Whether it be saving first-cut silage or taking paddocks out of the rotation, it is important not to forget the nutrients this process removes from the soil.

The most important of which are phosphorus (P) and potassium (K). Nitrogen (N) is not as much of a concern, as it will have been spread prior to cutting and will be applied again afterwards. Instead, it’s P and K we need to hone in on and replenish after silage has been saved.

According to Teagasc, a typical bale of silage weighing 800kg fresh (200kg dry matter) contains 10 units of nitrogen (N), 1.6 units of P and 10 units of K.

So, depending on how many acres are being taken out for silage, substantial amounts of P and K can be removed.

To really hammer home that point, e.g. four/five bales an acre will remove around six to eight units of P/ac and 40/50 units of K/ac, Teagasc says.

Units of N, P and K removed per acre depending on number
of bales per acre. Data source: Teagasc

The importance of this cannot be underestimated, as a rough rule of thumb is that 50 units K/ac is enough to change a soil K index.

Therefore, it is important to remember that ‘what comes off the ground must go back on’, because if no slurry and only straight N, such as CAN or protected urea was applied before and after cutting the surplus bales, there will be a large shortage of P and K.

Regarding ground that has had silage taken from it, it is advised to apply slurry to put back what nutrients were taken off. If no slurry is available, a compound fertiliser can be used.

Units of N, P and K applied per acre in slurry depending on
slurry thickness and application rate. Data source: Teagasc