Nitrate leaching and adsorption in a krasnozem from Redland Bay, QLD. III. Effect of nitrate concentration on adsorption and movement in soil columns

Abstract

Nitrate adsorption and movement was studied in soil from depths of 0-15, 40-90 and 160-300 cm. Adsorption was determined at concentrations ranging from 0.5 x 10-3 to 0.5M potassium nitrate and movement by adding 0, 3, 12 and 120 mg nitrogen15 ml of a potassium nitrate solution to packed columns and leaching with deionized water or 0.2M potassium sulphate. In the 0-15 cm soil, nitrate exclusion was evident in both the adsorption and movement studies at low concentrations, but no effect was measured at high concentrations. In the two subsoils, adsorption increased with concentration to 1.9 m-equiv./100 g when equilibrated with 0.5M potassium nitrate. In the subsoils the depth of leaching of nitrate increased with nitrate concentration; the nitrate distribution was skewed; and the rate of nitrate movement was less than that of water. Addition of sulphate to the subsoils resulted in nitrate movement being similar to that of water. The results are discussed in terms of nitrate adsorption. Comparisons with field observations provide further evidence that adsorption is a major process influencing leaching in these soils.