Yield response and N-fertiliser recovery of rainfed wheat growing in the Mediterranean region

Yield response and isotopic N-fertiliser recovery of rainfed wheat were assessed as influenced by fertiliser rate and timing. A popular bread wheat cultivar, Seri 82, was planted in a 4-year experiment from 1994/1995 to 1997/1998. Urea fertiliser was applied at rates of 0-240 N ha-1 in two split applications. Fertiliser-N recovery and residual N remaining in the soil after wheat harvest were measured using 15N-labelled fertilisers. The highest wheat grain yield ranged from 4.9 to 6.9 t ha-1 with 240 kg N ha-l fertiliser. The 4-year results showed that wheat benefited least from the fertiliser applied near planting. N-fertiliser recovery was higher from fertiliser 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 remainder at tillering can minimise leaching risks. Another benefit of this strategy would be an overall increase in N-fertiliser recovery. Residual fertiliser-N left in soil after wheat harvest was proportional to N application rates and mainly confined to the upper 40 cm depth. 15N recovery by wheat at maturity was 50-60%, indicating that 40-50% of fertiliser-N remained in the soil or was lost. Over 95% of total fertiliser 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 fertiliser-N below 90 cm were not likely during the growing season for rainfed wheat grown on these heavy-textured soils (Palexerollic Chromoxeret) of the Mediterranean region. © 2001 Elsevier Science B.V.BAP-TYS-95/08 International Atomic Energy Agency: TUR/7947 International Atomic Energy AgencyThis work was financially supported by the International Atomic Energy Agency (IAEA), Vienna, Austria, through Research Contract TUR/7947. Thanks are extended to the Technical Staff at the IAEA’s Agricultural Laboratory, Seibersdorf, Austria for 15 N analyses. Authors are also grateful for the partial support received from C.U. Faculty of Agriculture, Adana through Research Grant BAP-TYS-95/08