Nitrogen‐15 Recovery and Release by Rye and Crimson Clover Cover Crops

A grass‐legume biculture may be preferred over a legume monoculture cover 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 clover ( Trifolium incarnatum L.) were grown in monoculture and as a biculture in a 2‐yr field experiment on a Typic Kandiudult to assess cover crop recovery of fertilizer 15 N and the subsequent corn ( Zea mays L.) uptake of cover crop residue 15 N. Potassium nitrate labeled with 10 atom % 15 N was applied to microplots at 50 kg N ha ‐1 1 wk after seeding the cover crops, which were monitored for recovery of fertilizer 15 N. Labeled residue was placed in a new microplot to monitor release of residue 15 N and its recovery by corn. Averaged across both years, rye monoculture recovered 39% of the labeled 15 N fertilizer compared with 19% in the rye‐crimson clover biculture and 4% in the crimson clover monoculture. Following corn harvest and averaged across both years, total recovery of 15 N fertilizer from the original microplots (cover 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 winter weeds. In 1993, corn recovery of residue 15 N was lowest in the rye monoculture (4%) compared with other treatments (20–35%). Results indicated that a rye‐crimson clover biculture was capable of recovering greater residual 15 N than a crimson clover monoculture, but less than rye monoculture.