How to strike the right balance on soil nutrients
This year’s grass growth surge has seen greater activity in taking pasture that has gone too strong for grazing
With silage wagons and balers busy in Irish fields, farmers should not forget that whatever nutrients come out must go back into the ground.
Dr Stan Lalor from Grassland Agro gave advice on soil fertility and nutrient usage at Lakeland Agri grassland farm walk in Monaghan recently.
Approximately 200 farmers attended the event, with Lakeland Agri setting out the practical benefits of its RumiSmart Sustain programme for driving efficient farming practises.
Even one round of bales removes a lot more P and K from the field than grazing does, Dr Lalor said. This is because the cows recycle a lot of P and K in their dung and urine while grazing. When a field is cut and baled, all the nutrients in the grass are removed from the field.
"A simple rule is that is that for every four bales that go out of the gate, you need to put 1,000 gallons of slurry back in the gate. This will balance the P and K removed. In bales. You don't need to worry about the grass cover, or the field size… Just count the bales.
"So, if you have 20 bales from a paddock, you need to go back in with 5,000 gallons of slurry to replenish the P and K removed," he said.
"This means the fertiliser plan can be kept simple in line with the rest of the grazing ground for the rest of the year.
"Even if the slurry doesn't go out the day it is baled, it can be a guide to target a slurry application over the coming months, or even next spring."
In terms of the nutrients, Dr Lalor outlined that 1,000 gallons of thick slurry (7pc DM) is the equivalent to a 50kg bag of 5-5-30; but dilute, watery slurry (3.5pc DM) is closer to a bag of 5-3-15.
Dr Lalor also gave an overview of how farmers should approach fertiliser spreading over the course of the year.
"Farmers need to have a plan for their fertiliser and slurry usage… that starts with the soil pH and getting the right levels of lime after your soil tests," he said.
"Slurry is a free resource for most farms but it is a waste if it's going to the wrong fields. Target silage fields and low soil K fertility areas to get best value out of slurry."
When planning chemical fertiliser, Dr Lalor said farmers should look at the whole calendar year.
"When it comes to nitrogen, a good rule is a little and often throughout the year," he explained.
"Then you want to front-load your phosphorus early in the year. The biggest yield response to phosphorus will be in the spring so you want to be getting half or three-quarters of your P requirements in the first or second round fertiliser (application),"
He added that potassium should be targeted later in the year.
"Too much K early in the year can increase the risk of grass tetany," he said.
This year's grass growth surge has seen greater activity in taking pasture that has gone too strong for grazing
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