Crop Production in a Wheat‐Cotton Doublecrop Rotation with Conservation Tillage

Cotton (Gossypium hirsutum L.) production has dramatically increased in the Southeast, but the role of conservation tillage in doublecropped cotton systems has not been clearly defined. Therefore, from 1988 to 1994, we investigated double‐cropped wheat (Triticum aestivum L.) and cotton on plots that had been in continuous conservation vs. conventional tillage since 1979. The experimental site was located near Florence, SC, on a Norfolk loamy sand (fine‐loamy, siliceous, thermic ‘Ispic Kandiudult). Conventional tillage consisted of multiple diskings and cultivations; surface tillage was eliminated for conservation tillage. Wheat yields were not significantly affected by tillage, but cotton yields were significantly higher for conservation tillage (P ≤ 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 failure because of early freezes, and a June drought prevented the planting 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 300 to 1850 lb/acre for conservation and conventional tillage, respectively. The early maturing cultivar, ‘Deltapine (DP) 20,’ had the highest seed cotton yields with means of 1442 and 1123 lb/acre for conservation and conventional tillage, respectively. Development of earlier maturing cotton and wheat cultivars will be important for this cropping system in the northern Coastal Plain portion of the Cotton Belt. Research Question Conservation tillage can conserve and improve natural resources and increase crop productivity, but it must be adapted and optimized for the cropping systems of a physiographic area. Cotton production has dramatically increased in the Southeast, but the roles of doublecropping systems and continuous conservation tillage have not been clearly defined for cotton. In addition, the performance of cotton cultivars grown under continuous conservation tillage in short seasons has not been determined. In this study, our objectives were (i) to determine the influence of continuous conservation tillage on doublecropped wheat‐cotton grown on a Coastal Plain soil and (ii) to determine the performance of specific cultivars to late planting and conservation tillage. Literature Summary Long‐term conservation tillage with a corn rotation has been found to increase the organic matter content and crop yield potential of a Norfolk loamy sand in South Carolina. However, in other studies, crop residues alone were not sufficient to maintain the soil C content of southern Piedmont soils once the soil had been converted from conservation to conventional tillage. Higher wheat yields have been reported for Coastal Plain soils with conventional tillage as a result of poor stands in conservation tillage, but improved planting systems for wheat conservation tillage were equal to or better than conventional tillage. In dryland conditions of the Texas southern High Plains, reduced tillage of rotated or continuous cotton was superior to conventional tillage of continuous cotton. In central Arkansas, there was a 35 to 65% yield reduction of doublecropped cotton compared with full‐season cotton. At Tifton, GA, yield of doublecropped cotton was 54% of the full‐season cotton for stubble planting and 71% for planting after stubble burning and bottom plowing. It was concluded at Tifton that yield of doublecropped cotton could be improved by development of earlier cultivars. The evaluation of the effects of long‐term conservation tillage on production of cotton in the Coastal Plain soils has not been evaluated. Study Description From 1988 to 1994, we investigated a 2‐yr rotation of corn (data not reported in this manuscript) and doublecropped wheat‐cotton on plots that had been in continuous conservation vs. conventional tillage since 1979. The experimental site was located near Florence, SC, on a 6.55‐acre plot of Norfolk loamy sand. Conventional tillage consisted of multiple diskings and cultivations; surface tillage was eliminated for conservation tillage. Cotton planting dates ranged from 7 to 18 June, and 5 of the 7 yr had more than 145 frost‐free days. Three full‐season cultivars ‘PD 1,’ ‘PD 3,’ and ‘Deltapine (DP) 90,’ were compared with two shorter season cultivars, DP 20' and DP 50.' In 1994, the PD cultivars were eliminated from the experiment, and ‘Stoneville (St) 132,’ ‘St 453,’ and ‘St 907’ were compared with the three DP cultivars. Applied Questions Was wheat and cotton production better under conservation tillage than under conventional tillage? In 1991, wheat yields were 31% higher for conservation than conventional, and in 1992, wheat yields were 62% lower for conservation tillage. Otherwise, the wheat yields were not significantly different for tillage. The 5‐yr means of 2039 and 2057 lb/acre for conservation and conventional tillage, respectively, were close to the South Carolina average for the study period, 2400 lb/acre. The DP cotton cultivars grown under conservation tillage were consistently higher in yields than those grown under conventional tillage. PD 1 yielded better under conventional tillage. Seed cotton yields ranged from about 500 to 2200 and 300 to 1850 lb/acre for conservation and conventional tillage cotton, respectively (Tables and ). Did the short season reduce cotton yields? Doublecropped cotton production was affected greatly by growing conditions, particularly at planting and harvest. Delays in planting because of drought or excess rainfall can cause loss of growing days or stand failure, and early frost can reduce or eliminate yield. During the cotton growing seasons, rainfall ranged from 20 to 36 in. Frost‐free days ranged from 123 to 163, and heat units ranged from 1846 to 2273°F. Early season freezes (123 to 125 frost‐free days) ruined the late‐planted cotton crops in 1988 and 1992 because the cotton bolls had not opened prior to the freezes. A June drought caused crop establishment failure in 1993. This underlines the importance of sufficient water to insure stand establishment and reduce risk when short‐season cotton is planted immediately after wheat harvest. The best yields were in 1991 when the mean of doublecropped PD 3 was 60 and 48% of the full‐season PD 3, respectively, under conservation and conventional tillage. The shorter season DP 20 was about the same with mean yields of 62 and 46%, respectively, under conservation and conventional tillage. Were cultivars different in yield? The ranking of yields for the DP cultivars corresponded to their order of earliness, with DP 20 highest and DP 90 lowest. All three DP cultivars were consistently higher in yield with conservation tillage than with conventional tillage. The PD cultivars were less consistent in their response to conservation tillage, and PD 1 had a higher mean yield for conventional tillage. However, these results consistently indicated that the early DP cultivars (20 and 50) were superior to the PD cultivars for production under conservation tillage at the latitude of this investigation. PD cultivars were similar to the later‐maturing cultivar, DP 90. The three DP cultivars produced higher yields than did the St cultivars. Seed cotton yield of cultivars grown under conservation and conventional tillage from 1989–1992. Year Tillage PD 1 PD 3 DP 20 DP 50 DP 90 Mean ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ lb/acre ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ 1989 Cst 1236 989 1528 1432 921 1221 Cvt 1127 1095 1321 1172 822 1107 1990 Cst 626 928 943 1140 1303 988 Cvt 1269 716 868 558 758 834 1991 Cst 1631 2132 2190 1962 1940 1971 Cvt 1804 1717 1632 1872 1504 1706 LSD 0.05 for a cultivar in a tillage and year = 376 LSD 0.05 for a cultivar in a tillage and year = 379 Mean ‡ Cst 1164 1350