Reduced fertiliser use to curb soil fertility

Soil fertility remained unchanged on drystock farms at just 13pc within the optimum range for pH, P and K. Photo: Picture posed

Ciaran Moran Twitter Email

February 07 2023 02:30 AM

Cuts to fertiliser use on the back of record high prices will run down soil nutrient reserves and result in declining soil fertility on farms, Teagasc has warned.

It comes as close to 60pc of grassland on drystock farms now has a lime requirement, a Teagasc review of 2022 soil test results has shown.

The results show that 47pc of dairy farm samples and 57pc 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 39pc of soils still remain below the target soil pH of greater than 6.5.

Teagasc has said early indications suggest that lime use in 2022 will exceed one million tonnes for the second year in a row.

Mark Plunkett, Soil and Plant Nutrition Specialist at Teagasc, said lime application is now a priority on grassland and tillage farms as there has been large reductions (-25pc) in the applications of both P and K fertilisers.

“Lime now has a major role to play in regulating the supply of soil N, P and K and the efficient use of applied nutrients in the form of cattle slurry and chemical fertilisers,” he said.

“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,” he said.

Overall, soil fertility showed some positive trends, with a stabilisation in proportion of soils with an overall optimum soil fertility for pH, P and K on both drystock and tillage farms, while improvement in soil fertility was shown on dairy farms in 2022.

All farm types showed an improvement in soil P and K fertility, with the exception of tillage farms, where soil K levels declined slightly for the first time in 11 years.

The soil samples from dairy farms indicate a 4pc increase in soils with optimum soil fertility to 20pc in total.

Soil with optimum fertility on tillage farms increased slightly to 19pc currently, while soil fertility remained unchanged on drystock farms at just 13pc within the optimum range for pH, P and K.

Dr David Wall, Soil Fertility Researcher at Teagasc, said farmers must be conscious of what has happened with fertiliser use on farms over the past year.

“Unfortunately, if reduced fertiliser (P & K) use continues during 2023, it will likely lead to further running down of soil nutrient reserves and declining soil fertility.

“These potential reductions in soil fertility will only be detected when these fields are resampled 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.”