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Timing Nitrogen Application to Enhance Spring Wheat Yields in a Mediterranean Climate

Dep. of Agronomie, IAV-Hassanll, B.P. 6202, Rabat-Instituts, Rabat, Morocco

D. H. Smith^*

Dep. of Agronomy, Colorado State Univ., Ft. Collins, CO 80523.

^* Corresponding author.

Information on spring wheat (Triticum aestivum L.) response to variation in timing of N fertilizer application is lacking. Our objective was to determine the response of autumn-sown spring wheat in a typical Mediterranean climate to application of N at selected stages of development. For two growing seasons and two cultivars, N fertilizer was applied at 0 kg N ha^–1 or a seasonal total of 120 kg ha^–1 in split applications, starting with 40 kg N ha^–1 at floral initiation; the remainder was applied (i) at the onset of stem elongation, (ii) at anthesis, or (iii) in equal parts at the two stages. During both seasons, total dry matter and grain yields of the two cultivars were increased by N application. The greatest response occurred when the final increment of N was applied just prior to stem elongation; the lowest responses occurred when N was withheld at the onset of stem elongation and the final increment was applied at anthesis. Increases in grain yields caused by N application were associated with increased kernel number production per unit area. The kernel number response was accounted for by increased numbers of spikes produced per unit area, increased kernel numbers per spike, or both. Spring wheats grown under these conditions responded to variation in timing of N application in a manner similar to that observed in winter wheats in continental climates. The response to N fertilization was maximized with application just prior to the stage of growth when N demand by the crop was greatest.

Received for publication December 17, 1992.

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