Delineation of management zones and response of spring wheat (Triticum aestivum) to irrigation and nutrient levels in Saudi Arabia

This study was conducted to assess the soil spatial variability and determine the optimum fertilizer rate and irrigation regime to optimize grain yield of wheat. The experiment was carried out in a clay loam soil with center pivot irrigation system. Management zones of the field were delineated based on laboratory analyzed and geo-referenced soil EC, surface elevation from ASTER DEM (AST3A1) and historic composite Normalized Difference Vegetation Index (NDVI) from Landsat ETM+satellite imagery. A split plot experiment design with three replications was adopted. Main plot treatments consisted of four irrigation levels at 100, 90, 80 and 70% evapotranspiration (ET_c) and three fertilizer levels with 300:150:200 (low); 400:250:300 (medium) and 500:300:300 (high) kg N:P₂O₅:K₂O ha^-1 formed sub-plot treatments. The highest grain yield of 6.09 t ha^-1 with water use efficiency (WUE) of 7.65 kg ha^-1 mm^-1 was obtained at 100% ETc and lowest rate of fertilizer. Irrigation at 70% ETc with fertilizer level of 300:200:200 kg N:P₂O₅:K₂O ha^-1 produced yield of 6.06 t ha^-1 at WUE of 10.67 kg ha^-1 mm^-1. This treatment combination resulted in saving of 30% water used in irrigation without sacrificing the yield.