Serpentine-superphosphate and dolomite as magnesium sources on Whakarewarewa sandy loam

摘要

Abstract Serpentine-superphosphate at 4 cwt per acre per annum and superphosphate plus dolomite at equivalent total Mg and P rates were compared with normal superphosphate (equal total P) in a field experiment on a pumice soil deficient in P and marginally deficient in Mg for pasture growth. Both Mg sources appreciably raised exchangeable Mg levels in the soil and maintained pasture Mg levels above 0.20% for most of each year over a period of 4 years. Yield responses to Mg increased from nil in 1961–2 to 20% in 1964–5, under the total removal system used. Increases in herbage Mg concentrations (22 to 73%) were closely related to the square roots of the ratios of exchangeable Mg levels in the plus-Mg and no-Mg treatments. Four cwt serpentine-superphosphate was equivalent to approximately 1.3 cwt dolomite in its effect on soil and plant Mg levels. Potassium chloride at 1 and 3 cwt per acre significantly increased yields in the plots receiving P and S fertiliser. It significantly reduced exchangeable Mg in t...