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Production Papers

Fertilizer Nitrogen Efficiency in Durum Wheat under Rainfed Mediterranean Conditions: Effect of Split Application

^a Dep. de Ciencias y Recursos Agrícolas y Forestales, Univ. of Córdoba, Campus de Rabanales, Edificio C-4 "Celestino Mutis," Ctra. Madrid km 396, 14071 Córdoba, Spain
^b Dep. de Ciencias Agroforestales, Univ. of Huelva, Spain
^c Dep. de Producción Vegetal y Tecnología Agraria, Univ. of Castilla La Mancha, Spain

^* Corresponding author (cr1lobel{at}uco.es)

Received for publication January 12, 2005. Efficient N fertilizer management is critical for the economic production of wheat and the long-term protection of environmental quality. A 3-yr field experiment on a rainfed Vertisol was designed to study the effects of N fertilizer timing on the efficiency of N in durum wheat (Triticum turgidum L. var. durum Desf.). A single rate of 150 kg N ha^–1 was used with different fractions being applied at planting, tillering, and stem elongation. A ¹⁵N experiment was also conducted within the main experiment area, with microplots, to quantify N uptake from fertilizer and soil. Mean wheat recovery of N fertilizer ranged from 12.7% when applied at sowing to 41.6% when applied as a topdressing at the beginning of stem elongation. The mean annual contribution of soil residual N and mineralization was 167 kg N ha^–1, representing a considerable proportion of total wheat N uptake—ranging from 80.4% when N fertilizer was applied in the fall to 56.3% when it was applied at stem elongation. This would account for the poor and inconsistent response of grain yield and N efficiency indices, and for the importance of soil N in Vertisols for predicting wheat N fertilizer requirements, due to the carryover effect. It is recommended that N fertilizer be applied mainly as a topdressing in durum wheat, between tillering and stem elongation, to enhance crop N use efficiency (NUE) and reduce losses through leaching and runoff.

Abbreviations: HI, harvest index • NUE, nitrogen use efficiency • NF, nitrogen-15 fertilizer • NR, labeled-fertilizer nitrogen recovery • NU_pE, nitrogen uptake efficiency • NU_tE, nitrogen utilization efficiency

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