Residual effects of nitrogen fertilization and winter cover cropping on nitrogen availability

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.