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.

Agricultural fields are an important anthropogenic source of atmospheric nitrous oxide (N 2 O) and nitric oxide (NO). Although many field studies have tested the effectiveness of possible mitigation options on N 2 O and NO emissions, the effectiveness of each option varies across sites due to environmental factors and field management. To combine these results and evaluate the overall effectiveness of enhanced-efficiency fertilizers [i.e., nitrification inhibitors (NIs), polymer-coated fertilizers (PCFs), and urease inhibitors (UIs)] on N 2 O and NO emissions, we performed a meta-analysis using field experiment data (113 datasets from 35 studies) published in peer-reviewed journals through 2008. The results indicated that NIs significantly reduced N 2 O emissions (mean: À38%, 95% confidential interval: À44% to À31%) compared with those of conventional fertilizers. PCFs also significantly reduced N 2 O emissions (À35%, À58% to À14%), whereas UIs were not effective in reducing N 2 O. NIs and PCFs also significantly reduced NO (À46%, À65% to À35%; À40%, À76% to À10%, respectively). The effectiveness of NIs was relatively consistent across the various types of inhibitors and land uses. However, the effect of PCFs showed contrasting results across soil and land-use type: they were significantly effective for imperfectly drained Gleysol grassland (À77%, À88% to À58%), but were ineffective for well-drained Andosol upland fields. Because available data for PCFs were dominated by certain regions and soil types, additional data are needed to evaluate their effectiveness more reliably. NIs were effective in reducing N 2 O emission from both chemical and organic fertilizers. Moreover, the consistent effect of NIs indicates that they are potent mitigation options for N 2 O and NO emissions.

[1] The Intergovernmental Panel on Climate Change (IPCC) regularly publishes guidelines for national greenhouse gas inventories and methane emission (CH 4 ) from rice paddies has been an important component of these guidelines. While there have been many estimates of global CH 4 emissions from rice fields, none of them have been obtained using the IPCC guidelines. Therefore, we used the Tier 1 method described in the 2006 IPCC guidelines to estimate the global CH 4 emissions from rice fields. To accomplish this, we used country-specific statistical data regarding rice harvest areas and expert estimates of relevant agricultural activities. The estimated global emission for 2000 was 25.6 Tg a À1 , which is at the lower end of earlier estimates and close to the total emission summarized by individual national communications. Monte Carlo simulation revealed a 95% uncertainty range of 14.8-41.7 Tg a À1; however, the estimation uncertainty was found to depend on the reliability of the information available regarding the amount of organic amendments and the area of rice fields that were under continuous flooding. We estimated that if all of the continuously flooded rice fields were drained at least once during the growing season, the CH 4 emissions would be reduced by 4.1 Tg a À1. Furthermore, we estimated that applying rice straw off season wherever and whenever possible would result in a further reduction in emissions of 4.1 Tg a À1 globally. Finally, if both of these mitigation options were adopted, the global CH 4 emission from rice paddies could be reduced by 7.6 Tg a À1

Rice cultivation is an important anthropogenic source of atmospheric methane (CH 4 ), the emission of which is affected by management practices. Many field measurements have been conducted in major rice-producing countries in Asia. We compiled a database of CH 4 emissions from rice fields in Asia from peer-reviewed journals. We developed a statistical model to relate CH 4 flux in the rice-growing season to soil properties, water regime in the rice-growing season, water status in the previous season, organic amendment and climate. The statistical results showed that all these variables significantly affected CH 4 flux, and explained 68% of the variability. Organic amendment and water regime in the rice-growing season were the top two controlling variables; climate was the least critical variable. The average CH 4 fluxes from rice fields with single and multiple drainages were 60% and 52% of that from continuously flooded rice fields. The flux from fields that were flooded in the previous season was 2.8 times that from fields previously drained for a long season and 1.9 times that from fields previously drained for a short season. In contrast to the previously reported optimum soil pH of around neutrality, soils with pH of 5.0-5.5 gave the maximum CH 4 emission. The model results demonstrate that application of rice straw at 6 t ha À1 before rice transplanting can increase CH 4 emission by 2.1 times; when applied in the previous season, however, it increases CH 4 emission by only 0.8 times. Default emission factors and scaling factors for different water regimes and organic amendments derived from this work can be used to develop national or regional emission inventories.

Agricultural activities have greatly altered the global nitrogen (N) cycle and produced nitrogenous gases of environmental significance. More than half of all chemical N fertilizer produced globally is used in crop production in East, Southeast and South Asia, where rice is central to nutrition. Emissions of nitrous oxide (N2O), nitric oxide (NO) and ammonia (NH3) from croplands in this region were estimated by considering background emission and emissions resulting from N added to croplands, including chemical N, animal manure, biologically fixed N and N in crop residues returned to fields. Background emission fluxes of N2O and NO from croplands were estimated to be 1.22 and 0.57 kg N ha−1 yr−1, respectively. Separate fertilizer‐induced emission factors were estimated for upland fields and rice fields. Total N2O emission from croplands in the study region was estimated to be 1.19 Tg N yr−1, with 43% contributed by background emissions. The average fertilizer‐induced N2O emission, however, accounts for only 0.93% of the applied N, which is less than the default IPCC value of 1.25%, because of the low emission factor from paddy fields. Total NO emission was 591 Gg N yr−1 in the study region, with 40% from background emissions. The average fertilizer‐induced NO emission factor was 0.48%. Total NH3 emission was estimated to be 11.8 Tg N yr−1. The use of urea and ammonium bicarbonate and the cultivation of rice led to a high average NH3 loss rate from chemical N fertilizer in the study region. Emissions were displayed at a 0.5° × 0.5° resolution with the use of a global landuse database.

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Knowledge-based nitrogen (N) management, which is designed for a better synchronization of crop N demand with N supply, is critical for global food security and environmental sustainability. Yet, a comprehensive assessment on how these N management practices affect food production, greenhouse gas emission (GHG), and N pollution in China is lacking. We compiled the results of 376 studies (1166 observations) to evaluate the overall effects of seven knowledge-based N management practices on crop productivity, nitrous oxide (N O) emission, and major reactive N (Nr) losses (ammonia, NH ; N leaching and runoff), for staple grain (rice, wheat, and corn) production in China. These practices included the application of controlled-release N fertilizer, nitrification inhibitor (NI) and urease inhibitor (UI), higher splitting frequency of fertilizer N application, lower basal N fertilizer (BF) proportion, deep placement of N fertilizer, and optimal N rate based on soil N test. Our results showed that, compared to traditional N management, these knowledge-based N practices significantly increased grain yields by 1.3-10.0%, which is attributed to the higher aboveground N uptake (5.1-12.1%) and N use efficiency in grain (8.0-48.2%). Moreover, these N management practices overall reduced GHG emission and Nr losses, by 5.4-39.8% for N O emission, 30.7-61.5% for NH emission (except for the NI application), 13.6-37.3% for N leaching, and 15.5-45.0% for N runoff. The use of NI increased NH emission by 27.5% (9.0-56.0%), which deserves extra-attention. The cost and benefit analysis indicated that the yield profit of these N management practices exceeded the corresponding input cost, which resulted in a significant increase of the net economic benefit by 2.9-12.6%. These results suggest that knowledge-based N management practice can be considered an effective way to ensure food security and improve environmental sustainability, while increasing economic return.

Agricultural fields are significant sources of anthropogenic atmospheric nitrous oxide (N 2 O). We compiled and analyzed data on N 2 O emissions from Japanese agricultural fields (246 measurements from 36 sites) reported in peer-reviewed journals and research reports. Agricultural fields were classified into three categories: upland fields, tea fields and rice paddy fields. In this analysis, data measured over a period of more than 90 days for upland fields and 209 days for tea fields were used to estimate annual fertilizer-induced emission factors (EF) because of limitations in the available data. The EF is defined as the emission from fertilized plots minus the background emission (emission from a zero-N control plot), and is expressed as a percentage of the N applied. The mean of N 2 O emissions from upland fields with well-drained soils was significantly lower than that from poorly drained soils. Mean (± standard deviation) N 2 O emissions measured over a period of more than 90 days from fertilized upland fields were 1.03 ± 1.14 kg N ha −1 and 4.78 ± 5.36 kg N ha −1 for well-drained and poorly drained soils, respectively. Because the ratio of the total areas of well-drained soils and poorly drained soils was different from the ratio of the number of available EF data for each soil category, we used a weighted mean to estimate EF for all upland fields. The EF was estimated to be 0.62 ± 0.48% for all fertilized upland fields. Mean N 2 O emissions and the estimated EF for fertilized tea fields measured over a period of more than 209 days were 24.3 ± 16.3 kg N ha −1 and 2.82 ± 1.80%, respectively. The mean N 2 O emission and estimated EF from Japanese rice paddy fields were 0.36 kg N ha −1 and 0.31 ± 0.31% for the cropping season, respectively. Significant uncertainties remain in these results because of limitations in the available data.