An evaluation of the effects of changing wastewater irrigation regime for the production of alfalfa (Medicago sativa)

The purpose of this study was to explore the effects of improving the quality and reducing the quantity of wastewater used to irrigate alfalfa. These effects were measured in terms of vegetative matter production and composition, and soil and leachate quality. The Tula Valley, which has been irrigated with wastewater from Mexico City for over 100 years, was used as a focus for the investigations. Greenhouse experiments were conducted using columns of soil and a crop of alfalfa. Two different water qualities were compared under three irrigation rates. It was found that with the current wastewater quality in the Tula Valley. it may be possible to reduce the application rate by 43% without negatively affecting crop nutrition. This would achieve a reduction in leachate organic matter by 35%, and leachate salts (Na, K) by 40%. After construction of the new treatment plant is completed, an intermediate irrigation rate would reduce leaching to the aquifer of organic matter by 45%, and salts (Na) by 25%, without affecting the productivity and quality of alfalfa, or the retention of nutrients and organic matter in the soil. The results of this exploratory study need to be confirmed and expanded on by land parcel trials. (c) 2012 Elsevier B.V. All rights reserved.