COTTON RESPONSE TO SORGHUM AND SOYBEAN ROTATIONS AT VARIOUS NITROGEN RATES

J.E. Matocha, K.L. Barber and F.L. Hopper

ABSTRACT

Four rotation systems involving cotton, grain sorghum and soybean were compared in conservation (reduced till) and conventional tillage systems. All crop rotation and tillage systems were evaluated at multiple rates of nitrogen fertilizer. The experimental site was located at the Texas A&M University Research Center Farm at Corpus Christi on Victoria clay (Udic Pellusterts). Measurements of treatment effects included grain and lint yields and soil nitrates at profile depths extending to three feet. The study was initiated in 1990, an extremely dry year which produced catastrophic crop yields.

Preliminary results for the first two years indicated the rotation effects of cotton (and sorghum) boosted grain yields but had no significant effect on lint yields. The influence of cotton in the rotation had less effect on grain yields as the fertilizer N rate was increased. At the same time sorghum in the rotation had no effect on lint yields regardless of N fertilization. Cotton and sorghum produced essentially the same yields when grown under conventional or reduced tillage. Cotton responded to the 60 lb N/A rate in the 2-yr. cot:2-yr sorg rotation but only to 30 lb N/A rate in the 1-yr Sb:1-yr cot system. Nitrogen response was greatest in the conventional till system. Yields of continuous grain sorghum appeared to follow a positive linear relationship with N rate in both tillage systems. This relationship was not as strong in the cot.,sorg. rotation system. Soil in the 1-yr cot:l-yr Sb rotation had the highest soil nitrate content in the surface 24 inches while soil in continuous sorghum had the lowest under both N control and N fertilized conditions. These data suggest that soybean can make a significant contribution to N nutrition of cotton.





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Document last modified July 8, 2004