Analysis of soil wetting patterns in subsurface drip irrigation systems – Indoor alfalfa experiments

Abstract

When using subsurface drip irrigation (SDI) to grow field crops, concerns may exist for water availability to plants, because emitters and plants cannot be lined up perfectly. The spatial distribution of water around SDI emitters is largely determined by soil hydraulic properties and characteristics of root water uptake (RWU). Experiments were performed in an indoor facility to quantify the effects of alfalfa RWU on characteristics of wetting patterns in three soil textures. In all soils, the majority of RWU took place in a layer below the emitters, where soil moisture was most dynamic. Unique wetting patterns developed in the three soils in response to irrigation events. However, when irrigation applications were aimed to replace potential evapotranspiration, these unique patterns disappeared within 24 hr. When irrigation was supplied in excess for a 21-d period, an effective wetted zone developed over time. Both the extent of and moisture distribution within the wetted zone varied between the three soil textures. An analysis of spatial moments showed that the moisture plume characteristics stabilized within seven days of irrigation and RWU. Zones of effective drying were observed in all three soils during the 21-d period. The alfalfa crop was not negatively affected by the presence of these zones, because (compensatory) RWU was concentrated around the SDI emitters. The results of these experiments imply that the design of SDI line spacing can be less focused on soil type when root system size is considered. This does require the presence of sufficient early season moisture for the crop to develop a complete root system.