The use of compost as a soil amendment in San Francisco has the opportunity to make a significantly positive impact in the community by promoting healthy soils, increasing crop yields, and combating malnourishment. In addition, we hope to create a sustained source of income to support our work through the sale of the compost we produce.
Composting, the process of achieving decomposed organic material with high levels of microbial biodiversity and essential plant nutrients, is the truest form of recycling. With the help of various micro and macro-organisms such as bacteria, actinomycetes, fungi, earthworms, and other bugs, our undesirable organic materials can be processed into reusable raw materials. The composting process brakes down organic materials, cleans them – even sterilizing them of dangerous human and plant pathogens – and then converts the materials into plant-available nutrients and building blocks for good soil structure. The result of a well-managed composting system is the surest fertilizer in the world, and the best material to quickly rebuild topsoil and sustain soil fertility in San Francisco.
The community of San Francisco produces large amounts of organic materials, namely, plantain peals that can be used to make compost. Food scraps and yard wastes constitute approximately 76% of the waste generated by the community. That translates to about 1.5 metric tons of organic material per week if everyone in the community participates. Over the first two weeks of the collection schedule for organic materials (Monday, Wednesday, Friday) we have actually seen about 800 kilograms per week. This provides us with large amounts of decomposable materials that are ideal for the production of nutrient-rich compost for family gardens and local agricultural projects.
The last week of August we began our first compost pile using the GROW BIOINTENSIVE® method promoted by Ecology Action. This method is designed to simplify the composting process, does not require the use of animal manures, and nurtures a more uniform decomposition of the organic material, which results in less turning of the pile, perhaps only once. The steps we followed are explained below.
1. We first selected the site for the pile, at the southeastern corner of the composting site, and cleared away all the weeds and old stumps.
2. Next we marked off a 1.5m x 1.5m area.
3. We then used a pickax to open up the soil to a depth of 30cm. This will increase respiration and microbial migration between the soil and the compost pile, and assure adequate drainage. Canals will be dug later to prevent nutrient leaching during the rainy season.
4. Large sticks were then collected, broken up, and arranged in an 8cm layer over the tilled soil. This bulky material will increase airflow throughout the pile.
6. Next, a 5cm layer of fresh (green) material was spread evenly over the pile.
7. Using a shovel we then sifted about 1cm of the local topsoil to stimulate the microbial activity in the pile. We would prefer to use mature compost instead of the poor local topsoil, but until we make the compost ourselves we will have to use the locally available resource. Thankfully, the area was used as a family garden prior to our use and the topsoil has some organic material and the occasional earthworm, a good indicator of soil fertility.
9. We then repeat steps 6, 7 and 5, in that order, as we collect more organic material from homes. This process will continue until the pile attains a height of 1.2m, finishing it off with a final layer of dry material.
10. Finally, the pile will be soaked with water until it reaches field capacity. We however, have periodic deposits like most home-based composting systems and we pour water over the pile after each deposit, if available. Field capacity is the amount of water that can be held by the material, without running off, similar to sponge that will not drip, but will release water if squeezed.
11. Once the pile has reached a height of 1.2m the pile will be left to decompose for a period of three weeks or once the temperature of of the pile has begun to lower. After that time the pile will receive its first turning. Any further turnings will be determined through daily observation of the pile. We estimate that it will take approximately 4-8 weeks more, in our tropical climate, for the first pile of compost to be fully matured and ready for agricultural applications.
*Other composting methods will also be tested to see which works best for the available organic materials and climate. Please, if anyone out there has had any experience with composting large quantities of plantain peels we would love for you to share it with us.