NITROGEN RELEASE FROM CRIMSON CLOVER IN RELATION TO PLANT-GROWTH STAGE AND COMPOSITION

Increased N-use efficency and economic savings may result from a better understanding of N release patterns from legume residues. A 2-yr field experiment was conducted on a Cecil fine sandy loam (clayey, kaolintic, thermic Typic Kanhapludult) to examine the effects of crimson clover (Trifolium incarnatum L.) growth stage on dry matter accumulation, N concentration, and chemical composition in relation to N release under no-tillage management. Crimson clover was harvested in the spring at four growth stages (late vegetative, early bloom, late bloom, and early seed set). Air-dried plant material in 1-mm mesh nylon bags was placed on the soil surface; retrieved at 1-, 2-, 4-, 8-, and 16-wk intervals; and analyzed for total N, C, cellulose, hemicellulose, and lignin concentrations. Averaged over 2 yr, dry matter production increased from 2.3 to 5.6 Mg ha-1, and N concentration declined from 30.2 to 21.2 g kg-1 as crimson clover matured from late vegetative to early seed set growth stages. Cellulose concentration increased by 66%, hemicellulose by 37%, and lignin by 87% from late vegetative to early seed set. Estimated clover N release at the 8-wk retrieval was 28, 40, 40, and 54 kg ha-1 in 1989 and 51, 67, 73, and 55 kg ha-1 in 1990 for the late vegetative, early bloom, late bloom, and early seed set growth stages, respectively. Results indicated that allowing crimson clover to attain the late bloom stage prior to desiccation and planting of the summer crop can maximize clover top-growth N content and subsequent N release.