Losing P and profit

Phosphorus can be lost in a number of ways, all of which can affect profits.

“Phosphorus (P) is needed for plants to grow in New Zealand’s naturally P deficient soils, but too much P in waterways can cause excessive growth of aquatic plants and algal blooms”, says Ballance Innovation Leader, Dr Jamie Blennerhassett.
“P losses to the environment, whether from losing topsoil or improperly applying fertiliser, can also affect farm profits, so it’s good business sense to minimise them where you can” he says. 
Runoff losses
“Most farm systems lose P, and this happens mainly via runoff. The actual amounts of P lost to waterways in runoff are relatively low, typically 0.1 to 1.7 kg P/ha/year. But even low amounts can have a significant negative impact on water quality”, says Dr Jamie Blennerhassett.
Runoff from land contains soluble P (readily available to plants) and P bound to soil particles. Negatively-charged phosphate binds to positively-charged soil components such as clay minerals containing aluminium, iron and calcium in the upper layers of soil. The soil’s ability to retain P in this way is indicated by its ASC (anion storage capacity).
Fertiliser losses
When P is applied to land, around 80 to 90 per cent is eventually used by plants, so around 10 to 20 per cent is ultimately lost.
A soluble P fertiliser, such as superphosphate or di-ammonium phosphate (DAP), spread too close to waterways or applied less than two weeks before irrigation or heavy rainfall (an average of 30 mm within 21 days) can, via runoff, contribute up to 90 per cent of total P losses from pasture. If this lost P enters waterways, it will be available to aquatic plants and algae.
Choose the right phosphate fertiliser for your farm and you’ll get the most cost-effective product that’s best suited to the conditions to minimise environmental losses.
For any help or guidance on choosing the perfect phosphate fertiliser for your farm, speak to your local Nutrient Specialist or contact our Customer Services team on 0800 222 090.