Muriate of potash (MOP) can be applied at any time of the year and according to Teagasc is “an effective way to build soil K levels rapidly”.
On the latest Tillage Edge podcast Professor Mike McLaughlin discussed if MOP delivered harmful chlorine to soils.
Chlorine is toxic in soils, but chloride is not – and chlorine mainly exists in soils in the form of chloride according to Professor Mike McLaughlin, from the University of Adelaide.
Prof. McLaughlin who is a research professor in soil science at the University of Adelaide in Australia and who has collaborated for more than ten years on various soil projects in Teagasc, said there are a number of issues to consider in relation to MOP.
He said it is possible to get high concentrations of chloride around an MOP granule and as a result it is possible to get seedling burn with MOP.
Prof. McLaughlin added: MOP will not harm soil health. But there is an issue linked to seedling burn.
“We measure that using a salt index for fertilisers. This is particularly so when fertiliser is being delivered with seed. And, in such circumstances, it is important that the fertiliser has a low salt index.
“MOP has a high salt index, but when the total amount of chlorine going into the soil is assessed, chloride coming into the soil from atmospheric deposition is also important,” he warned.
Prof. McLaughlin also said it was important to be acutely aware of geographical location.
“Soils close to the coast in Ireland are pre-disposed to sea spray, which brings a lot of chloride and sulphate on to the land.
“So, the actual mass balance, depending on the soil system and its location, could see high levels of chloride coming in from the atmosphere,” he said.
According to Prof. McLaughlin, some ground waters also contain high levels of chloride.
“Adding muriate of potash to soils over time does not degrade soils because of chloride. It will leach very quickly from soils into aquifers, ground waters and rivers,” he stated.
Potassium
Ireland is home to a number of potassium (K) fixing soils with certain parts of Co. Meath an ideal example of this.
Prof. McLaughlin was asked during the podcast if there any steps that can be taken by farmers to minimise this process.
“Fixation of K is not as big a challenge as that associated with the fixing of phosphorous,” he said.
“But there are certain soils containing certain minerals with the ability to bind K,” he outlined.
“It’s a bit like the phosphorous scenario: If growers keep on adding muriate or sulphate of potash, eventually the ability of soils to fix K is reduced.
“While, initially, the inherent fixing ability of the soil may lock up a proportion of the added potash, over time a position of balance will be reached.
“At this stage, the efficiency of K usage will be quite high. Adding organic matter is always positive,” Prof. McLaughlin added.
He also said that it can help to improve a soil’s physical structure and quality.
“Organic matter is also a very valuable source of potassium, phosphorous and trace elements,” Prof. McLaughlin advised.