To build up and use fertile Terra Preta, you can follow several methods. Below you will find three detailed descriptions of the most common methods. You can read only a specific one, if you already know what your interested in, or you can look at all of them.
We are going to follow the compost method on site.
The easiest, although not the fastest, method to produce Terra Preta is to amend your compost with biochar. For this you will need a compost bin to recycle your kitchen and garden waste. You also need 10-20% of the compost volume in biochar
The biochar needs to be crushed into bits no bigger than pea size. We recommend that you moisten the biochar before crushing, so it doesn’t stir up a lot of dust. Crushing can happen by just smashing it with heavy objects, such as rocks, logs or driving over it with a car. Just be careful not to hurt yourself.
When the biochar is being crushed, the individual pieces will naturally vary in sizes. This is a good thing, as the smallest coal particles can be transported deeper in the ground by rain.
Whenever you empty your organic kitchen waste onto the compost bin, simply pour some crushed biochar over it so that everything is lightly covered.
When your compost bin is full, wait six weeks and then turn it over. After another six to ten weeks your compost should have turned into Terra Preta and you can sieve it. This soil is loaded with nutrients and might burn the roots of some plants. You can either let it sit for a while to make sure this doesn’t happen, or you can mix it with soil that you want to fertilize. Some heavy feeding plants can be planted directly into the Terra Preta compost as soon as they are developed enough.
Features of this method
The quickest method of obtaining Terra Preta is to directly apply charcoal to your soil. However, if you where to do just that, your soil would become somewhat sparse for the course of one to two years. This is because biochar holds on to nutrients, especially nitrogen, and will be grabbing it from its surrounding. Thus, extra nitrogen needs to be provided.
You will need around 2kg crushed biochar per square meter of soil, a liquid source of nitrogen (for example cow or chicken manure, urine or organic fertilizer) and ideally -but not necessarily- effective microorganisms.
Start with mixing up to 10% microorganisms with the nitrogen source and add both to the crushed biochar. The biochar will absorb a lot of the liquid, so keep adding it until it is overall moist. Then distribute it evenly on your soil and work it in the top 10-20cm.Water your soil lightly and after a day you can start planting.
To load your biochar with nitrogen, you can also cover the floor of a chicken coop or cowshed.This way so the animals defecate directly on it and you only need to collect you nitrogen loaded coal and mix ist into your earth.
Features of this method
This is the preferred but at the same time the most complicated method to recycle organic kitchen waste. It uses a bin that you can either buy or make yourself (Link following). You will need said bin, crushed biochar, something to compress the waste, effective microorganisms and a spray bottle for them. The effective microorganisms need anaerobic conditions, which means that you should open the bin only once a day. Collect your organic waste over the day and in the evening add it to the bokashi.
Start by cutting your waste into smaller bits and build a layer in the bin. Then spray it a few times with the microorganisms and cover everything with crushed charcoal, so that the layer underneath is barely visible. Then compress the whole thing, for example with a wooden block. This helps the process. Repeat until all your waste of the day is processed, then vlose the lid airtight. After a while, it should smell sour-fruity when you open the bin. If it smells rotten, there might have been air entering the bin. If this is the case, discard the contents.
The bin has a tap on the bottom, from which you can pour a sour-smelling liquid, that the bokashi will start to produce after a few days. You can dilute this 1:100 with water and fertilize your plants with.
When the bin is full, leave it closed for about six weeks. After that it should have formed a white to orange mold layer on top. This is a sign, that its finished. Amend your soil with the bokashi four to six weeks prior to planting or work it in the soil 10-20cm away from existing plants. Although it might still look like fresh kitchen waste, the microorganisms have transformed it chemically and it will decompose in a matter of days once applied to soil.
Features of this method
We would only recommend this method to enthusiastic hobby gardeners