Irrigation water in Rioverde region, San Luis Potosi, Mexico

Approximately 15,132 ha of farmland in the region of Rioverde are irrigated, mainly from two sources: the Manatial de la Media Luna (a spring which provides 7 m(3)/s of water) and a series of small wells. The latter consists of 239 deep wells and 67 shallow wells, which together generate 74,000,000 m(3) per year Water from both sources varies greatly in its composition and concentration of dissolved salts. The use of this water for irrigation had distinct effects on the physical and chemical properties of the soil, on the irrigation equipment, and on plant growth, which were reflected in the productivity and profitability of the crops. The objective of this work was to characterize the quality of the water used for irrigation and its, impact on agricultural production. Data were compiled from samples analyzed in the laboratories of the Instituto de Investigacion de Zonas Deserticas (Desert Zone Research Institute) and the Distrito de Desarrollo Rural # 130 (Rural Development District # 130). Average values for electrical conductivity sodium absorption ratio, pH, cations, and anions were obtained and organized in tables to determine classes of water as determined by their chemical characteristics. Later those data, which were complete for the chemical characteristics listed above, were categorized using multivariate ordination techniques. The results showed that the water in the region corresponds to the following geochemical groups: water with calcium sulfates and water with calcium bicarbonates. The water with the best quality for irrigation comes from the spring and wells in the southern part of the region, while the water with poorer quality is used in the north.