The influence of rate and frequency of superphosphate application on pasture yield

Abstract

Single (biennial) and split (annual) dressings of superphosphate, supplying the same quantity of fertilizer in the two year period, were compared on established pastures at eighteen sites. The granitic, sedimentary, and basaltic soils used, differed in their requirement for the fertilizer. While current response to the fertilizer was independent of the total amount of superphosphate previously applied there was evidence of a residual value for the fertilizer on these soils. This apparent contradiction is discussed. Significant responses to superphosphate application were recorded at eight sites. Even on the most responsive of the eight soils, a total dressing of 2 cwt an acre in the two year period satisfied the pasture requirements. Frequency of application had little effect on pasture yields. However, where it did affect yields, the split application was favoured in the second year due to the low residual value of the fertilizer on those soils. As soils of low residual value could not be readily distinguished on the basis of fertilizer history, it is suggested that superphosphate should be applied to pastures on the responsive non-basaltic soils as annual dressings of 1 cwt an acre. There was no evidence that more frequent applications were needed for winter than for mature pasture production.