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Changing climate has direct linkage with growth and metabolism in plants and is likely to alter nitrogen (N) uptake from fertilizers. Hence, a field study was conducted using 15N labeled urea in micro-plots to study the effects of elevated CO2 and/or temperature on fertilizer-N use in a soybean-wheat cropping sequence. Crops were grown in open top field chambers (OTCs) under two CO2 (386 and 558–561 ppmv), two temperature (ambient, 1.4-1.5 °C above) and three N levels during 2017-18. The N treatments were 50, 100 and 150% of the recommended dose (N50, N100 and N150). Labeled (15N) urea (10% atom excess) was applied to soybean. Elevated CO2 and/or temperature showed significant effects on seed yield, total N uptake, fertilizer-N uptake, per cent N derived from fertilizer (Ndff) and per cent fertilizer-N use in the soybean-wheat crop sequence. Total N uptake in soybean significantly increased under elevated CO2 and/or temperature treatments, mainly due to higher N uptake in seeds. Effect of climate on fertilizer-N uptake and utilization in the soybean-wheat cropping sequence varied with level of N application. The 15N labeled fertilizer-N uptake and per cent fertilizer-N use was significantly higher under co-elevation of both CO2 and temperature at N100 and N150, but, was mostly similar among the climate treatments at N50. In the soybean-wheat crop sequence, 13–40% of the applied fertilizer was used, with significantly higher use with co-elevation of both CO2 and temperature. Out of the applied fertilizer, 20–51% got retained in the surface soil and 43–73% was traced in the soil-plant system. Significantly higher fertilizer-N use in the soybean-wheat crop sequence under co-elevation of CO2 and temperature indicates increasing role of fertilizer-N to harvest the CO2 mediated enhancement in grain yield under the future climate conditions.

Organic livestock production in the U.S. requires that a significant amount of feed comes from grazed pasture. While principles of grazing management for temperate grasslands are well known, organic livestock production may result in unique plant-soil dynamics with ramifications for farmer decision-making and management. We reviewed the literature for direct or indirect evidence that organic pasture management results in altered plant-soil dynamics and assessed whether organic management might necessitate modifications or additions to managed grazing principles. The literature directly addressing these questions is sparse. We found some evidence that organic management can stimulate soil biota but no evidence for grassland yield, soil stocks, or soil transformation rate differences between organic and non-organic pastures. Given the constraint on fertilizer and herbicide inputs in organic management, established principles of managed grazing – rotating livestock frequently through paddocks such that plants are uniformly grazed but left with significant residual biomass and time for regrowth – are critical for maintaining dense, productive swards in organic pasture management.

Biochar has been proposed to ameliorate soil properties and plant growth. However, it remains unclear how the interaction between biochar and nitrogen (N) fertilizer impacts soil inorganic nitrogen (SIN) leaching and availability in dryland systems. Therefore, a two-year field experiment was carried out on the Loess Plateau in northern China to study the effects of biochar combined with N fertilizer on the leaching and availability of SIN. Biochar applied at 0, 20 and 40 t ha−1 (B0, B1 and B2, respectively) interacted with three N fertilization levels (0, 120 and 240 kg N ha−1; N0, N1 and N2, respectively). Winter wheat (Triticum aestivum L.) was cultivated in a winter wheat-summer fallow cropping system. We measured wheat aboveground biomass and residual SIN in the soil profile (0–60 cm at 10 cm intervals) using standard extraction methods (2 M KCL, shaking at 25 °C for 1 h). Additionally, to ascertain whether field-aged biochar captured SIN and to determine residual SIN availability, we also used a modified extraction method (2 M KCL, shaking at 60 °C for 2 h) and ion exchange membranes (IEMs) to extract SIN from plow layer soil (0–20 cm). Our results indicated that biochar application alone in the absence of N fertilization had no significant effect on wheat biomass or residual SIN in the soil profile. However, compared with the application of N fertilizer alone, the application of biochar at 20 t ha-1 combined with N fertilizer not only increased wheat biomass by 12.2–13.8% but also significantly decreased residual NO3−-N in the subsoil by 13.2–74.7%. Nevertheless, long-term N fertilization at 240 kg N ha-1 led to large amounts of residual NO3−-N without a significant increase in crop biomass, which inevitably increased the risk of leaching during the fallow period. Although the application of biochar at 40 t ha-1 combined with N fertilizer more effectively decreased residual SIN in the subsoil, this approach was impractical because it decreased wheat biomass. Furthermore, the difference between NO3−-N extracted via the modified method and via the standard method increased with biochar application under each N level. Thus, field-aged biochar absorbed a certain amount of NO3−-N, thereby sequestering N in the soil after two years of N fertilization. Hence, biochar could reduce the residual NO3−-N available for leaching during the fallow period. However, notably, overuse of biochar could reduce the amount of NO3−-N available not only for leaching but also for crops. Ultimately, the application of biochar at 20 t ha-1 combined with N fertilization at 120 kg N ha-1 is a promising dual-win strategy for improving N availability while concurrently mitigating SIN leaching.

Domestic livestock grazing is one of the dominant forms of land use globally. However, there are variable findings concerning the impacts of different grazing regimes on soil condition. We quantified the impacts of contrasting livestock grazing regimes on soil properties within nationally endangered temperate box-gum woodlands in south-eastern Australia. We sampled total soil nitrogen, phosphorus, carbon and bulk density at 65 woodland sites with a history of either continuous, strategic or rotational livestock grazing, as well as livestock grazing exclusion. We evaluated the influence of both historical and current management practices upon soil properties in the context of broad-scale soil forming factors such as climate, geology and topography. We found evidence of a strong relationship between total soil phosphorus and nitrogen, while phosphorus also was influenced by site-scale native tree cover. Total soil phosphorus and nitrogen were related to the combined effects of pasture type and long-term fertilizer history (>10 years prior to sampling). No significant differences in soil nutrients or bulk density were detected between different grazing treatments, likely due to the importance of total grazing pressure (i.e. from all exotic and native herbivores) and the level of environmental variation between sites. However, total soil phosphorus was significantly higher in soils sampled in the season following a grazing event, irrespective of grazing intensity or duration. Total soil nitrogen and carbon exhibited a similar pattern. This is likely a result of multiple processes such as direct input of organic matter to the soil and stimulation of soil microbial communities. These findings have important implications for the strategic management of woodland understorey vegetation as soil nutrients have been identified as important drivers of native plant diversity.

Global expansion of high-input annual grain crops and associated nitrogen (N) fertilizer use can have negative consequences for the environment and human health. Nitrate nitrogen (NO3-N) leaching from fertilized annual crops can contaminate groundwater and pollute natural aquatic ecosystems and rural drinking water sources. Intermediate wheatgrass (IWG; Thinopyrum intermedium) is a perennial grass being domesticated to serve as the world’s first widely available perennial grain crop. Our objective was to measure water quality variables and crop yields in order to model NO3-N leaching beneath IWG, maize, and switchgrass under three N fertilizer treatments; low N (0 kg N ha−1), medium N (maize = 80, switchgrass and IWG = 40 kg N ha−1), and high N (maize = 160, switchgrass and IWG = 120 or 160 kg N ha−1). The switchgrass and IWG medium N treatments also included alfalfa as an intercrop. The NO3-N concentration in soil solution 50 cm below the surface was one and two orders of magnitude lower in high N fertilized IWG compared to switchgrass and maize, respectively. Soil solution NO3-N increased with N fertilizer in all crops. Soil water content was less at 50 and 100 cm depths in IWG compared to switchgrass and maize but was unaffected by N fertilizer treatment. Using the Denitrification and Decomposition (DNDC) model, average annual NO3-N leaching estimates in the high N treatments were 21.7 kg N ha−1 for maize and 3.7 and 0.2 kg N ha−1 for switchgrass and IWG, respectively. Despite consistent biomass yields through time, IWG grain yields decreased with stand age at all N fertilizer treatments. Alfalfa did not persist in the IWG and switchgrass medium N treatments, thus other legumes should be tested for intercropping with perennial grain crops. Intermediate wheatgrass has great potential to provide food-quality grain and biomass while preventing NO3-N leaching.

The impacts of rapid industrialization on spatio-temporal changes in soil pH have drawn major attention from the scientific community and decision-makers. A total of 1185 topsoil samples (0–20 cm) were collected from southern Jiangsu Province of China in 1980, 2000, and 2015, and the geostatistical sequential Gaussian simulation (SGS) was used to quantify the spatio-temporal patterns of changes in soil pH and identify the areas with significantly-declined pH. A significant topsoil acidification occurred in major croplands of the study area, with mean decrements of 0.56 and 0.52 units over the periods of 1980–2000 and 2000–2015, respectively. A significant decrease in pH occurred in the areas surrounding Taihu Lake during 1980–2000, and a further decrease was evident predominantly in the northeast during 2000–2015. Over the entire 35-year period, the soil pH for approximately 79% of the study area declined significantly. The decline over the first two decades (1980–2000) was largely attributed to increased chemical fertilizer inputs and the development of industries, while the further enhanced industrial emissions resulting from the significant expansion of factories were the primary reason for the accelerated soil acidification in the subsequent 15 years (2000–2015). Results from this study may serve as a basis for developing management strategies to achieve better soil quality in similar areas moving toward industrialization.

The excessive application of phosphorus fertilizer has caused available phosphorus (AP) surplus in cultivated soils. By using the Soil and Water Assessment Tool (SWAT), the soil AP surplus and its relationship with fertilization and environmental changes was estimated for the wheat-maize rotation production area in the Baiyangdian basin, which is a typical arid region in North China Plain. Due to the little runoff, the model was validated by the measured AP concentration in deep soil profiles of the cropland. The results indicated that with an evident overuse of phosphorus fertilizer, the average rate of AP surplus in soils in the basin was about 10.3% of the applied fertilizer. A large part of the applied phosphorus (57.2%) was accumulated in active mineral forms. The phosphorus fertilizer recovery efficiency averaged 41.4%, ranging between 29.3% and 51.7%. This lower efficiency was expected to be the main reason for the serious AP surplus in cultivated soils. As a result, it was predicted that for every 100 kg ha−1 of P fertilizer added, the AP of the plough layer (0–20 cm) will be increased by an average of 3.35 mg kg−1 (around 10 kg P ha−1) in the study area. Furthermore, the soil AP surplus was predicted to reach a higher level under the condition of lower precipitation because of less runoff-induced erosion and leaching to deeper layers. From 1993–2010, the soil AP accumulation was 445.7 kg ha−1 in the study area, with an average accumulation rate of 24.8 kg ha−1yr−1, which belongs to the highest level worldwide. Through combining the measured data with the simulated results, it was suggested that excessive phosphorus fertilizer application along with low phosphorus fertilizer recovery efficiency will increase the risk of P leaching, which threatens the security of groundwater.

In a study on the emissions of nitrous oxide (N2O) from maize production in South-West Germany, N2O emissions where measured with an automated chamber system over two consecutive cropping seasons, including an intermediate fallow period. Urea-based fertilizer treatments included a fertilizer only control (U), as well as the use of pyraclostrobin, which showed inhibitory effects on denitrification in a laboratory experiment. Pyraclostrobin was used alone (U + P) and in combination with a NBPT/NPPT urease inhibitor (UI + P) and a reduced fertilizer rate (70% UI + P). The U control emitted 1.03 ± 0.22 and 1.94 ± 0.61 kg N2O-N ha−1 in the cropping seasons of 2012 and 2013, respectively. Fallow emissions mainly occurred after a soil freeze-thaw period and were 0.24 ± 0.08, 0.23 ± 0.09, 0.22 ± 0.06, 0.32 ± 0.21 kg N2O-N ha-1 for U, 70% UI + P, U + P and UI + P, respectively. In the cropping season 2012, no effects of the UI + P and U + P treatments could be observed. In 2013, UI + P increased N2O emissions by 13% when compared to the U control, while a significant reduction of 24% was observed for the U + P treatment. The 70% UI + P treatment resulted in significantly lower (∼30%) N2O emissions and only slight reductions (7–10%) of grain yields in both years. Climate conditions varied strongly between seasons (416 and 704 mm total rainfall in 2012 and 2013, respectively) which most likely also influenced the performance of the inhibitors. Direct emission factors (EFd%) also increased strongly in 2013 (0.28 ± 0.12 in 2012 vs. 0.94 ± 0.41 in 2013 for U) but were generally lower than the 1% IPCC default value. Values for nitrogen recovery efficiency and yield-scaled N2O emissions were most preferable for the 70% UI + P treatment and indicate that reduced fertilizer rates in combination with inhibitors could represent a viable means for N2O mitigation without significant yield penalties in agricultural systems.

Tailoring agricultural practices to enhance the soil carbon (C) stock is seen as a promising mitigation tactic to offset greenhouse gas (GHG) emissions in croplands. Tea plantations are not only the important part of economic industry but also one of the crucial agricultural sources of non-carbon dioxide emissions. Although many studies have measured GHG emissions from tea plantations, it remains unknown about the effect of knowledge-based mitigation options on the entire C budget from Chinese rapidly expanding tea plantations. Thus, we carried out a 2-year field trial to provide an insight into the influence of organic fertilizer substitution for synthetic fertilizer and biochar amendment on net ecosystem carbon budget (NECB), net greenhouse gas budget (NGB), and yield-scaled greenhouse gas intensity (GHGI) from a subtropical tea plantation. Results showed that when averaged a 2-year experimental period, both full organic substitution and biochar amendment contributed significantly to the increment in NECB, mainly due to the enhanced soil organic C content in the tea field. Compared with the conventional farm practice, the application of full organic substitution can induce a 52% decrease in both NGB and GHGI. Regardless of fertilizer type, both NGB and GHGI were negative and 2.4 times lower in the treatments with biochar amendment relative to the control. In addition to their roles in maintaining soil health and alleviating soil acidification, our results suggest that organic fertilizer substitution and biochar addition may achieve low carbon development for tea plantations. Our findings will inform efforts to implement and evaluate these tailored mitigation options in tea plantations at a national scale.

Surface mulching is an effective strategy to increase yields in rainfed agroecosystems. The plastic film residue and overuse of chemical fertilizer cause a serious non-point source pollution and high production input cost. With mulching, farmers typically attempt to maintain the balance of soil nutrients and reduce fertilizer use while ensuring high yields. Straw strip mulching (SM) is a new mulching technique, but the effects on nutrient uptake have not been studied yet. Therefore, 19 field comparative experiments were conducted in four growth seasons of winter wheat with three mulching treatments: (1) straw strip mulch (SM), a partial ground mulching using whole corn stalks that alternate with planting strips without mulch; (2) full-field plastic film mulching (PM); and (3) no mulching with wheat sown in rows, as a control (CK). Compared with CK, on average over all experiments, SM increased grain yield by 11.5%, biomass by 19.0%, the total aboveground uptakes of nitrogen (N), phosphorus (P) and potassium (K) by 16.1%, 18.4% and 22.9%. There were no significant differences between SM and CK in N and P requirements, the N, P and K concentrations in grain. The increased total aboveground uptake of each nutrient was closely associated with higher biomass, grain yield and straw yield (r = 0.66 −0.84, P

Manure amendment in croplands is common practice for soil carbon sequestration, and may also reduce greenhouse gas emissions. Few studies focus on the effects of manure application on the net greenhouse gas emissions (NGHGE, the global warming impacts of soil carbon sequestration and CH4 and N2O emissions) in double-rice cropping fields. Herein, a field experiment was conducted to analyze the effects of pig manure application in combination with reduced chemical fertilizers on the NGHGE, soil properties, and yields in a double-rice paddy field in 2012–2015. Four treatments were included: 0 N (no nitrogen fertilizer); 1/2 N (chemical nitrogen fertilizer reduced by 50%); N (100% chemical nitrogen fertilizer); and 1/2 N + PM (pig manure complemented with chemical fertilizer application). The average annual CH4 emissions for 1/2 N + PM were 53%, 50%, and 32% higher than those for 0 N, 1/2 N, and N treatments, respectively (p

Different types of fertilizer can significantly change soil fertility. The response of soil bacterial communities to different fertilization regimes has been studied widely, but the inconsistent results urged us to systematically study the effect of multiple environmental factors on bacterial diversity and composition under different fertilization regimes. Here, we conduct a meta-analysis of a global dataset from 105 publications to explore the effect of mineral nitrogen, straw, and manure addition on soil bacterial alpha-diversity (Shannon and Chao1 indices) and community composition. Mineral nitrogen and straw addition decreased the Shannon (mineral nitrogen: –4.48%; straw: –11.83%) and Chao1 (mineral nitrogen: –0.97%; straw: –11.57%) indices, while manure addition increased the Shannon (0.53%) and Chao1 (5.64%) indices. The three types of fertilizer all favored the growth of Proteobacteria, Actinobacteria, and Bacteroidetes and inhibited the growth of Acidobacteria and Nitrospirae. Manure addition had the greatest increase in the abundance of Proteobacteria, Bacteroidetes, and the least decrease in abundance of Nitrospirae. Manure addition increased soil organic carbon, total soil nitrogen, and soil microbial biomass carbon more than mineral nitrogen and straw addition. Mineral nitrogen and straw addition decreased soil pH, while manure addition increased soil pH. Soil environmental and climate factors significantly drove changes in bacterial alpha-diversity and community, particularly soil pH. In conclusion, manure addition is the preferred fertilization management for most agricultural ecosystems. These results can be used as a valuable reference for agricultural management strategies to maintain belowground bacterial diversity and composition in agroecosystems across the globe.

Environmental impacts on freshwater ecosystems persist due to inputs of excess fertilizer to agricultural landscapes. Conservation efforts, such as cover crops, are being encouraged to reduce nitrogen (N) and phosphorus (P) runoff from fields, but their effects on working lands are rarely documented. We quantified reductions of nitrate-N and soluble reactive phosphorus (SRP) losses from cropland in response to widespread planting of cover crops in two agricultural watersheds (Indiana, USA) over four water years (2016–2019). We collected water samples bimonthly from tile drains and stream sites to measure nitrate-N and SRP losses across scales. Cover crops consistently reduced tile drain nitrate-N loss by 27–72%, while SRP reductions were more variable, ranging from 7%–58%. Subwatershed nitrate-N yields were consistent across each watershed, while headwaters disproportionately contributed SRP to the stream, suggesting targeted cover crop implementation may be required to reduce SRP export. Finally, watershed-scale nitrate-N export was reduced by 2–67% (5/8 site-years) and SRP export by 31–88% (7/8 site-years) in spring. However, given the effect of interannual variability in runoff and spatial heterogeneity in N and P loading, regional-scale planting of cover crops may be needed to confer consistent reductions in annual export, with meaningful impacts on downstream water quality.

Excess chemical fertilizer application results in substantial N2O emission. Manure application into agricultural soil can reduce chemical fertilizer input while maintaining crop yield. However, little is known about the potential effects of reduction in chemical fertilizer with green manure or organic manure on yield-scaled N2O emissions in orchards. A two-year experiment was carried out in a citrus orchard, including (i) chemical fertilizer (urea), 0%, 70%, 85% and 100% of N supplied, respectively (CK, C70, C85, CF), (ii) organic manure (rapeseed cake) incorporation with 0%, 70%, 85% and 100% of N supplied from chemical fertilizer (OM, OMC70, OMC85, OMCF), (iii) green manure (smooth vetch) incorporation with 0%, 70%, 85% and 100% of N supplied from chemical fertilizer (GM, GMC70, GMC85, GMCF) treatments. The soil physical-chemical properties, N2O emissions and yields were measured during 2018–2019. N2O emissions were 1.57 and 1.80 kg N ha−1 yr−1 under CF treatment in 2018 and 2019, respectively, and decreased by 25.4%−31.6% under C70, 32.5%−55.4% under OMC70 and OMC85 treatments and by 16.1–32.2% under GMC70 and GMC85 treatments. The 70% N rate of chemical fertilizer was the optimal N rate for maximizing yield in no manure, organic manure and green manure treatments, respectively. The C70, OMC70 and GMC70 treatments both significantly decreased yield-scaled N2O emission with the lowest emission in OMC70 treatment relative to CF treatment. N2O fluxes in OMC70 and OMC85 treatments were mainly controlled by the DOC/NO3- ratio, while soil NH4+ was the dominant factor controlling N2O fluxes in GMC70 and GMC85 treatments, suggesting that more NH4+ provided from green manure than from organic manure contributed to higher N2O emission. We conclude that applying organic manure incorporation with 30% reductions of chemical fertilizer is a fertilizer management strategy worth pursuing for sustainable productivity and environmental protection in citrus orchards.

Catch crop (green manure) planting is considered an efficient strategy to improve soil fertility in agro-ecosystems. Methane (CH4) emissions from paddies subjected to continuous green manure amendment though is a topic that remains unexplored. To clarify the impact of continuous green manure amendment on rice yield and CH4 emissions, a long-term trial (established in 2003, Yixing, China) was designed with the field observations conducted between 2019 and 2020. Two green manure crops (milk vetch, ryegrass) were selected as the catch crop with fallow as the control, all trialed at two N application rates i) low N dosage deriving from the optimum effect between yield-N fertilizer (LN, 200 kg ha-1), and ii) a higher N dose as the empirical farmer's dose (HN, 270 kg ha-1). The results showed that continuous green manure amendment notably increased soil organic carbon (SOC) compared to that of the control, while HN significantly increased the dissolved organic nitrogen compared to LN. The rice yield among treatments remained similar, ranging from 8.6 t ha-1 to 9.4 t ha-1 (two years’ average). CH4 emissions were notably related to green manure, and remained unaffected by N application rate. Ryegrass amendment after 18 years remarkably stimulated the CH4 emissions compared to other treatments, while the difference between milk vetch-amended and fallow treatments was found insignificant. Ryegrass increased soil mcrA gene with the abundance becoming the highest under HN. Methanogens abundance and SOC content were the main factors affecting CH4 emissions under ryegrass addition. Moreover, the CH4 emission intensity was aligned with CH4 emissions mainly due to the similar rice yield. Overall, continuous milk vetch planting is a recommended catch crop strategy that increases soil fertility and maintains rice yield without increasing CH4 emissions.

To determine the role of maize plants and their interaction with nitrogen (N) fertilizer in regulating subsoil methane (CH4) fluxes, we conducted a two-year field experiment on a semiarid farm in northwestern China. Four treatments were evaluated: unplanted soil without (C0) or with (CN) N fertilization and planted maize without (P0) or with (PN) N fertilization. Soil surface fluxes and profile dynamics of CH4 at depths of 0–50 cm in situ were monitored. The CH4 concentrations decreased with increasing soil depth. Seasonal and vertical variations in CH4 diffusive fluxes varied with maize phenology. The CH4 fluxes in the 0–20 cm layers accounted for 48.9–57.5% of the total fluxes in the 0–50 cm layers. The surface CH4 uptake was positively correlated with soil temperature during the fallow season and negatively correlated with soil water-filled pore space (WFPS) and exchangeable NH4+ concentration during the growing season. Compared with the unplanted treatments, the presence of maize plants significantly decreased soil WFPS and increased surface CH4 uptake during the growing season. The two-year mean cumulative diffusive CH4 fluxes were also significantly increased by 33.1–36.3% at depths of 10–30 cm and by 15.8–66.4% at depths of 10–40 cm in the P0 and PN treatments, respectively. Compared with the P0 treatment, the PN treatment significantly increased the surface CH4 uptake and cumulative CH4 uptake at depths of 0–40 cm in 2015. There was no significant difference in the CH4 surface and subsoil fluxes between the C0 and CN treatments. Our results suggested that N fertilization stimulated CH4 diffusion and uptake mainly by promoting maize growth and subsequently the soil water consumption on a dryland farm.

Growing public concern over agricultural nitrogen (N) pollution is now reflected in consumers’ food choices and shareholders’ resolutions, causing rapid changes in global food supply chains. Nitrate (NO3) leaching represents the primary N source for groundwater contamination and freshwater ecosystem degradation. However, simplified science-based indicators are still lacking to facilitate improved N management practices at the farm-level. We conducted a global analysis of published field studies to evaluate N balance (N inputs minus N outputs) as a robust predictor for NO3 losses. Using 82 studies (1110 observations) for rainfed cereal crops in temperate regions, we 1) quantified the response of NO3 losses to changes in N balance for major rainfed cereal crops while accounting for environmental and management variables; and 2) assessed the feasibility of improving water quality through lower N balance under different scenarios using the case study of maize (Zea mays L.) data from the US Corn Belt. Observations were grouped in studies from the US and non-US regions. Results show that NO3 losses increased exponentially as N balance increases for both the US and non-US regions, though they were 60% higher in the US at a given N balance. Scenario analysis revealed that reducing the N rate from the agronomic optimum to the lower point within the economic optimum N rate range decreased NO3 losses by 13% without impacting economic returns. The case study for maize showed that improvements in N use efficiency that increase grain yield at a given fertilizer rate can substantially reduce N balance and mitigate NO3 losses. This study provides an evidence-based foundation for food supply chain companies to mitigate global NO3 pollution, specifically by using the generalized relationships presented here to track progress in NO3 leaching mitigation. To further resolve uncertainties and improve region-specific estimates for NO3 losses, we propose a tiered monitoring and assessment framework similar to the IPCC (Intergovernmental Panel on Climate Change) methodology for N2O emissions, widely implemented in science and used for policy.

Nitrogen (N) fertilizer provides an essential nutrient for rice production, but it also leads to nitrous oxide (N2O) emissions. We investigated twenty years’ literature and conducted two years of field experiments to assess the effects of N fertilizer application on N2O emissions, N use efficiency (NUE), and rice yield in the middle and lower reaches of the Yangtze River, China. This work described the time series of N2O emissions during the total rice-growing period based on the literature’s dataset; the peak N2O fluxes (about 1800 µg m−2 h−1) were observed at 0.4–0.55 relative days after transplanting (during the mid-season drainage period). Moreover, we established a positive linear correlation between the seasonal N2O emission and N fertilizer input in this study region (R2 = 0.36). The literature’s results suggested that 30%–60% total N fertilizer input as spikelet fertilizer helps obtain an approximate 38% NUE and 8.8% grain yield rise in lower N2O emissions. Regarding the field experiments’ results, they confirmed that the rate of basal fertilizer had a significant influence on N2O emissions. The results also found that the yield scaled N2O emissions would decrease with more spikelet fertilizer input. Furthermore, an improvement in N fertilizer utilizes efficiency (agronomic efficiency and partial factor productivity) with the more spikelet fertilizer application while the total N fertilizer would not change. The grain yield in the spikelet fertilizer plots was approximately 20% higher than in the no spikelet fertilizer plots. Altogether, this study indicates that reducing N applied in the earlier growth stages could be an effective and easy-to-follow approach to increase NUE and grain yield while reducing N2O emissions in paddy production.

The impact of soil water repellency (SWR) on soil phosphorus (P) mobility in surface water runoff remains contentious. Although SWR may cause a significant increase in surface runoff, especially in post-summer rainfall events, whether it contributes to background phosphorus losses remains unclear. Surface runoff and P concentrations in runoff were measured on hilly Allophanic pastoral soils with different water repellency levels using seven runoff collectors. Phosphorus fertilizer was broadcasted at 18 kg P ha−1 in the summer over dry soils. Runoff volumes and P concentrations were measured after each natural rain event prompting surface runoff. The highest runoff/rainfall ratios were observed at the early rainfall events following the dry summer and then decreased significantly by the end of autumn and winter. The post-summer surface runoff correlation with SWR had an R2 of 0.46, and hydrophobic soils had significantly higher runoff ratios than wettable soils. Measurements of the dissolved reactive phosphorus (DRP) and total phosphorus (TP) in the surface runoff showed decreasing exponential trends, with the highest values recorded in the first runoff event following P fertilizer application, where over 90% of losses occurred (incidental losses). After the incidental loss phase, DRP concentrations were related to surface runoff ratio, soil P extractability by water, and SWR. Our data point to non-incidental TP loads being related to SWR (R2 = 0.53). The present results will improve the understanding of the SWR effect on surface runoff and will reconcile the controversy regarding its contribution to non-incidental P losses.

Reactive N in the runoff from paddy fields is considered to be the dominant contributor to the deterioration of river and lake water quality in China. However, there has been little researches on the interaction between N fertilizer rates and N losses via runoff from the paddy water during the summer rice-growing seasons. In the present study, we monitored the rice grain yield, N agronomic efficiency (AEN), and N losses via runoff from fertilizer N rate-response experiments applied to rice in the Taihu Lake region over 6 years. Total N loss via runoff averaged 19.3 kg ha−1 per rice season, corresponding to 7.1% of fertilizer N input at the regional N rate of 270 kg ha−1. Seasonal cumulative ammonium-N, organic N, and total N losses via runoff were all positively correlated with the fertilizer N rates (n = 1141, P

Organic amendment often affects both crop yield and greenhouse gas (GHG) emission. Yet the impact of organic amendment on yield gains and GHG emissions is still unclear, particularly in long-term soybean-wheat cropping system. Based on a 30-year soybean-wheat cropping system experiment, the impact of organic amendments (i.e. straw and manure) on soil properties, crop yield, N2O and CH4 emissions, and net ecosystem economic budget (NEEB) were investigated. The treatments were: chemical NPK fertilizer (NPK), chemical NPK plus low amount of wheat straw (NPKLS), chemical NPK plus high amount of wheat straw (NPKHS), chemical NPK plus pig manure (NPKPM), chemical NPK plus cattle manure (NPKCM), and a control with no fertilizer applied (CK). The long-term straw and manure amendments enhanced soybean yield by 13.1% and 44.0%, and improved wheat yield by 6.4% and 9.9%, respectively. Meanwhile, they stimulated N2O emissions by 25.1% and 49.0% respectively, without significant effect on CH4 emissions, compared to the chemical NPK fertilizer treatment (NPK). The results of structural equation model showed that soil properties tested explained 76% of the variations observed in N2O emissions, which were directly affected by soil nitrification capacity, pH and denitrification capacity. Although straw and manure amendments increased the total GHG emissions investigated by 25.7% and 48.6% respectively, they showed insignificant effects on the greenhouse gas intensity (GHGI), and increased NEEB by 8.6% and 21.1%, respectively, compared to the NPK treatment. This indicates that the benefits arising from crop yield improvement through the use of organic amendments can cover the carbon fees caused by increased GHG emissions. Our findings suggest that organic amendment can be an effective strategy to simultaneously increase crop yield while mitigating greenhouse gas emissions from the perspective of carbon fees.

Refereed/Peer-reviewed Occasional one-time tillage (strategic tillage, ST) is an effective tool for managing weeds and crop diseases in no-till and conversative farming systems. However, there is limited understanding of the impacts of ST on soil microbiome and their associated soil processes, particularly in dryland agriculture. This study aims to quantify the effect of one-off ST - after three years - on soil microbiomes and functions in a long-term no-till farming system under crop stubble and fertilizer management practices. The results showed that ST had marginal effects on microbial richness and diversity, enzyme activities, and catabolic function, but significantly affected the abundance of some microbial taxa (Actinobacteria, Firmicutes, Verrucomicrobia, Basidiomycota and Ascomycota) that are relevant to carbon (C) degradation. Stubble retention, regardless of tillage and fertilizer management, mainly increased the abundance of copiotrophs such as Proteobacteria (e.g., Rhizobiales) and Actinobacteria (e.g., Streptomyces and Micromonosporaceae), and affected Ascomycota and Basidiomycota. Among the management practices, stubble retention was the main factor that contributed to increased richness and diversity of the soil bacterial and fungal community. Supplementary fertilizer application, regardless of tillage and stubble management had minimal impact on bacterial and fungal richness and diversity, enzyme activity and catabolic function. The variation in bacterial community structure was influenced mainly by soil pH (c.a. 10%), while only a small but significant effect (< 7%; P = 0.001) was attributed to tillage and stubble management. Wheat grain yields ranged between 5 and 5.3 t ha-1 and were not affected by tillage, stubble, nor fertilizer management practices. Similarly, these management practices did not influence total soil C or nitrogen concentrations. Our findings show that strategic tillage, when used to address specific constraints in no-till systems in dryland agriculture, does not have a significant effect on total soil C, microbial ecology nor catabolic function.

The return of crop residue to the soil has been suggested as a nutrient-conserving practice that effectively increases soil fertility and crop nutrition. However, the overall direction and magnitude of changes in the agroecosystem nitrogen (N) cycle in response to crop residue return are poorly quantified. In the present study, a global synthesis was performed to assess the effects of crop residue return on 17 variables associated with agroecosystem N cycles, including N pools, N fluxes, and other related parameters. The results showed that crop residue return stimulated crop yield by 5.5%, and N pool sizes in soil, crop, and microbes by 10.7%, 20.8%, and 34.9%, respectively, suggesting that this technique functions to conserve N, improve soil fertility, and optimize N supply for agricultural crop-soil systems. These responses were positively affected by the rate and duration of residue application, suggesting that the effects of crop residue return may be cumulative. Moreover, crop residue return had no effect on N2O emission and N leaching when all agroecosystems were assessed, but when upland fields were separately assessed, they showed an increase in N2O emission (+16.6%) and a decrease in N leaching (−9.1%). However, the stimulatory effect on N2O emission in upland fields was much lower than the effect seen with fertilizer use (+117.2%). There was no positive relationship between residue return rate and N2O emission. The addition of N fertilizer could inhibit the stimulatory effect of crop residue return on the crop yield and soil total N pool. The challenge for modern agriculture to meet the food demands of a growing population will require sustainable practices. Given the low return rate of crop residue at present, these results emphasize the importance of using this environmentally friendly practice to enhance the sustainability of agriculture and reduce agricultural pollution.

An On-Farm Water Storage (OFWS) system is a structural Best Management Practice (BMP) that prevents downstream nutrient loading by capturing irrigation tailwater and storm runoff from agricultural fields. OFWS systems, as a result, also act as a source of water for irrigation with the potential to recycle nutrients captured in runoff events. A monitoring study was conducted for an OFWS system located on a corn and soybean farm in East Mississippi from June 2014 to August 2016 to analyze the effectiveness of the system for reducing downstream nutrient runoff, supplying water for irrigation, and recycling nutrients in captured water that is reapplied to the field. Nitrate and dissolved phosphorus (DP) concentrations in the storm runoff events captured by the OFWS system storage pond and prevented from going downstream measured as high as 179 mg L−1 and 0.69 mg L−1, respectively. Water can be lost downstream from the storage pond overflow pipe when the pond is at its maximum capacity in March-April of each year, but nitrate concentrations were less than 10 mg L−1 in the storage pond in March-April for both years of the study, and DP concentration was less than 0.053 mg L−1 in the water that could be lost downstream, which showed that OFWS systems can be effective in reducing downstream nutrient loading by capturing storm runoff events. Over three growing seasons, roughly 357,000 m3 of water was used for irrigation from the OFWS storage pond in a region which has traditionally been under dryland production. This shows that OFWS systems can serve a dual purpose of reducing nutrient runoff and providing water for irrigation in East Mississippi, where groundwater is not a cost-efficient source of water for irrigation. Irrigated corn yields were higher than non-irrigated corn yields by an average of 1532; 2285; and 3950 kg ha−1 in 2014, 2015, and 2016, respectively; and irrigated soybean yields were higher than non-irrigated soybean yields over the same years by an average of 302; 1411; and 800 kg ha−1, respectively, demonstrating the importance of irrigation in East Mississippi. Analysis of nutrient concentrations in water samples collected simultaneously from both the irrigation system (sprinkler), which is fed from the bottom of the pond, and the storage pond grab samples showed that nitrate concentrations in the irrigation samples were lower than in the storage pond, but ammonia concentrations were higher in the irrigation water samples. Low nitrate concentrations and variability in nitrate concentration in the irrigation water as compared to the storage pond water showed that some of the nitrogen load is being recycled but not enough for the producer to reduce commercial fertilizer application.

In the Taihu region of China, overuse of chemical nitrogen (N) fertilizer is often associated with low nitrogen recovery (NRE) and leads to serious groundwater pollution caused by N leaching losses. Controlled-released nitrogen fertilizers (CRNFs) and mechanized deep placement are promising alternatives to broadcasting urea to increase crop yield and NRE in machine-transplanted rice production. However, their interactions with regard to soil N status, N leaching and crop performance are unclear. A two-year (2015 and 2016) field experiment was conducted in a randomized complete block using two fertilization techniques (broadcast and deep placement by mechanical side-dressing fertilization) and three CRNFs (sulphur-coated urea (SCU), polymer-coated urea (PCU) and a bulk blended mixture (BBF)). Conventional high-yield fertilization (four split applications of urea at 216 kg N ha−1 (CK)) and 0–N treatments were established as controls. The results showed that the variation in NH4+-N concentration in the percolation and surface water varied across the different CRNFs, irrespective of the techniques used. NO3− -N concentration in the percolation water varied with water conditions in the field. Deep placement with CRNF correspondingly increased mineral N concentration in percolation at depths of 20 and 60 cm but reduced it in the surface water compared to that of the broadcast, although the benefits varied depending on the CRNF type and growth stage. Deep placement of SCU and PCU significantly increased N leaching and the mineral N in the 40–60 cm soil layer compared to that of the broadcast, due to the intensive N release during tillering and ineffective stage when the rice plant had a weak N uptake capability. Deep placement of SCU had the highest N leaching of 6.65 and 5.34 kg N ha−1 during 2015 and 2016. In contrast, BBF exhibited the lowest N leaching, regardless of fertilization placement, which apparently synchronized N release rates with rice N uptake patterns. In the present study, BBF obtained higher rice yields and N recoveries, without significantly enhancing mineral N leaching losses, when compared to CK. Our results suggest that the use of BBF is a promising alternative to a conventional high-yield fertilization practice, especially if combined with deep placement.

Oxidizable organic carbon is a valuable indicator of soil quality, early changes in soil organic carbon (SOC) content, and changes in stabilities of SOC induced by soil fertilization practices. To improve SOC accumulation under soybean-corn cropping system in flat farmland on the Loess Plateau, we examined the effects of nine fertilization treatments [bare land (BL), control (CK), nitrogen (N), phosphorus (P), N + P (NP), manure (M), M + N (MN), M + P (MP), M + N + P (MNP)] on dynamics of SOC and four fractions of oxidizable organic carbon (OC) [very labile (CVL), labile (CL), less labile (CLL) and recalcitrant (CNL)], and stability of SOC over the period of 1997 to 2013. Although SOC content in treatments without fertilization or with inorganic fertilization remained relatively stable between 1997 and 2013, long-term no fertilization or inorganic fertilization caused a depletion of the very labile C (CVL) fraction and increased the stability of SOC. Long-term application of manure promoted an accumulation of SOC in the topsoil between 1997 and 2013, mainly by sequestering labile C (CVL and CL) in the 0–20-cm soil layer, and the dynamics of SOC and CVL contents under these treatments fitted a logistic regression model, which decreased the stability of SOC between 2008 and 2013. SOC content in the subsoil (20–40 cm) under cultivation with organic fertilization increased between 1997 and 2006, but then decreased between 2007 and 2013. Organic fertilization increased CVL and CL contents in the 20–40-cm layer between 1997 and 2010, but then decreased them between 2010 and 2013, and increased the stability of SOC between 2011 and 2013. Our findings indicated that manure fertilization was more effective in promoting SOC enrichment of the soil surface layers by increasing CVL, relative to inorganic fertilization and no fertilization, whereas long-term manure fertilization was associated with a risk of decreasing labile carbon in the 20–40-cm layer and the stability of SOC in the 0–20-cm layer. Manure fertilizer should thus be used cautiously in farmland on the Loess Plateau to guarantee long-term soil carbon stock.

Nitrogen fertilizer management can impact soil organic C (SOC) stocks in cereal-based cropping systems by regulating crop residue inputs and decomposition rates. However, the impact of long-term N fertilizer management, and associated changes in SOC quantity and quality, on the fate of N fertilizer inputs is uncertain. Using two 15-year N fertilizer rate experiments on continuous maize (Zea mays L.) in Iowa, which have generated gradients of SOC, we evaluated the legacy effects of N fertilizer inputs on the fate of added N. Across the historical N fertilizer rates, which ranged from 0 to 269 kg N ha−1 yr−1, we applied isotopically-labeled N fertilizer at the empirically-determined site-specific agronomic optimum rate (202 kg N ha−1 at the central location and 269 kg N ha−1 at the southern location) and measured fertilizer recovery in crop and soil pools, and, by difference, environmental losses. Crop fertilizer N recovery efficiency (NREcrop) at physiological maturity averaged 44% and 14% of applied N in central Iowa and southern Iowa, respectively (88 kg N ha−1 and 37 kg N ha−1, respectively). Despite these large differences in NREcrop, the response to historical N rate was remarkably similar across both locations: NREcrop was greatest at low and high historical N rates, and least at the intermediate rates. Decreasing NREcrop from low to intermediate historical N rates corresponded to a decline in early-season fertilizer N recovery in the relatively slow turnover topsoil mineral-associated organic matter pool (0–15 cm), while increasing NREcrop from intermediate to high historical N rates corresponded to an increase in early-season fertilizer N recovery in the relatively fast turnover topsoil particulate organic matter pool and an increase in crop yield potential. Despite the variation in NREcrop along the historical N rate gradient, we did not detect an effect of historical N rate on environmental losses during the growing season, which averaged 34% and 69% of fertilizer N inputs at the central and southern locations, respectively (69 kg N ha−1 and 185 kg N ha−1, respectively). Our results suggest that, while beneficial for SOC storage over the long term, fertilizing at the agronomic optimum N rate can lead to significant environmental N losses.

As the primary rice-producing country in the world, China has applied increasing amounts of synthetic fertilizers on rice fields, which has a large impact on environmental pollution and human health. In this study, a comprehensive inventory of fertilizer application to rice fields was compiled for China from 1979–2015. In 2015, fertilizer application was estimated to be 0.96 × 109 kg for early rice, 2.67 × 109 kg for single rice, and 1.11 × 109 kg for late rice. Based on the fertilizer application and region-specific emissions factors, ammonia (NH3) volatilizations from growing-season rice fields were estimated over the same period. We found that the total NH3 emissions increased during 1979–1998, while decreased during 1998–2015 with fluctuations. The decreasing trend of NH3 emission was likely attributed to changes of application proportions of ammonium bicarbonate (ABC) and other fertilizers. ABC and urea were the two dominant contributors, and contributed over 90% of the total NH3 emissions. Spatially, high emissions were identified in the Middle-lower Yangtze River Plain, Huaihe River Basin, Taihu Lake region, Pearl River delta and Sichuan basin. Monthly emissions patterns were estimated according to rice calendars. The damage from NH3 emissions was estimated as 26.79 billion yuan and accounted for 0.04% of the Gross Domestic Production of China in 2015. Finally, we discussed the NH3 reduction strategies from the perspective of both the government and farmers and suggested that an incentive scheme should be established to guide farmers to optimize traditional agricultural management.

Rising use and costs of agri-chemical inputs to support agricultural production have placed an economic burden on farmers while contributing to environmental and human health issues. Ecologically based nutrient and weed management – the use of ecological processes to replace external chemical inputs – may represent a strategy to support crop growth while achieving positive environmental and economic outcomes. In dryland agroecosystems around the world, farmers are increasingly transitioning toward no-till and intensified cropping systems, in which unvegetated fallow periods are replaced with crops. This study seeks to determine if cropping system intensification represents an ecologically based strategy for managing nutrients and weeds relative to traditional crop-fallow systems, and to understand the implications for crop production and profitability. We quantified total and potentially mineralizable nitrogen (N), arbuscular mycorrhizal fungal (AMF) colonization of wheat roots and implications for plant phosphorus (P) uptake, 6 years of crop yields, fertilizer and herbicide use, and net operating income across dryland, no-till cropping systems in the semi-arid High Plains, USA. Three levels of cropping system intensity were represented ranging from wheat-fallow (unvegetated fallow every other year) to continuous cropping (no fallow years). After accounting for variability due to environment and site characteristics, total and potentially mineralizable N were 12% and 30% greater in continuous rotations relative to wheat-fallow, respectively. Mid-intensity (fallow every 2 or 3 years) and continuous rotations had roughly 2 and 3 times more AMF colonization than wheat-fallow, respectively, and AMF colonization was positively correlated with wheat plant P concentration. Farmers practicing continuous cropping applied 22 and 34 kg ha−1 less N fertilizer per crop compared to wheat-fallow and mid-intensity, respectively, despite similar and 60% greater annualized crop production than mid-intensity and wheat-fallow rotations, respectively. Additionally, farmers who practiced continuous cropping used less than half the total herbicide used by wheat-fallow farmers. Net operating incomes of continuous and mid-intensity rotations were an estimated 47 USD ha−1 yr−1 (80%) and 42 USD ha−1 yr−1 (70%) more than wheat-fallow, respectively. These results suggest that cropping system intensification, and especially continuous cropping, represents an opportunity to achieve more grain production while managing weeds and nutrients with fewer agri-chemical inputs, leading to greater profitability and improved environmental outcomes in no-till agroecosystems.

China is the world’s largest emitter of gaseous ammonia (NH3), a compound that poses severe risks to human and ecosystem health. Adding biochar and inhibitors to soils has been suggested as a method to increase carbon sequestration and reduce nitrous oxide emissions, however, the effects of the amendments on NH3 emissions are poorly understood. We conducted a field experiment to evaluate the effect of applying biochar combined with a urease inhibitor (hydroquinone, HQ) and a nitrification inhibitor (dicyandiamide, DCD) on NH3 emissions, rice yields, and N use efficiency (NUE) during two growth seasons. Four replicates of seven treatments comprising no urea fertilizer (control), urea (N), biochar (B), urea + biochar (NB), NB + urease inhibitor (NBUI), NB + nitrification inhibitor (NBNI), and NB + urease and nitrification inhibitors (double inhibitor) (NBDI), were arranged in a randomized complete block design. Wheat straw biochar was applied once, in June 2014. Biochar in the NB treatment increased NH3 losses by 14.1% in the first rice season (P