81% of the variance in annual CH 4 uptake. WFPS negatively correlated to CH 4 uptake in the growing season (R 2 = 0.16-0.35, P < 0.001). CH 4 uptake increased with soil temperature through the entire observed period (R 2 = 0.38-0.63, P < 0.001) and the non-growing season (R 2 = 0.51–0.74, P < 0.001). We conclude that grazing has the potential to increase CH 4 uptake from the atmosphere and consequently, contribute positively to CH 4 related part of C budget. [ABSTRACT FROM AUTHOR]

Despite broad information on greenhouse gas (GHG) emissions from the soil surface, only few studies have examined the depth related GHG concentration and production within the soil. We coupled chamber surface GHG flux measurements with analysis of subsurface GHG concentrations at five depths (0, 10, 30, 50 and 70 cm) using silicon tubes in a grassland and cropland soils in a semi-arid agro-pastoral ecotone over a full year. Grassland and cropland soils behaved as net CO 2 and N 2 O sources, but sinks of CH 4. CO 2 and N 2 O concentrations increased but CH 4 decreased with soil depth. Subsurface GHG fluxes calculated using Fick's law decreased with depth. The modeled GHG and measured surface fluxes agreed much better for CO 2 than N 2 O or CH 4. Spring-thaw and rainfall events triggered N 2 O pulses, CH 4 uptake peaks and CH 4 concentration drops. Annual emissions or uptake based on chamber method were 4820–7580 kg C ha−1 yr−1, 2.4–1.5 kg C ha−1 yr−1, and 0.13–0.14 kg N ha−1 yr−1 for CO 2 , CH 4 , and N 2 O across the grassland and cropland, respectively. Modeled annual accumulation of GHG fluxes dropped with depth, whereas the topsoil (0–20 cm) contributed about 65% for CO 2 , 68% for N 2 O and 72% for CH 4 of the total profile. The vertical distribution of GHG fluxes reflected those of soil organic carbon and root biomass. The grassland had higher annual CO 2 flux but lower CH 4 uptake than the cropland. Annual N 2 O fluxes were similar between the two ecosystems. • CO 2 and N 2 O concentrations increased but CH 4 decreased with soil depth. • Spring-thaw and rainfall events triggered N 2 O pulses, CH 4 uptake peaks. • More than 65% of the GHG efflux originated from the top 20 cm soil. • The vertical distribution of GHG fluxes reflected those of SOC and root biomass. [ABSTRACT FROM AUTHOR]

A comprehensive synthesis of 32 long-term experiments in China is performed by comparing yields and SOM contents and their time by nutrient management responses (TNMR) to determine whether and to what extent combined application of organics amendments and fertilizers (organics + fertilizers) can increase productivity and soil organic matter (SOM) content and enhance the sustainability of diverse cropping systems. TNMR is defined as percentage changes over time in yields and SOM contents in external nutrient input treatments relative to initial and control plots and represents the net effects of nutrient management strategies on yields and SOM contents. Organics + fertilizers significantly increased yields over three crops (wheat, maize and rice) on average by 29% relative to sole organics and 8% to fertilizer only. Higher TNMR values in yields were found with organics + fertilizers in the sequence wheat (53%) > maize (40%) > rice (8%). Significant and positive time trends in TNMR of organics + fertilizers in wheat and maize yield may imply enhanced sustainability of cropping systems. Addition of organics (alone or combined with fertilizers) increased SOM contents and their TNMR over fertilizers applied alone. However, benefits varied between organics and organics + fertilizers by land use type. The latter led to higher SOM contents than (for dry land) and similar to the former (for dry-flooded and flooded systems). 2.3 and 1.4 times higher TNMR of organics + fertilizers in SOM content in dry land than dry-flooded and flooded systems implies that dry land was more responsive in SOM content increase upon adoption of organics + fertilizers than the latter. Overall, despite variation in the quantitative magnitude in crop or land use type, compared with application of organics or fertilizers only, a combination of both represents the most effective way to produce more food, build up SOM and enhance sustainability, especially in dry land cropping systems. [ABSTRACT FROM AUTHOR]

Overgrazing and intensive farming have led to severe land degradation in the past half century in the agro-pastoral ecotone of northern China. Currently, complete and periodical exclusions of grazing are commonly adopted for the restoration of these degraded grasslands. However, little is known about the effects of such land uses on nitrous oxide (N 2 O) emission in this region. Using static chamber technique, we quantified annual N 2 O emissions (from May 2012 to September 2013) from four land uses: summer-grazed grassland (SG), winter-grazed grassland (WG), ungrazed grassland since 1997 (UG) and oat cropland (OC). N 2 O emissions occurred mainly after farmyard manure fertilization and during spring thaw periods. Annual N 2 O fluxes from the SG, WG, UG and OC were 0.19, 0.15, 0.43 and 0.98 kg N ha −1 yr −1 , respectively. The spring–thaw N 2 O emissions from UG and OC dominated the annual emission and accounted for 70% and 65% of the annual fluxes, respectively. In contrast, the contributions of spring thaw fluxes to total annual N 2 O emissions for SG and WG were only 32%. N 2 O fluxes during spring thaw season were positively related to soil NH 4 + + NO 3 − content accounting for 80% of N 2 O flux variability across all land uses. Land use conversion from the native grassland to cropland increased N 2 O flux both during growing and spring thaw seasons due to farmyard manure application. Instead, grazing has the potential to decrease annual N 2 O losses mainly through reducing spring–thaw N 2 O emissions. [ABSTRACT FROM AUTHOR]

In China, considerable cropland previously under grain production has been rapidly converted to greenhouse vegetable production by farmers since 1980s. Vegetable crops generally require higher nitrogen (N) inputs from manure amendments and more frequent tillage and irrigation operations compared to grain crops. Here, we compared potential denitrification-derived N 2 O emissions across the soil profile (0–90 cm depth) between grain and greenhouse vegetable fields. Denitrification enzyme activity (DEA) was assessed in the top 0–15 cm soil layer. Soil samples from five wheat ( Triticum aestivum L.) – maize ( Zea mays L.) fields, paired with adjacent vegetable greenhouse fields, were collected across typical vegetable production regions. Conversion from the grain fields to the greenhouse vegetable fields led to greater potential denitrification-derived N 2 O emissions in the 0–15 and 15–30 cm depths, respectively, with 4 and 3 times higher cumulative emissions over the 10-day incubation. Continuous manure amendments and chemical N input increased water extractable organic carbon and nitrate concentrations, which significantly enhanced potential denitrification-derived N 2 O production in the 0–30 cm soil depth of vegetable crop fields. The differences in microbial community for the two cropping systems did not seem to affect the surface N 2 O production potential since denitrification enzyme activity were not significantly different between the two production systems. There was a small to negligible potential N 2 O flux in 30–90 cm soil depths for both production systems because of limited carbon availability and microbial activity. Managing surface labile carbon and mineral N pool may be critical in reducing regional N 2 O emissions in China's greenhouse vegetable production systems. [ABSTRACT FROM AUTHOR]

Abstract: Soil organic matter (SOM) and enzymes are essential for nutrient cycling, and are considered as important indicators of soil quality. The effects of organic and mineral fertilization on soil organic carbon (SOC), total nitrogen (TN) and enzyme activities in bulk soil and particle-size fractions were investigated under a winter wheat/maize cropping system in the North China Plain. The experiment established in 1993 includes three treatments: (1) unfertilized control (CK); (2) mineral fertilizers (MF); and (3) farmyard manure (FYM). Application of FYM significantly increased SOC and TN contents and activities of six enzymes: invertase, β-glucosidase, urease, acid and alkaline phosphatases and dehydrogenase in bulk soil and in all particle-size fractions as compared to those in MF and CK. Highest contents of SOC and TN were found in coarse sand and lowest in the silt fraction. The C/N ratios decreased with decreasing particle-size fractions. β-Glucosidase and acid phosphatase activities predominated in coarse sand fraction, reflecting high substrate availability. The urease activity was highest in clay-size fractions, depending on mineral sorption processes. The SOM and enzyme activities in the coarse sand were the most sensitive to fertilization. The smallest response of SOM in the clay fraction to fertilization confirmed that SOM on clay is the most stable C pool. The 15-year fertilization experiment clearly showed that FYM represented the best management practice for improving soil quality and microbial activity. [Copyright &y& Elsevier]

Abstract: The Loess Plateau in northwest China is one of the most eroded landscapes in the world, and it is urgent that alternative practices be evaluated to control soil erosion. Our objective was to determine how three different tillage practices for monoculture of winter wheat (Triticum aestivum L.) affected soil organic carbon (SOC) and N content after 11 years. Conventional tillage with residue removal (CT), shallow tillage with residue cover (ST), and no-tillage with residue cover (NT) were investigated. Carbon and N in various aggregate-size classes and various labile organic C fractions in the 0–15- and 15–30-cm soil layers were evaluated. The ST and NT treatments had 14.2 and 13.7% higher SOC stocks and 14.1 and 3.7% higher total N (Nt) stocks than CT in the upper 15cm, respectively. Labile C fractions: particulate organic C (POC), permanganate oxidizable C (KMnO4-C), hot-water extractable C (HWC), microbial biomass C (MBC) and dissolved organic C (DOC) were all significantly higher in NT and ST than in CT in the upper 15cm. KMnO4-C, POC and HWC were the most sensitive fractions to tillage changes. The portion of 0.25–2mm aggregates, mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates from ST and NT treatments were larger than from CT at both 0–15- and 15–30-cm soil depths. The ST and NT treatments had significantly higher SOC and Nt in the 0.25–2mm fraction at both depths and significantly higher Nt content in the upper 15cm. Positive significant correlations were observed between SOC, labile organic C fractions, MWD, GMD, and macroaggregate (0.25–2mm) C within the upper 15cm. We conclude that both variants of conservation tillage (NT and ST) increase SOC stock in the rainfed farming areas of northern China and are therefore more sustainable practices than those currently being used. [Copyright &y& Elsevier]

• SOC and grain yield was measured with biochar and straw addition in maize-rice vs rice-rice system. • Straw addition has no effect on SOC accumulation for both cropping systems over a 4-year periods. • Biochar significantly improved more SOC in rice-maize system than rice-rice system. • Higher SOC under rice-maize system with biochar addition were linked increased soil aggregation. • Both biochar and straw addition led to higher late rice yield. Crop rotation of flooded rice with an upland crop like maize on previous continuous paddy soils is an emerging cropping system in South China. A four-year experiment was conducted at a research area in Hunan province, having a long history of double paddy-rice cropping throughout the year. Maize was introduced as an upland crop in rotation with paddy rice, thus providing two parallel cropping systems i.e., the previous flooded rice-rice (R–R) and the new maize-rice rotation (M–R) systems. We used three treatments in both cropping systems; namely, farmer's practice (without external C input) as a control, straw addition, and biochar addition. The straw and biochar were added to soil in late rice season on an equal C input basis (3000 kg C ha−1yr-1). In the R–R plots, rice straw was added while in M–R plots maize straw was added during late rice field preparation. Our results show that there were no changes in soil organic carbon (SOC) concentration when R–R was replaced by M–R rotation. Straw addition had no effect on SOC but improved late rice yield. Biochar addition significantly increased SOC and late rice yield in both cropping systems. Moreover, biochar addition resulted in a more significant accumulation of SOC (9% higher) in M–R than R–R. Among soil aggregates, only the 0.25–2 mm fraction had a significantly higher SOC concentration with biochar relative to the control and straw return; and this increase was significantly more pronounced under M–R (28% higher) than R–R cropping system. In general, a significantly higher proportion of small macro-aggregates (0.25–2 mm) were found under M–R, while smaller aggregates (0.05–0.25 and <0.05 mm) were more abundant under R–R. δ13C analyses from M–R plots reveal that the quantity of maize-derived C was marginally higher in the straw treatment than control, but this was not reflected in any significant impact on total SOC of the bulk soil or of aggregates. In conclusion, no detectable changes in SOC were observed over four years experimental period following shift from R-R to M-R cropping system. M-R system with biochar addition led to higher productivity and environmental benefits. [ABSTRACT FROM AUTHOR]

• Reduced tillage, residue retention increased C and N versus conventional management. • Enzyme activity increased with conservation management. • Conservation management increased enzyme activities in all particle-size fractions. • Magnitude of increases greater for enzyme activities than C and N stocks. • Enzyme activity sensitive indicator of soil health in response to management change. Soil organic matter (SOM) concentration and enzyme activity are important biochemical indicators of soil health for assessing the sustainability of agricultural management practices. However, little is known about the long-term effects of tillage and crop residue management on SOM and enzyme activities in soil particle-size fractions on the Loess Plateau of Northern China. The objective of this study was to investigate the effects of 11 years of combined tillage and crop residue management treatments on soil organic carbon (SOC), total nitrogen (TN) concentrations and enzyme activities in bulk soil and particle-size fractions from a rainfed wheat (Triticum aestivum L.) monoculture system in this region. We hypothesized that reduced tillage and increased residue retention would increase SOC, TN and enzyme activities in both bulk soil and particle-size fractions, and that enzyme activity would serve as a more sensitive indicator of soil health in response to management. Compared with conventional tillage and residue removal (CTRR), reduced tillage and stubble mulch residue retention (RTSM) increased bulk soil activities of most enzymes (sulfatase +68%, invertase +62%, β-glucosidase +58%, dehydrogenase +46%). These increases were greater than the relative increases in total SOC (34%) and TN (33%) concentrations, supporting our hypothesis of a stronger response in microbial activity to management than total element stocks. The RTSM treatment also increased SOC and TN concentrations, as well as β-glucosidase, acid phosphatase and urease activities in all particle-size fractions (2000-250, 250-53, 53-2 and < 2 μm) compared with the CTRR treatment. Both β-glucosidase and acid phosphatase showed a general decrease from coarse- to fine-sized fractions, and resembled the distribution of SOC and TN concentrations in particle-size fractions. Conversely, urease activity was greater in sand and clay fractions, which was decoupled from SOC and TN distributions. Our results indicate that biological indicators of soil health were more sensitive than C and N stocks to cumulative long-term changes in tillage and residue management. [ABSTRACT FROM AUTHOR]

Organic and mineral fertilization increase crop productivity, but their combined effects on soil quality index (SQI) and ecosystem multifunctionality (EMF, defined as the capacity of soils to simultaneously provide multiple functions and services) are not clear. We conducted a 13-year field trial in North China Plain to examine how five maize-derived organic fertilizers (straw, manure, compost, biogas residue, and biochar) at equal C input rate (3.2 t C ha -1 ), with or without nitrogen (N) fertilization influenced topsoil (0-15 cm) physico-chemical properties, activities of enzymes responsible for carbon (C), N, and phosphorus (P) cycling, as well as SQI and soil EMF. Organic fertilizers with or without N increased SQI by 51-187 % and EMF by 31-351 % through the enhancement of soil physical (mean weight diameter of soil aggregates) and chemical properties (C, N, and P contents) as well as C, N, and P acquisition enzyme activities, albeit the biochar effects were of minor importance. N application increased EMF compared to soil without N. Soil quality increased with EMF. Random forest analysis revealed that microbial biomass C and N, available P, permanganate oxidizable C, dissolved organic C and N, mean weight diameter of aggregates, hot water extractable C, and electrical conductivity were the main contributions to soil EMF. We conclude that application of maize-derived organic fertilizers, especially compost and straw, with optimal N fertilization is a plausible strategy to increase SQI and EMF under a wheat/maize system., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Avoiding excessive agricultural nitrogen (N) use without compromising yields has long been a priority for both research and government policy in China 1,2 . Although numerous rice-related strategies have been proposed 3-5 , few studies have assessed their impacts on national food self-sufficiency and environmental sustainability and fewer still have considered economic risks faced by millions of smallholders. Here we established an optimal N rate strategy based on maximizing either economic (ON) or ecological (EON) performance using new subregion-specific models. Using an extensive on-farm dataset, we then assessed the risk of yield losses among smallholder farmers and the challenges of implementing the optimal N rate strategy. We find that meeting national rice production targets in 2030 is possible while concurrently reducing nationwide N consumption by 10% (6-16%) and 27% (22-32%), mitigating reactive N (Nr) losses by 7% (3-13%) and 24% (19-28%) and increasing N-use efficiency by 30% (3-57%) and 36% (8-64%) for ON and EON, respectively. This study identifies and targets subregions with disproportionate environmental impacts and proposes N rate strategies to limit national Nr pollution below proposed environmental thresholds, without compromising soil N stocks or economic benefits for smallholders. Thereafter, the preferable N strategy is allocated to each region based on the trade-off between economic risk and environmental benefit. To facilitate the adoption of the annually revised subregional N rate strategy, several recommendations were provided, including a monitoring network, fertilization quotas and smallholder subsidies., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Biochar (BC) application to low fertility soils is a promising approach to increase crop yield, improve soil quality, and mitigate climate change simultaneously. Only few studies evaluated the combined effects of BC and nitrogen (N) fertilization rates on crop productivity and N losses under field conditions. The objectives were to investigate combined effects of BC (2 rates) and N (5 rates) fertilization on crop productivity and N losses in a long-term field experiment started in 2008 in a winter wheat/summer maize rotation system in the North China Plain. Linear-plateau models best described the responses of wheat and maize yields to N rates. N 2 O fluxes, NH 3 volatilization, and soil mineral N contents increased exponentially with N fertilization rates. Despite the effect of BC on wheat or maize yields was negligible, BC retains of mineral N at 240 kg N ha -1  yr -1 . BC application increased NH 3 volatilization by 31% in wheat season and 26% in maize season because of pH increase. BC reduced N 2 O emissions by 8-23% in the wheat season and by 24% at lower N rates (≤60 kg ha -1 ) in the maize season, due to BC induced complete denitrification to N 2 . BC stimulated N 2 O emissions by 18-26% compared to soils without BC in maize season at N rates higher than 60 kg ha -1 . The combination of increased mineral N retention and C availability with BC addition increased nitrification and/or denitrification rates, leading to increased N 2 O emissions. For the wheat/maize rotation system, BC application decreased N 2 O emissions at lower N rates (≤120 kg ha -1  yr -1 ) but had no effects at higher N rates., (Copyright © 2019 Elsevier B.V. All rights reserved.)