The surge in grass growth over the last three weeks has left a lot of grass on farms across the country, and cutting surplus paddocks for baled silage has been common practice over this period.
Grass growth has slowed down over the last week due to soil moisture deficits, but with scattered showers across the country and more rain forecasted, hopefully, grass growth will recover again.
Taking out surplus paddocks for bales is an effective measure to stay on top of grass during the grazing season, and maintaining quality in front of the cows as well as milk production.
When grass growth is at about 70kg of dry matter (DM)/ha/day, farmers need to be going through the rotation in 20 days in order to get back around to covers of 1,400kg/DM/ha, when the plant is at the three-leaf stage and full of quality.
However, if the rotation goes over this length – which very easily happens at times of high growth – quality begins to become an issue and the cows can go back in their milk when grazing stemmy, low quality, heavy covers.
Many farmers made the decision to take out paddocks for bales in order to keep this quality grass ahead of the cows, which has proved very effective, but whatever comes off those paddocks needs to be replaced.
Replacing nutrients on surplus paddocks
Once surplus paddocks have been cut, the nutrients that were taken off need to be replaced straight away in order to get the paddock back into the next rotation as soon as possible.
A typical bale of silage weighing 800kg of fresh weight – which is 200kg of dry matter (DM) – contains 10 units of nitrogen (N), 1.6
units of phosphorus (P), and 10 units of potash (K), according to Teagasc.
N removed from these paddocks is generally not a problem, as these paddocks would have been applied with N fertiliser before cutting and again after cutting for the next grazing.
However, the P and K that is being removed also needs to be replaced and if four to five bales/acre are removed, then six to eight units of P/ac and 40-50 units of K/ac will be needed to replace the offtake.
It is crucial that this is replaced as, in general, 50 units of K/ac is enough to change a soil K index.
If these paddocks only receive protected urea after cutting, there will be a large shortage of P and K in the paddock and it will struggle to recover for the next round.
The N, P and K offtakes from certain covers are as follows:
Pre-cutting yield (kg DM/ha)
Bales/ac
N units/ac
P units/ac
K units/ac
1,500
3
30
4.8
30
2,000
4
40
6.4
40
2,500
5
50
8
50
Spreading slurry on these paddocks is the most economical way of replenishing these soils, However, farmers should get their slurry tested to know what rate to spread their slurry at.
Thick cattle slurry with a 6% DM, when using low emission slurry spreading (LESS), is six units of N, five units of P, and 32 units of K for every 1,000gal, but this may differ substantially from farm to farm and quite often dairy slurry tends to be lighter.
If slurry is not available on the farm, which may be the case for many farms after the dry spring that was experienced, a P and K compound should be used.
Farmers must ensure that they have a P allowance before spreading compounds, and an appropriate fertilising routine should be discussed with your adviser.
If there is no P allowance on the farm and you have no slurry in the yard, then a product like 19:0:15 plus sulphur (S) could be an option.
