Thesis - Open Access
Master of Science (MS)
Annual applications of 125, 90, and 50 cm of secondary-treated municipal effluent were applied to a 0.76 cm/hr glaciated soil growing alfalfa for 3 years. All treatments had weekly applications with the depth of application varying from 1.5-3.2 cm for the low rate plot to 3.8-8 cm for the high plot. The amounts applied paralleled the evapotranspiration curve of the crop with weekly applications lowest in the spring and fall and highest during the summer. Water quality varied from 1500-3000 Siemens /cm for the electrolyte concentration, from 5-11 for the sodium adsorption ratio, and from 0.1-12. 4 ppm for nitrate nitrogen. A water table developed within 1.2 meters of the surface for the 90 cm plot (treatment 35G) and within 1.1 meters of the surface on the 125 cm plot (treatment 50) at the end of the second irrigation season. Treatment 50 had lost 1-2% of the plant population at the end of the second year and 15-20% by the end of the third year of irrigating. Leaching fractions of 0.08-0.10 for total moisture should not be exceeded to prevent water table problems from developing near the surface. Annual soil applications of gypsum were added to the 90 cm plot (treatment 35G) to determine the efficiency in removing exchangeable sodium from the soil colloid exchange sites. After two annual applications of powdered gypsum, no significant difference between the gypsum plot (treatment 35G) and the non-gypsum plot (treatment 35) was detected in the top 1.2 meters. However, the sodium level for 35G in observation wells at the center of the plot were 2-5 times higher than the non-gypsum plot with the same annual rate of effluent. Sulphate levels were 4-8 times higher on 35G versus 35 and magnesium was 4 times higher. Calcium was replacing magnesium and sodium on the exchange complex at depths below 1.2 meters. Nitrate levels in the soil varied according to the nitrate levels in the effluent. In situ soil water extracts were monitored with depth and time across treatments. There was no difference in the nitrate levels in the soil according to treatment. Nitrate nitrogen levels were the highest in the ground waters beneath the plot with the thickest sand layer in the subsoil. Soil dispersion caused by sodic irrigation water for the top 3 cm of soil was evident at the end of the three-year project on the 50 cm annual application plot (treatment 20). Concentrating effects of ET and low leaching caused high sodium adsorption ratios of the soil solution during the irrigation season on treatment 20. Treatments 50, 35, and 35G did not show signs of soil dispersion on the top 3 cm.
Library of Congress Subject Headings
Soils, Salts in
South Dakota State University Theses
Number of Pages
South Dakota State University
Bischoff, John H., "Optimum Irrigation Loading Rates of Highly Saline Wastewater on a Montmorillonitic Soil" (1983). Electronic Theses and Dissertations. 4324.