ALBERT

Description: The effect of wastewater irrigation on soil salinity and crop yield was determined in a study at Swift Current, Saskatchewan. A toposequence consisting of the Orthic Regosol series, Calcareous Brown series, Orthic Brown series and Cumulic Orthic Brown series of the Birsay Association was seeded to alfalfa and irrigated with effluent from a secondary sewage lagoon. Since the applied effluent had a mean EC of 2.6 dS/m, soil salinization was a major concern. For 8 yr the four soils were sampled for salinity to a depth of 150 cm each fall. During the 8-yr period, alfalfa was sampled for dry matter yield twice each year from each soil. The results indicate that irrigation by 10–15% more than the normal recommended application rate (i.e., when low saline surface water is used for irrigation) will ensure sufficient leaching to maintain salt content in the root zone at a level not deleterious to plant growth. After 8 yr of effluent irrigation, new steady state salinity profiles were developed in the Orthic Regosol, Calcareous Brown and Orthic Brown series. At this steady state condition the salt contents in the upper 60 cm of the root zone in these three soil series were generally similar. They increased from the initial low ECe value of 0.6 dS/m to 2.5 dS/m. Salinity increased with depth toward the bottom of the root zone where the Orthic Brown series had an ECe value of 4.0 dS/m, while the Orthic Regosol and Calcareous Brown series had values of 6.0 dS/m. Effluent irrigation resulted in a small net reduction of salts in the 150-cm profile of the Orthic Regosol and the Calcareous Brown series, but caused an increase of salts in the Orthic Brown profile. In the Cumulic Orthic Brown series the salt content throughout the profile increased continually from a very low initial level, and had not reached a steady state condition after 8 yr of irrigation. The development of a high water table in this area resulted in salt movement into the root zone of the Cumulic Orthic Brown series that was distinctly higher than those of the other three series and caused alfalfa yields to decline from being highest at the start of this study to only about 80% of yields on the Orthic Brown series at the end. The observed yield reductions emphasize the importance of having adequate drainage to effect salt removal by leaching when crops are irrigated with saline sewage effluent. Key words: Wastewater irrigation, soil salinity, alfalfa yield