Consequences of banding nitrogen fertilizers in soil

Abstract

An account is given of the interactions which occur when urea or ammonium sulphate is banded in a clay soil. The spatial distributions of ammonium, nitrate, and nitrite around the band are given as functions of time and are discussed in relation to results from a series of incubations of homogeneous mixtures of various nitrogen compounds and soil. The diffusion of the banded fertilizers and their products through the soil presents the nitrifying organisms with a wide range of environments. The patterns of nitrification are therefore complicated. Nevertheless, they are explicable in terms of the main results of the incubations which were that (a) nitrification was completely inhibited if the osmotic suction of the soil solution was higher than 10 bars, if the ammonium-N concentration in the soil solution was above 3000 ppm, or if the pH was greater than 8, (b) nitrite accumulated if the pH was between 7 and 8, (c) nitrate accumulated if the pH was less than 7, and (d) above a minimum concentration of fertilizer the rate of nitrate formation was independent of the concentration unless the latter was so high that either pH, osmotic suction or ammonium concentration became inhibitory.