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Maximising The Effectiveness Of Phosphate Fertilisers

As one of the three macronutrients, Phosphorus is a critical part of any crop’s nutritional profile. It is a major contributor to pasture/plant growth, as well as healthy flowering and root development in all crops.

Crops can exhibit phosphorus deficiency symptoms when soils have plentiful levels of P and this is because phosphorus has a unique characteristic of low availability due to slow diffusion and high soil fixation properties. i.e. phosphorus can be tied up very quickly in low pH soils with Aluminum and Iron and in high pH soils with Calcium. Phosphorus is also difficult for plants to access under hot and dry conditions. Cold and wet conditions can lead to phosphorus loss through the soil profile causing environmental damage. These P characteristics can be a major limiting factor for plant growth, not through under fertilisation but under utilisation.

Prices for phosphate fertilisers have skyrocketed over recent years, and this has put a significant financial strain on farmers. To mitigate the financial impact of increasingly expensive fertilisation regimes, farmers should look to improve techniques and alternative methods, including soil conditioning amendments, that allow for more efficient use of Phosphorus as well as Mycorrhizal fungi which are specifically adapted to plants for phosphorus acquisition from soils. This will decrease the levels of fertiliser needed, and thereby provide more cost-effectiveness. The key here is more efficient fertilisation, as opposed to current methods of simply adding more products which is ecologically and financially unsustainable. 

Why is Phosphorus so expensive?

It’s tempting to lay the blame on COVID-19, along with every other business disruption, but there are a number of factors at play. The mineral phosphate is obtained through rock mining and 70% of the world’s Phosphate reserves are located in North Africa. China, Russia, South Africa and the United States all have limited quantities of the mineral rock which are being used to shore up their own domestic food production. Political issues and the increased cost of fuel, and the price of hiring bulk carriers to transport the fertiliser, is also contributing to price increases. This has pushed farmers to find alternative sources of phosphate locally.

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What can we do about it?

Phosphorus use has declined since its high in 2003 to 2005. Price hikes due to economic difficulties around 2008 encouraged farmers to refine on-farm practices and increase the efficiency of phosphorus use, which has paid dividends. Moving forward, finding better ways to increase the bioavailability of phosphorus in the soil will be a primary focus.

New Zealand farms have long struggled with losing phosphorus to the environment. Not only does this represent money out of the farmer’s pocket, it also causes the development of toxic algal blooms in precious freshwater bodies. 

Best practice for phosphorus application requires that it be applied in the right amounts at the right time.

Right amounts

The amount of phosphorus needed is highly individualised. Many things need to be considered, including the type of crop, stocking rates if applicable, and the condition of the soil. Soil properties like pH levels, iron content and water retention capacity also play a major role. A high iron content tends to fix phosphorus, rendering it unavailable for uptake. This is a particular issue in volcanic ash soils. Meanwhile, low water retention, such as that in sandy soils, can lead to excessive phosphorus loss through leaching. 

Conduct soil tests to ascertain what nutrients are currently in the soil, and consult with your soil scientist to get a better understanding of what may be required in your particular circumstances. 

Right time

When maintaining phosphorus levels, it is best to hold off in times of increased rainfall to prevent leaching. If heavy rainfall cannot be avoided, a slow release form like reactive phosphate rock will reduce the risk of runoff. If soil testing indicates low levels of phosphorus, and an increase in production is required quickly, soluble phosphorus should be applied sooner rather than later. 

How Roots, Shoots and Fruits can help

Increasing the bioavailability of nutrients to crops can be achieved, in large part, by better conditioning of the soil. Think of adding Phosphorus applications with soil amendments such as Humic acid to hold the P in the soil and Fulvic Acid to move the Phosphorus to the plant quickly. 

Look at different forms of Phosphorus fertiliser such as a highly systemic foliar phosphorous acid.

RSF’s Rootella products provide an excellent solution. Rootella contains mycorrhizal fungi, which work symbiotically with your crops. Mycorrhizal fungi form complex networks of fine strands that connect with your crop’s roots and extend their effective reach. These organisms have grown and adapted to optimise plant phosphorus uptake requirements from soils, they prefer low soil phosphorus levels and achieve excellent results. 

Mycorrhizal fungi additionally increase the stability of the soil which improves water retention. Plants transpiration rates increase via inoculation of these organisms achieving higher water use efficiency (another important factor moving forward).  By holding water closer to your crop’s roots, nutrients become easier to absorb. This allows for more effective use of phosphate fertilisers, meaning less fertiliser is needed, which saves on costs.

It’s clear that, while phosphates can be a significant cost factor for farmers, increasing the efficiency of phosphorus utilisation by crops through soil amendments can reduce this financial burden.

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