Effects of treatment plant effluent on soil properties

serve water resources throughout the world. Because water cannot be manu factured, it is necessary to control its use and reuse. Agriculture requires large quantities of water each year. If waste water plant effluent, which until now has been wasted, could be used for agricultural purposes, pollution of surface and ground water supplies would decrease and more fresh water would be available for do mestic use. Review of the Literature Reclaimed wastewater effluent has been used to irrigate lawns and golf courses.1 Dye2 reported that effluent from an ac tivated sludge treatment plant contained nitrogen, phosphorus, and potassium that could be utilized by growing plants. High yields of forage and grain have been obtained from barley (Hordeum vulg?re L.), oats (Avena sativa L.), and wheat (Triticum aestivum L.) using wastewater effluent.3-6 Laak7 observed that increasing pretreatment of domestic wastewater prior to soil application increased the length of time that the soil surface could be irrigated with wastewater before it became clogged and impervious to water. Additional in formation is needed on effects of continued use of wastewater effluent on soil proper ties. Methodology Studies were conducted at Cortaro, Ariz., to determine effects of continued use of wastewater effluent as a source of ir rigation water and plant nutrients to pro duce agricultural crops on selected soil properties. Effluent from the Tucson, Ariz., wastewater plant was used to grow 372 Journal WPCF barley (Hordeum vulg?re L.), cotton (Gossypium hirsutum L.), lettuce (Lac tuca sativa L.), and sorghum (Sorghum vulg?re Pers.) for a 14-yr period (1956 through 1969). This effluent had received the standard activated sludge treatment and contained approximately 24, 8, and 10 mg/1 of nitrogen (N), phosphorus (P), and potassium (K), respectively. The chemical composition of a representative sample of the effluent used is given in Table I. The soil was a Grabe silt loam (sand-40 percent, silt?40 percent, clay-20 percent, organic matter-1.5 percent ). Table II gives the cropping history for the 14-yr period. Soil irrigated with only wastewater efflu ent and no additional fertilizer was com pared with soil irrigated with well water and fertilized with recommended amounts of N, P, and K.8 Well water in the area contained about 4, 0.1, and 4 mg/1 of N, P, and K, respectively. Wastewater effluent and well water were applied as recom mended for irrigated crop production in Arizona.9 After 14 yr of continuous crop production, random soil samples were taken from four locations in the field that had been irrigated with only wastewater effluent and in the field that had been .irrigated with well water and fertilized with recommended N, P, and K. At each location, the Ap horizon (plow layer, 0 to 25 cm) and C horizon (sub-soil 38 to 51 cm) were sampled separately. The experi ment was a completely randomized design with two treatments and four replications. Chemical analyses were made for pH, soluble salts, nitrates, phosphates, calcium plus magnesium [ ethylenediaminetetra acetic (edta) titration], and organic mat ter. Physical measurements were recorded