Research finds that farmers are using 25% more N fertiliser than required
Many farmers were using 25% more than what was required, but with the rapid rise in the price of fertiliser and the Nitrate Directive restrictions there has been a huge cut back in N fertiliser without loss of production.
With good clover swards, such as in the Teagasc Solohead farm, 70 units of fertilizer N (including N for silage) are sufficient to support a stocking rate of at least 2 cows per hectare (1.25 acres per cow). This is the stocking rate that exists on most dairy farms with fertiliser N.
Based on research, many top farmers moved away from using very high level of N such as 300 units per acre. They found that at 200 to 220 units N per acre they can comfortably maintain a stocking rate of 1 livestock unit per 1 to 1.1 acres if the P, K and lime levels are correct. Animal performance is generally better because animals do not have to waste energy getting rid of excess N in the body and of course there is a substantial saving in fertilizer N costs. Good rye grass pastures and reseeds can utilize higher levels of N than poor old swards and produce about twice as much grass.
Currently, there is a trial at Clonakilty Agricultural College comparing grass pastures with grass/clover pastures both receiving normal levels of N fertiliser. At an early stage in this trial the grass/ clover pastures are performing significantly better than grass only pastures. For example cows on the grass/ clover pastures were producing an extra 2 litres milk per cow per day in early October this year.
A scientific analysis shows that a total of 300 to 350 units N. per acre are required to support 1 cow per acre. However background soil should supply 100 units N and recycled dung and urine around 50 units leaving a requirement for 200 to 220 units of fertiliser N/acre. Of course fertiliser N requirement can be reduced much further in clover rich pastures.
Teagasc work indicates that there is more than sufficient N in the soil to meet potential growth demand from October to late February.
As distinct from other nutrients the recovery and utilization of applied N is very poor. Scientific calculations indicate that on dairy farms stocked at one 1300 gallon cow per acre receiving 280 units of N per acre, only about 25% of the fertiliser and feed N is recovered in milk and meat.
At lower levels of N use (200 units) about 40% should be recovered while in the old REPS system with 1300 gallon cows, 67% is recovered.
It is therefore extremely important not to be using more N than is required.
