Pasture responses to magnesium fertilisers on a yellow-brown pumice soil

Marked and consistent yield responses to magnesium (Mg) fertilisers were recorded over a 2-year-period from clover-dominant pasture growing on a yellow-brown pumice soil in the Central Plateau region of the North Island. Annual applications of serpentine superphosphate (24 kg Mg/ha), dolomite (25 kg Mg/ha), and magnesium sulphate (24 kg Mg/ha) respectively raised dry matter yield to 92, 94, and 96% of the maximum, produced by 48 kg Mg/ha, applied as magnesium sulphate. Mean Mg concentrations in white clover were increased from 0.11% in plots receiving no applied Mg to 0.18, 0.18, 0.22, and 0.29% respectively where Mg was applied in the 4 forms described. The mean critical Mg concentration of 0.22% associated with near-maximum yield was higher than those obtained in similar trials conducted earlier on Mg-deficient forest nursery sites in the region. Possible reasons for this are discussed. It is concluded that pasture on similar lighttextured soils with low Mg status may also benefit from Mg additions.