Tillage Effects on Wheat and Sunflower Grown in Rotation

Methods of fallowing commonly used in the Southern Great Plains are relatively ineffective for increasing soil water contents, and subsequent crop yields on a total area basis are less with fallow than with continuous cropping. Consequently, improved cropping practices are needed that increase soil water storage during fallow or that decrease the total time devoted to fallow in a cropping sequence. The objective of this study was to determine the effects of disk, sweep, limited-, and no-tillage on soil water storage and yields of dryland sunflower (Helianthus annuus L.) and irrigated wheat (Triticum aestivum L.) when grown in rotation. The tillage treatments were applied during the 10-month fallow period between harvest of irrigated wheat and planting of dryland sunflower. Wheat was planted immediately after sunflower harvest. Average gains in soil water content during fallow ranged from 3.8 cm with disk tillage to 7.2 cm with no-tillage. These differences were statistically significant, but subsequent sunflower seed yields, which averaged 1.26, 1.24, 1.24, and 1.38 metric tons/ha with disk, sweep, limited-, and no-tillage treatments, respectively, were not significantly different. Grain yield of wheat planted after sunflower averaged 4.17 metric tons/ha. There were no significant residual effects of the tillage treatments on wheat yields. For 1977 and 1978, wheat yields in this study (excluding limited-tillage) averaged 3.40 metric tons/ha compared with 2.22 metric tons/ha in an irrigated wheat-fallow-dryland grain sorghum [Sorghum bicolor (L.) Moench] study with the same tillage treatments. The wheat-sunflower rotation resulted in more timely planting and higher yields of wheat than the wheat-sorghum rotation. The wheat-sunflower rotation allows timely planting of wheat and sunflower, provides for two crops in 2 years, and thus should increase total yields as compared with systems involving an extra fallow period.