WINTER COVER CROPPING INFLUENCE ON NITROGEN MINERALIZATION, PRESIDEDRESS SOIL NITRATE TEST, AND CORN YIELDS

The mineralization and availability of cover crop N to the succeeding crop are critical components in the management of soil N to reduce N l eaching. The effects of several leguminous and non-leguminous cover cr ops on soil N availability, N mineralization potential, and corn (Zen mays L.) yield were examined. The cover crops had variable effects on soil N availability and corn yield and N uptake. Because of the rapid mineralization of the cover crops following incorporation, the inorgan ic N levels in the soil sampled in mid-May 1992 (4 weeks after incorpo ration of cover crops), rather than the potentially mineralizable N, r ate constants, initial potential mineralization rate, or cumulative N mineralized over 14 weeks, correlated well with N concentrations, C:N ratios, or the N added in the cover crops. However, the inclusion of p otentially mineralizable N with inorganic N in a multiple regression i mproved the variability in the corn yield and the N uptake accounted f or. Since extensive mineralization had occurred before the 21 May samp ling, the potentially mineralizable N was affected more by the soil or ganic N and C than by the N concentrations of the cover crops. The pre sidedress NO3--N test levels were well predicted by the inorganic and potentially mineralizable N (R(2)=0.89, P<0.01), although the test lev els were better in predicting corn yield and N uptake. Lf the availabl e soil N test needs to be made earlier than recommended by the preside dress NO3--N test, both inorganic and potentially mineralizable N are needed to better predict the corn yield and N uptake in the soils.