N-15 RECOVERY AND RELEASE BY RYE AND CRIMSON CLOVER COVER CROPS

A grass-legume biculture may be preferred over a legume monoculture co ver crop due to the scavenging ability of a grass species, especially when high residual soil N levels are present following summer droughts in the Atlantic Coastal Plain. Rye (Secale cereale L.) and crimson cl over (Trifolium incarnatum L.) were grown in monoculture and as a bicu lture in a 2-yr field experiment on a Typic Kandiudult to assess cover crop recovery of fertilizer N-15 and the subsequent corn (Zea mays L. ) uptake of cover crop residue N-15. Potassium nitrate labeled with 10 atom % N-15 was applied to microplots at 50 kg N ha(-1) wk after seed ing the cover crops, which were monitored for recovery of fertilizer N -15. Labeled residue was placed in a new microplot to monitor release of residue N-15 and its recovery by corn. Averaged across both years, rye monoculture recovered 39% of the labeled N-15 fertilizer compared with 19% in the rye-crimson clover biculture and 4% in the crimson clo ver monoculture. Following corn harvest and averaged across both years , total recovery of N-15 fertilizer from the original microplots (cove r crop, corn biomass, and soil N) was 29% for crimson clover, 75% for rye, 55% for rye-crimson clover biculture, and 20% for the native wint er weeds. In 1993, corn recovery of residue N-15 was lowest in the rye monoculture (4%) compared with other treatments (20-35%). Results ind icated that a rye-crimson clover biculture,vas capable of recovering g reater residual N-15 than a crimson clover monoculture, but less than rye monoculture.