Furrow irrigation of grain sorghum in a tropical environment. II. Influence of period of inundation on the utilization of soil and fertilizer nitrogen by the crop

Abstract

Grain sorghum was grown in plots that had been fertilized, before sowing, with either 0, 80 or 170 kg Ha-1 nitrogen (N), and furrow irrigated for periods of 0 (sprinkler irrigated control), 3, 6, 12 or 24 h. The apparent uptake of fertilizer nitrogen declined from 63 to 7% as the period of inundation increased from 0 to 24 h. Large quantities of nitrate (up to 82 kg N ha-1) remained in the surface soil layers of all furrow irrigated ridges at crop maturity, in contrast to the sprinkler irrigated ridges (up to 4 kg N ha-1). At all inundation periods a constant proportion of the applied nitrogen was moved to the ridge tops, where it was unavailable for plant uptake. The differences in the recovery of applied nitrogen between the crops given 0 (sprinkler) and 3 h irrigation was mainly attributed to the surface accumulation of nitrate in the latter. Further reduction of nitrogen uptake with longer periods of inundation are attributed to differential rates of loss of nitrogen from the soil by denitrification and leaching.