NITRATE LEACHING AND ADSORPTION IN A KRASNOZEM FROM REDLAND BAY, OLD .1. LEACHING OF BANDED AMMONIUM-NITRATE IN A HORTICULTURAL ROTATION

NH4NO3 at a rate of 165 kg N ha-1 was placed in bands 76 cm apart in a krasnozem. The fertilized plots were either kept bare or cropped using a horticultural 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 N initially in the soil, 72% (201 kg N 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 N ha-1 (< 2 mg nitrate N kg-1) in the surface 160 cm of the profile. In the bare plots, nitrate movement/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.