Nutrient and organic matter levels in a range of New Zealand soils under pasture

Abstract

Some chemical characteristics of the organic matter and the nitrogen, phosphorus, and sulphur levels in 21 soils under established pasture were measured. The soils were representative of the major New Zealand soil groups. Nitrogen, organic P, and organic S levels indicate the accumulation of these elements in the soil organic matter during pasture development. A significant proportion of the soil organic matter (10070 or more of the total C and N) appears to be present as un decomposed or partially decomposed plant and animal residues (‘light fraction’) which can be extracted by density separation in heavy liquids. Organic P extracted by 0.5M NaHC03, which has been suggested as a measure of labile organic P, is a major proportion (25-85%, mean 54%) of the total NaHC03- extractable P. The proportions of sulphur in HI-reducible forms are low (18 – 41 %, mean 26%) and this is probably a feature of soils under pasture. Organic P in the yellow-brown loams appears to be at or approaching an equilibrium level but residual fertiliser P may still be accumulating in inorganic forms. © 1987 Taylor & Francis Group, LLC.