Fall-planted cover crops are a strategy for scavenging residual reactive N. In the northern U.S. Corn Belt, the short growing season continues to limit adoption of cover crops. Planting cover crops following wheat (Triticum aestivum L.) in a three-crop rotation (wheat [cover crop]–corn [Zea mays L]–soybean [Glycine max L. (Merr.)]) increases establishment time. Two cover crops noted for N scavenging, annual ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot) and radish (Raphanus sativus L. ‘Tillage’), were selected. We hypothesized that corn yield could be maintained with less N fertilizer when following a cover crop compared with no cover crop as determined by direct comparison and regression analyses. The study was repeated 3 yr and had three cover crop treatments: annual ryegrass, radish, and the no-cover-crop control. A second treatment, factorially applied in corn years, was N application rates relative the recommended rate of 0× (0 kg N ha^–1), 0.25× (39–48 kg N ha^–1), 0.5× (78–95 kg N ha^–1), and 1× (157–190 kg N ha^–1). When cover crops were planted after wheat, about 60 kg N ha^–1 yr^–1 was measured in the roots and shoots of radish and annual ryegrass, representing 35 or >60% of the inorganic N in the soil. Corn yield averaged 5% higher following radish and 13% lower following annual ryegrass compared with the no-cover control. Both cover crops scavenged residual N, but neither cover crop treatment supported the hypothesis that corn yield could be maintained with less N fertilizer compared with no cover crop.

中文翻译：

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萝卜和一年生黑麦草改变玉米产量对氮肥率的响应

秋季种植的覆盖作物是清除残留活性氮的一种策略。在美国北部玉米带，较短的生长季节继续限制覆盖作物的采用。在小麦 ( Triticum aestivum L.) 之后以三轮作物（小麦 [覆盖作物]-玉米 [ Zea mays L]-大豆 [ Glycine max L. (Merr.)]）种植覆盖作物可增加定植时间。两种以清除氮素而著称的覆盖作物、一年生黑麦草 ( Lolium perenne L. ssp. multiflorum (Lam.) Husnot) 和萝卜 ( Raphanus sativusL. '耕作'），被选中。我们假设与通过直接比较和回归分析确定的没有覆盖作物相比，在种植覆盖作物时可以使用较少的氮肥来维持玉米产量。该研究重复了 3 年，并进行了三种覆盖作物处理：一年生黑麦草、萝卜和无覆盖作物控制。在玉米年中因子应用的第二个处理是相对于 0×（0 kg N ha ^–1）、0.25×（39-48 kg N ha ^–1）、0.5×（78-95 kg N ha ^–1 ) 和 1× (157–190 kg N ha ^–1 )。在小麦之后种植覆盖作物时，大约 60 kg N ha ^–1  yr ^–1在萝卜和一年生黑麦草的根和芽中测量到，占土壤中无机氮的 35% 或 >60%。与无覆盖对照相比，种植萝卜的玉米产量平均高 5%，种植一年生黑麦草的玉米产量平均降低 13%。两种覆盖作物都能清除残留的氮，但两种覆盖作物处理都支持这样的假设，即与没有覆盖作物相比，使用较少的氮肥可以保持玉米产量。