For a farm open day this spring, Teagasc researchers in Ireland spread the same quantity of the same slurry three different ways onto a demonstration area of grassland.
Only four weeks later, grass growth from two of them was nearly double the other one.
Reported by researcher Willian Conlan, the under-performer was splash-plate distribution. The best was trailing shoe with dribble hose a very close second. The differences in grass covers after four weeks’ regrowth were huge: – Splash Plate: 1,200KG DM/ha – Dribble hose: 2,100KG DM/ha – Trailing show: 2,200kg DM/ha
The explanation is elegantly simple, says Liz Russell from Envirosystems – “Minimal foliar contamination with slurry.
“Imagine spraying slurry onto your house windows. In addition to family disapproval, you’d spend the next few weeks living in semi-darkness until the window cleaner comes or there’s some particularly heavy rainfall to wash the opaque film off the glass.
“Likewise with grass, a surface layer of dried slurry reduces light energy reaching the leaves, thereby restricting photosynthesis.
“So if you want more grass regrowth from slurry – and who doesn’t – then look at alternative ways to spread slurry rather than spraying,” says Liz.
Also from Teagasc, Joe Kelleher adds: “Spreading slurry with a trailing shoe, dribble bar or injector system can reduce the ammonia emissions up to 97% of those emitted with a splash plate.”
Where the grassland receiving slurry is pasture, Mr Burchill also reports that cows can return to grazing after only two to three weeks following soil surface placement of slurry.
Those with experience of splash-plate distribution report that a five or six-week interval is advisable. Otherwise in silage crops, even a minimum of residual foliar contamination risks-high pathogen levels on cut grass. This would not only produce a poor, possibly butyric, fermentation but also make cows unwell or worse if bugs like Listeria or Clostridia, for example, were present.
In addition to this physical fine-tuning of slurry application, Liz says; microbial treatment can add another dimension of gains and safeguards, of which her company has much evidence.
“Seeding your slurry store with the right probiotic microbes in feeding soil with more aerobic and fewer anaerobic bacteria. This supports earthworms, invertebrates, and micro-organisms, on all of which a fertile and productive soil depends”.
EnviroSystems recommended a ‘Slurry Store To Money Store’ action list:
Organise trailing shoe or dribble hose application.
Manage storage for runny slurry – no more than 6% dry matter – so it soaks into the soil quickly
Analyse slurry and work out the right application rates in conjunction with bag fertiliser. Average quoted nutrient contents because they can mislead.
Look into how microbial treatment can improve slurry’s fertiliser value and free-flow consistency.
Finally, don’t apply too much slurry. Better too light at 1,500 gallons per acre (17 tonnes per hectare) and topped up from bagged fertiliser rather than overspending and spoiling the next cut.