Teagasc did a National Farm Survey on fertiliser use for 2005-2015. It detailed the average quantities of Nitrogen (N), Phosphorus (P) and Potassium (K) macro-nutrients and lime applied at farm level and the types of fertiliser used on grassland & tillage farms.

Trends in fertiliser use by nitrates zone, land use class, farm system, stocking rate and agri-environmental scheme participation were studied. Unfortunately the survey shows that there was a serious decline in the usage of fertilisers and only around 20% of farmers were using lime year-on-year.

Taking into account the increasing numbers of dairy cows, and a fodder crisis in 2018 there is an urgent need to increase and optimise the use of fertilisers and lime.

In 2010, we had just over one million dairy cows in the Republic of Ireland and in 2017 – we have about 1.4 million cows.

N application rates on grazing area were highest in 2005 at 82 kg ha-1, before declining by 15-30% to 57-70 kg ha-1 from 2008 to 2012.

P application rates on grazing area were also highest in 2005 (7 kg ha-1), before declining by 43-57% to 3-4 kg ha-1 between 2008 and 2012 and increasing again to 5 kg ha-1 by 2015..

K application rates were highest in 2005 at 15 kg ha-1, before declining by 47-60% from 2008 to 2012.

Higher application rates of N, P and K were generally associated with farms in nitrates zone A (South and East of the country), farms of wide land use potential, dairy farms and with higher stocking rates.

There was significant volatility in N application rates on silage area, with the lowest and highest application rates recorded in 2008 (96 kg ha-1) and 2013 (121 kg ha-1) respectively. The 2013 recovery was as a result of the poor weather in 2012 and resultant fodder crisis.

P application rates on silage ground were highest at the start and end of the study period (11-12 kg ha-1) but declined by between 25-42% to 7-9 kg ha-1 during the years 2008 to 10.

Overall, K application rates ranged from 17-25 kg ha-1, with the highest application rates in 2005 (25 kg ha-1) and the lowest in 2008 (17 kg ha-1).

N application rates on the main cereal crops (wheat, barley and oats) were highest at 158 kg ha-1 in 2015. This was 10% higher than starting period levels and nearly 20% higher than the low in 2008 of 133 kg ha-1.

P application rates on cereals were broadly similar at the start and end of the study period (25-27 kg ha-1) having dipped by 30% (18-19 kg ha-1) in 2009/2010.

K application rates were at a high of 80 kg ha-1 in 2015 up from 60 kg ha-1 in 2005. N application rates were 11 highest on winter crops.

Application rates of P over the study period were highest on winter and spring barley at 26 and 24 kg ha-1 respectively.

Average K application rates were highest across winter crops, with winter wheat and barley having similar average applications rates over the study period at 77 kg ha-1 followed by oats at 69 kg ha-1.

On average just over 20% of farms were using lime year-on-year over the study period. The lowest rate was in 2006 at 16% and the highest in 2013 at 26% of total farms. Higher rates were associated with farms of wide land use potential, dairy farms and higher stocking rates.

With high fertiliser costs it is vital that the correct rate is applied evenly, advises Dermot Forristal of the Teagasc.

If the incorrect rate is applied, grass or crop yield is lost or fertiliser is wasted, and crop or grass quality can be reduced. In cereals, crop lodging causes greater losses. Variations within the spreading width mean some of the crop gets too little, some too much.

Uneven spreading is obvious if green striping is seen in the crop or grass, but losses are also incurred at lower levels of unevenness where no striping is visible.

The cost of inaccurate spreading is difficult to estimate could be up to €80/ha so the increasing use of GPS system for precision application of crop nutrients is very welcome trend indeed.

These GPS equipped fertiliser spreaders are usually only available from agri contractors who are now using large machines for bulk spreading of fertilisers.

The use of a large machine is also making better use of scarce and expensive labour as farm contractors find it ever more difficult to source suitable machinery operators.