Nitrate-Nitrogen and Chloride Leaching in Onion Under Furrow and Drip Irrigation Systems.

Water is a limited resource for crop production in arid and semi-arid climates. The purposes of this study were to estimate: (1) the amount of NO₃-N leaching below the root zone, (2) the leaching fractions and (3) irrigation efficiencies (4) NO₃-N, Chloride and water balance for two onion fields under furrow and drip irrigation systems located in the Mesilla Valley of Southern New Mexico. The monthly soil samples collected up to a depth of 110 cm were analyzed for nitrate-nitrogen and chloride. Soil samples were also collected twice during the growing season at 1.5 and 2 m depths from both fields. The total amounts of N fertilizer applied to furrow and drip irrigated fields were 383 and 292 kg ha^-1, respectively. A total amount of 92 and 81 cm of water was applied to furrow and drip irrigated field, respectively. The amount of NO₃-N in the drainage water was calculated by using chloride tracer technique. During the entire growing season, the NO₃-N loadings below the root zone were 240 kg ha^-1 in furrow and 79 kg ha^-1 in the drip irrigated fields. A higher leaching fraction of 0.19 was obtained for the furrow irrigated field than 0.17 for drip irrigated field as higher amount of water was applied in the former. The irrigation efficiencies (1-LF) at the furrow and drip irrigated fields were 81% and 83%, respectively. The nitrogen use efficiencies were 23.4% in furrow and 31% in drip irrigated fields. The water application efficiencies were 72% and 73% in furrow and drip irrigated fields, respectively. Shifting from furrow irrigation to drip irrigation can reduce NO₃-N leaching and improve N use efficiency by reduced water inputs.