Reduce P and K application rates at your peril – PDA

Written by Agriland Team

A recent survey carried out by the Potash Development Association (PDA) confirms that a significant number of tillage farmers in England and Wales did not apply potash (P) and phosphate (K) to their cereal and oilseed rape crops over the past five years.



A PDA spokesperson said: “In the current climate, there is no doubt that there are significant financial pressures on many farm businesses, with low yielding crops from the difficult 2020 season causing some potential cashflow issues.

“Cutting out unnecessary costs is clearly important regardless, but any decision to reduce inputs should be clearly thought out and the implications fully understood.”

Trials confirm that where soil indices are above the target index, there is scope to reduce phosphate and potash inputs, in order to run down overly high indices.



However, if soils are at the target index value, any reduction in inputs compared to the maintenance dressing will only serve to erode the soil levels and create a bigger bill to rectify the situation in the future.



The PDA spokesperson continued: “This can be made worse depending on how quickly soil levels deplete, which will vary for different soils.

“Once they are at the target index, it is usually much more cost effective to maintain this level, than letting them become depleted and having to suffer the burden of building them back up to the target.”

According to the PDA, choosing not to apply P or K on any soils that are not above the target index for the crop being grown, should not be seen as an ‘easy win’ for cost saving.



Soil nutrients such as P and K are fundamental




Soils that are well supplied with nutrient are fundamental to help buffer crops against any adverse weather conditions faced during the season.



Attempting to rectify issues during the season can be unpredictable at best, especially considering the unreliable weather patterns that have occurred over the last few seasons.



Phosphate and potash removed from a field at harvest has a measurable cost; even if it was not applied as a dressing to the crop, it will have come from the reserve in the soil, thus effectively reducing the capital value of this asset.



The PDA spokesperson further explained: “Although the days of yield being king appear to be over, where an investment has been made to plant a crop, an economically optimal yield will always be the aim.

“These crops will require sufficient quantities of all nutrients for growth, which in the case of potash, is significantly greater than the amounts that are removed at harvest.

“Maintaining soils at the target index is the safest way to ensure these crops are able to access the required quantities at the appropriate times to optimise growth, yield and therefore financial returns,” the spokesperson concluded.



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