FERTILIZER REQUIREMENTS OF MAIROA ASH SOILS

Abstract

Field experiments conducted on soils derived from Mairoa ash beds showed that they respond markedly to phosphate and require heavy phosphate applications for the maintenance of high pasture production. Thus, on Dunmore and Otorohanga silt loam annual rates of 375 and 750 kg/ha of superphosphate were needed for maintenance of 85 and 95% of maximum production, respectively. After cessation of phosphate dressings, the decline in pasture production was dramatic, even on plots with high initial dressings. In cases where soil test values for potassium were below 10, moderate and statistically significant potash responses were measured. Small annual applications of carbonate of lime (312 kg/ha) gave a slight but statistically non-significant increase in production (3%). However, heavier applications (625 and 1250 kg/ha) significantly decreased production on Dunmore silt loam, at pH of 5.8, after the sixth and seventh annual applications.