Date of this Version
Thesis (M.S.)—University of Nebraska—Lincoln, 1967. Department of Agricultural Engineering.
Proper irrigation of agricultural crops for increased production is becoming increasingly important.Automation provides a means for obtaining the irrigation efficiency need for high production without prohibitive labor requirements being involved.An integral part of an automatic irrigation system is a soil moisture sensing device.The gypsum electrical resistance blocks might be used as such a sensor.Before electrical resistance blocks can be used in this capacity, more must be understood about the factors which influence them and their operational behavior.
The purpose of this study was to evaluate the feasibility of using electrical resistance blocks as soil moisture sensors in automated irrigation systems.The specific factors studied were the nitrogen concentration of the soil solution and soil type.
Resistance blocks were placed in air dry soil and different concentrations of nitrogen solution were added. Levels studied were 0, 70, 140, and 210 parts of nitrogen per million parts of distilled water.Soils used were Grundy silt loam and O’Neill loamy sand.Moisture content changes in the soil were produced by placing the soil and resistance blocks on a ceramic plate in a pressure extractor and varying the pressures.Pressures studied were 1/3, 1, and 2 bars.
Conclusions drawn from the results of this study were: 1) use of present day gypsum electrical resistance blocks as soil moisture sensors in automated systems is not feasible; 2) nitrogen concentration levels of the soil solution up to 210 ppm did not significantly influence, at the 5% level of significance, gypsum electrical resistance blocks placed in Grundy silt loam and O’Neill loamy sand soils and subjected to pressure differentials of 1/3, 1, and 2 bars; 3) uniformity of electrical resistance blocks must be more strictly controlled by using proper manufacturing procedures; 4) nitrogen concentration of the soil solution affected resistance blocks placed in O’Neill loamy sand soil more than blocks placed in Grundy silt loam soil.For blocks in O’Neill loamy sand soil, an increase in nitrogen concentration of the soil solution decreased resistance readings of the blocks.For blocks in Grundy silt loam soil, an increase in nitrogen concentration of the soil solution decreased resistance readings of the blocks except for the 70 ppm nitrogen level which increased resistance readings of the blocks.
Advisor: D. M. Edwards