Key points
- CRP chief executive Chris Castle says reactive phosphate rock (RPR) can dramatically reduce fertilizer runoff without lowering farm production.
- Dr. Bert Quin, who designed New Zealand’s national RPR versus superphosphate field trials in the 1980s, estimates switching to RPR would cut phosphorus runoff losses by 80 percent.
- CRP holds New Zealand’s only material source of RPR, a resource it estimates is worth $5 billion to $7 billion.
- Six countries control 98 percent of world phosphate reserves, with Morocco holding 85 percent of that total.
Chatham Rock Phosphate Ltd. advised this week that improved water quality will result from the use by farmers of Chatham rock phosphate.
Fertilizer runoff into waterways can be dramatically reduced, without any loss of production, by using naturally occurring reactive phosphate rock (RPR), according to Chatham Rock Phosphate chief executive Chris Castle.
Mr. Castle said scientific studies over many years have shown RPR offers strong environmental benefits.
Studies comparing the use of RPR and superphosphate on farmland show that, when applied directly, RPR is both a very effective sustained-release fertilizer and not susceptible to runoff.
CRP holds New Zealand’s only material source of RPR.
The findings of the studies — some going back decades — are supported by Dr. Bert Quin, probably New Zealand’s pre-eminent expert on the use of different phosphate rocks as phosphate fertilizers. Dr. Quin designed and co-ordinated New Zealand’s national series of RPR versus superphosphate field trials while working as a senior government agricultural research scientist during the 1980s.
Dr. Quin believes phosphate nutrient continues to enter waterways from agricultural land mainly because predominantly water-soluble types of chemically manufactured phosphate fertilizer is used, especially single superphosphate, which supplies phosphorus (P) and sulphate-sulphur.
“Super is prone to runoff of applied phosphorus into waterways during runoff events in the first eight to 10 weeks after application, entering streams, rivers and lakes, and causing eutrophication in the form of excessive water-weed growth and algal blooms,” says Dr. Quin. “It can even be leached right through soils with low phosphorus retention such as those in Northland and on the West Coast.”
Dr. Quin estimates switching from superphosphate to RPR and RPR/DAP (diamonium phosphate) blends would reduce average runoff losses of phosphorus by 80 per cent.
“This would take P losses back below the trigger levels that have resulted in most of our lakes becoming eutrophied. Within five to 10 years, water quality in the Rotorua lakes, for example, would be massively improved.
“By far the most cost-effective option for phosphorus is reactive phosphate rock or RPR. This is a natural mineral, formed on the sea floor originally, which is a very effective source of sustained-release phosphorus, ideal for maintaining high-producing pasture and extremely resistant to runoff losses.”
Dr. Quin says that he has been very disappointed that the New Zealand fertilizer industry, ironically largely composed of a duopoly owned by farmers, has not had the courage to follow the example set by Summit-Quinphos over the period from 1989 to 2007.
“For their management to replace true RPR with agronomically ineffective direct application phosphate rock from Morocco is as cynical as anything I have seen,” he says. “The time is right for people with the political will and determination to save New Zealand’s environment to stand up and force change.”
He also says anecdotal evidence over the nearly 30 years that some New Zealand farmers have been using RPR shows maintenance requirements for phosphorus start to drop significantly because of both reduced runoff and reduced fixation onto soil clay particles. The higher P runoff from soluble P in the eight to 10 weeks after application comes largely from particles and granules of the soluble fertilizer being floated off in runoff. RPR particles are 50 per cent heavier. At the other end of the scale, the very low pH that exists around granules of super leads to increased fixation of P onto allophanic clay particles. So, it is a lose-lose for super.”
He believes there is a need for specific advice for farmers regarding managing or minimizing any minor lag in production following a switch to RPR. “The easiest way is to use a bit of DAP mixed with the RPR for the first two years.”
About Chatham Rock Phosphate
Ltd.
Chatham Rock Phosphate is the custodian of New Zealand’s only material resource of environmentally friendly pastoral phosphate fertilizer.
Using this phosphate will support sustainable farming practices, including healthier soils and reduced accumulation of the heavy metal cadmium, dramatically lowering P runoff to waterways and shrinking fertilizer needs over time.
The resource has an estimated worth of $5-billion to $7-billion, representing one of New Zealand’s most valuable mineral assets and is of huge strategic significance because phosphate is essential to maintain New Zealand’s high agricultural productivity.
New Zealand’s current access to phosphate is vulnerable to economic and political events in the six countries controlling 98 per cent of the world’s phosphate reserves, with 85 per cent of the total in the western Saharan state of Morocco.
Other New Zealand and international research
Reports of research into P runoff into waterways by New Zealand and overseas scientists considered by CRP were:
RPR revisited (1): research, recommendations, promotion and use in New Zealand by Dr. Quin and M. Zaman;RPR revisited (2): long-term farmer experience helps define the role of RPR in grazed pastures by M. Zaman and Dr. Quin; Phosphorus fertilizer form affects phosphorus loss to waterways: a paired catchment study by R.W. McDowell, R.P. Littlejohn and J.D. Blennerhassett; Evaluation of two management options to improve the water quality of Lake Brunner, New Zealand by R.W. McDowell; Potential phosphorus losses in overland flow from pastoral soils receiving long-term applications of either superphosphate or reactive phosphate rock by R.W. McDowell, R.M. Monaghan and P.L. Carey;Rainfall intensity and phosphorus source effects on phosphorus transport in surface runoff from soil trays by Francirose Shigaki, Andrew Sharpley and Luis Ignacio Prochnow;Phosphorus leaching in an acid tropical and triple superphosphate by E. Gikonyo, A.R. Zaharah, M.M. Hanafi and R. Anuar; Effectiveness of rock phosphate, coastal superphosphate and single superphosphate for pasture on deep sandy soils by M.D.A. Bolland, M.F. Clarke and J.S. Yeates.
- RPR revisited (1): research, recommendations, promotion and use in New Zealand by Dr. Quin and M. Zaman;
- RPR revisited (2): long-term farmer experience helps define the role of RPR in grazed pastures by M. Zaman and Dr. Quin;
- Phosphorus fertilizer form affects phosphorus loss to waterways: a paired catchment study by R.W. McDowell, R.P. Littlejohn and J.D. Blennerhassett;
- Evaluation of two management options to improve the water quality of Lake Brunner, New Zealand by R.W. McDowell;
- Potential phosphorus losses in overland flow from pastoral soils receiving long-term applications of either superphosphate or reactive phosphate rock by R.W. McDowell, R.M. Monaghan and P.L. Carey;
- Rainfall intensity and phosphorus source effects on phosphorus transport in surface runoff from soil trays by Francirose Shigaki, Andrew Sharpley and Luis Ignacio Prochnow;
- Phosphorus leaching in an acid tropical and triple superphosphate by E. Gikonyo, A.R. Zaharah, M.M. Hanafi and R. Anuar;
- Effectiveness of rock phosphate, coastal superphosphate and single superphosphate for pasture on deep sandy soils by M.D.A. Bolland, M.F. Clarke and J.S. Yeates.
