The effect of placement and irrigation on the efficiency of use of 15N labelled urea by sugar cane

When urea, labelled with 15N, was applied to a green harvested crop of ratoon cane, grown on a duplex soil at Mackay, the efficiency of use was low. By burying the urea in the interrow and maintaining high soil water levels by irrigation, 60% of the applied N was lost 72 days after fertilising. This loss of fertiliser-N was probably due to denitrification. By burying the urea in the row, under rainfed conditions, the loss of fertiliser-N was 40%. The row placement gave the cane quicker access to the fertiliser than the interrow placement, so increasing uptake. It is suggested that denitrification may have contributed to the low cane yields in Mackay in the 1990 season.