Tillage and Residue Effects on Wheat, Sorghum, and Sunflower Grown in Rotation

Tillage methods affect soil surface conditions and amounts of crop residue retained on the soil surface, which, in turn, affect water infiltration and subsequent evaporation. The objectives of this study were to determine the effect of tillage methods and wheat residue levels on soil water storage and use, and on crop growth and yields. The study, conducted on Pullman clay loam (fine, mixed, thermic Torrertic Paleustolls), involved an irrigated winter wheat (Triticum aestivum L.)-dryland grain sorghum [Sorghum bicolor (L.) Moench]-dryland sunflower (Helianthus annuus L.) cropping system. A 330-d fallow period occurred between wheat harvest and sorghum planting and a 210- to 270-d fallow period (overwinter) occurred between sorghum harvest and sunflower planting. Wheat was planted 30 to 60 d after sunflower harvest. After wheat harvest, residues were partially removed from one-half of the plots; residues on the other half were not removed. Then, moldboard-, disk-, rotary-, sweep-, and no-tillage treatments were applied. Soil water content increases during fallow after wheat averaged 89, 109, 85, 114, and 141 mm for the respective tillage treatments, and averaged 97 and 118 mm for the low and high residue treatments. Precipitation averaged 316 mm during fallow. The differences in stored water significantly affected sorghum growth; grain and forage yields; and seed test weight, weight/seed, and protein. Sorghum grain yields averaged 2.56, 2.37, 2.19, 2.77, and 3.34 Mg/ha with the respective tillage treatments. The tillage treatments had no residual effect on subsequent sunflower and wheat yields. However, including sunflower in the rotation apparently allowed extraction of water from deeper in the profile than that extracted by sorghum, thus increasing the utilization of water resources for crop production. In addition, the earlier harvest date for sunflower allowed wheat to be planted at a more optimum time than that which is possible when wheat is planted after grain sorghum harvest.