RESEEDING, BIOMASS, AND NITROGEN-CONTENT OF SELECTED WINTER LEGUMES IN GRAIN-SORGHUM CULTURE

Winter legumes as green manure crops in grain sorghum, Sorghum bicolor L. Moench, production on clay soils in the southern USA would be facilitated by increased knowledge of growth responses and reseeding capability of legume cultivars. This study evaluated 'Tibbee' crimson, Trifolium incarnatum L.; 'Bigbee' berseem, T. alexandrinum L.: 'Yuchi' arrowleaf, T. vesiculosum Savi.; and 'Woogenellup' subterranean, T. subterraneum L. clovers and 'Woodford' big flower vetch, Vicia grandiflora Scop., for reseeding, biomass and N content at seven growth termination dates (GTD): 20 and 31 March, 10 and 21 April, and 1, 13, and 22 May 1986. The field experiment was initially planted on 15 Oct. 1985 on a Mhoon silty clay (fine-silty, mixed, nonacid, thermic, Typic Fluvaquents). No legume was able to reseed the first year when the GTD was on or before 10 April. Crimson and subterranean clover and big flower vetch successfully reseeded at a GTD of 21 April. Berseem clover did not reseed unless the GTD was as late as 13 May, and arrowleaf clover did not reseed at any GTD. The legumes that reseeded the first year also reseeded a second year. Maximum biomass:N (kg ha-1) accumulation was 5500:150 for crimson; 6550:190 for berseem; 6350:152 for subterranean; 6300:203 for arrowleaf clovers; and 2700:80 for big flower vetch. Maximum biomass and N accumulation occurred by the date of reseeding for all five legumes; thus, growth of these legumes need not extend beyond this date to realize all of the green manure benefits. Nitrogen content of all legumes, except big flower vetch, was theoretically sufficient to meet the requirements of a grain sorghum crop without additional N fertilizer.