LEGUME MULCH AND NITROGEN-FERTILIZER EFFECTS ON SOIL-WATER AND CORN PRODUCTION

Hairy vetch (Vicia villosa Roth), as a winter annual legume cover crop, can increase grain yield of no-till corn (Zea mays L.). Optimizing management of this system depends on understanding beneficial effects. This field study examined effects of hairy vetch (HV) and N fertilizer on soil water content, crop growth, N assimilation, and water-use efficiency. Cover-crop treatments, each with 0 and 255 kg ha-1 of fertilizer N, were (i) winter fallow, (ii) aboveground HV removed at corn planting, (iii) HV left in place, and (iv) HV left in place and supplemented with that removed from (ii). Transpiration by HV before corn planting reduced soil water content, decreasing early growth of corn during years of low spring rainfall. By 2 to 4 wk after planting, however, soil water content under HV mulch was similar to winter fallow. Soil water content was higher with HV mulch only during the second 4-wk period following planting and only in the upper 7.5 cm of the profile. Greater soil water use associated with N fertilizer occurred after about 8 wk in 2 of the 3 yr. Hairy vetch treatments at the zero-N fertilizer level increased corn growth, N assimilation, grain yield, and water-use efficiency. The high-N treatment negated these benefits of HV. Because of this and the lack of mulch effects on soil water during later stages of crop growth, we concluded that N supplied to no-till corn was the principal, immediate benefit of HV during this study.