Effect of Tillage and Preplant Irrigation on Sorghum Production

Abstract

Reducing irrigation water requirements with furrow irrigation systems is important in the Southern High Plains. Growing grain sorghum, without a preplant irrigation, can potentially reduce irrigation water use and increase crop water use efficiency (WUE), defined as yield/ET. ET includes irrigation, rainfall, and soil water depletion during the crop season. A four-year study was conducted at Bushland, Texas where three tillage methods were evaluated for their effect on off-season soil water storage, furrow irrigation water intake, grain yield, and WUE; both with and without preplant irrigation. Treatments receiving a preplant (PP) irrigation averaged 483 mm (19 in.) of irrigation intake compared with only 280 mm (11 in.) for the treatments without a preplant irrigation (No-PP). This was a 70% increase in irrigation intake for the PP treatment with only a 10% increase in grain yield. The extra pumping cost for the PP irrigation was about $10.00/ha ($4/acre) more than the value of the increased grain yield. Tillage method did not affect over-winter soil water storage and only slightly affected irrigation intake, grain yield, and WUE. Only about 25% of the PP irrigation water intake was recovered in soil water storage. Irrigation intake is defined as the amount applied through graded furrows minus the tailwater runoff. Although the No-PP soil profile averaged 204 mm (8 in.) of soil water in storage (82% of field capacity) to 1.8 m (6 ft) deep, the lack of late April or early May precipitation in two of the four years resulted in a relatively dry seedbed at planting time. Thus, the No-PP irrigation treatment planting was delayed from May until occurrence of early June rainfall. The later planting dates (June 14 and 22) reduced grain yield up to 10%, however, WUE was increased up to 20% by avoiding the preplant irrigation.