Soil pH and exchangeable aluminium in contrasting New Zealand high and hill country soils

Abstract

Soil acidity and associated aluminium (Al) toxicity severely limit the establishment and growth of legumes in New Zealand high country pastures. A survey of 13 soils differing in location, soil order, parent material and climate, showed soil pH to range from 4.9 to 6.4 and exchangeable Al (0.02M CaCl2) concentrations of <0.5 to 23.3 mg/kg. At all sites and at varying soil pH 􀁄􀁑􀁇􀀃 􀁓􀁕􀁒􀂿􀁏􀁈􀀃 􀁇􀁈􀁓􀁗􀁋􀁖􀀏􀀃 􀀤􀁏􀀃 􀁚􀁄􀁖􀀃 􀁓􀁕􀁈􀁖􀁈􀁑􀁗􀀃 􀁄􀁗􀀃 􀁆􀁒􀁑􀁆􀁈􀁑􀁗􀁕􀁄􀁗􀁌􀁒􀁑􀁖􀀃 above the toxicity threshold for sensitive legumes. Brown soils had the overall highest Al concentrations from 0.8 to 23.3 mg/kg, and volcanic soils the lowest from <0.5 to 6.7 mg/kg. The soil and environmental factors other than soil pH that drive variability in soil exchangeable Al require further investigation. Keywords: soil pH, soil exchangeable aluminium, toxicity, soil type