SOIL-WATER VARIABILITY UNDER SUBSURFACE DRIP AND FURROW IRRIGATION

Non-uniformities in soil hydraulic properties and infiltration rates a re considered to be major reasons for the inefficiencies of some surfa ce irrigation systems. These non-uniformities may cause non-uniformiti es in soil water contents and could potentially affect plant growth. T o investigate whether the non-uniformities in soil water contents can be overcome by well-managed irrigation systems, fields with clay loam soils and planted to cotton were irrigated with a continuous-flow, a s urge flow, and a subsurface drip system. Measurements of water content s in each field were taken throughout the growing season at several de pths. The water contents measured within the top 0-0.9 min the three i rrigations systems were evaluated in terms of their spatial and tempor al variabilities. The analyses indicated that on this soil, use of the surge flow system did not lead to increased spatial uniformities of s oil water contents compared with the continuous-flow system. Use of th e subsurface drip system resulted in very non-uniform soil water conte nts above the depth of the emitters. Variability in water contents bel ow the emitter depth was comparable to the surface irrigation systems.