Soil fertility across Ireland remained stable in 2022, according to Teagasc. However, caution is advised going forward, particularly where fertiliser use is concerned.
A recent review of 2022 soil test results show that, for the second year running, the number of soil samples taken across Ireland has increased.
The largest increase in soil sample numbers was on drystock farms, which increased by 19% in 2022.
There was a stabilisation in proportion of soils with an overall optimum soil fertility for pH, phosphorous (P), and potassium (K) on both drystock and tillage farms, while improvement was shown on dairy farms in 2022.
This follows two years of decline in optimum levels of soil fertility on grassland farms.
All farm types showed an improvement in soil P and K fertility, with the exception of tillage farms, where soil K levels declined for the first time in 11 years.
The soil samples from dairy farms indicate a 4% increase in soils with optimum soil fertility, to 20% in total.
Soil with optimum fertility on tillage farms increased slightly to 19% currently, while soil fertility remained unchanged on drystock farms at just 13% within the optimum range for pH, P, and K.
Mark Plunkett, soil and plant nutrition specialist at Teagasc, said: “With 39% to 57% of our soils requiring lime application it is now a priority on grassland and tillage farms to apply lime based on soil analysis to optimise soil pH.
“At a time of large reductions of both P and K fertilisers, lime now has a major role to play in regulating the supply of soil nitrogen (N), P, and K, and the efficient use of applied nutrients in the form of cattle slurry and chemical fertilisers,” Plunkett added.
Soil pH levels have remained relatively unchanged but large deficits in lime application on grassland farms remain.
The soil test results show that 47% of dairy farm samples and 57% of dry-stock farm samples have pH levels below the target pH of greater than 6.3.
On tillage farms, overall soil pH levels are higher, yet 39% of soils still remain below the target soil pH of greater than 6.5.
Early indications suggest that lime use in 2022 will exceed 1 million tonnes for the second year in a row.
According to Teagasc, these lime applications will reduce the levels of soil acidity in the years ahead, but further correction of soil pH on farms will be critical to increase fertiliser use efficiency, especially where fertiliser P and K use has been reduced due to increasing cost of fertiliser in recent years.
Dr. David Wall, soil fertility researcher at Teagasc Johnstown Castle, said: “These soil test results indicate that national fertility levels have broadly held stable.
“However, we must be conscious of what has happened with fertiliser use on farms over the past year. Unfortunately, if reduced fertiliser [P and K] use continues during 2023 it will likely lead to further running down of soil nutrient reserves and declining soil fertility,” Dr. Wall added.
He explained: “These potential reductions in soil fertility will only be detected when these fields are re-sampled in a few years’ time.
“Soil fertility is a key driver of nitrogen use efficiency and crop yield, and plans must be put in place to protect the productivity of agricultural soils and long-term sustainability of farming businesses,” according to Dr. Wall.
Teagasc says that the impact of reduced use of P and K in 2022 is likely to show as reduced fertility in future years if this reduction is not reversed. Levels used in 2022 are unlikely to replace offtakes.