The North China Plain,where summer corn(Zea mays L.)and winter wheat(Triticum aestivum L.)are the major crops grown,is a major agricultural area in China.Permeable soils make the region susceptible to groundwater poll...The North China Plain,where summer corn(Zea mays L.)and winter wheat(Triticum aestivum L.)are the major crops grown,is a major agricultural area in China.Permeable soils make the region susceptible to groundwater pollution by NO_3-N,which is applied to fields in large amounts of more than 400 kg NO_3-N ha^(-1)as fertilizer.A field experiment was established in 2002 to examine the relationship among N fertilization rate,soil NO_3-N,and NO_3-N groundwater contamination.Two adjacent fields were fertilized with local farmers' N fertilization rate(LN)and double the normal application rate(HN),respectively,and managed under otherwise identical conditions.The fields were under a traditional summer corn/winter wheat rotation.Over a 22-month period,we monitored NO_3-N concentrations in both bulk soil and soil pore water in 20-40 cm increments up to 180 cm depth.We also monitored NO_3-N concentrations in groundwater and the depth of the groundwater table.No significant differences in soil NO_3-N were observed between the LN and HN treatment.We identified NO_3-N plumes moving downward through the soil profile.The HN treatment resulted in significantly higher groundwater NO_3-N,relative to the LN treatment,with groundwater NO_3-N consistently exceeding the maximum safe level of 10 mg L^(-1),but groundwater NO_3-N above the maximum safe level was also observed in the LN treatment after heavy rain.Heavy rain in June,July,and August 2003 caused increased NO_3-N leaching through the soil and elevated NO_3-N concentrations in the groundwater.Concurrent rise of the groundwater table into NO_3-N- rich soil layers also contributed to the increased NO_3-N concentrations in the groundwater.Our results indicate that under conditions of average rainfall,soil NO_3-N was accumulated in the soil profile.The subsequent significantly higher- than-average rainfalls continuously flushed the soil NO_3-N into deeper layers and raised the groundwater table,which caused continuous groundwater contamination with NO_3-N.The results suggest that under common farming practices in the North China Plain,groundwater contamination with NO_3-N was likely,especially during heavy rainfalls,and the degree of groundwater contamination appeared to be proportional to the N application rates.Decreasing fertilization rates, splitting fertilizer inputs,and optimizing irrigation scheduling had potential to reduce groundwater NO_3-N contamination.展开更多
麦-玉一年两熟的江淮、黄淮地区秸秆混土还田保护性耕作模式,麦秸秆-土壤混合的种床缺乏准确的物料相互接触参数,阻碍了机械化玉米精密播种过程中关键部件、种粒、肥料与混合种床相互作用研究,进而制约了机具优化与改进。采用物理与EDE...麦-玉一年两熟的江淮、黄淮地区秸秆混土还田保护性耕作模式,麦秸秆-土壤混合的种床缺乏准确的物料相互接触参数,阻碍了机械化玉米精密播种过程中关键部件、种粒、肥料与混合种床相互作用研究,进而制约了机具优化与改进。采用物理与EDEM离散元方法结合研究非连续体麦秸秆-土壤混合物之间相互作用,选用Bonding V2黏结模型搭建柔性麦秸秆段“元颗粒”,选取Hertz-Mindlin with JKR模型对一定湿度的土壤进行参数标定。首先,以圆桶提升麦秸秆和土壤种床混合物堆积角为响应值,采用Plackett-Burman筛选试验和最陡爬坡试验分别对显著影响因素从大到小排序和缩近最佳取值范围。利用Box-Behnken试验构建了显著影响因素与堆积角二阶回归模型,对显著因素交互项进行响应曲面分析,利用Design-Expert软件优化模型并以实测堆积角39.94°为目标响应值,计算得土壤JKR表面能0.500、土壤-秸秆动摩擦系数0.065 8、土壤-秸秆JKR表面能0.262及土壤-土壤动摩擦系数0.155,仿真验证误差1.08%,表明标定的接触模型参数可靠。该研究可为麦-玉保护性耕作模型下混合种床与机具精密播种相互作用研究提供参考和理论依据。展开更多
基金Project supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(No.kzc x2-yw-406)the National Basic Research Program of China(No.2005CB121103).
文摘The North China Plain,where summer corn(Zea mays L.)and winter wheat(Triticum aestivum L.)are the major crops grown,is a major agricultural area in China.Permeable soils make the region susceptible to groundwater pollution by NO_3-N,which is applied to fields in large amounts of more than 400 kg NO_3-N ha^(-1)as fertilizer.A field experiment was established in 2002 to examine the relationship among N fertilization rate,soil NO_3-N,and NO_3-N groundwater contamination.Two adjacent fields were fertilized with local farmers' N fertilization rate(LN)and double the normal application rate(HN),respectively,and managed under otherwise identical conditions.The fields were under a traditional summer corn/winter wheat rotation.Over a 22-month period,we monitored NO_3-N concentrations in both bulk soil and soil pore water in 20-40 cm increments up to 180 cm depth.We also monitored NO_3-N concentrations in groundwater and the depth of the groundwater table.No significant differences in soil NO_3-N were observed between the LN and HN treatment.We identified NO_3-N plumes moving downward through the soil profile.The HN treatment resulted in significantly higher groundwater NO_3-N,relative to the LN treatment,with groundwater NO_3-N consistently exceeding the maximum safe level of 10 mg L^(-1),but groundwater NO_3-N above the maximum safe level was also observed in the LN treatment after heavy rain.Heavy rain in June,July,and August 2003 caused increased NO_3-N leaching through the soil and elevated NO_3-N concentrations in the groundwater.Concurrent rise of the groundwater table into NO_3-N- rich soil layers also contributed to the increased NO_3-N concentrations in the groundwater.Our results indicate that under conditions of average rainfall,soil NO_3-N was accumulated in the soil profile.The subsequent significantly higher- than-average rainfalls continuously flushed the soil NO_3-N into deeper layers and raised the groundwater table,which caused continuous groundwater contamination with NO_3-N.The results suggest that under common farming practices in the North China Plain,groundwater contamination with NO_3-N was likely,especially during heavy rainfalls,and the degree of groundwater contamination appeared to be proportional to the N application rates.Decreasing fertilization rates, splitting fertilizer inputs,and optimizing irrigation scheduling had potential to reduce groundwater NO_3-N contamination.
文摘麦-玉一年两熟的江淮、黄淮地区秸秆混土还田保护性耕作模式,麦秸秆-土壤混合的种床缺乏准确的物料相互接触参数,阻碍了机械化玉米精密播种过程中关键部件、种粒、肥料与混合种床相互作用研究,进而制约了机具优化与改进。采用物理与EDEM离散元方法结合研究非连续体麦秸秆-土壤混合物之间相互作用,选用Bonding V2黏结模型搭建柔性麦秸秆段“元颗粒”,选取Hertz-Mindlin with JKR模型对一定湿度的土壤进行参数标定。首先,以圆桶提升麦秸秆和土壤种床混合物堆积角为响应值,采用Plackett-Burman筛选试验和最陡爬坡试验分别对显著影响因素从大到小排序和缩近最佳取值范围。利用Box-Behnken试验构建了显著影响因素与堆积角二阶回归模型,对显著因素交互项进行响应曲面分析,利用Design-Expert软件优化模型并以实测堆积角39.94°为目标响应值,计算得土壤JKR表面能0.500、土壤-秸秆动摩擦系数0.065 8、土壤-秸秆JKR表面能0.262及土壤-土壤动摩擦系数0.155,仿真验证误差1.08%,表明标定的接触模型参数可靠。该研究可为麦-玉保护性耕作模型下混合种床与机具精密播种相互作用研究提供参考和理论依据。
