Clover sward can replace two thirds of nitrogen at 1.25 acres per cow
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 Solo-head farm, 70 units of fertiliser N (including N for silage) are sufficient to support a stocking rate of at least two cows per hectare (1.25 acres per cow).
This is the stocking rate that exists on most dairy farms without clover swards.
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 one 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 fertiliser N costs.
Good ryegrass pastures and reseeds can utilise higher levels of N than poor old swards, and produce about twice as much grass.
Scientific analysis shows that 300 to 350 units of N per acre are required to support one cow per acre.
However, background soil should supply 100 units of N, and recycled dung and urine about 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, 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, 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 1,300 gallon cows, 67% is recovered. It is therefore extremely important not to be using more N than is required.
Soil tests will not show how much N should be used.
This will depend on farm output, crop history, soil type, etc. Early autumn P, K and lime applications are beneficial on areas that are very deficient in these nutrients. Otherwise sufficient P and K can usually be applied through the proper use of N compounds throughout the grazing season.
