Global food demand is increasing rapidly, as are the environmental impacts of agricultural expansion. Here, we project global demand for crop production in 2050 and evaluate the environmental impacts of alternative ways that this demand might be met. We find that per capita demand for crops, when measured as caloric or protein content of all crops combined, has been a similarly increasing function of per capita real income since 1960. This relationship forecasts a 100-110% increase in global crop demand from 2005 to 2050. Quantitative assessments show that the environmental impacts of meeting this demand depend on how global agriculture expands. If current trends of greater agricultural intensification in richer nations and greater land clearing (extensification) in poorer nations were to continue, ~1 billion ha of land would be cleared globally by 2050, with CO(2)-C equivalent greenhouse gas emissions reaching ~3 Gt y(-1) and N use ~250 Mt y(-1) by then. In contrast, if 2050 crop demand was met by moderate intensification focused on existing croplands of underyielding nations, adaptation and transfer of high-yielding technologies to these croplands, and global technological improvements, our analyses forecast land clearing of only ~0.2 billion ha, greenhouse gas emissions of ~1 Gt y(-1), and global N use of ~225 Mt y(-1). Efficient management practices could substantially lower nitrogen use. Attainment of high yields on existing croplands of underyielding nations is of great importance if global crop demand is to be met with minimal environmental impacts.

【目的】研究双季稻区晚稻季条件下，不同类型水稻品种产量、生育期、温光利用差异及其相互关系，为双季稻区适宜品种的选用提供科学依据与技术支撑。【方法】2010—2013年，在长江中游双季稻地区（江西上高），以杂交粳稻（包括籼粳交偏粳型杂交稻、籼粳交偏籼型杂交稻和粳型杂交稻）、常规粳稻、杂交籼稻3种类型水稻品种为试验材料，采用湿润育秧大苗移栽方式，系统比较双季晚稻不同类型水稻品种产量、生育期、温光利用差异及其相互关系。【结果】双季晚稻不同类型水稻品种产量表现为杂交粳稻＞常规粳稻＞杂交籼稻的趋势，差异显著或极显著。与杂交籼稻相比，4年杂交粳稻的实产增产率为19.20%—28.95%，常规粳稻实产增产率为9.21%—12.17%；通过足量的群体穗数与较大的穗型协调形成足够的总颖花量，并有保持较高的结实率和千粒重，是粳稻综合改良产量结构获得高产的基本途径。杂交粳稻和常规粳稻各生育期均相应推迟，且两者生育期亦延长，其中杂交粳稻生育期平均延长17.1 d，常规粳稻生育期平均延长9.5 d。不同类型品种生育期积温和光照时数及其不同生育阶段温光利用率均表现出杂交粳稻＞常规粳稻＞杂交籼稻的趋势，其中杂交粳稻生育积温和光照时数及其利用率最多，分别为3713.3℃、931.9 h、90.9%、93.5%。【结论】双季晚稻不同类型水稻品种产量、生育期及温光利用的差异大，适宜的粳稻品种可充分利用生育期长优势，提高温光资源利用率，最终提高产量。据此按照全国粳稻生产发展规划的要求，综合考虑双季稻接茬特点与热量条件以及栽培轻简化机械化的需求，筛选出一批适合当地种植的晚粳稻高产品种，供大面积生产选用，即甬优538、甬优8号、甬优2640、甬优1538、甬优1540、长江19、长江21、小叶迟熟、镇稻5108。

【目的】运用整合分析方法（meta-analysis），首次在大尺度范围定量研究高效氮肥施用对中国水稻产量和氮素吸收量的影响，以评估高效氮肥施用的经济效益并为高效氮肥在中国推广使用提供科学依据。【方法】通过搜集整理国内外48篇文献的大田试验数据资料，建立水稻产量和氮素吸收量数据库，进而应用整合分析方法，比较分析高效氮肥施用对中国水稻产量和氮素吸收量的整体影响及高效氮肥的有利施用条件。【结果】与施用常规化肥相比，高效氮肥施用使中国水稻产量和氮素吸收量分别增加了7.5%（95%置信区间：6.7%—8.4%）和10.5%（95%置信区间：9.5%—11.4%）。分析其影响因素，发现在碱性土壤（pH≥7.5）施用高效氮肥使水稻产量和氮素吸收量分别提高了约10.5%和18.8%，其效果好于在酸性（pH≤6.5）和中性（pH 6.5—7.5）土壤上施用；包膜缓/控释氮肥较稳定性氮肥有效，尤其在氮素吸收量方面，硝化抑制剂与常规氮肥相比没有影响，而包膜缓/控释氮肥则使氮素吸收量提高17.9%；高效氮肥仅作为基肥一次性施入土壤使水稻产量和氮素吸收量较分次施入土壤分别提高了4.2%和7.5%，同时可以考虑将高效氮肥与常规肥料混合施用，既节省费用，又可以取得同样的增产效果；当施氮总量为120—180 kg•hm-2时，高效氮肥的增效作用最为明显，分别使水稻产量和氮素吸收量提高6.5%和12.1%；就地域分布而言，在中国北方施用高效氮肥可以取得更好的效果，使水稻产量和氮素吸收量较南方施用高效氮肥分别提高了3.4%和3.0%。【结论】在中国稻田中（尤其是碱性土壤）施用高效氮肥，尤其是包膜缓/控释氮肥（作为基肥一次性施入土壤），且控制施氮总量在120—180 kg•hm-2时，对提高水稻产量和氮素吸收量效果较好。在中国稻田中，硝化抑制剂，尤其是3,4-二甲基吡唑磷酸盐对提高水稻氮素吸收量效果不佳；高效氮肥在中国稻田中的施用受水稻种植方式（直播或移栽）以及高效氮肥施肥方式（仅施高效氮肥或者与常规肥料混合施用）的影响较小；在中国北方施用高效氮肥效果可能更佳。

It is widely recommended that crop straw be returned to croplands to maintain or increase soil carbon (C) storage in arable soils. However, because C and nitrogen (N) biogeochemical cycles are closely coupled, straw return may also affect soil reactive N (Nr) losses, but these effects remain uncertain, especially in terms of the interactions between soil C sequestration and Nr losses under straw addition. Here, we conducted a global meta-analysis using 363 publications to assess the overall effects of straw return on soil Nr losses, C sequestration and crop productivity in agroecosystems. Our results show that on average, compared to mineral N fertilization, straw return with same amount of mineral N fertilizer significantly increased soil organic C (SOC) content (14.9%), crop yield (5.1%), and crop N uptake (10.9%). Moreover, Nr losses in the form of nitrous oxide (N O) emissions from rice paddies (17.3%), N leaching (8.7%), and runoff (25.6%) were significantly reduced, mainly due to enhanced microbial N immobilization. However, N O emissions from upland fields (21.5%) and ammonia (NH ) emissions (17.0%) significantly increased following straw return, mainly due to the stimulation of nitrification/denitrification and soil urease activity. The increase in NH and N O emissions was significantly and negatively correlated with straw C/N ratio and soil clay content. Regarding the interactions between C sequestration and Nr losses, the increase in SOC content following straw return was significantly and positively correlated with the decrease in N leaching and runoff. However, at a global scale, straw return increased net Nr losses from both rice and upland fields due to a greater stimulation of NH emissions than the reduction in N leaching and runoff. The trade-offs between increased net Nr losses and soil C sequestration highlight the importance of reasonably managing straw return to soils to limit NH emissions without decreasing associated C sequestration potential.© 2018 John Wiley & Sons Ltd.

After entering the twenty-first century, biochar has become a focal point of multidisciplinary research because of its special characteristics, broad application, and promising development prospects. Basic and applied research on the application of biochar in the areas of agriculture, environment, and energy have increased dramatically in the face of food security, environmental pollution, and energy shortage. Although there are some disputes about biochar research, many studies have demonstrated the importance of biochar research from the perspective of scientific advancement and practical application. This paper briefly recalls the history of biochar application; introduces research progress on the basic characteristics of biochar and its associated production technologies; summarizes the research status and existing problems of biochar application in the areas of agriculture, environment, and energy; and analyzes the potential problems and development trends of biochar research in the future.

The single high-dose application of biochar to increase rice yield has been well reported. However, limited information is available about the long-term effects of increasing rice yield and soil fertility. This study was designed to perform a 6-year field experiment to unveil the rice yield with time due to various biochar application strategies. Moreover, an alternative strategy of the Annual Low dose biochar application (AL, 8 × 35% = 2.8 t ha−1) was also conducted to make a comparison with the High Single dose (HS, 22.5 t ha−1), and annual Rice Straw (RS, 8 t ha−1) amendment to investigate the effects on annual rice yield attributes and soil nutrient concentrations. Results showed that the rice yield in AL with a lower biochar application exceeded  that of HS significantly (p < 0.05) in the 6th experimental year. The rice yield increased by 14.3% in RS, 10.9% in AL, and 4.2% in HS. The unexpectedly higher rice yield in AL than HS resulted from enhanced soil total carbon (TC), pH, and available Ca. However, compared to AL, liable carbon fraction increased by 33.7% in HS, while refractory carbon fraction dropped by 22.3%. Likewise, biochar characterization showed that more oxygen functional groups existed in HS than in AL. Decreasing inert organic carbon pools due to the constant degradation of the aromatic part of biochar in HS led to a lower soil TC than AL, even with a higher amount of biochar application. Likewise, the annual depletion lowered the soil pH and available Ca declination in HS. Based on the obtained results, this study suggested AL as a promising strategy to enhance rice productivity, soil nutrient enrichment, and carbon sequestration in the paddy ecosystem.