Growth rates have exceeded demand on many farms across the country once again, as the dry spell a couple of weeks ago fades into the distant memory for many farmers.
The high growth rates over the past few weeks, in most parts of the country, which have seen farms growing up on 100kg DM/ha, have presented farmers with the chance to take out excess paddocks for bales.
Although the unsettled weather has made it difficult to cut excess grass, when the opportunity does present itself, it should be taken.
Therefore, if a paddock is to be taken out of the rotation, it is important to remember that ‘what comes off the ground must go back on’.
According to Teagasc, a typical bale of silage weighing 800kg fresh (200kg dry matter) contains 10 units of nitrogen (N), 1.6 units of phosphorus (P) and 10 units of potassium (K).
Therefore, depending on the number of bales that are made, the amount of N, P and K that is removed can be big.
The amount of N, P and K removed from paddocks through baled silage can be substantial
Farmers should be more concerned about replacing the P and K lost more so than the N, as the N that is removed in the bales is not as much of a problem, due to the fact that N fertiliser is spread on the paddock before harvesting and afterwards for the next grazing.
So, more importantly, the P and K lost needs to be replenished. According to Teagasc, four-to-five bales/ac will remove around six-to-eight units of P/ac and 40-to-50 units of K/ac.
This is important, as a rough rule of thumb is that 50 units of K/ac is enough to change a soil K index.
The table (below) outlines the units of N, P and K removed per acre depending on the number of bales harvested per acre.
Data source: Teagasc
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 shortage of P and K in that paddock.
Teagasc recommends targeting slurry to these paddocks after cutting to replace these nutrients that have been removed. If no slurry is available a compound fertiliser can be used.