Phosphorus application in excess of crop needs has increased the concentration of P in surface soil and runoff and led many states to develop P-based nutrient management strategies. However, insufficient data are available relating P in surface soil, surface runoff, and subsurface drainage to develop sound guidelines. Thus, we investigated P release from the surface (0-5 cm depth) of a Denbigh silt loam from Devon, U.K. (30-160 mg kg-1 Olsen P) and Alvin, Berks, Calvin, and Watson soils from Pennsylvania (10-763 mg kg-1 Mehlich-3 P) in relation to the concentration of P in surface runoff and subsurface drainage. A change point, where the slopes of two linear relationships between water- or CaCl2-extractable soil P and soil test phosphorus (STP) (Olsen or Mehlich-3) meet, was evident for the Denbigh at 33 to 36 mg kg-1 Olsen P, and the Alvin and Berks soils at 185 to 190 mg Mehlich-3 P kg-1. Similar change points were also observed when STP was related to the P concentration of surface runoff (185 mg kg-1) and subsurface drainage (193 mg kg-1). The use of water and CaCl2 extraction of surface soil is suggested to estimate surface runoff P (r2 of 0.92 for UK and 0.86 for PA soils) and subsurface drainage P (r2 of 0.82 for UK and 0.88 for PA soils), and to determine a change point in STP, which may be used in support of agricultural and environmental P management.

农业生产对全球气候变暖、水资源短缺和环境污染具有重要影响。碳足迹和水足迹分别是评估温室气体排放和水资源消耗的指标。采用生命周期评价方法,对吉林省水稻生产的碳足迹和水足迹进行核算,分析碳足迹和水足迹的时空变化特征及其构成。结果表明:2007—2017年吉林省水稻生产的碳足迹年均值为0.74 kg·kg^-1。甲烷排放是水稻生产碳足迹的主要组分,占比为41.55%,其次为化肥施用导致的温室气体排放,占比为21.18%。2007—2017年吉林省水稻生产的水足迹呈波动下降趋势,年均值为147 L·kg^-1,其中:水稀缺足迹为122 L·kg^-1,约占83%,水劣化足迹为25 L·kg^-1,约占17%。碳足迹和水足迹的高值区和低值区在空间上分布不一致,吉林省西部和中部地区的水足迹较大、碳足迹较小,而东部、中东部地区碳足迹较大、水足迹较小。相关分析表明,碳足迹和水足迹呈负相关。

明确黑龙江省黑土区玉米田氮肥减施效应和碳足迹特征，对于本地区合理施肥、发展低碳农业和保障农业可持续发展具有积极作用。本研究基于玉米肥料田间试验，分析不同氮肥减施比例对玉米产量、氮素吸收利用及损失的影响，利用生命周期法估算农资投入和田间操作引起的直接或间接碳排放量，分析碳足迹变化。结果表明：与农民习惯施肥处理相比，在黑龙江省黑土区减施氮肥10%～20%(赵光农场施氮量127.2 kg/hm2、青冈县施氮量130.9 kg/hm2、双城区施氮量186.5 kg/hm2)不影响玉米产量及氮素吸收，可提高氮肥回收率和农学效率(增幅分别在9.5%～25.7%和9.9%～28.2%之间)，增加经济收益，减少土壤N2O排放、氨挥发和氮素淋溶损失，过量减施氮肥会导致玉米减产降效减收。合理减施氮肥显著降低玉米田单位产量碳足迹，降幅在4.2%～12.4%之间。综上，黑龙江省黑土区玉米田合理减施氮肥可稳产、增效、降损和增收，并可大幅度降低玉米田碳足迹。

As a major agricultural country, the comprehensive accounting of the dynamics and composition of the carbon footprint of major crops in China will provide a decision-making basis for environmental management and agricultural green development in the whole process of the major crop production system in China. To investigate the spatiotemporal dynamics of the carbon footprint for major crops in China, a life cycle-based carbon footprint approach was used to evaluate the carbon footprint per unit area (CFA) and per unit yield (CFY) of eight crops for the period of 1990 to 2019. Our results showed that the CFA for all major crops showed an increasing trend with time before 2016 but slowly decreased afterward, while the CFY decreased by 16–43% over the past 30 years due to the increase in crop yield. The three main grain crops, rice (4871 ± 418 kg CO2-eq · ha−1), wheat (2766 ± 552 kg CO2-eq · ha−1), and maize (2439 ± 530 kg CO2-eq · ha−1), showed the highest carbon footprint and contribution to the total greenhouse gas (GHG) emissions, mainly due to their larger cultivated areas and higher fertilizer application rates. CH4 emission was the major component of the carbon footprint for rice production, accounting for 66% and 48% of the CFA and CFY, respectively, while fertilizer production and usage were the largest components of carbon footprint for dryland crops, making up to 26–49% of the CFA and 26–50% of the CFY for different crops. The present study also highlighted the spatial and temporal patterns of the carbon footprint for major crops in China, which could serve as references for the development of best management practices for different crop production in China, to mitigate agricultural GHG emission and to pursue low-carbon agriculture.

水稻是中国及全球食物系统的重要组成部分，以食物系统视角研究其生命周期碳足迹对实现水稻食物系统低碳转型和绿色发展具有重要意义。该研究基于中国2018年22个水稻主产省份的统计数据，结合生命周期评估（LCA）法和国际水稻研究所（IRRI）开发的CF-Rice水稻碳足迹计算工具，计算并分析了中国水稻食物系统“从摇篮到销售”的碳足迹及其结构组成、地区差异和水稻类型差异。结果表明：1）以单位产量碳足迹进行比较（以CO₂ eq计），晚籼稻 (2.31 kg?kg^?1)>中籼稻 (1.32 kg?kg^?1)>粳稻 (1.13 kg?kg^?1)>早籼稻 (1.08 kg?kg^?1)；以单位面积碳足迹进行比较（以CO₂ eq计），晚籼稻 (9.15×10³ kg?hm^?2)>中籼稻 (6.34×10³ kg?hm^?2)>粳稻 (5.56×10³ kg?hm^?2)>早籼稻 (4.16×10³ kg?hm^?2)；2）稻田甲烷（CH₄）是水稻食物系统碳足迹最主要的组成部分，占36.2%－71.5%，其次是施肥，占8.69%－20.0%，收获环节占8.41%－18.5%，产前环节占4.97%－12.1%，机械作业、仓储、加工、包装和运输环节虽占比较小（均<10%）但也不容忽视；3）早籼稻、中籼稻和晚籼稻没有表现出明显的空间分布规律，而粳稻呈现出自北向南碳足迹增加的趋势，具体表现为：除山东外，东北地区（黑龙江、吉林、辽宁）和华北地区（内蒙古、河北）的粳稻碳足迹低于华东地区（安徽、江苏、浙江）、华中地区（河南、湖北）和西南地区（云南）；4）从温室气体的构成来看，CH₄对水稻食物系统碳足迹的贡献率最高，达到20.1%－76.4%，其次为二氧化碳（CO₂），贡献率为21.1%－72.3%，氧化亚氮（N₂O）的贡献率最低，仅有1.76%－10.7%。水稻食物系统碳足迹的地区和类型差异主要与气候条件、种植管理措施和排放因子有关，因此，控制稻田CH₄排放，优化水肥管理，减少能源消耗及粮食损失和浪费可有效降低水稻食物系统碳足迹。

由温室气体排放引起的全球变暖问题已受到公众的广泛关注。农业生产对温室气体排放有重要影响,水稻是中国主要粮食作物,而稻田又是CH₄的主要排放源,因此研究其生产过程的碳足迹对实现农业节能减排具有意义。本研究基于2004-2014年水稻生产相关统计数据,利用碳足迹评价方法核算了中国水稻生产碳足迹及其变化趋势。研究结果表明：①中国水稻生产温室气体排放量、单位面积碳足迹呈逐年增长,而单位产量碳足迹则出现下降趋势,年均增长量分别为21.24亿kgCO₂-eq、32.58kgCO₂-eq/hm²和-2.82kgCO₂-eq/t;②不同省份由于水稻生产条件差异,其碳足迹存在较大差别,如年均单位面积碳足迹最高的江苏达7411.91kgCO₂-eq/hm²,最低的黑龙江为4305.87kgCO₂-eq/hm²;③年均单位产量碳足迹方面,最高海南为1419.35kgCO₂-eq/t,最低吉林为602.12kgCO₂-eq/t;④综合比较单位面积与单位产量碳足迹发现,华南双季稻稻作区（广西、广东、福建等）,华中双季稻稻作区（江苏、湖南、江西等）,其单位碳足迹均高于全国平均水平;⑤水稻生产碳足迹组成中占比最大的部分为稻田CH₄排放,达85.05%,农资投入导致的温室气体排放仅占14.95%,其中化肥投入占总碳足迹的10.25%。最后,本文建议通过改进农田管理措施（如间歇性灌溉、改进施肥、合理使用农业投入品）,提高水稻机械化生产效率来有效减少水稻温室气体排放。