N still proving a popular chemical fertiliser
Many farmers were using 25% more than what was required, but there has been a huge cutback in N fertiliser since then without loss of production. The cutback was due to the rapid rise in fertiliser prices and nitrate restrictions. Figures indicate a reduction of 38% in fertiliser N usage since 2003.
With good quality clover swards such as at the Teagasc Solohead farm, 70 units of fertiliser N (including N for silage) are sufficient to support a stocking rate of at least 2.2 cows per hectare. This is higher than the rate that exists on most dairy farms depending on the chemical.
Based on research findings, many top farmers have moved away from using very high levels of N such as 300 units per acre. They found they can comfortably maintain a stocking rate of one livestock unit per acre, at 200 to 220 units of N per acre.
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 fertiliser spending.
Good quality ryegrass pastures and reseeds can utilise higher levels of N than poor quality old swards. Some farmers are using extra N to counteract poor grass swards, low pH or low P and K. This is a costly policy.
Analysis shows that a total of 300 to 350 units N per acre are required to support one cow per acre. However, background soil nitrogen should supply 100 units, and recycled dung and urine about 50 units, leaving a requirement for 200 to 220 units of the chemical per acre.
Of course, fertiliser N requirements can be reduced much further in clover-rich pastures.
Much of the very early applied N, and N that was applied after late September did not contribute to increased production. It may have made the grass greener, but reduces profitability, and may have posed a risk to the environment. Teagasc says there was more than sufficient N in the soil to meet potential growth demand from October to late February.
nNitrogen Utilisation: As distinct from other nutrients, the recovery and utilisation of applied N is very poor. Scientific calculations indicate that on dairy farms stocked at one 1,300-gallon cow per acre, with application of 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 1,300 gallon cows, 67% is recovered.
It is clearly important not to be using more N than is required.
