Improving Irrigation Practice to Reduce Risk of Nitrogen Percolation into Deeper Aquifers in Vegetable Cultivation in Suburban Ha Noi; Viet Nam

摘要

This research demonstrates the advantages of drip irrigation with scheduling (DIS) over furrow irrigation (Fl) for improving water use efficiency (WUE) and reducing the risk of potential nitrogen (N) con-lamination of groundwater in cabbage cultivation on alluvial soils of the Red River, North Viet Nam. Compared with Fl, the DIS practice improved the irrigation WUE of the vegetable from 2.11 ±0.35 to 5.23±0.41 kg/m3 during the autumn-winter (October-December), and from 2.15±0.27 to 5.31 ±0.35 kg/m3during the winter-spring (February—ApriI) cropping seasons. Overall, DIS saved between 42 percent and 46 percent of water in comparison with Fl during the autumn-winter and winter-spring seasons, respectively. It appears that with Fl, ammonium (NH4+) percolates beyond the rooting depth of the crop, but in DIS it does not. Percolation could potentially cause groundwater contamination with NH4+. The delta nitrogen-15 (615N) values of ammonium in Fl increased with increasing NH4+ concentration implying that there were at least two sources of N release, namely from inorganic fertilizer and from the manure applied. The o~(15)N of the soil nitrate (NO_3") in Fl was almost unchanged with increasing NO_3" concentration, varying from 1%o to 5%o, suggesting that N0_3" was derived only from inorganic fertilizer. With DIS, soil NhV was found to be from the manure whereas NO_3" was from inorganic fertilizers.