Yield, water use and root distribution of wheat as affected by pre-sowing and post-sowing irrigation

Abstract

Irrigation water is a limited resource, and therefore irrigation practices must be rationalized for high water-use efficiency. Little is known about the influence of stored water in deep soils on the water needs and the post-sowing irrigation requirements of crops. A 3-year field experiment was conducted to determine the effects of combinations of light and heavy pre-sowing irrigations with two post-sowing irrigation regimes on yield, root growth, water use and water-use efficiency of wheat on a deep alluvial sandy loam soil. Post-sowing treatments consisted of (i) five 75-mm irrigations at five growth stages, and (ii) irrigations based on pan evaporation, i.e. at IW/PAN-E ratio of 0.75 (75 mm of irrigation water were provided as soon as the open-pan evaporation minus rainfall since previous irrigation was 100 mm). The latter regime required 175 mm less water than that with irrigation at growth stages. Profile water utilization was inversely related to post-sowing irrigation water. Where pre-sowing irrigation was light, post-sowing irrigations based on pan evaporation yielded significantly less than those based on growth stages. With heavy pre-sowing irrigation, irrigation based on the pan evaporation yielded as much as five irrigations at growth stages. The former decreased the mean water application by 153 mm and increased the water-use efficiency by 26%. Irrigation based on pan evaporation stimulated greater utilization of stored water by increasing the rooting density in deeper layers. It is indicated that for higher water-use efficiency and yield, wheat should be sown after a heavy pre-sowing irrigation, and post-sowing irrigation should be based on 0.75 pan evaporation.