Soil Water Movement during Growth of Sorghum Using Subsurface Irrigation

Even by 2020, the major source of food for many will still be from land-based agriculture. Resources cannot be exploited in a blundering way.Since irrigation is agriculture’s largest consumptive user of water, it will have to be twice or thrice times as efficient as at present. Subsurface irrigation systems would not only increase water use efficiency but also reduce human labor requirements.One important segment of the subsurface irrigation system that has not been thoroughly developed is the knowledge of flow and distribution patterns of the water after it is injected into the soil. The purpose of this study was to learn how to predict the interaction between the growing plant and the placement of a lateral in a subsurface irrigation system to properly design and manage a subsurface irrigation system. Two greenhouse type plexiglass soil bin models were built and instrumented with electrical resistance blocks as soil moisture sensors.Silty clay loam was used as irrigable soil.Irrigation water was applied through ½ inch I.D. polyethylene tube placed at depths of 18-inches and 12-inches below the soil surface.Wetting front movement patterns were photographed.Volumes of water applied were noted for calculating the model intake rates at their corresponding time values.Sorghum plants were grown on the model for determining soil moisture extraction patterns for various stages of plant growth.Heights of the plants and stem diameters of the plants were measured to study the plant growth.Plants were irrigated when the soil moisture level had dropped approximately to that of field capacity of the soil, 1/3 bar. Conclusions drawn from this study were: 1) wetting front movement patterns were symmetrical about the vertical plane passing through the center of lateral and ellipsoidal in shape; 2) the laterals should be placed at a spacing of 35 inches in field row crops; 3) the lateral depth of 18-inches is preferable over 12-inches; 4) study of growth of plants in subsurface irrigation system confirmed the S-shaped curve; 5) plant growth was 54% during the 14-hour day time; 6) an irrigation scheduling program can be determined using Delmhorst electrical resistance blocks as soil moisture sensors; 7) almost 100 percent of soil moisture removed as evapotranspiration is extracted from the top one foot of soil at various stages of plant growth in a subsurface irrigation system 8) model intake rates in a subsurface irrigation system can be expressed in a manner similar to that of furrow irrigation system; and 9) subsurface irrigation systems show great promise for the future. Advisor: D. M. Edward