Yield Probabilities for Cotton and Grain Sorghum Grown Under Dryland Conditions on the Texas High Plains

Yield probabilities were calculated for cotton (Gossypium hirsutum L.) and grain sorghum [Sorghum bicolor (L.) Moench] grown continuously and in rotations under dryland conditions on the Texas High Plains. The probabilities were calculated using the gamma function technique on data from three rotations (or cropping systems) of a 36-year dryland study conducted at Lubbock, Texas during the period 1914-1949. Differences in yields between rotations were also tested for statistical significance. The mean lint yield of the continuous-cotton cropping system was 19 kg/ha greater than that of the cotton in the cotton and grain sorghum rotation, but this difference was not statistically significant. Also, the shape parameter estimates (“g” values) for these two rotations were the same. Therefore, calculated yield probabilities for them were essentially equal. Yields of dryland cotton should exceed 150, 250, 400, and 600 kg/ha approximately 30, 50, 25, and 10% of the time, respectively. The mean yield of grain sorghum grown in rotation with cotton was significantly higher than that from the continuous-grain sorghum cropping system. Also, the “g” value obtained from the rotation was slightly higher than that obtained from the continuous-grain sorghum cropping system. Therefore, the grain sorghum yield for a given probability level will be higher in rotations with cotton than from a continuous cropping system. A dryland, continuous-grain sorghum cropping system should produce yields exceeding 750, 1,200, 2,000, and 2,750 kg/ha approximately 70, 50, 25, and 10% of the time, respectively. Slightly higher, yields can be expected when grain sorghmn is grown m alternate years with cotton. Also, l0 to 20% higher dryland yields can be expected if hybrids are substituted for open-pollinated varieties.