NUTRIENT INPUTS TO SOILS AND THEIR UPTAKE BY ALFALFA THROUGH LONG-TERM IRRIGATION WITH UNTREATED SEWAGE EFFLUENT IN MEXICO

The effects of long-term waste water irrigation on soil fertility and nutrient supply to alfalfa (Medicago sativa) have been investigated in an area near Mexico City. Waste water irrigation has improved the nut rient balance of the soil in respect of total nitrogen and available p hosphorus. In contrast Na has displaced Ca and diminished the Ca satur ation of the soil. In consequence, Ca in alfalfa tissue has decreased and phosphorus and sodium increased after 80 years of waste water irri gation. Estimates of the N-balance suggest that substantial amounts of hi are being lost, probably with consequent eutrophication of the gro undwater.