Despite a significant drop in fertiliser usage by Irish farmers, scientists have discovered that many of them are still over-using fertiliser or are using too little for optimal production.
Teagasc, the agriculture and food development authority, found that between 1995 and 2000 22 per cent less phosphorous fertiliser was bought, 18 per cent less potash and 5 per cent less nitrogen.
Far less fertiliser was used on farms participating in the Rural Environment Protection Scheme (REPS) - half the nitrogen and 36 per cent less phosphorous than on non-REPS farms.
The survey, involving a representative sample of more than 1,100 farmers, found a wide variation in fertiliser application between different types of farms.
Teagasc researchers from the Johnstown Castle research centre in Wexford found that dairy farmers used almost four times as much nitrogen and nearly twice as much phosphorous and potash per hectare compared to sheep and cattle farmers.
They found that a growing number of farmers were following Teagasc scientific advice on fertiliser levels for grassland, silage and tillage crops. However, a significant number of farmers are over-using fertiliser or are using too little for optimal production.
The survey showed that the most intensive dairy farmers were using levels of nitrogen, phosphorus and potash on grassland in line with Teagasc recommendations. However, dairy farmers with lower stocking rates (less than 2.25 livestock units/hectare) were using more nitrogen than necessary while their levels of phosphorus and potash were below those recommended by Teagasc for optimal production.
Nitrogen applications by beef farmers were well below Teagasc recommended levels and the same was true of sheep farms.
They also found a significant swing by farmers to the use of compound fertilisers containing high nitrogen and lower phosphorous and potash levels.