Nitrate leaching and adsorption in a krasnozem from Redland Bay, QLD. I. Leaching of banded ammonium nitrate in a horticultural rotation

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Abstract
Ammonium nitrate at a rate of 165 kg nitrogen ha-l was placed in bands 76 cm apart in a krasnozem. The fertilized plots were either kept bare or cropped using a horticultuial rotation. Soil samples were collected at various time intervals to a depth of 300 cm. The amount of leachate was estimated from the water balance equation and the relative movement of nitrate with water determined. Of the mineral nitrogen initially in the soil, 72% (201 kg nitrogen ha-1) remained as nitrate between the depths of 40 and 120 cm following a bean crop. Prolonged cover cropping with oats decreased the amount of nitrate to less than 44 kg nitrogen ha-1 (< 2 mg nitrate nitrogen kg-1) in the surface 160 cm of the profile. In the bare plots, nitrate movement per 10 mm of leachate decreased with depth, lateral movement was gradual, and vertical movement was concentration dependent below 160 cm. These results are discussed in terms of the direction of water flow, soil structural properties and nitrate adsorption.