CROP PRODUCTION IN A WHEAT-COTTON DOUBLECROP ROTATION WITH CONSERVATION TILLAGE

Cotton (Gossypium hirsutum L.) production has dramatically increased i n the Southeast, but the role of conservation tillage in doublecropped cotton systems has not been clearly defined. Therefore, from 1988 to 1994, we investigated doublecropped wheat (Triticum aestivum L.) and c otton on plots that had been in continuous conservation vs. convention al tillage since 1979. The experimental site wits located near Florenc e, SC, on a Norfolk loamy sand (fine-loamy, siliceous, thermic Typic K andiudult). Conventional tillage consisted of multiple diskings and cu ltivations; surface tillage was eliminated for conservation tillage. W heat yields were not significantly affected by tillage, but cotton yie lds were significantly higher for conservation tillage (P less than or equal to 0.01). Cotton planting dates ranged from 7 to 18 June, and 5 of the 7 yr had more than 145 frost-free days. Two years had crop fai lure because of early freezes, and a June drought prevented the planti ng of cotton in 1 yr. In the 4 yr with harvestable yields, seed cotton yields among the eight cultivars ranged from about 500 to 2200 and 30 0 to 1850 lb/acre for conservation and conventional tillage, respectiv ely. The early maturing cultivar, 'Deltapine (DP) 20,' had the highest seed cotton yields with means of 1442 and 1123 lb/acre for conservati on and conventional tillage, respectively Development of earlier matur ing cotton and wheat cultivars will be important for this cropping sys tem in the northern Coastal Plain portion of the Cotton Belt.