Effect of irrigation water quality, sulfuric acid and gypsum on plant growth and on some physical and chemical properties of Pima soil

Field and laboratory experiments to determine the effect of the quality of irrigation water and the combination effects of the quality of water and chemical amendments (Gypsum and H ₂SO₄) on growth and yields of sudangrass, total soluble salt and ionic distribution and the infiltration rates of a Pima soil were conducted. Pima soil was classified as calcareous saline-sodic soil. A field experiment was conducted on the University of Arizona Experimental Farm at Safford, Arizona, for a period of five years. During the first three years, three qualities of water as supplied by well, river and city were used. During the last two years, these waters were coupled with two chemical amendments, gypsum and sulfuric acid. The experiment was a randomized split plot design with nine main plots and 27 subplots and three replications. The rates of the amendments were arbitrarily chosen 1 and 1.72 ton/acre of H ₂SO₄ and gypsum respectively. Four harvests were made over the two-year period and city water treatment gave the best growth and yield of sudangrass as compared to well and river water treatments. H ₂SO₄ and gypsum increased the yield significantly in comparison to the control in 1975. No significant effects of the chemical amendments on the growth and yield of sudangrass were obtained in 1976. Significant negative correlations between the EC and ESP of the first two feet of soil and yield of sudangrass were obtained. Soil analysis indicated that significant decrease in the pH and ESP of the soil resulted from H ₂SO₄ application with the three water treatments. Gypsum reduced pH and ESP significantly just with well water treatment. Due to the stratified texture of soil profile, ions and salts accumulated in the center of the sampled profile. Infiltration rates were higher for well water treatments than for city water treatments. H ₂SO₄ increased the infiltration rates significantly with all water treatments; gypsum increased infiltration only with well water treatment. Infiltration was further studied in the laboratory using soil columns. Two rates of acid and two rates of gypsum were used (1 or 5 and 1.72 or 8.6 ton/acre H ₂SO₄ and gypsum respectively). The higher rate of H ₂SO₄ gave the highest infiltration rate and the lowest infiltration rates were obtained with control with all water treatments. The low rate of H ₂SO₄ and the high rate of gypsum gave similar infiltration rates with the three water treatments. Gypsum treated soil columns required more water to be leached to a specific EC than H ₂SO₄ treated and control columns. More salt can be removed from the soil per unit volume of water with H ₂SO₄ treatment than gypsum or untreated soil. The poorest quality of irrigation water required the least time and amount of water needed to reach equilibrium between the solid and solution phases of soil. The EC of effluent was found to be an index to predict the presence of gypsum and lime in the soil under very low water penetration. Regression equations were developed to predict the time and depth of water required to leach one foot of Pima soil column to a specific EC with a given quality of water and a given type and rate of chemical amendments (H ₂SO₄ and gypsum). A regression equation was developed to estimate the EC of the saturation extract from that of 1:1 soil :water ratio for Pima soil.hydrology collectio