Teagasc researchers find high NFRV for soiled water
Results suggest that soiled water applied at 22kg of N/ha could replace 17kg of N/ha (CAN), while maintaining the same grass production.
A dairy farm of 100 cows produces around 600kg of N in soiled water annually. This could replace 480kg of fertiliser N, 570kg of K and 80kg of P (assuming 100% availability of K and P).
Assuming a CAN price at €330/tonne, muriate of potash (50%) at €450/tonne and superphosphate (16%) at €425/tonne gives savings of €575/year in N, €513 in K and €212 in P.
The total cost saving could be €1,300 per year to the farmer.
CAN and soiled water were assessed and compared in a field plot experiment on two grassland soils, one free-draining and the other poorly drained.
Researchers said soiled water should be applied in the May to August period to maximise uptake and yield response.
On average, soiled water applied from February to September had 80% NFRV, and a high NFRV on both soil types.
In contrast, NFRVs of only 15 to 50% are typically found for slurry, decreasing through the growing season.
Soiled water is more dilute and infiltrates better into the soil, reducing N losses (in the ammonia emitted to the air), and delivering N effectively, and more evenly, to the grass roots, apparently spreading N more evenly to a larger area of the sward, even compared to fertiliser pellets.
Soiled water application may also stimulate release of additional plant-available soil N.
Yields increased steadily with increasing soiled water application rate up to 22kg N/ha and then levelled out, suggesting that around 20kg N/ha (around 35,000 litres per hectare) may be an optimal application rate.
It was also found that substituting soiled water for fertiliser N during the growing season may decrease both nitrate leaching and nitrous oxide emissions — both potentially damaging to the environment.
Researchers at Moorepark have also found that treatment of soiled water with a woodchip filter followed by a sand filter, shows potential as a low-cost, minimal maintenance recycling system, to allow re-use of water to wash down yards, decreasing water usage and production of soiled water on farm.
Eventually, filtered soiled water and spent woodchips could be land-applied, supplying nutrients and organic matter to enhance soil fertility.
