Polyhalite as a multi nutrient fertilizer - potassium, magnesium, calcium and sulfate

摘要

Polyhalite is a hydrated sulfate of potassium (K), calcium (Ca) and magnesium (Mg) with the formula: K2Ca2Mg(SO4)(4)center dot 2H(2)O. The main objective of the present study was to investigate and compare the efficiency of polyhalite as a fertilizer supplying K, Ca, Mg and sulfur (S) relative to equivalent soluble salts. The specific objectives were to investigate: 1. The release and transport of Ca, Mg, K and S in soil; 2. Uptake of these minerals by wheat plants and 3. Biomass production of wheat plants. To meet these objectives, two pot experiments (20 l pots filled with dune sand) were conducted in which the effects of four doses of polyhalite (0, 500, 1,500 and 2,500 kg/ha) and one dose of Ca, Mg and K sulfate salts (equivalent to the 1500 kg/ha polyhalite dose) were investigated. In a third experiment, residual effects of the fertilizers were studied using the pots from the first experiment. Different leaching fractions were used in the experiments (30% in the first one and 7-10% in the second and third experiments), to investigate the effect of water management on mineral transportation in the soil and plant uptake. Polyhalite was found to be a more efficient fertilizer for supplying K, Ca, Mg and S relative to equivalent soluble salts. To meet the plant required ratios for Ca, Mg and K, the polyhalite dose should be applied accordingly to provide sufficient Ca and Mg, and additional fertilizers should be used as a source of K. Transport and leaching of Ca, Mg, K and S in soil following polyhalite application was lower than following the application of the equivalent sulfate salts. The residual effect of polyhalite fertilizer on the subsequently grown crop was higher than the effect from the equivalent sulfate salts, especially regarding Ca, Mg and S. Irrigation management, as determined by the leaching fraction, has a strong impact on the efficiency of polyhalite as a source of K, Ca, Mg and S for plant nutrition.