AGRONOMY ADVICE: Not all phosphate fertilisers are equal – use the right one for you
We would all likely assume that the difference between various phosphate fertilisers are fairly minimal and not worth agonising over. After all, phosphate is phosphate, surely? Not so, according to Natalie Wood, Country Arable Agronomist at Yara.
“There are actually different forms of phosphate (P) that could be in a solid fertiliser product,” says Natalie. “All of them behave slightly differently. Knowing this in advance can be extremely useful for your farm, helping you to select a product that will help support the results you expect to see.”
We asked Natalie for insight into the different forms of phosphate found in fertilisers and the differences one might expect as a result.
Q: Where would we find Orthophosphate (Ortho-P)?
“Ortho-P is found in DAP, TSP, MAP as well as most NPK compounds. Ortho-P is immediately available which means that the crop can utilise the P straight away. This is perfect if the crop has the ability to take all that P up in one go. However, it’s likely that the biomass won’t be enough to utilise all the P at an early spring timing.”
Q: What are the effects of that?
“If P isn’t used it can become unavailable. It becomes fixed or precipitates out with ions in the soil. This can all happen quite quickly; up to 40% of applied Ortho-P can be lost to the plant only 2 weeks after you applied it.”
Q: How does Polyphosphate compare?
“Polyphosphate takes a while to become plant-available as it has to break down into Ortho-P first. As it is able to penetrate the soil and is initially protected from being fixed, products with Poly-P are able to supply P over a longer period of time with fewer losses.”
Q: And, finally, what about Dicalcium Phosphate?
“Dicalcium Phosphate (DCP) requires citric acid to break down into a plant-available form. The plant exudes this acid from its roots when they are “looking” for nutrients, meaning that DCP only becomes available at that stage. As a result, DCP can stay in the soil, without fixing, until required – this is why, at Yara, it is called P-Extend.”
Q: What would be your main advice for someone seeking to get the most from their phosphate fertiliser?
“It’s not a case of one being better – they’re just different. Any products which contain all three forms; Ortho-P, Poly-P and DCP is the surest way to supply phosphate to your crop for longer, making sure it’s never lacking that key nutrient. Whatever you decide, P is vital. All of our YaraMila products contain P-Extend for example, to guarantee that extra and extended source of P.”
Providing a robust supply of P is vital for effective crop growth. Choosing the right fertiliser for your farm can ensure that your results achieve expectations and avoid any unexpected problems.