Duration Of Ponding Research Articles

Flood irrigation of wheat on a transitional red-brown earth. II. Effect of duration of ponding on availability of soil and fertilizer nitrogen

Grain yield of wheat growing on a transitional red-brown earth was reduced by long periods of ponding during irrigation. To determine whether fertilizer N loss was a major cause of this yield decline, 15N-labelled urea was applied to microplots at the same time and rate as the crop was topdressed with urea (end of tillerfng, 100 kg N ha-1). In addition, 15N-labelled nitrate was used to assess denitrification potential during and after each irrigation. Prior to the first irrigation (19days after urea application), 76% of the urea N was immobilized in the plants (33%) and soil (43%), 15% was present as soil mineral N, and 9% was not accounted for. The majority (85%) of the urea-derived mineral N was present as ammonium in the 0-0.1 m soil layer. After the first irrigation, amounts of mineral N in the soil remained very low at 3-6 kg N ha-l in the 0-0.2 m layer, with only 5-15% of this in the nitrate form. There was no significant effect of duration of ponding on plant or soii recovery of urea N after any irrigation. Mean plant recovery increased to 52%, over the first 55 days following urea application, while soil recovery declined to 22%. Beyond this stage changes in plant and soil recoveries were negligible. Plant total N content increased throughout the season due to ongoing mineralization of native soil N; however, there was negligible net mineralization of recently immobilized 15N beyond day 55. At physiological maturity, 46% of the N acquired by the plants was derived from the fertilizer. Losses of urea N increased to 25% over the first 55 days, and appeared to be due to nitrification-denitrification. Field studies with labelled nitrate indicated that denitrification potential in the soil was high throughout the experimental period. After the final two irrigations there were some significant (P < 0.05) effects of duration of ponding on N loss from urea, with lowest losses in the sprinkler, 1 h and 12 h treatments. The data indicate that, on the transitional red-brown earth, the adverse effect of long periods of ponding on wheat yield was not due to decreased availability or uptake of fertilizer or soil N in the longer term.

Flood irrigation of wheat on a transitional red-brown earth. I. 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.