W. K. Kellogg Biological Station, Michigan State University, 3700 East Gull Lake Drive, Hickory Corners, Michigan 49060, USA.
Ecol Appl. 2010 Apr;20(3):648-62. doi: 10.1890/09-0077.1.
Soils in conventional agroecosystems are purposely held in a nitrogen (N)-saturated state to maximize crop yields. Planting winter annual cover crops when fields are usually fallow has been proposed to ameliorate N losses from soils. In this study we introduced winter annual cover crops into an N rate study with plots fertilized at 0, 34, 67, 101, 134, 168, and 202 kg N/ha in maize (Zea mays L.) to determine how winter annual cover crops affect yields, N2O and NO3- fluxes, and N pools. At the six-leaf stage and during flowering, incorporation of cover crop into soil resulted in a 30% reduction in maize biomass. Three weeks after fertilization, KCl-extractable soil mineral N was 75-87% lower in covercropped soils than in no-cover soils, indicating that N had been immobilized in the covercropped soils. At physiological maturity, there was no difference between cover and no-cover treatments in crop yield, which was maximized at 9 Mg/ha in 2006 and 7 Mg/ha in 2007. Where N rates exceed crop requirements, cover crop incorporation may reduce N exports as NO3- and N2O. Tighter N cycling in conventional agroecosystems could be fostered by matching N rates to the amount of N removed with grain and using N immobilization to retain N and support yields. If N immobilization is viewed as a means for efficient fertilizer N use rather than a process that decreases crop productivity, growers might be more willing to adopt cover-cropping practices.
传统农业生态系统中的土壤通常处于氮（N）饱和状态，以最大限度地提高作物产量。当农田休耕时，种植冬季一年生覆盖作物被提议用来减少土壤中的氮损失。在这项研究中，我们在施氮量为 0、34、67、101、134、168 和 202 kg N/ha 的玉米（Zea mays L.）的氮率研究中引入了冬季一年生覆盖作物，以确定冬季一年生覆盖作物如何影响产量、N2O 和 NO3-通量以及氮库。在六叶期和开花期，将覆盖作物掺入土壤会导致玉米生物量减少 30%。施肥后 3 周，覆盖作物土壤中 KCl 可提取的土壤矿质氮比无覆盖作物土壤低 75-87%，表明氮已在覆盖作物土壤中固定。在生理成熟时，覆盖作物和无覆盖作物处理在作物产量上没有差异，2006 年最大产量为 9 Mg/ha，2007 年最大产量为 7 Mg/ha。在氮用量超过作物需求的情况下，覆盖作物的加入可能会减少氮的输出，如 NO3-和 N2O。通过将氮用量与籽粒去除的氮量相匹配，并利用氮固定来保留氮和支持产量，可以促进传统农业生态系统中氮的更紧密循环。如果将氮固定视为提高肥料氮利用效率的一种手段，而不是降低作物生产力的过程，那么种植者可能更愿意采用覆盖作物的做法。
