Phosphate is a key element for plant growth in New Zealand soils, but urgent change is required in how we use it to prevent environmental degradation before it’s too late, says Hamilton-based Soil Scientist Dr Gordon Rajendram (PhD).
New Zealand soils and phosphate have a long history together, going back to World War Two when New Zealand soils were deficient and phosphate was imported as RPR and made into Superphosphate.
“The issue with this is that the continuous use of Phosphate over the last 70 years will mean it is no longer deficient in most soils and can be detrimental to the other nutrients or lime being applied,” says Soil Scientist Dr Gordon Rajendram (PhD).
The traditional method of farming was primarily focused on production. More grass, more protein, more milk and meat produced while environmental issues were not a concern.
But farming has changed, he says. Now we want to produce as much as possible but also keep any phosphate applied to stay in the soil and not runoff as particulate P or leach into subsoils.
“Much of the loss is related to the soil type, climate, Anion storage capacity (ASC) or otherwise known as P retention, and overuse of soluble forms of P. P as a nutrient is one of the most expensive nutrients per kg,” advises Gordon.
The scientific evidence is telling us not to use a highly water-soluble P fertiliser, as this type of fertiliser is far more likely to end up in waterways and particularly on low phosphate retentive soils.
“It is not nitrogen in waterways which is the issue, its P, only need small quantities to get into waterways to trigger eutrophication (algal blooms),” comments Gordon.
It as Professor Walker once said, ‘Superphosphate has done more for NZ than any politician ever has’ this is true but we need to move on as this old technology”.
About Dr. Gordon Rajendram – The Soil Scientist
Dr. Gordon Rajendram worked at AgResearch, Ruakura Research Centre, Hamilton for 22 years. He has developed two field calibrated soil tests ( N & S) which are used for agronomic advice in New Zealand. He also quantified the leaching of cation & anions from pastoral systems and this has been included in the Overseer nutrient model. He now consults to farmers and fertiliser companies.
Contact Dr. Gordon Rajendram – The Soil Scientist:
Phone: 021 466 077
Phone: 0274 587 724