Building a solid foundation - sulphur, phosphorus and potassium requirements for the sedimentary soiIs of North Canterbury

Abstract

The soils of North Canterbury occur mainly on steep land (31%), hilly land (28%), rolling downs and downlands (11%) and terraces and floodplains (30%). Most soils are predominantly formed from greywacke and tertiary sediments and some 85% comprise yellow-grey earth, yellow-grey earth to yellow-brown earth intergrade, yellow-brown earth and recent soil groups. In terms of the relationship between pasture production and fertiliser nutrient use these major soil groups are considered as a single entity, namely "sedimentary" soils (a reference to their derivation from sedimentary rocks). The relationships (production functions) between pasture production and soil test level for sulphur (S), phosphorus (P) and potassium (K) are shown to be of the "diminishing returns" type for the sedimentary soils and the point at which near-maximum production (97%) occurs is defined as the "biological optimum" soil test level. Biological optimum sulphate-S and organic-S levels-are-l.0 and 15 respectively, for O-l.s-en- P. -is _ 20 and quick-test K is 6. Once the biologrcal optimum soil test levels have been attained then maintenance fertiliser nutrient rates are appropriate. In order to correct S deficiency sedimentary soils require an average of 35 kg S/ha. To move up the pasture production curve an average of 5 kg P/ha above maintenance will increase Olsen P by 1 unit. Potassium requirements depend on soil group within the sedimentary soils. -Keywords:~biological~optimum, North Canterbury, nutrient requirements, phosphorus, potassium, sedimentary soils, Sulphur