Soils responding to Sulphur on the increase
As industry in general has cleaned up its act in terms of the amounts of pollutants it is releasing into the atmosphere, this has had the knock on impact of reducing the amounts of sulphur being deposited on farmland.
Speaking at a recent Agricultural Science Association nitrates technical event Stan Lalor of Teagasc said: “In terms of sulphur there is a supply out of atmospheric deposition. Compared to the UK Ireland would never have been as high because we would not have had the same amount of industrialisation over the years.”
“However we would have still seen a reduction in sulphur deposition over the last 30 years. I would say to put a figure on this has fallen from 10 – 12kg/ha back to the current level 5-6kg/ha. There has been a decline in recent years but not to the same extent as in the UK.”
Lalor continued: “A lot of work was done on sulphur by Matt Murphy in Johnstown Castle in the 70’s and 80’s and a lot of the information we have goes back that far. He would have found at that time that 30 per cent of Ireland would require sulphur for optimum yield.”
“But potentially that might be increasing. If in the 80’s research showed 30 per cent of samples might respond to sulphur. Potentially that could now be higher given the fact we have reduced atmospheric deposition levels.”
According to Lalor, sulphur basically is required by plants because it is closely associated with nitrogen use. He said: “Both nitrogen and sulphur are key components in the amino acids that make up protein. For every 12kg of nitrogen in a crop, there will be 1kg of sulphur. Sulphur will be required in that kind of ratio.”
Lalor commented: “Unfortunately there has been a little less focus on sulphur because there is no soil test for it. Because as is the case with nitrogen it is not as easy to predict soil sulphur requirements as for P and K.”
However, Lalor then pointed to the results of the work on soil texture, indicating that lighter textured soils will be the ones who respond very strongly to sulphur.
He cited: “Lighter, free draining soils particularly those going back into grass from a long time in tillage will usually have a very good response to sulphur.”
Advice on Sulphur.
Lalor advised: “For silage, sulphur should be applied at 20kg/ha per cut. In grazed swards it should be applied at 20kg/ha per year.”
When to apply
He said: “For silage it will go out with the N. But for grazing you’re talking about splitting that 20kg/ha per year across the summer from late spring up until July.”
Lalor stressed: “If farmers haven’t used sulphur before. I would always advise a little bit of caution. Sulphur can be associated with trace elements particularly selenium and copper.
“There is the potential to over do sulphur. So it important to be careful with the application rates,” he concluded.