Soil, dirt, mud, clay they all refer to one of the most remarkable elements of creation, the skin of the Earth. In soil science, dirt is actually a dirty word when we think how precious it is, it is the foundation of life, we all come from it and go back to it. So where does it come from?
Soil is made of 2 major components:
1. Minerals: coming from broken pieces of rocks. Sand, silt and clay make the soil texture depending on their relative proportions.
2. Organic matter: plant and animal residues in various stages of decomposition and living organisms that reside in the soil. Soil is the most abundant ecosystems on Earth, composed by a majority of microbes which can go up to one billion cells per gram of soil. It is estimated that the number of species varies according to soil type, location and depth but it ranges from 50 000 per gram to over a million per gram.
What makes the soil content so important for our plants?
The organic matter in soils are fundamental to maintain various function such as structure, aggregating, biodiversity, water retention, absorption and retention for pollutants, buffering capacity, and the cycling and storage of plant nutrients.
The soil has the ability to provide the conditions required for plant growth by bringing plant nutrients, especially nitrogen, phosphorus, and sulfur, along with micronutrients. The micro organisms, aka the soldiers, reduces organic matter into basic elements before being consumed and used by plants, process called rotting.
From rotting to composting: Meet the soldiers
What we all know as composting is simply the rotting process of breaking down the complex organic matter in simple substances that plants can use as nutrients, but speeded up.
So what’s going on in your compost pile?
- Chef Soldiers: Microorganisms
Ferran Garcia-Pichel’s Lab
Our decomposition experts, take advantages of changing temperatures, moisture, oxygen and pH to transform our wastes in goodies for plants. Those microbes experts are 80-90% composed of bacteria and we have to differentiate the aerobic and anaerobic, the rest being mainly fungi.
So aerobic bacteria need oxygen and we want those, the anaerobic bacteria decompose without the use of oxygen and that’s what we don’t want. Why? Because they are slow and they stink.
Anaerobic bacteria includes ammonia like substances (amines), rotten eggs smell substance (hydrogen sulphide), cadaverine and putrescine. What a combo!!!
So if your compost stinks like a slimy rooting garbage now you know why. So what you need to do is just to oxygen the pile to shift the bacteria to aerobic.
Have you ever stick your fingers in your compost bins?… Probably not, I know right it looks gross and it’s moving…
Well if you wanna try you’ll probable notice the temperature, and how it changes. That is because bacteria have different preferences. Some like the coolest temperature, around 13°, why would you want to live in the cold, are they psycho? no they are psychrophiles bahaha yes yes that’s their real name. Other bacteria, the mesophiles, like to party between 20 to 35°C. And then we have the thermophiles that work between 40 to 70°C but only for few days (Those guys are the ones making the hot springs in Yellowstone sooooo colorful). Temperature changes at different decomposing phases, and the bacteria involved take actions when needed.
- Soldiers Macroorganisms
While Bacteria take care of the organic matter by using chemicals, the macroorganisms decompose in a physical way, they chomp and grind the large pieces in smaller bits.
So what are they ?
They are your worms, insects, bugs, spiders, slugs, beetles, ants, nematodes, snails, millipedes…
Earthworms are usually the popular ones, like the cool kids (just because their poop is gold for a gardener). Worms eat the organic matter, then the digestion made by enzymes and fermenting substances produces a fine grounded compost substance. The poop actually called casts, have high bacteria count, organic material, nitrogen, calcium, magnesium phosphorus and potassium. On top of that they are pooping machines, they can produce their own weight in castings each day.
Those cool kids are also great for mixing soil as they slighter through it and they work closely with the chief soldiers. Worms digest for bacteria and bacteria digest for worms, in the end, the worms eat the bacteria and the whole cycle continues… ho life !!!
What makes a good compost?
– Good rotation to allow all those party guys to make their jobs, with good level of oxygen.
– Good temperature and moisture.
– Good ration of carbon (source of energy for microbes) to nitrogen (protein production). Since all organic matter is made up of carbon and nitrogen, to optimize the performance it has been estimated by the compost scientists, yes this is a profession, a ratio of 25-30 parts carbon to 1 part of nitrogen.
If too much carbon, decomposition is slow, if nitrogen is high, it stinks. So how do you control this? Well wet/green wastes (fruits, veggies, grass clippings…) are rich in nitrogen, while dry/brown material (dried leaves, straw, and wood chips) are carbon rich. Every gardeners have to find their own balance, depending on where you live ratio can be different.
So why is it important to compost and not let our food going to landfills?
1. It improves your soil:
– It is a rich natural fertilizer, it returns nutrients to the soil to help maintain soil quality and fertility = no need to use chemicals.
– It improves texture and air circulation for heavier soils and helps increase the water retention for sandy soils.
– By providing nutrients it improves plant growth and lead to better yields.
2. Reduce Greenhouse Gases:
– When organic matter goes to landfills, it gets covered up and has to decompose without oxygen. So the problem is not the smell and the speed of the process, it’s that methane is released in the atmosphere, which is a greenhouse gas playing a major role along with CO2 in the greenhouse gases effect.
– On the other side, when organic matter is decomposed, CO2 is released but it is the type that is getting reabsorbed by plants (cf. my previous post about climate change).
3. To be honest, how cool is that to see the all process at home, from eating the food, through the process of decomposition back to your soil.
Let go to San Francisco for our feel good story
Composting is fully accepted in the SF culture, and everyone participates in composting. Well… not so much because SF people are crazy about our party soldiers but maybe because it is mandatory… under the San Francisco Mandatory Recycling and Composting Ordinance passed in 2009. Fines of up to $500 can be given for those who refuse to comply.
The mandates converts 600 tons of organics waste into nutrient-rich oil compost each DAY to be used in to produce food and wine. Farmers of the region can benefit of this through inexpensive and accessible compost at about 9 dollars per cubic yards.
They are trying to reach zero waste where everything is reduced, reused, recycled, composted and nothing goes to landfills or high temperature material incinerators.
SF manages to recycle and compost 80% of its wastes. This project was possible by offsetting the costs of the wastes collection by charging the consumers of $34-38 per residents per month, and by selling the recyclables and the compost. People can a get discount from their bill by the volume they diverted from the landfills.
SF restaurants offering take-out provide the food in fully compostable containers, so the whole box including leftover food can go straight into the compost bin. The city has also passed ordinances to ban polystyrene, styrofoam food containers, plastic bottles and plastics bags. Fees and penalties have been implemented for those who continues to use or sell these materials. By 2009 San Francisco had reached 94% compliance with its restaurants.
So what are we waiting for to fill up our cities with those cool soldiers?
Top photo from Surajith S, other photos from author of this blog.
Insam, H., de Bertoldi, M. (2007). Microbiology of the composting process L.F. Diaz, M. de Bertoldi, W. Bidlingmaier, E. Stentinford (Eds.), Compost Science and Technology. Waste Management Series, Elsevier Ltd., 25-48. doi: 10.1016/S1478-7482(07)80006-6
Insam, H., Franke-Whittle, I., Goerna, M. (2010). Microbes at Work. From Wastes to Resources. Springer Berlin Heidelberg. doi: 10.1007/978-3-642-04043-6