Straw-mulch Rate Effect on Soil Water Storage and Sorghum Yield^†

Abstract

A field study was conducted to determine the effects of straw mulch rates on soil water storage during fallow and on subsequent grain sorghum [Sorghum bicolor (L.) Moench] production. Wheat [Triticum aestivum (L.)] straw at rates of 0 (check), 1, 2, 4, 8, or 12 metric tons/ha was placed on field plots in July 1973, 1974, and 1975. A different area, previously cropped to dryland wheat, was used each year. Atrazine [2-chloro-4(ethylamino)-6-(isopropylamino)-s-triazine] was applied for volunteer wheat and weed control before mulch placement. Soil water content was measured periodically from July until the following May, when grain sorghum was planted, and during the sorghum growing season. Available soil water at planting averaged 12.3 and 21.4 cm for the 0- and 12-metric tons/ha mulch treatments, respectively. The additional water, along with greater infiltration and lower evaporation during the growing season, increased grain yields, which averaged 1,780 and 3,990 kg/ha for the respective treatments. Water-use efficiency increased from 55.6 kg/ha-cm for no mulch to 115.0 kg/ha-cm for 12 metric tons mulch/ha.