Saturday, 15 July 2006

Genotypic Responses of Corn to Phosphorus Fertilizer Rates in Calcareous Soils of Turkey.

Hayriye Ibrikci1, Can A., Ulger1, Kursat Korkmaz1, Abdullah Oktem1, Gokhan Buyuk1, Omer Konuskan1, Boujamaa Amar2, Ebru Karnez1, Gonul Ozgenturk1, Hacer Oguz1, and John Ryan3. (1) Cukurova Univ, Faculty of Agriculture, Soil Science Dept, Adana, Turkey, (2) Institut Mondial du Phosphate, Casablanca, Morocco, (3) ICARDA, P.O. Box 5466, Aleppo, Syria

Phosphorus (P) is an important and essential crop nutrient; its deficiency is invariably a common yield-limiting factor, especially in unfertilized calcareous clay soils, because calcium carbonate reduces P solubility. When such soils are fertilized, the resultant chemistry in such that adsorption and desorption characteristics contribute to reducing fertilizer-P use efficiency. The Mediterranean is a region where much emphasis is being placed on the role of fertilizers in enhancing crop production. Turkey is typical of many countries of this drought-stressed water–short zone. While considerable research has dealt with fertilizer aspects, little emphasis has given to plant variation with respect to P use. There is abundant evidence to show that plants vary in their capacity to exploit the soil's reserves of available P; some plants grow well in soils with limited plant-available P even without added P fertilizer. In this particular study, selection and adaptation of P-efficient corn genotypes was seen as one possible approach to the problem of enhancing P efficiency. Thus, a greenhouse experiment and four field trials were carried out for two years on various calcareous soils (Vertic Torrifluvent, Vertic Calciorthid, Entic Chomoxerert and Typic Xerofluvent). Experimental treatments in the greenhouse were three soil series (Cekcek, Ikizce, Harran I), ten corn genotypes (traditional to modern) and five P application rates (0, 25, 50, 100 and 200 mg kg-1). Treatments in the field trials were five P application rates (main plots 0, 18, 36, 54 and 70 kg P ha-1) and three corn genotypes (subplots C7993, DK6022 and Tector). These genotypes were selected from the greenhouse experiment as efficient-responsive, efficient-nonresponsive and inefficient-responsive based on their P-efficiency. The field trials were arranged in a split plot design in four replications. Nitrogen and potassium were applied as basal dressings. Dry matter and P uptake by plants increased with P application rates in the greenhouse experiment. Genotypes were classified for their P-efficiencies. Yield and P uptake of the three genotypes in the field trials linearly increased up to 54 kg P ha-1 application rate with genotype DK6022 being the most P-efficient/responsive genotype. The studies indicted that as corn genotypes respond to P-fertilizer application differently and that this trait could be utilized to exploit native and applied P more efficiently specially at low levels of available P and when fertilizer use is limited. This differential response derives from the morphological, physiological and genetic variability among the genotypes. The results indicate that genotypic efficiency is important for fertilizer management. However, the contribution of the efficiency is not a substitute for fertilizers, especially if high yields are required. Nevertheless, breeding for P-use efficiency should be a component of any program to improve crop yield potential.

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