Cover crops (CC) in corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] rotations may prevent N loss and provide other ecosystem services but CC productivity in the western Corn Belt is limited by the short growing season. Our objective was to assess CC treatment and planting practice effects on CC biomass, spring soil nitrate concentrations, and soybean yield at two rainfed sites in eastern and one irrigated site in south‐central Nebraska over 4 yr. Cover crop treatments (cereal rye [Secale cereale L.] [RYE] and a mix of rye, legume, and brassica species [MIX]) were planted by broadcast interseeding into corn stands in September (pre‐harvest broadcast) or drilling after corn harvest (post‐harvest drilled) and terminated 2 wk before planting soybean. Cover crop biomass and N uptake varied between years, but generally at the eastern sites, pre‐harvest broadcasting produced more biomass than post‐harvest drilling (1.64 and 0.79 Mg ha⁻¹, respectively) and had greater N uptake (37 and 24 kg ha⁻¹, respectively). At the south‐central site, post‐harvest drilling produced more than pre‐harvest broadcasting (1.44 and 1.20 Mg ha⁻¹, respectively). RYE had more biomass than MIX (1.41 and 1.09 Mg ha⁻¹, respectively), but the same N uptake. Soil nitrate reductions after CC were small. In 3 of 12 site‐years, soybean yielded less after pre‐harvest CC. Yield reductions were not correlated to CC biomass, but were likely due to greater weed pressure. High CC productivity is necessary for high N uptake, and requires site‐specific selection of planting practice and CC treatments.

中文翻译：

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覆盖西部玉米带的农作物生产力和随后的大豆产量

玉米（Zea mays L.）和大豆[ Glycine max（L.）Merr。]轮作的轮作可能防止氮素流失并提供其他生态系统服务，但西部玉米带的CC生产力受到生长期短的限制。我们的目标是评估内布拉斯加州东部两个雨养点和内布拉斯加州中南部一个灌溉点的CC处理和种植实践对CC生物量，春季土壤硝酸盐浓度和大豆产量的影响，历时4年。覆盖作物处理（谷物黑麦[ Secale谷物L.] [RYE]和黑麦，豆类和芸苔属的混合物[MIX]）通过播种在9月播种到玉米架上（收获前播种）或在玉米收获后进行钻探（收获后钻孔）并终止种植种植大豆前2周。不同年份的覆盖作物生物量和氮吸收量有所不同，但通常在东部站点，收获前广播产生的生物量要比收获后钻井多（分别为1.64和0.79 Mg ha ^-1），并且氮吸收量更大（37和24 kg ha ^-1）。在中南部站点，收获后的广播产生了比收获前的广播更多的广播（分别为1.44和1.20 Mg ha ^-1）。黑麦的生物量比MIX（1.41和1.09 Mg ha ^-1），但吸收的氮量相同。CC后土壤硝态氮的减少很小。在12个站点年中有3个，收获前CC后大豆单产下降。产量降低与CC生物量无关，但可能是由于杂草压力增大所致。高CC生产力对于高N吸收是必需的，并且需要特定位置选择种植实践和CC处理。