RESIDUAL EFFECTS OF NO-TILL CROP RESIDUES ON CORN YIELD AND NITROGEN UPTAKE

The residual effects of crop residues on N availability and crop growt h are largely unknown. A field experiment was conducted from 1986 thro ugh 1988 at Lincoln, NE, to determine the residual effects on no-till corn (Zea mays L.) production and N uptake of 0, 50, 100, and 150% of the amount of crop residues produced by the previous crop during the p revious 5 yr. These effects were evaluated with and without tillage (d isking), N fertilizer (60 kg N ha(-1)), and hairy vetch (Vicia villosa Roth ssp. villosa, 'Madison') winter cover crop. Increasing the previ ous crop residue rate increased organic C, total N, and NO3-N in the u pper 30 cm of soil as much as 10, 12, and 66%, respectively. Growth an d N uptake by corn (3 yr average) generally increased as previous resi due rate increased. Corn grain and stover production was 17 and 25% gr eater for the highest compared with the lowest previous residue rate. Uptake of indigenous soil N, but not fertilizer N, also increased as p revious residue rate increased. Cover crops generally increased growth and N uptake with no fertilizer, but had little effect with N fertili zer. Soil properties, crop growth, and N uptake generally were not aff ected by tillage or interactions among the variables. These results in dicate that increasing no-till crop residue rates increased the capabi lity of this soil to provide N to growing crops for many years. It app ears this effect is somewhat self perpetuating.