Nitrogen fertilizer balance of irrigated wheat grown on a red-brown earth in Southeastern Australia

Abstract

Effects of three irrigation treatments on the N fertilizer balance of wheat (cv. Condor) grown on a red-brown earth in the Goulburn Irrigation region were investigated. Irrigation treatments included a rainfed control, and irrigation on either a 14 or 7-day cycle beginning in the spring. Fertilizer N was applied to the soil at sowing at 150 kg N ha-1. The percentage recovery of 15N-labelled fertilizer in the biomass increased to a maximum of about 40% within 120 days after sowing (das 120) and then remained constant. Approximately 58 kg N ha-1 of fertilizer was recovered in the biomass. It was in the stem-plus-leaf component at das 100 and was later redistributed into the developing head. At maturity a maximum of 36% of the fertilizer was recovered in the head. Residual fertilizer in the soil, including roots, decreased with time. Sixteen to 20% of the applied N was recovered in the surface 0.10 m. Fertilizer movement to depth was limited and less than 1% was recovered below 0.20 m. The small 15N recovery at depth, and the lack of influence of irrigation on the distribution of 15N in the soil, suggest that loss of N by leaching was minimal. Total recovery of fertilizer N in the plant and soil did not vary during the period das 85 to maturity. The mean recovery was 60% suggesting that 40% of the fertilizer was lost during the initial 85 days after sowing. The losses occurred early in the season when crop N accumulation was small and soil NO3 was high. Rainfall during the early part of the season probably caused denitrification. © 1989.