6. Important facts about superphosphate and RPR Superphosphate is advertised as having 9.0% P. But how much of this 9% is actually plant available? An indication of this is how much of the total P is citric soluble. Currently, it is about 8% P. The difference is largely unreacted phosphate rock that did … Read more
5. The effect of the sulphur form used on the ratio of S to P required Background Pasture plants need to take up 7 kg of sulphur (S) for every 10 kg of phosphorus (P). So, if both nutrients are being applied in reasonably efficient forms, a fertiliser containing 9% P should … Read more
4. What every farmer should know about cadmium (Cd) Background The cadmium (Cd) issue arose in New Zealand and Australia purely and simply because the manufacturing phosphate rocks both countries originally used to make superphosphate (Nauru and Christmas Islands) contained elevated levels (50-100 ppm) of Cd. All of this Cd ended up … Read more
3. Using RPR in low soil P, low rainfall, high pHor extremely high P retention (>97% PR) Background RPR is a natural, slow-release mineral formed on the sea floor over hundreds of thousands of years. Deposits that have been raised above sea level by changes in sea level or earthquakes are cheaper … Read more
2. How to define a true RPR Background Any phosphate rock will release some P into plant-available form when applied to acid soils. The question is, in the pastoral context, will it release P at a sufficiently fast rate to maintain the needs of a high production pasture? Most phosphate rocks do … Read more
1. Economic and environmental benefits of reactive phosphate rock (RPR) Background Both the economic and environmental benefits of using RPR as the source of phosphate on New Zealand’s soils have been deliberately understated by the fertiliser manufacturing industry in the past decade. With no significant independent importation and scientific promotion of RPR, … Read more