Efficiency of fertilizer use by a rain-fed wheat crop following split-application of fertilizer nitrogen

Abstract

The efficiency of use of a split-application of nitrogen fertilizer was measured in wheat plots at ICARDA, northern Syria. Nitrogen (60 kg N ha-I) was applied as a split-dressing; 30 kg N ha-I at sowing (NovemberlDecember) and 30 kg N ha-I at tillering (March). Urea was used in 1991/92 and ammonium sulphate in 1992/93. Fertilizer applications were (i) ISN-labelled at both sowing and tillering, (ii) ISN-Iabelled fertilizer at sowing, unlabelled fertilizer at tillering, (iii) unlabelled fertilizer at sowing, ISN-labelled fertilizer at tillering. Dry matter production and total nitrogen content of the above-ground plant material were unaffected by the time of ISN-label application. The mean amounts of nitrogen recovered in the grain were 61.5 kg N ha-I in 1992 and 69.9 kg N ha-I in 1993. Fertilizer nitrogen recovered by the wheat averaged 11.3% after ammonium sulphate and 17.2% after urea, with greater recoveries from an autumn application in both cases. Generally less than 10% of the nitrogen in the plant at harvest was derived from the ISN-labelled fertilizer. Mineralization of soil nitrogen provided on average 82.9 kg N ha-1 (1992) and 93.3 kg N ha-I (1993) to the wheat. Under these conditions N fertilizer made only a small contribution to current production, most of the plant nitrogen was derived from soil. Fertilizer use efficiency was maximized by application at sowing.