Soil nutrient status of the Bay of Plenty region and the implications to pasture productivity and fertiliser requirements

Abstract

The soil nutrient status of sheep and beef, and dairy farms in the Bay of Plenty region was examined using results from over 4700 soil samples analysed by MAF between 1988 and 1991. The proportion of farms in various soil test categories was determined and related (using known relationships) to the potential responsiveness of pastures to fertiliser nutrient additions. About 70% of farms had soil phosphorus (P) tests below optimum values, indicating that pasture production would be increased by addition of P fertiliser on these farms. Similarly,about 50% of farms hadbelow-optimum levels of sulphur (S) and potassium (K). Pasture production on most farms was limited by more than one nutrient and a relatively high proportion of pumice soils had low levels of P, S and K. Pumice soils are prone to large leaching losses of added sulphate S and field experimental results indicated that elemental S (in sulphur superphosphate) was more efficient at increasing pasture production on these soils than sulphate S (in superphosphate). Soil test data was also used to indicate that about onethird of sheep and beef, andone-half of dairy farms were suitable for use of slow-release reactive phosphate rock (RPR) as a source of P, as indicated by soil pH56.0 and MAF fertiliser P requirements at or above maintenance levels. Keywords soil test, fertiliser requirement, phosphorus, sulphur, potassium, slow-release fertiliser