Agronomy and Horticulture Department


Date of this Version



Published in Field Crops Research 71 (2001) 113-122.


Yield response and isotopic N-fertilizer recovery of rainfed wheat were assessed as influenced by fertilizer rate and timing. A popular bread wheat cultivar, Seri 82, was planted in a 4-year experiment from 1994/1995 to 1997/1998. Urea fertilizer was applied at rates of 0-240 N ha-1 in two split applications. Fertilizer-N recovery and residual N remaining in the soil after wheat harvest were measured using 15N-labelled fertilizers. The highest wheat grain yield ranged from 4.9 to 6.9 t ha-1 with 240 kg N ha-1 fertilizer. The 4-year results showed that wheat benefited least from the fertilizer applied near planting. N-fertilizer recovery was higher from fertilizer applied during tillering compared with application at emergence. The results suggest that applying one-third or less of the total N at planting and applying the remained at tillering can minimize leaching risks. Another befit of this strategy would be an overall increase in N-fertilizer recovery. Residual fertilizer-N left in soil after wheat harvest was proportional to N application rates and mainly confined t the upper 40 cm depth. 15N recovery by wheat at maturity was 50-60%, indicating that 40-50% of fertilizer-N remained in the soil or was lost. Over 95% of total fertilizer application to wheat could be accounted for in the wheat crop or soil after harvest at the 240 kg N ha-1 rate. The results, therefore, suggest that leaching losses of fertilizer-N below 90 cm were not likely during the growing season for rainfed what grown on these heavy-textured soils (Palexerollic Chromoxeret) of the Mediterranean region.