FLOOD IRRIGATION OF WHEAT ON A TRANSITIONAL RED-BROWN EARTH .1. EFFECT OF DURATION OF PONDING ON SOIL-WATER, PLANT-GROWTH, YIELD AND N-UPTAKE

Long periods of waterlogging during irrigation are thought to adversely affect wheat growth and yield. This work quantifies these effects for wheat (Triticum aestivum L. cv. Bindawarra) growing on a transitional red-brown earth. The crop was irrigated on four occasions during spring. At each irrigation six ponding treatments were imposed involving sprinkler irrigation (SP) or flooding for 1, 12, 24, 48 or 96 h. Each plot always received the same treatment. Nitrogen fertilizer was applied at sowing (23 kg N ha-1 as ammonium phosphates) and at the end of tillering, 3 weeks before the first irrigation (100 kg N ha-1 as urea). There was also a 1 h ponding treatment which did not receive urea at the end of tillering. Grain yield on the 48 h and 96 h ponding treatments was significantly lower than on SP, 1 h and 12 h. Yield declined by 69 kg ha-1 for each day that water was ponded on the surface, or by 55 kg ha-1 for each day that the estimated soil water depletion was below 25 mm. The wheat crop suffered stress due to lack of aeration for periods varying from 42% (1 h and SP) to 68% (96 h) of the time interval between early stem elongation and physiological maturity. The grain yield and N uptake data indicate that the site was highly responsive to N fertilizer. However, there was no significant effect of ponding treatment on total N uptake, suggesting that the yield differences between the ponding treatments were not caused by differences in N availability. The results demonstrate that yield loss through waterlogging can be minimized by changing to irrigation management practices that minimise the period of ponding.