Nitrate and Chloride Leaching in a Swelling Clay Soil

Abstract

AbstractLeaching losses of applied NO3−‐N and Cl− from a swelling clay soil were measured using an undisturbed field drainage lysimeter. Nitrate‐N and Cl−, applied at 110 and 279 kg/ha, respectively, were detected in drainage water collected at a depth of 125 cm after the first large rainstorm. Applied fertilizer was leached when percolating rainwater carried the applied materials through large connected pores, bypassing other soil water inside soil structural units. Even though applied fertilizer began to be lost with the first rainstorm, concentrations of NO3−‐N and Cl− were not high until large amounts of water had drained below the root zone. For example, Cl− concentrations during the first 25 mm of drainage increased by about 7 ppm. The greatest increase in Cl− concentration did not occur until 60 mm of drainage accumulated after fertilizer application.Much more native soil nitrate was leached than soil nitrate concentrations in unfertilized plots would have indicated. The data indicate that leaching losses of nitrate from mineralization may be greater than those of applied nitrate when accumulated drainage is <50 mm following fertilizer application.