20th April 2023
Boy, do we produce a lot of manure.
In the EU alone we produce 1400 million tonnes of manure (and that’s just the animals!)
This causes problems – think methane being released into the atmosphere, for example.
But it also has the potential for some serious benefits for our soil and ecosystems IF it is used correctly.
Now a new review has highlighted exactly what the benefits (and drawbacks) of manure are – and how we can use manure to maximum effect.
Benefits of manure
The benefits of manure are not just limited to nutrients and soil structure – as it can also be used to generate gas which can be used for electricity production.
Not mentioned in the study, but useful for thrifty gardeners, is the ability of manure to generate heat.
This can be used to heat greenhouses, generate enough heat to start off seedlings in the early spring AND keep plants going through the winter.
So what are the problems with manure?
All that waste can cause serious problems. In fact, in the EU livestock production causes:
- 80% of total ammonia emissions
- 10–17% of greenhouse gas (GHG) emissions
- 40–50% of diffuse nitrogen
- 70% of inorganic phosphorus
Storing large quantities of manure can also cause groundwater pollution. Nitrogen leaches into groundwater, while phosphorus can cause algal blooms.
Manure can also harbor pathogens such as e-coli, which are hazardous to human health.
And while it’s tempting to apply manure directly to the soil, uncomposted manure can contain heavy metals and an excess of nutrients, which can cause problems if the manure is over-applied.
Manure is also likely to contain weed seeds, and the additional weed control needed is likely to more than offset work saved by applying uncomposted manure.
How composting improves manure
Fortunately, composting manure overcomes many of its problems.
- The heat generated by composting can kill weed seeds.
- The composting process destroys pathogens.
- Composting manure can stabilize pH, improve electrical conductivity, and increase organic matter in the soil.
- Applying composted manure can increase pH, electrical conductivity, and organic matter content of the material, improving soil quality and fertility.
However, the scientists did note that adding compost to the soil was not a quick fix.
In contrast to artificial fertilizers, which tend to provide a quick shot of nutrients, manure compost helps provide a long-term benefit to the soil.
It does this by improving:
- Soil structure: Through water retention capacity, aeration and resistance to compaction and erosion.
- Soil chemical properties: By providing both macroelements (mainly nitrogen, phosphorus, and potassium) and microelements and stabilizing soil pH.
- Soil biological properties: By promoting beneficial microorganisms and enhancing soil fertility. These microorganisms help plants both by providing nutrients and by producing a hormone-like substance that promotes plant growth.
The researchers also warned farmers not to over-use compost – while sensible applications have major benefits, too much can actually harm the soil.
What wasn’t mentioned in the study, but which you have to be careful of, is the use of herbicides such as Aminopyralid or Clopyralid in manure.
Some herbicides can pass through the animals and the composting process, and damage plant growth.
That means that when you have finished composting your manure, it’s best to try growing a few plants like beans (which are susceptible to herbicide) before using the compost in quantity.
Goldan et al, 2023, Assessment of Manure Compost Used as Soil Amendment—A Review, MDPI.com