Physical Description:
Colour varies with rock types from pink to brown or black particles, with yellow crystals of elemental sulphur.
Uses:
RPR 15S is a 50:50 mixture of reactive phosphate rock (currently Ben Guerir) and Sulphur Super 30 and as such contains slow release phosphate, calcium and elemental sulphur. This is not suitable for capital fertiliser application but best suited for maintenance applications. It is most suited to hill and high country farms at maintenance soil fertility levels where rainfall is good to high and soil pH levels below optimum. This product may also be used for organic farming systems as both of the components are Bio-Gro certified.
Benefits:
RPR 15S a slow release fertiliser which may have environmental benefits where high rainfall and surface runoff occurs subsequent to fertiliser application. However, once the P and S components are dissolved in soil solution the fate of these nutrients are no different than for soluble P and S fertilisers. RPR requires soil acids to dissolve the rock phosphate to plant available forms. The lower the soil pH and the finer the particles the quicker this reaction takes place. Elemental S is slow release sulphur as it requires the action of Thiobacillus bacteria in the soil to convert the elemental S to sulphate S and the speed of this dissolution is moisture and temperature dependent as well as faster for finer particles.
Application:
Spreading rates for RPR 15S vary greatly mostly depending on P and S requirement. Actual spreading rates will vary according to farm type, climate, productivity and soil type - it is best to confirm rates with a Field Officer. The rate spread should be determined by the need for the major nutrients and the frequency of application.
Due to the fine particle size of this product special care is needed to achieve an even spread. Spreader calibration should be carefully checked and the bout width will probably need to be reduced.
Storage & Handling:
As with most solid fertilisers, RPR 15S can be stored over a season as long as it is kept in a cool, dry, well ventilated area.