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Price implications for P&K applications

May 2022

Cost and price rises are a frequent focus in the world right now, but especially within agriculture due to the circumstances in Ukraine and the sanctions imposed on Russia as a result. Although within arable farming, 2022 should produce reasonable returns, livestock farmers may not be so fortunate, whilst there is much greater uncertainty beyond this for all. Nitrogen prices have increased by 200% from March 2021 to March 2022, whilst phosphate and potash prices have both increased by over 100% in the same time frame. The only certainty that exists, is that volatility will remain high, and the risks of growing crops have increased significantly alongside the rewards.

It can be very understandable in times like these, to place greater scrutiny on all inputs, to ensure that the returns on the investment that are sometimes promised are achieved. However, farmers must be careful not to reduce inputs which are crucial but whose benefits are not visual or directly obvious. Potash fertiliser is one of the best examples of this danger.

All plants, except legumes, require a larger supply of potash than any other nutrient – even nitrogen.   If the total requirement is not available or if the rate of supply at periods of peak growth is limiting, plant performance will be impaired leading to lower yields and poorer crop quality. These adverse effects will be worse if nitrogen and potash are out of balance and in difficult growing seasons where there is more stress – especially drought. Typical peak requirements for different crops are shown in Table 1 which also shows offtake figures.

Table 1. Crop uptakes & offtakes (kg/ha)
  Typical uptake Offtake
Cereals (grain only) 320 50
Winter cereals (grain & straw) 320 95
Spring Cereals (grain & straw) 320 110
Oats (grain & straw) 320 150
Oilseed rape 375 40
Potatoes 480 300
Sugar beet 450 100
Peas & beans 190 50
Maize 370 175
Silage 1 cut 150 120
  2 cuts 250 200

Plants obtain their potash requirements from the soil which must contain large enough reserves within normal rooting depth to provide for peak uptake. Crop offtake should be replenished by manure and fertiliser potash additions. However, because of the large total requirement of potash, there are still many soils – usually the lighter textured ones – where reserves are not adequate. Because of current financial pressures basal fertiliser use may be deliberately cut-back. In these situations, replacement of offtake will become increasingly costly and difficult to ‘catch-up’ the longer it is left. Clearly, where soils are above the target index, there are opportunities to reduce the level of inputs without causing any issues to the crop and resultant financial penalties.

Although it has been highlighted many times before, the importance of making the most of any organic manures has never been greater. Making sure applications are fully accounted for and applied to those fields that are most in need (below the target index) will be of high importance going forward.

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