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Optimum design and management of irrigated wheat production is limited by the scarcity of information available on yield variability. The purpose of this study was to evaluate the spatial variability in soil-water parameters and the effects compared to grain yield response under level-basin irrigation. Three levels of seasonal irrigation water and two border lengths were used. Grain yields were found to increase significantly with the amount of water applied and soil water depletion (estimate of crop evapotranspiration), although yield variability was greater with reduced or deficit irrigations. Variations in soil water content were responsible for about 22% of the variability in grain yield, indicating that other soil and crop- related factors had a significant influence on production. Spatial dependence was exhibited over a greater distance at the wetter compared with the drier irrigation regimes.

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No description available.

An understanding of the expected variability in irrigated crops under field size, surface irrigation conditions is needed to improve irrigation designs and water management scheduling procedures. The objective of this work is to describe water application uniformity under an efficient level -basin irrigation system and the variability of water use (soil water depletion) for three levels of irrigation and two basin lengths for a wheat crop. High water distribution uniformities with a level -basin irrigation system did not necessarily result in maximum irrigation application efficiencies where variations in soil -water factors were greater on a drier irrigation treatment than medium or wet treatment. Variations in soil water depletion were found for all irrigation treatments with the largest variation (13 %) occurring for the drier treatment. Spatial dependence was exhibited for soil water depletion but not necessarily for seasonal irrigation water applications.

Additional data to calibrate and refine current guidelines for interpreting soil test values is an ongoing need in Arizona. This includes information for soils testing above and below the level that may currently be considered adequate for optimum plant growth. An experiment was conducted at the Maricopa Agricultural Center during the 1985-86 crop year to evaluate the response of durum wheat to the application of phosphorus (P), potassium (K), magnesium (Mg), or zinc (Zn) on a soil testing adequate or higher for all of these nutrients. Grain yields from plots receiving every combination of three of the four nutrients were compared to yields obtained when all four nutrients were applied. No significant change in grain yield was measured as a result of witholding any one of the nutrients. Current guidelines used to interpret soil test results for wheat production correctly predicted the nutrient status of this soil with respect to P, K, Mg, and Zn.