WINTER COVER CROPPING INFLUENCE ON NITROGEN IN SOIL

Winter cover crops may affect the short and long-term N availability i n soil depending on the quantity, quality, and degradation rate of bio mass returned to the soil, Ne examined the effects of several cover cr ops on soil inorganic and organic N levels in a winter cover crop-sila ge corn (Zea mays L.) double-cropping system that mas initiated in 198 7. High biomass N concentrations (BMN) in the above- and belowground b iomass of the leguminous cover crops corresponded to high levels of in organic N and water-soluble N, but low levels of water-soluble C and c arbohydrate compared with the nonleguminous cover crops. The BMB above which there was net N mineralization 4 wk after residue incorporation mas 17.9 g N kg(-1). The organic N from the aboveground biomass degra ded rapidly. The first-order rate constants for the degradation of org anic N and C in the cover crops were significantly correlated, This, c oupled with a significant correlation between the soil organic N (SON) levels and cumulative biomass C added, indicated tile importance of b iomass C inputs in organic N retention in tile soil, The cover crops h ad variable short-and long-term effects on soil N availability. Wherea s rye (Secale cereale L. cv. Tetra Petkus) and annual ryegrass (Lolium multiflorum Lam. cv. Billion) were ineffective in increasing soil ino rganic N levels, they were more effective than hairy vetch (Vicia vill osa Roth subsp. villosa), Austrian winter pea (Lathryrus hirsutus L.), and canola (Brassica napus L. cv. Santana) in increasing SON accumula tion because of a higher biomass potential and a larger input of bioma ss C.