SOME FACTORS AFFECTING LOSSES OF AMMONIA FROM UREA AND AMMONIUM SULPHATE APPLIED TO SOILS

Summary Urea supplying 100 1b of N/acre was either broadcast on the surface or mixed with four soils (two clay‐loams, two sandy‐loams) and losses of ammonia were measured when the soils were maintained at 40, 50, or 60 per cent water‐holding capacity (WHC) and incubated at 5°or 25°C. Urea and ammonium sulphate were similarly applied to two calcareous soils at 40 per cent WHC and 5°or 25°C. Losses varied most among soils, from 2 per cent of the N applied from an unmanured clay‐loam to 13 per cent from an unmanured sandy‐loam. Changing temperature and water content affected losses little on average, but their effects differed with different soils. Losses of ammonia were similar from urea and from ammonium sulphate applied to the calcareous soils. Analyses at the end of the experiments showed that: (i) nitrite tended to accumulate in the sandy and calcareous soils, accumulation being favoured by lower temperature and wetter soil; (ii) ammonia was lost at 25° C from calcareous soils until all the ammonium‐ N had been nitrified, from the slightly alkaline clay soils until nine‐tenths had been nitrified, and from the neutral sandy soils until half had been nitrified.