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 cotnent 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.
Long‐term management practices affect the reserve of mineralizable soil N, and so can influence the amount of supplemental N fertilizer required in crop production. This study was conducted to (i) evaluate the residual effects of long‐term N fertilization and winter cover cropping on corn (Zea mays L.) N nutrition, and (ii) examine the ability of selected soil indices to detect management‐induced differences in soil N availability. In 1986, N fertilizer and winter cover crops were eliminated from plots which, from 1976 through 1985, had received varying tillage treatments, N fertilizer additions, and either hairy vetch (Vicia villosa Roth), rye (Secale cereale L.), or no winter cover crop. A history of N fertilization increased corn yield and N uptake (by an average of 20.4 kg N/ha). A history of winter cover cropping with hairy vetch increased corn yield and N uptake (by an average of 28.0 kg N/ha). Rye cover cropping generally had small or inconsistent effects relative to no cover crop. Tillage generally had insignificant effects on corn yield and N uptake. Soil N availability indices were determined on surface samples (0–15 cm) taken 2 wk after corn planting. The anaerobic incubation provided a poor index of N availability. Total soil C and Kjeldahl N were affected by tillage, though not by cover crop or fertilization history, and were marginally correlated with crop response. The autoclave index was only slightly superior to total soil C and Kjeldahl N as a N‐availability index. The soil NO3‐N concentration was highly correlated with corn yield, and N uptake. Though this study was conducted for 1 yr at one site, results indicate that measurement of surface soil NO3‐N made shortly after corn planting can provide a valid index of the effects of past crop and soil management practices on soil N availability to corn.
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