Moisture Sensor Placement for Regulation of Furrow Irrigation Systems

In the past 10-15 years man has become increasingly aware of the fact that his once bountiful supply of water is decreasing rapidly in the face of expanding water consumption. With an increasing demand of water for domestic, industrial, and recreational purposes, agriculture will not have an open-ended supply of water in the future. Water must be more efficiently used to combat the dwindling supply of water for agriculture. Since irrigation is agriculture’s largest consumptive user of water, increased efficiency in irrigation operations will result in large water savings. Automating surface irrigation systems would not only increase water use efficiency but also reduce human labor requirements. One important segment of the automated system that has not been thoroughly developed is the control mechanism which uses moisture sensing devices to determine the need of irrigation. No method has been developed for placing these devices in the soil profile so that they will efficiently regulate the automated system. Thus, it becomes apparent that proper moisture sensor placement is the key to developing more efficient surface irrigation systems. The purpose of this study was to develop a theoretical procedure to follow in placing a moisture sensing device in the soil profile to regulate an automatic furrow irrigation system. A hypothetical surface irrigation system was developed on the basis of the variables affecting shallow surface flow in furrows. Values were assigned to these variables by using governing principles and practices proven correct in past irrigation studies. The hypothetical field layout was then used in developing a procedure for determining vertical sensor placement. Computed positions of vertical sensor placement were compared with the results of laboratory studies fun on O’Neill loamy sand and Grundy silt loam soils. The laboratory studies were also used to study the effect of lateral sensor placement on efficient irrigation. Conclusions drawn from this study were: 1) a procedure for proper vertical sensor placement, based upon characteristics of surface flow, the intake rate of soil, and the water holding capacity of the soil, was developed and shown to be successful when compared to laboratory results run on O’Neill loamy sand and Grundy silt loam soils; 2) the procedure developed for vertical sensor placement was not completely theoretical due to the fact that an empirical constant depending on soil texture had to be derived for determining the water holding capacity of the soil directly from the depth of wetting front movement beneath the furrow; 3) lateral sensor placement in the soil profile depended more on the time period of water application than it did on either of the soil textures investigated; 4)lateral sensor placement was found to be limited to placement at or very near the centerline of the furrow for the soil textures that were used. Advisor: D. M. Edward