Farmers opting to take phosphate and potash (P and K) holidays over recent years may well see this impact negatively on Irish soil fertility levels.
This was one of the themes discussed by Teagasc’s Dr. David Wall during his presentation to a recent soil health webinar.
The event had been hosted by Teagasc to confirm the linkage between inherent soil fertility standards and Ireland’s ability to maintain current food output levels.
P and K
According to Wall, the reduction in P and K usage over the past couple of years is linked to the strong preference of Irish farmers for compound fertilisers.
The fall-off in the use of these fundamental soil nutrients is a direct consequence of farmers’ desire to reduce nitrogen (N) application rates. This followed in the wake of the price spike that impacted on the N market during 2022/2023.
According to David Wall, all farmers must commit to maximising the availability of the plant nutrients already in the soil.
“Soil N is free. Its availability, however, is very much pH dependent,” he explained.
“It has been shown that farmers can secure grass offtakes in the range of 4t to 6t of dry matter per acre, assuming that conditions permit the maximum availability of the nitrogen that is already in all soils.”
The Teagasc research scientist confirmed the direct link between soil management standards and the output achieved by farm businesses.
“Nitrogen and phosphorous are very active soil nutrients. They pose the greatest risk in terms of their potential escape into the atmosphere and the aquatic environment,” he added.
“Looking to the future, food output levels must be maintained while also reducing greenhouse gas emissions, improving water quality standards and protecting biodiversity.”
Specifically where N is concerned, David Wall pointed to the need for farmers to make best use of this plant nutrient and ensure that surplus levels remaining in the soil at the end of a growing season are kept to an absolute minimum.
“Both rainfall and denitrifying bacteria will consume surplus nitrogen,” he said.
“This represents a loss for the farm. The accompanying environmental impact of these processes can be measured courtesy of the quantities of N escaping to the atmosphere and water courses.”
N use efficiency in soil
Wall discussed a suite of measures that both grassland and tillage farmers can apply in order to improve N use efficiency within their businesses.
These include the use of low emission slurry spreading (LESS) systems, the establishment of clover in grass swards and the preferential use of protected urea as a chemical nitrogen source.
But, all of these are underpinned by the attainment of optimal soil fertility levels, with pH values a key driver in this context.