Building a solid foundation for pasture production in Northland: P, K, S and lime requirements

Abstract

The generally strongly weathered, leached soils of Northland consist of four major soil groups. The yellow-brown earths and podzols and yellow brown sands are formed from sedimentary rocks, while brown granular clays and red and brown loams are formed from volcanic rocks. In terms of the relationship between pasture production and fertiliser nutrient requirements, for both sedimentary and volcanic soils, the production functions are shown to be of the "diminishing returns" type, and the point at which near-maximum production (97%) occurs is defined as the "biological optimum" soil test level. Biological optimum test values for sedimentary and volcanic soils are: Olsen P 20 and 22; quicktest K 6 and 7; sulphate-S 10; organic-S 15; and pH 5.9. Once biological optimum soil test levels have been attained then maintenance fertiliser nutrient rates are appropriate. In order to move up the pasture production curve an average of 7 and 11 kg P/ha above maintenance will increase Olsen P by 1 unit for Northland sedimentary and volcanic soils respectively. Similarly, on average 60 kg K/ha will raise quicktest K by 1 unit on volcanic soils, but capital requirements for K on sedimentary soils in Northland are not known. An average of 35 and 25 kg S/ha will correct S deficiencies on sedimentary and volcanic soils. Keywords: biological optimum, lime, Northland, nutrient requirements, phosphorus, potassium, sedimentary soils, sulphur, volcanic soils