With sustainable farming initiatives crucial to the move towards carbon neutral livestock farming, a key strategy is making better use of slurry as a farm resource, while reducing its adverse environmental impact. The answer to improving slurry as a fertiliser and to reducing its effect on climate and the environment is to compost it.
We all recognise the phenomenal effect of composting dung, which converts it from smelly, rotting waste into a life-giving soil conditioner. Composting is a microbial process that converts dead vegetative matter into a living plant food that improves soil health. Dung composts naturally over time when exposed to air. The lack of oxygen in slurry tanks makes this process more challenging, which is where Digest-it gives support by providing both composting microbes that can operate under anaerobic conditions and their dependent nutrients. As such Digest-it is a liquid biological composting agent.
Independent research by the Kingshay Farming Trust showed that Digest-it treated dairy slurry had a 17.2% higher Nitrogen content after 8 weeks compared to Untreated slurry. This equates to an extra 4 units per 1000 galls. This result was statistically significant at a greater than 95% probability. In this trial "good" aerobic bacteria had increased by 34%, which helps to explain the Nitrogen increase, as the more volatile Ammoniacal Nitrogen fraction gets converted into the more stable Organic Nitrogen form. This trial, which was only conducted over a short 8-week period also reported a 13% reduction in the crust depth.
Ammonia is an insidious pollutant that causes acid rain and represent a health risk to both livestock and human operators. Legislation is in place for a significant reduction in Ammonia emissions by 2030.
Microbial changes observed in slurry treated with Digest-it would be expected to reduce Ammonia emissions. This hypothesis was tested in a 12-week trial at Mountbellew Agricultural College (2022), which involved daily ammonia gas concentrations being measured in two 50,000 gallon slurry tank that were designated either Untreated or Digest-it Treated. Over the 12-week trial Ammonia emissions from slurry treated with Digest-it were 31% lower compared to the Untreated Control. Over time the reduction in Ammonia gas progressively increased from 21% in month 1 to 27% in month 2 and 42% in month 3. This highly significant effect of Digest-it on Ammonia emissions provides confidence it can be an important strategic tool in reducing air pollution to meet national targets.
Long term grassland trials to measure the effects of Digest-it treated dairy slurry on grass dry matter yield have been conducted annually for the past 7 years (2017 - 2023) at the Devenish Dowth Research Farm in Co. Meath on a highly productive silage field (13 tonnes DM/ha/year), which from soil analysis had a satisfactory lime status, available P and K levels and mineral balance.
Dairy slurry was drawn from two 50,000 gall slurry tanks, either side of a winter shed central feed passage. One of the tanks was treated with Digest-it (1 litre per 5,000 gall slurry), while the other remained untreated. Untreated and Digest-it treated slurry was applied to trial plots in early spring at 2000 galls/acre. 1st cut silage DM yields were recorded in May of each year. In 2023, for the first time a further 2000 galls/acre of untreated and Digest-it treated slurry was applied after 1st cut and the effect on 2nd cut silage DM was measured.
Over the 7 year period the average response of 1st cut silage DM to Digest-it treated slurry was 19% or an extra 1.2 tonnes DM/ha. This is worth €215 per ha in additional net value. When in 2023 the combined effect of Digest on both 1st and 2nd cut silage DM was measured it amounted to an extra 2.1 tonnes DM /ha, worth an extra €376 per ha, which equates to a Return on Investment of 12.5:1.
The positive response of grass growth to Digest-it treated slurry is due to the combined effect of an improved slurry nutrient concentration and the impact of "good" microbes on boosting Nitrogen mineralisation from organic matter. Overall an improvement in Nitrogen Use Efficiency results.
As part of the long-term Digest-it evaluation a worm count was undertaken in October 2022 on the Untreated and Digest-it treated dairy slurry grass plots. Earthworms are considered to be the "canary in the mine" when it comes to assessing soil health. Results show Digest-it increased worm numbers by 36% compared to untreated slurry, which equates to an extra 1.0 million worms per ha. Worms play a vital role in carbon storage, nutrient cycling and building stable soil structures that support soil health and water infiltration. They also play a key role in increasing nitrogen mineralisation from organic matter, which is undoubtedly a crucial contributor to the increased grass yield from Digest-it treated slurry. Furthermore, the higher level of "good" microbes supplied by Digest-it treated slurry would have improved soil conditions for earthworms to thrive and contribute to soil health.
Digest-it is a liquid slurry additive and should be added to tanks at the start of winter housing at a rate of 1 x 20 litre drum per 100,000 galls slurry (1 litre per 5,000 galls slurry).
Estimate the amount of slurry to be produced through until tank draw down in late Jan/Feb and add the appropriate Digest-it volume, as a single dose. Digest-it can be poured directly onto slats, although it is advisable to dilute with water to get good coverage across the tank. Avoid dosing Digest-it at the point parlour washings enter the tank and in the immediate vicinity of robots.
Repeat Digest-it dosing following tank drawdown in spring to cover the period until tanks are emptied after 1st cut.
Slurry represents an economically important nutrient source for grassland production but is increasingly under pressure due to its adverse effects on water quality and ammonia emissions. Trial work reported here from research locations has demonstrated the efficacy of Digest-it to achieve key objectives of improving slurry fertiliser value, reduce ammonia emissions, increase worm numbers and soil health, and grow more grass. Digest-it has been shown to be an effective farm input to improve dairy economics and assist in meeting environmental targets, by making better use of farm based resources.
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