EFFECT OF IRRIGATION AND TILLAGE PRACTICES ON NITRATE LEACHING

摘要

Nitrate is the ubiquitous chemical contaminant in the world s aquifers and the levels of contamination are increasing. Nitrate leaching·has been found to be dependent upon soil properties, plant characteristics, and climatic conditions. Agricultural activities on farmlands (e. g. Irrigation and tillage practices) can affect the soil properties that are mostly associated with nitrate leaching. Irrigation increases the potential for nitrate accumulation in the groundwater in two ways: first, the increase in water content in the root zone creates a greater potential for leaching and second, it increases the potential crop yield with a corresponding increasing N requirements. Consequently, it can result to a larger amount of leachable nutrient in the root zone. In effect, wetter soil and larger N applications produce a synergetic effect to increase the potential for nitrate accumulation in the groundwater. Tillage practices on the other hand, directly affect the leaching characteristics as it influences the soil water balance and soil mineralization rate. In addition, tillage promotes soil aeration and, therefore it increases mineralization and decreases denitrification. Pore size distribution is also affected by tillage. For instance, tillage practices can disturb the large pores (macro pores) whereas, no till allows the macro pores to develop and persist. The nitrate leached to groundwater through macro pores may either increase or decrease, depending in soil hydrologic conditions.