WINTER LEGUME COVER CROP BENEFITS TO CORN - ROTATION VS FIXED-NITROGEN EFFECTS

The use of winter legume cover crops for erosion control and to provid e additional N to the soil is well established. Other potential benefi ts to legume cover crops besides N additions have been recognized, but have not been quantified, The objective of this study was to separate the fixed-N effects from the rotation effects in a winter legume cove r cropping system. A field study was initiated in 1989 on a Norfolk lo amy sand (fine, loamy, siliceous, thermic Typic Kandiudult) in east-ce ntral Alabama. Corn (Zea mays L.) was grown following (i) 'Tibbee' cri mson clover (Trifolium incarnatum L.), (ii) a partially ineffective-no dulating crimson clover, CH-1, (iii) rye (Secale cereale L.), and (iv) winter fallow, The plots were split into four Fates of fertilizer N ( 0, 56, 112, and 168 kg N ha(-1)) in a split-plot experimental plan. An evaluation of different methods of distinguishing fixed-N vs. rotatio n effects of the winter annual legume cover crop to a subsequent corn crop was made. Regression analysis of the effect of N application rate s on Nt fixation by crimson clover (fertilized with 45 kg N ha(-1)) in dicated that CH-1 clover biomass contained approximately 40 and 101 kg N ha(-1) and Tibbee clover contained approximately 51 and 119 kg N ha (-1) in 1990 and 1991, respectively. In both years of the study, crims on clover substantially increased corn yield compared with winter fall ow, with a yield increase at the highest fertilizer N application leve l of 7 and 22% for 1990 and 1991, respectively, Estimates of yield inc reases due to rotation ranged from negative to 40%. The data indicated that winter cover crops improve corn yield and that besides soil N av ailability, there was very little difference between the beneficial ef fects of clover and the rye cover crops to corn.