The great soil fertility deficit


The levels of infertility in our soils are astounding, writes Matt O’Keeffe.

The fertility deficit has been confirmed by the fertiliser industry and by Teagasc, as shown in their soil sampling results. Peter Ging, president of the The Fertilizer Association of Ireland sums up the situation: “Lime status on Irish soils is far below what is required for optimum productivity. If you don't have the soil pH correct then all the other inputs, including nitrogen, phosphate and potash, will not deliver their full value. The farmer will find himself in a position where he is only utilising three quarters of the fertiliser applied.”

Lime application halved in 40 years
Lime has been applied to Irish soils for generations. The hundreds of disused lime kilns scattered across the Irish landscape bear testimony to a deep understanding of the value of lime application by previous generations of farmers. In recent decades, however, lime application has decreased to the extent that the majority of Irish soils are at suboptimal pH levels. Forty years ago, the average annual lime application was running at around 1.7 million tonnes per annum. By the mid-1980s, however, that figure had halved, with only in the region of 800,000 tonnes applied on average each year. That’s reckoned to be about half of what is needed to maintain soil pH levels. While there has been some increase in lime spreading in recent years, the tonnages go nowhere near what is required. Soil samples analysed by Teagasc show that, on average, up to 60 per cent of grassland and tillage soils are below the optimum pH. In some regions, up to 80 per cent of soils are lime deficient. Unless these deficiencies are remedied in the years ahead, the ambition to lift our grassland productivity will not be achieved.

Irish soils at suboptimal fertility
There have been some limited improvements in the past couple of years. However, at the current rate of improvement it will take decades to bring the majority of soils up to optimum levels of fertility. Right now, as verified by Teagasc, 12 per cent of soils have optimum soil pH, P and K levels. That means soils with pH greater than 6.2, and soil phosphorus (P) and potassium (K) indexes of 3 or 4. To put those figures in stark context, Teagasc reckons that 88 per cent of the soils analysed have suboptimal levels of soil pH or P or K, or a combination of all three. Not only that, but studies of soil samples going back over the past decade prove conclusively that soil P and K levels are continuing to decline, with 63 per cent and 59 per cent of soils at index 1 and 2 for P and K, respectively. On grassland farms, the percentage of soils at K index 1 has increased from 11 per cent in 2014 to 22 per cent in 2017.
Some progress has been made. Soil pH has risen in the past 12 months to the stage where over 50 per cent of soils now have a pH of 6.2 or above. That still leaves forty-six per cent of soils below the optimum pH targets.

Countrywide soil fertility problems
A county-by-county analysis of Teagasc soil sample results show that there is widespread fertility deficits in soils across the country. In Monaghan last year, of 1,000 samples taken, 62 per cent were in P index 1 or 2, with one-third of the total in Index 1. Fifty per cent of the soils sampled were at K index 1 or 2. Over one-third of the samples showed pH levels below the necessary 6.2 pH status. Because of deficiencies in lime, P or K, or a combination of all three, a staggering 88 per cent of the thousand soil samples analysed for Monaghan last year showed suboptimal levels of fertility.
Moving south to Cork, the picture is no better in terms of soil fertility. Twenty-seven per cent of Cork soil samples last year had a soil P index of 1,with a further 29 per cent analysed as being at soil P index 2. Soil K measurements showed over 50 per cent to be at index 1 or 2; where 3 or 4 are recognised as the optimum levels needed for maximising productivity on the lands sampled.
In the heartland of Irish dairy farming it might have been expected that pH levels would be better than those found in Monaghan. In fact, the figures were considerably poorer with 43 per cent of the soils sampled showing pH levels below the necessary minimum of 6.2.

Cross-sectoral problem
Right across the country the story is the same, with suboptimal soil fertility levels endemic in every region and county. Neither do the figures vary greatly between dairy and drystock farms on average. Only 12 per cent of Irish soils are at optimum fertility. Even that figure somewhat flatters livestock farms because, on average, tillage farms tend to have higher soil fertility levels and these raise the overall fertility levels. There are various reasons for this, probably including land quality, the pressing importance of ensuring reasonable soil fertility to minimise crop deficiencies and also the likelihood that tillage farmers are, on average, better soil fertility managers than their livestock counterparts.

Remedial actions needed
At this stage it is not a matter of criticism. It is much more important to devise strategies to remedy the situation. Food Wise 2025 targets will not be achieved without greatly improving the fertility of our grassland farms. In addition, there will have to be considerable increases in productivity to offset stagnant and falling EU payments to farmers in the years ahead. Teagasc is prioritising the issue of soil sub-fertility as part of its programme to lift grass productivity through Grass 10. In addition, the advisory and research organisation is working in tandem with the Fertilizer Association of Ireland to improve soil fertility across the country. The lime and fertiliser manufacturers have been financially supportive of the Teagasc initiative with the express purpose of improving Ireland’s soil fertility status.

A sweet note
On a somewhat positive note, soil pH levels have improved on both dairy and drystock farms in 2017, entirely associated with an increase in lime spreading since 2012. The national figure is now tipping towards one million tonnes, a considerable increase on the previous decade, though far below what is required to deliver the kind of productivity improvements being sought on Irish grassland farms in the coming years.

Tags: Matt O'Keeffe soil infertility