Biological oxidation of ammoniacal fertilizers as affected by the physical properties of soil.

The study was made on the nitrification of ammonium sulphate and ammonium nitrate in nine soils, widely different in their texture and calcium carbonate content. Fertilizers were added to the soils in amounts to represent a cross section of a fertilizer band, ranging from 100 to 1000 ppm ammoniacal nitrogen. Results indicate the high capacity of all soils for nitrifying appreciable amounts of ammonium nitrogen during a short time. Both fertilizers nitrified rapidly and at about the same rate when applied in amounts less than 500 ppm NH4-N, but nitrification was rather rapid in soils rich in clay mineral and harbouring a denser population of nitrifying bacteria. At higher levels of NH4-N additions, ammonium as sulphate nitrified faster than as nitrate, especially in the high concentrations of NH4-N. Nitrite was detected in small amounts of less than 10 ppm in some soils, particularly in the coarse-textured ones, regardless of the type and amount of the fertilizer applied. Considerable amounts of nitrite accumulated in other soils and persisted for long time as a result of addition of high levels of NH4-N, especially in the form of ammonium nitrate.