Nitrogen nutrition of grain sorghum under sprinkler and furrow irrigation in the tropical dry season. I. Plant establishment, nitrogen uptake, and grain yield

Abstract

Abstract Two irrigation methods were compared during the dry season in northern Australia on grain sorghum grown on a cracking clay soil. Seedling survival and vigour, grain yield, and nitrogen uptake of crops supplied, at sowing, with four levels of banded nitrogen fertiliser (urea) differed markedly between sprinkler and furrow irrigation. At the highest rate of fertiliser (340 kg N ha −1 ) furrow irrigation induced a severe reduction in seedling survival and vigour compared to the lower three fertiliser rates under furrow irrigation and also to all fertiliser rates under sprinkler irrigation. The adverse response to furrow irrigation was attributed to the upward movement, from the fertiliser band to the root zone, of toxic concentrations of ammonia and nitrite. These intermediate products in urea transformation to nitrate were apparantly less toxic and less persistent under sprinkler irrigation. Grain yield was higher at all levels of applied N under sprinkler irrigation compared to furrow irrigation. This difference was associated with greater N uptake and resulted in higher apparent recovery of applied N. An analysis of N uptake in relation to light energy intercepted indicated that sprinkler irrigation resulted in more efficient use of applied N than furrow irrigation. It appeared that under furrow irrigation the availability of N was reduced by movement away from the active root zone and/or a greater proportion of the applied N was lost. Nitrate profiles in the soil at the end of crop growth indicated that under furrow irrigation a substantial amount of nitrate remained in the surface layer of the ridges and also in a layer deep in the profile. Under sprinkler irrigation, on the other hand, almost all the nitrate-N had been removed by the crop, except at the highest fertiliser rate.