RESIDUAL EFFECTS OF INTERSEEDED HAIRY VETCH ON SOIL NITRATE NITROGEN LEVELS

Increased use of winter legume cover crops has renewed interest in legume N mineralization patterns. This study was conducted to monitor the residual effect of a hairy vetch (Vicia villosa Roth) cover crop and fertilizer N on surface soil NO3-N concentration in no-till and conventional-till corn (Zea mays L.) in northeastern Nebraska on a Nora silty clay loam (fine-silty, mixed, mesic Udic Halplustoll). The experimental design was a split-split-split plot with three replicates. Main plots of conventional tillage and no-till were split into 0, 67, and 134 kg N ha-1 with and without hairy vetch. Soil samples were taken from the 0- to 7.5- and 7.5- to 15-cm depths five times during the 1987 growing season and three times in 1988. Inclusion of a hairy vetch cover crop interseeded during the previous growing season increased soil NO3-N concentration in the surface 7.5 cm between 50 and 64 d after corn planting and in the 7.5- to 15-cm soil layer between 50 and 78 d after corn planting during 1987. In 1988 (a dry growing season), hairy vetch did not significantly increase soil NO3-N concentration in the 0- to 7.5-cm soil layer at any sampling time, but did increase soil NO3-N concentration in the 7.5- to 15-cm depth 103 d after planting. This increase in soil NO3-N concentration occurred in hairy vetch plots after silking, which probably resulted in the additional N not being available for plant growth in 1988. Increased available N resulting from a legume cover crop like hairy vetch may be beneficial in N management programs in lower rainfall areas of the USA when amounts of precipitation are adequate for plant growth and N mineralization.