Drip Fertigation Uniformity and Moisture Distribution as Affected by Spatial Variation of Soil Properties and Lateral Depth and Injector Type

Abstract

Both spatial soil property variation and system hydraulic design can impact fertigation uniformity and distribution of water and nutrients in the soil for subsurface drip irrigation systems. The primary objective was to evaluate the relative importance of soil property variation, lateral depths, and chemical injector types to the uniformity of water and fertilizer discharged by emitters and of soil water contents. Field experiments were conducted on drip irrigation installations that had been operated for one irrigation season of corn. Three commonly used types of injectors, a water-driven piston proportional pump, a Venturi device, and a differential pressure tank, were evaluated with three lateral depths of 0, 15, and 30 cm. Spatial variability of several soil properties, including soil particle size composition, bulk density, initial and saturated water content, and saturated hydraulic conductivity were analyzed. The results demonstrated that injector type had a very significant effect on fertigation uniformity, while the influence of lateral depth was insignificant. A differential pressure tank that released fertilizer in a decreasing rate with time produced a considerably lower uniformity of fertilizer solution concentration and fertilizer applied than a Venturi device and a proportional pump. An injector that can inject fertilizers in a constant rate is preferred to obtain a uniform fertilizer distribution. Analysis of the variation in soil properties indicated that the saturated hydraulic conductivity can be classified as a medium degree of variability for the tested field, with the coefficient of variation (CV) ranging from 0.31 to 0.44. The nonuniformity of water content following an irrigation event was greatly dependent upon spatial variability of soil properties, but the effect of emitter discharge variation was unimportant. For the proper design and operation of subsurface drip irrigation systems, the field spatial variability should therefore be considered.