I grabbed this from a post by Mel Landers. It is a good update on the evolving practice of composting and biochar application. A lot of this has been influenced by terra preta in the Amazon. The point is that there is plenty of help out there with the many experiments been conducted. The results have been generally encouraging, even if most of these trials are examples of over kill.
That is fair though. The original terra preta was produced because stable households were established on a hectare or so of backyard garden over time scales that approached millennia and was at worst centuries. These backyards received everything.
Larger fields saw a modest inoculation of carbon to produce terra mulatto.
This was written as a response to contracts been established to recover market waste in several South American cities. The intent is to convert the material into salable compost improved with biochar rather than chemical fertilizer.
This is a good opportunity for you to evaluate what I have suggested for large scale production of dark earth soils. There would be no better organic compost/fertilizer/soil amendment than dark earth soil. You could compare the results with what you produce with your planned procedure. The addition of biochar after composting will lower its usefulness, as any nutrients that leach out during the process could be captured by the charred material during composting.
The addition of biocharr alone is still being suggested for the production of dark earth soils. Although the charred material will certainly make the soil a few shades darker, it will in no way produce anything close to the dark earth soils that were produced in the Amazon basin before the conquest. Charred material by itself is inadequate to provide a steady supply of nutrients for crops. A healthy soil includes a high amount of stable humus. The soils on my farm had a minimum of 5.8 % organic matter content. The dark earth soils have much higher than that and the main organic component is not charred material, but stable humus.
I would suggest, at the very least, a layer of charred material as a base of your compost pile, if you are going to use a hot process; although that would be difficult to maintain, considering the turning necessary in a hot compost system. I do not suggest a hot compost however. Besides, the nutrients lost to leaching, others are cooked away in a hot compost; especially the energy producing carbohydrates that would be used to produce stable humus in an anaerobic compost process. To me, humus is too valuable of a substance to just let its components speed up the decomposition process. It’s worth the wait for the more valuable compost that includes humus.
Please, take another look at the document I composed for the seminar entitled “Humus in the Tropics,” (I think!) it is a long document, but it will give you a better idea of the value of introducing humus into your customers soil. You could excerpt parts of it to make an argument for using a slower process to fulfill your contract, should you decide to use an anaerobic process to produce a compost high in stable humus.
I would suggest the following:
Source as much non-toxic organic waste as you can. If it is contaminated by microbes, O.K. but if there are chemicals…no need to go on. I don’t know what you might have in the way of dense organic matter there that could be charred. It may need to be shipped to you, preferably already charred. Get as much vegetative waste as you can and as much high sugar waste as well, such as fruit and vegetable skins left over from processing. Manure will probably be the easiest component for you to find nearby. It may be fairly high in sugars. Chicken manure is high in Nitrogen, but lower in sugars than cow manure, for instance. But, it is good to add to the mix.
If possible, reduce the biocharr to a powder, or at least finer than chunks. Put everything through a chipper shredder, adding a little of everything before starting back through the ingredients again; rough organic matter, soft organic matter, fruit and vegetable, fish waste, biochar, manure, bone meal…whatever you have. But, if you will be trying to produce a consistent product, make sure you add only what you are sure you have a steady supply of. Course sand would be a good addition to keep the materials loose. The dark earth soils of the Amazon are high in sand, due apparently from the scooping up of river muck during the dry season for its fertility.
Brewers waste would be a good addition as it would give you plenty of yeast in the mix. This will use the sugars to produce alcohol, which will turn to vinegar (ascetic acid). When you begin to smell the batch turning sour, cover it with an impermeable layer or put into a chamber to go into an anaerobic phase. It is this slow anaerobic decomposition which will produce the best compost; although it will take months to compost instead of the weeks it would take for a highly aerobic process. All the nutrients will remain in the biomass, absorbed by the biocharr and also by the large amount of humus which will have been produced by the anaerobic process.
Although worm manure is called lumbrihumus here in Latin America, it is not humus. Humus is produced by anaerobes over months of time, while long chain carbohydrates are exposed to their amazing glue like excrement. It does not glue the chains together. It actually causes chemical bonds to form., producing extremely complex carbohydrate molecules which are quite resistant to decomposition. Humus remains stable in soil for up to hundreds of years. Charred material remains stable in soil for up to thousands of years.
Charred material holds on to nutrients tighter than does humus. The two together are much more efficient as nutrient sinks for crop production. Acting in unison, they are vital for maximum production. But, whatever the soil amendment used, if the producer keeps disturbing the soil, production will not be at its maximum. The continual destruction of mycchorizal mycelia is common in modern agriculture, unless no-till is being used, Even then, fungicides and herbicides take a heavy toll on these fungi.
The other ingredient which is found in all the dark earth soils of the Amazon basin is pieces of fired clay. (in the form of broken pot shards) Fired clay is an even better chelating agent than charred material. When you notice the white film on the surface of flower pots, you know that mineral salts have been deposited in great quantity. But, there is much more inside the pot; in the micro-pores that form as the clay expands during firing. These fill with mineral salts as nutrient laden water passes across from one surface to the other. This can be duplicated in an anaerobic compost if fired clay is present. Somewhere in Europe there are mines that dig up clay bits that are quite similar to fired clay. These would be a great addition, if not too expensive. Broken pots or roof tiles, or ground used brick would work, if available. Though the compost should function well without the clay.
Raised beds are the best option in the field, built with your black earth, high organic matter soil incorporated with the native soil and covered by a thick layer of mulch, With tied ridges every five to six meters along these contoured beds, the producer can harvest 100% of the rain that falls, instead of the 7 – 8% that enters traditionally plowed soil.