My experience this week raises an interesting question though: If watering with what was really just a bit diluted fertilizer on soil composed of pure compost caused nutrient deficiency, how are you supposed to grow organic tomatoes? My situation is a little unique, there is plenty of light, temperature and humidity are always optimal, the plants need a lot of nutrients because they are growing fast. But fast growth is desirable, and it seems the the nutrients in the compost (1.8% phosphorus by dry weight, I have the compost analysis report) are poorly soluble. This means you either need to add tons of water to leach them out and lots get wasted, or you need a more highly soluble nutrient source.
I propose an organic farm two nutrient loop for nitrogen and phosphorus. Nutrients are continually exported from the farm in the crop biomass, so these must be replaced.
Municipal compost, food scraps, manure can all be imported and processed in an anaerobic digester. The nitrogen is in a highly soluble form of ammonia in the liquid portion of the digester effluent. It’s also sterile and can be used as a liquid fertilizer. The solids will contain some nitrogen, but also cellulose which can not be easily broken down in anaerobic digestion, and phosphorus which is generally not as soluble. Methane bio-gas is produced as well which can be captured for fuel.
Wood waste, construction and demolition waste of wood and drywall can also be imported at low to no cost. In fact, construction waste disposal is an additional income stream. These contain phosphorous, calcium, sulfur, and cellulose but very little nitrogen. These can be pyrolyzed, along with the digestor solids to produce biochar and heat. The biochar will have very little nitrogen, but the other nutrients should be converted into a more soluble form.
By using these two waste streams, the farm has a supply of high nitrogen liquid fertilizer, and by leaching the biochar, a high phosphorous liquid fertilizer. The concentration of both will fluctuate depending on input streams, but the rate of application can be adjusted daily to avoid nutrient deficiency after measuring leaf phosphorous and nitrogen levels with a portable spectrometer.
The entire process is somewhat capital intensive, space for accepting waste is needed along with an anaerobic digestor and pyrolyzation furnace, and associated plumbing for collecting and distributing the resultant fertilizer. However, it also provides free heat, or heat and electricity with a generator, and is carbon emission negative if the biochar is returned to the soil. In some possible future, carbon capture credits may be valuable, but biochar is excellent for the soil fertility regardless.
This is not something we’re actively pursing at the moment. Greenhouse design is the current priority, but this system could fit in well with a solar greenhouse, even reducing the need for heavy insulation by using the waste heat.
Sun Aquasystems 