According to a soil specialist based at the University of Adelaide in Australia, potassium (K) availability is linked to the moisture content of soils.
Prof. Mike McLaughlin made the comments on the most recent episode of the Tillage Edge podcast
He said: “There is a certain proportion of K that diffuses through the soils pores to the plant roots.
“When a soil is dry, diffusion through the soil will become quite tortuous.
“As a consequence, K deficiencies will often show up when there is a moisture limitation in the soil. This has actually happened in the past in Ireland.”
Moisture content of soils
Research has also shown that K levels in plants will also help them to withstand moisture deficits.
“Any stress on a plant is minimised by good nutrition. So crops that are under stress as a result of any nutrient deficiency will be more susceptible to disease, moisture stress and the impact of acidic conditions,” McLaughlin explained.
McLaughlin has previously researched the impact of phosphorous (P) nutrition on plants’ ability to punch into acidic sub-soils.
“We found that healthy crops are more capable of coping with these conditions,” he said.
The specialist also confirmed that adding P and K on a “little and often” basis to soils that have the ability to bind them up, is not the preferred fertiliser management strategy in these instances.
“Split applications of fertiliser work best for elements that are quite mobile through soil. These include N and sulphur,” he explained.
“With P and K, I used to be of the view that it is not feasible to side dress these elements.
“If they are applied to the soil surface, they tend to get a bit isolated. Recent research carried out in Canada on side dressed P and K has confirmed a direct response with maize.
“We need to look at this work in more detail. Climatic conditions throughout the growing season may well be an issue here,” he added.
The professor explained that some crops may also have feeder roots on the surface. These may be responsible for capturing P and K that have been applied as a side dressing.
“Generally, split dressings work best with fertilisers that are very mobile throughout a soil profile,” he said.
Phosphorus uptake
Where foliar applications of fertiliser are concerned, McLaughlin explained that P uptakes of up to 80% are achievable when this approach is taken.
“Plants are actually quite efficient in taking up P through their leaves.
“This was identified courtesy of a six-year research project that I was involved with in Australia.
“We did not do any work with foliar K. But I would imagine that this element can be transported into the leaf as well. The big issue is the amount of P and K that can be added in a foliar solution.
“Solubility of the P and K salts is an important factor. However, the added solutions must be quite dilute, otherwise they can burn the leaves of the crop,” he said.
A very salty solutions containing high levels of P and K will burn off the crops foliage accoridng to the specialist.
