Accumulation of organic matter in some New Zealand soils under permanent pasture

Abstract The patterns of accumulation of organic carbon, nitrogen, sulphur, and phosphorus in some North Island (N.Z.) soils have been studied with respect to time under good‐quality permanent pasture. Accumulation of organic matter and the consequent immobilisation of nitrogen, sulphur, and phosphorus were general in the top 3 in., while net mineralisation occurred in the next 3 in. if, at the time of ploughing, the soil had reached a steady‐state. In eight of the 10 soils studied immobilisation of nitrogen, sulphur, and phosphorus exceeded mineralisation. In only one soil were changes found below 6 in. Estimated half‐lives for these changes ranged from two to about 40 years, and were greater for allophanic soils. These estimates are subject to large errors. Steady‐state contents in allophanic soils were up to twice those in non‐allophanic soils. Organic carbon, nitrogen, and sulphur were present in relatively constant proportions, but organic phosphorus was more variable.