Johnstown-Castle-based, soil fertility specialist, Mark Plunkett, has been confirming the benefits of enhanced lime usage that has been recorded across Irish agriculture over recent years.
He addressed this specific issue, as part of his presentation to the recent soil health and fertility webinar, hosted recently by Teagasc.
However, there is a sting in the tail. According to Plunkett, soil fertility levels on Irish farms have started to tail-off over the last couple of years.
“This is a major concern. If we look at dairy farms, 50% of our soils need lime,” he said.
“Where drystock farmers are concerned, that figure is currently sitting at 65%. So something as basic as lime, which can deliver so many benefits, including improved nitrogen use efficiency, must be continually addressed.
“Grassland soils have an optimal pH value in the region 6.0 to 6.5. Where clover and multispecies swards are concerned, this figure rises to 6.5 to 6.8.
“And where tillage crops are concerned we are also looking at pH values in the range 6.5 to 6.8,” he added.
Tackling soil fertility
Research over many years has confirmed the use of ground limestone in raising soil pH values.
Plunkett explained: “Specifically, where grassland is concerned, farmers can release up to 70kg of nitrogen per hectare per year, simply by acting to improve spoil pH values.
“This is an annual release or turnover of nitrogen. And this feeds into reducing our chemical nitrogen target, which we have managed successfully to address over the past two years.”
Trials have also confirmed the strong correlation between enhanced soil pH values and phosphate utilisation by crops.
“Optimising soil pH values will also act to reduce greenhouse gas emission levels,” Plunkett further explained.
“Recent work undertaken at Johnstown Castle confirms that it is possible to reduce emissions by 38% if the soil pH is at its optimal value. This figure relates to a pH value in the range of 6.5 to 6.8, in terms of nitrous oxide.
“This is absolutely massive when one considers the low cost value of ground limestone,” he said.
The specialist explained that soil pH represents the “backbone” of all soil management strategies, when it comes to maximising inherent crop nutrient availability.
“We have been using one million tonnes of lime per annum over the last decade. This figure rose to 1.3 million tonnes in 2021 and 2022,” he said.
“However, this figure has fallen back in 2023 due to the fact that ground conditions were just so difficult throughout that entire year.”