Dairy: Boosting soil pH can yield big results
Up to 60 units of free background nitrogen will be released by spreading lime on low pH soils -This was one of the key messages at a recent open day on the farm of Hugh Brennan, Dromcollogher, Co. Limerick.
When spreading compound fertiliser in a field which has a soil pH of 5.5 you are losing two thirds of the phosphorus and one third of the nitrogen due to fact that these nutrients are tied up in the soil and are not made available to the growing plant.
This means that if you spread a bag of 18.6.12 in a field with a soil pH of 5.5, then the reality is that you are really only getting the benefit of 12 units of nitrogen and 3 units of phosphorus. This is why correcting soil pH always comes ahead of correcting phosphorus and potassium deficiencies.
With all this in mind, trials have shown that by increasing soil pH from 5.5 to 6.3, an extra 2ton of dry matter per hectare can be grown.
Nationally we are spreading approximately 750,000t of lime annually. However, to rectify the fact that two thirds of our soils nationally are deficient in lime, this figure needs to be doubled. In the 1970s, our parents were spreading far in excess of 1.5 million tonnes annually. So why is this generation so reluctant to spread lime?
Ger O'Sullivan, Teagasc, Killarney recently carried out an in-depth study to find out the reasons as to why today's farmer is cautious about applying lime.
The study showed that the four main barriers that were preventing farmers from applying lime were: weather, paddock availability, interactions with other fertilisers and finances.