To build or not to build soil fertility?
To build or not to build soil fertility was a question raised by Stan Lalor of Teagasc at a recent ASA technical event on the Nitrates Directive.
Lalor who is Research Officer in Johnstown Castle said: “It’s fine for me to say ‘right we should be targeting index one and two soils and all these fields in the country should be getting a lot of fertiliser to build them up to index three.’ But I think it is important to stand back and ask the question is that cost effective to build up P and K in particular in very situation.”
To put the question into context Lalor a study which has been running in Johnstown Castle since 1968. Highlighting Phosphorus (P) in particular he said: “One of the conclusions made from that study was it took 50kg of P surplus to change the soil test for phosphorus by 1mlg/litre. So if it takes 50 kg to move by 1mlg/litre it takes 125kg of phosphorus in that soil in Johnstown to move the soil test by one index.”
In terms of cost he outlined: “If you take that P costs €2kg that’s €250/ha just to raise P by one index. From index one to three that’s €500. It’s a significant amount of money. Farmers need to ask themselves are they going to get this back.”
Lalor commented: “A lot of drystock advisors have spoken to me and said they are looking at the profit monitor and see the fertiliser bill increased. But the bottom line hasn’t. It raises the question is it the right thing to do to build soil fertility and is there a return on the investment.”
Lalor was keen to say: “My answer would be what farmers need to be sure of it that you are fertilising a system that is going to use that extra grass.”
That’s the bottom line you need to be challenging the farm if soil fertility build up is an objective. The farm needs to be tested in terms of a system being put in place to utilise the extra grass that should result due to higher soil fertility.”