You are probably sitting there thinking – is this guy crazy? Compost is organic and so the brewed tea from compost or manure must also be organic. Read on and I just might convince you that compost tea is NOT very organic!
Compost Tea vs Manure Tea
Before I get started, let’s review some terms. There is both a manure tea and a compost tea. Since neither is a term used by the scientific community or governments the terms are not well defined and they are used to mean a variety of things.
Some proponents of the tea suggest that the term compost tea should only be used to refer to tea that is brewed with the addition of oxygen. Others don’t agree.
Consider that aged manure becomes compost. At what age is it still manure, and when does it become compost – hard to say. In fact so called finished compost made from manure is still mostly manure–complete composting takes many years (ref 1). So manure and compost are not all that different – they are both sources of organic material that contain nutrients needed by plants.
The tea can be made in two ways, as explained in my post called Compost Tea, with or without oxygen. These two methods do produce different results and the method of brewing is more important than the source of the organics.
A recent study compared ACT compost tea to using just compost and is described in Compost Tea – Does it Work?
What is in Compost Tea?
Compost tea is made by soaking manure or compost in water for a few days or weeks. The water becomes brown just like the tea you brew at home. Once the tea is ready, you remove the water leaving behind the nasty manure bits. The water is the tea and is used to water plants.
Some say this makes a ‘tremendous liquid fertilizer’, but as I discussed in the Compost Tea post, that is a highly exaggerated statement. I had a close look at the NPK values in the post Compost Tea NPK Values. So what is in the tea? To understand this we need to better understand manure.
Manure contains animal bedding – the hay and straw used to house the animals. Manure also contains a lot of undigested grass, hay and other feed given to the animal. This is especially true of horse manure since these animals have a very inefficient stomach. Manure also contains digested and partially digested material, as well as urine.
Urine is mostly water that contains soluble compounds. Soluble means that they dissolve in water. Think of the sugar in your tea. When water is added to the sugar, it dissolves in the water. It is still there, but you can’t see the solid form any more.
Nutrients like potassium, nitrate, nitrite etc are soluble and easily dissolve in the water during the brewing process. Simple sugars are also dissolved, just like in your home brewed tea. Phosphorous is notoriously insoluble. Most of it will remain as a solid in the manure and does not dissolve into the tea very well.
The vast majority of the manure is in the form of large molecules such as protein, starch, carbohydrates, fats etc. Large molecules like this are mostly not soluble. Your pasta does not dissolve when you cook it. The same is true for the undigested straw and grass left in the manure.
What this means is that the only thing that dissolves in the tea are simple molecules like the nutrients your plant needs.
Compost Tea is Not Really Organic!
Tea contains nitrates, nitrite, potassium and other minor minerals. It contains very few organic molecules since these are too large to dissolve in the water. They remain in the sludge at the bottom of the pail.
Since the nutrient molecules in tea are no different than the nutrients in commercial fertilizer which is considered to be non-organic, one must conclude that the manure tea is also non-organic.
It is true that the tea does contain some organic molecules, but that is never mentioned by the proponents of tea. The reality is that the vast majority of the ‘good’ organic value of manure or compost is sitting in the bottom of the pail and not in the tea.
Making manure tea is an ‘Organic Sin’. To better understand this, see my next post called Manure Tea is an Organic Sin.
1)What is Compost: https://www.gardenmyths.com/compost-compost/
2) Photo Source: Urban Organic Gardener