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Phosphate and Potassium fertilisers | Grow the future | Agronomists in field

Tyfu'r dyfodol

Ffordd o fyw yw ffermio ac yn sicr nid yw'n rhagfynegadwy. Dyna pam fod yn rhaid i'ch fferm fod yn ddigon effeithlon i dyfu cnydau sy'n gynaliadwy ac yn broffidiol nawr ac yn y dyfodol.

Phosphate and Potash fertilisers

Both phosphate and potassium are essential nutrients for healthy crops but these should neither be taken for granted nor ignored.

When it comes to P & K doing nothing isn't an option

Not applying phosphate and potassium or failing to fully replace the nutrients removed by previous crops is a false economy and will lead to yield losses.

Why are phosphate and potassium so important?

Potassium and phosphate are two essential plant nutrients with the plant requiring a consistent supply from the soil during the critical spring growth period. Phosphate is the ‘fuel’ of the plant as it traps the sunlight energy into chemical energy that is then used by the plant for many metabolic processes. Potassium is associated with many processes including nutrient movement and redistribution around the plant and water management.

Research has shown that having an ‘adequate’ soil P & K supply brings yield resilience with 0.65 – 2 t/ha being attributed to such ‘built in’ fertility. The Yield Enhancement Network have also associated high yields with fresh phosphate applications. Yield penalties can be severe if the soil supply is insufficient.

Phosphate

84 kg P₂O₅ /ha

Removed by a 10t/ha wheat crop

Potassium

104 kg K₂O/ha

Removed by a 10t/ha wheat crop

How much phosphate and potassium do crops need?

This graph indicates the nutrient removal by a winter wheat crop and these figures are based on the removal of both grain and straw from a 10 t/ha crop.

As a minimum, these amounts need to be replaced to maintain soil indices at current levels. Otherwise, there will be a decline in soil indices and a reduction in crop yields.

Crop demand for phosphate is greatest in early spring

Soil availability of phosphate is lowest in early spring

Can the soil supply sufficient phosphate and potassium?

The soil is able to supply crops with phosphate and potassium, provided the soil index has been maintained and is close to the target index. However, there is often a gap or lag between crop demand and soil availability.

When is crop demand for P and K greatest?

This graph indicates the nutrient demand of a winter wheat crop and clearly shows that the all-important demand happens in the spring for all the macronutrients. The months of March, April and May are so critical as the crop goes through its ‘grand growth phase’, putting on large amounts of biomass that ultimately becomes yield.

In spring, crops such as oilseed rape go through a period of rapid growth during which their uptake requirement of several nutrients increases, especially potassium (K). It is a vital building block for yield development and also helps protect the crop against disease. The demand for K in OSR may be in excess of 12kg/ha/day with a total requirement of up to 300kg K₂0 by the end of flowering, for a 3t/ha crop. In wheat the demand for K may exceed 10kg/ha/day with a total requirement of up to 250kg K₂0 by the end of flowering. Therefore, applying P and K in the spring, rather than the more conventional method of applying them on their own in the autumn makes sense.

So, when is soil nutrient supply at its lowest?

Having established that nutrient demand is greatest during the spring, it is then important to consider soil nutrient supply as this needs to be synchronised, meaning that demand and supply are not compromised. So, what factors impact on the soil nutrient supply? There are clearly a number of factors here including a soils physical state and its properties (texture, organic matter levels etc), its pH, chemical composition, moisture and temperature. These can be summarised by the following:

The more clay and humus in the soil, the higher the nutrient holding capacity.
Increased organic matter levels, improve the nutrient availability
The higher the levels of calcium, iron, aluminium, the poorer the availability
The optimum pH is around 6.4.
Cold, waterlogged soils have the lowest nutrient availability

Whilst some of the factors above are site-specific, the final point (cold and wet soils) are more generic, meaning that for most soils, nutrient supply will be at its lowest as it comes out of winter and into the spring months. It follows therefore that crop nutrient demand and soil supply are most likely to be out of sync on most farms.

Using a spring NPKS fertiliser makes most sense

Applying phosphate and potassium in the spring using a YaraMila compound NPKS fertiliser is the best option.

What are the benefits of applying spring NPKS fertiliser?

Applying phosphate and potassium in the spring as a YaraMila NPKS fertiliser brings several benefits:

Crop nutrient demand and soil supply are synchronised with no lag between the crop requirement for each nutrient and the ability of the soil to supply available nutrients.

More even application of nutrients with more landing sites compared to using more concentrated straight sources of phosphate and potassium, such as MOP, DAP or MAP, is a better distribution of nutrients.

Season-long supply of phosphate with YaraMila compound fertilisers containing a mix of different forms of phosphate, season long availability is achieved with some phosphate being immediately available and a proportion being released more slowly avoiding lock up in the soil: : Ortho-P for immediate availability, DCP to allow plants to actively trigger P availability when needed and Poly-P to protect the P from being fixed to supply P over a longer time. This system using different forms of P for extended phosphate availability is known as P-Extend and is common to all YaraMila compound fertilisers.

An increased crop yield over that of the traditional approach. Trials by NIAB/TAG and Yara have shown that spring applications of NPKS compound fertilisers can increase yields by, on average, 0.3t/ha (0.12t/acre) in winter wheat and winter barley. Trials by the Royal Agricultural University (RAU, Cirencester) in 2016 gave responses of more than double this – - with an increase in wheat yields of one tonne/hectare. Trials on oilseed in 2016 also showed a big response, with, on average, an extra 0.78 t /ha at each N application rate, worth over £250 / ha.

Reduced costs/ha and improved cash flow through reduced number of applications, especially at a busy time of year and the option to spread the cost of your purchase of P and K.

Recommended YaraMila NPKS fertilisers

The following YaraMila NPKS fertilisers contain all required nutrients in appropriate ratios and are recommended for all crops.

YaraMila 52 S

20.6-8.2-11.6 +6.5%SO3 - Compound NPKS fertiliser containing Nitrogen, Phosphate, Potash and Sulphur suitable for all crops.

YaraMila ACTYVA S

15.6-14.6-14.6+ 6.5 SO3 - Granular fertiliser often used for grassland, winter cereals and oilseed rape to supply phosphate and potash together with nitrogen and sulphur.

YaraMila EXTRAGRASS

27-5-5 + 6% SO3 - Compound granular fertiliser with sulphur with the ideal ratio for grazed or mown swards to get the grass off to a good start early in the season.

Read more about YaraMila NPKS fertilisers

Related publications

Here is a related publication to download as a useful reminder

PK holiday - Are you prepared to gamble upto 2t/ha?

2.2 MB

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