Agricultural practices, soil fertility management modes and resultant nitrogen leaching rates under semi-arid conditions

Under semi-arid or arid conditions, growing needs for agricultural commodities dictate the intensification of agricultural activities through the application of irrigation and fertilization practices aimed at increasing crop yields. A certain amount of the added irrigation water is designed to seep below the root zone and leach excessive salts accumulated in the irrigated soil. This entails, in part, recharging the ground water-table aquifers. Hence, intensification of agricultural activities introduces a long-term risk of groundwater pollution by unused fertilizers, e.g., nitrogen, salts and pesticides, herbicides, leached from the irrigated fields. To avert or minimize this risk, the amounts of applied water and fertilizer should be determined and minimized by optimizing them to match crop requirements. The objectives of the present work were to determine the amounts of water and salts leached below several agricultural areas subjected to differing soil fertility practices, and to try to relate them to the yields obtained. Published data and experimental data sets of water, chloride and nitrate concentration - depth distributions were used and analyzed. The results show that intensification of agricultural activities leads to increased hazards to surface and groundwater pollution and this can be diminished provided balanced irrigation - fertilization programs are developed for different crops, by using the results of leachate loads seeping from long-term fertility and irrigation studies (permanent plot experiments). (C) 1999 Elsevier Science B.V. All rights reserved.