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SUMMARYAn account is given of the iilteractions which occur when urea or ammonium sulphate is banded in a clay soil. The spatial distribiltions 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 Jncubations of homogeneous mixtures of various nitrogen compounds and soll. The ditIusion of the banded fertilizers and their products throilgh 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 hJgher than t0 bars, if the ammonium-N conceiltration 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 Iertilizer 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.An agronomic implication of the work is that if a given amount of fertilizer is applied to a given area of soll, the rate of nitrate formation per unit area may be controlled by banding the fertilizer and varying the band spacing.

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