Nutrient reserves in Southland soils

Abstract

The major plant nutrients in soils were measured from 53 Southland sites arranged along 4 transects which extended inland from the southern coast and one which extended westwards from Papatowai on the east coast to Manapouri in the west. Soil samples were taken from 8 depths: O-75.75-150, 150-225, 225-300, 300-450, 450-600, 600-750, and 750-900 mm, at each site. In zonal soils, sulphate accumulated deeper in the soil profile and declined logarithmically with distance from the southern coast. In recent soils there was little accumulation in the profile. Rainfall sulphur is the most likely source of the reserves. Magnesium accumulated deep in the profile of inland soils in western transects, suggesting that serpentine rock parent material was its source. Generally, available phosphorus, calcium, potassium, total nitrogen and organic carbon concentrations were greatest in the surface layer of soil and declined with soil depth. However, very high phosphate reserves were present deep in the profile at a few specific inland sites. Short-term sustainable agricultural systems could involve the utilisation of at least some of these reserves. This would require the encouragement of deeper-rooting of plants than currently occurs under pastoral systems. Keywords magnesium, nutrient reserves, phosphorus, Southland, sulphate, sustainable agriculture, transects