A new study has highlighted the benefit of a long-term liming strategy in arable rotations, with regular applications shown to significantly increase farm profitability.

Agricultural soils become acidic naturally and this leads to poor soil structure, lower nutrient use efficiency, lower crop performance and, ultimately, less profit for the farmer.

Lime applications used to be frequent in the UK when high levels of industrial sulphur dioxide were spewed into the atmosphere by industry, increasing soil acidification.

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Liming decline

Applications were also encouraged by a government liming subsidy before the UK joined the European Community in 1973.

As sulphur dioxide levels dropped and the liming subsidy was scrapped, lime applications declined.

So much so that since 2000, less than 2m tonnes of agricultural lime were produced and used, compared with between 3m and 4m tonnes in the 1980s and 1990s.

Furthermore, a recent survey suggested 41% of arable soils in the UK are below 6.5 – seen as the optimum soil pH for most arable crops – due to land being inadequately limed.

The main reason behind the decline is cost, but a recently published study shows that growers chasing short-term savings could be robbing themselves of significant long-term financial gains.

Long-term liming strategy

Jonathan Holland, researcher at the James Hutton Institute in Dundee, had previously shown the benefits of liming on yield of some crops using data from long-term trials at Rothamsted Research’s Harpenden and Woburn sites between 1962 and 1996.

However, to make a more compelling case for a long-term liming strategy, an economic analysis was needed, so he teamed up with agricultural economics expert Karl Behrendt of Harper Adams University to crunch the numbers.

They used current crop price and production cost information from the 2019 John Nix Pocketbook to calculate the impact of the various liming treatments (see box below) on crop gross margins and rotational profitability over time.

Returns

It took about 20 years before significant differences between treatments appeared, demonstrating that regular liming is rightly considered a beneficial long-term capital investment for growers.

The study also showed that higher rates of lime gave the best overall economic return on both sites, but maintaining regular applications was seen to be more important than the rate of lime in any single year.

Moreover, the economic benefit was not sensitive to the cost of liming, but the crop price received for harvested crop had a strong effect.

Although there were large differences on the impact of liming on yield and profitability between crops, overall, there was a £436/ha/year economic benefit of liming over not liming at Rothamsted and £208/ha/year at Woburn.

This reflected the difference in soil types between the two sites, with Rothamsted being a silty clay loam and Woburn a sandy loam.

Dr Holland says the analysis proves that the trend away from liming is putting a dent in overall farm income, something that will come under increasing pressure as direct payments are phased out in the years ahead.

Rotations

“Growers will need to focus on the fundamentals going forward and it’s vital not to forget the importance of lime, because it provides long-term benefits to both profitability and overall soil health,” says Dr Holland.

Prof Behrendt adds that when thinking about liming strategy, you have to be persistent to make it pay, and because some crops respond better to lime applications, rotation is a vital consideration in the strategy planning process.

“The next steps we are looking into is how we make those decisions for different farming systems on different soils types and under continually changing markets.

“Special consideration also needs to be given to the opportunities that variable-rate-application technology presents.”