Wheat Yield Variability in Irrigated Level Basins

Abstract

ABSTRACT SPATIAL variability in irrigated crops is a major problem in transferring plot-size yield and water use information to field-size, surface irrigation conditions. A 1985 study evaluated wheat yield variability for three irrigation schedules and two border lengths using a level-basin irrigation system. Mean grain yields increased significantly from the dry to wet irrigation treatments; however, yield and irrigation water application amounts were not positively correlated from location to location in the wet treatment. Variations in seasonal water applications, water use, and seasonal average soil water contents accounted for less than 35% of the variability in grain yield. Yields were not affected by differences in border lengths, but yield variability was significantly influenced by field position. Yield variability, as measured by the statistical coefficient of variation, was less extensive in a wet (12.5%) irrigation treatment than a medium (19.4%) or dry (32.4%) treatment. The maximum distance of spatially interdependent yields varied from 45 m (150 ft) in the medium to 19 m (60 ft) and 8 m (25 ft) in the wet and dry treatments, respectively. The optimum level of seasonal gross water applied for maximum wheat yields was 7% higher than that required for maximum water use efficiency; however, the uncertainty in both estimates was ± 18%. A recommendation to the irrigation farmer with a heterogeneous soil and an efficient level-basin irrigation system would be to schedule irrigations near full evapotranspiration requirements in order to minimize yield differences due to field variability, attain high wheat yields, and approach maximum water use efficiency..