New figures from the Department for Environment Food and Rural Affairs (Defra) have indicated that the national balance for phosphate (P) in England is in sharp and worrying decline.
According to the Potash Development Association (PDA), it is now only about 5% of the 230kt surplus from 1990.Â
While a net balance between nutrient inputs and outputs may be seen as ideal, the PDA said that this marginal surplus is an average for the country and does not give the true picture at an individual level.
It indicated that farm level balances are a better indication for each business.
While some, particularly those with livestock, are likely to find themselves still in a positive balance, this would suggest there are plenty of other businesses which are now in a deficit position.
Phosphate
While the published trend is for phosphate; all inputs and outputs, it is likely to be similar for potash (K) according to the PDA.
Despite UK soils usually containing large total quantities of phosphorus and potash, most of this will be unavailable in the short- to medium-term.
Whether an overreliance on soil buffering is behind the recent evidence showing a continued decline in P&K fertiliser use, or as is probably more likely, it is purely down to economics, either way it is a concerning trend.
Data from the British Survey of Fertiliser Practice show significant reductions in major nutrient use in Great Britain over the past 40 years.
The overall rate of fertiliser phosphate has decreased by around 67% and that of fertiliser potash by around 55%.
Meanwhile, rates of phosphate and potash application have remained greater in Scotland than in England and Wales.
Although this data does not include organic manure use, this would not make up the difference between what is removed and what is required as a large proportion of soils are continuing to fall into suboptimal levels of phosphate and potash.
Soils
According to the PDA, the latest data shows that around a quarter of all tillage soils are below the target level for P, K and magnesium (Mg), while the situation is even worse for grassland soils at 36-42%.
The argument for the economics regarding phosphate and potash applications can be more difficult than for nitrogen (N), as no direct yield response is likely if soils are at the target index level.
However, that does not mean there is no economic link. Optimal yields are only likely to be achievable where soils contain sufficient phosphorus and potassium in a readily available form.
Under these conditions, they are able to release enough of these nutrients into the soil solution on a daily basis to satisfy crop uptake requirements.
N is also likely to be used less efficiently where potash levels are suboptimal, reducing the returns from this valuable input and increasing the potential for negative environmental effects.
