Soil - Agroecology: The Ecology of Sustainable Food Systems - page 110

Composts

Table 8.3
Organic Waste Materials Employed in the
Production of Compost
Agricultural By-Products

Compost amendment of soil is an attractive way to add
organic matter for a variety of reasons. The particle-size
distribution of compost favors uniform field application; the
ratio of carbon to nitrogen is optimal; compost is usually
free of weed seeds; and soil diseases are often suppressed
by compost addition (Chen et al., 2004). Many different
sources of organic materials, from manures to agricultural
by-products to lawn clippings, are being converted into
useful soil amendments through the composting process
(Figure 8.7). Under controlled conditions, raw organic mat-
ter goes through the first stages of decomposition and humi-
fication, so that when it is added to the soil, it has stabilized
considerably and can contribute more effectively to the
soil fertility-building process. In this way, wastes — includ-
ing materials that would otherwise go to already bulging
landfills — are being converted into resources (Table 8.3).
Vermicompost, or compost produced through the
action of worms, is also becoming a popular source of soil
organic matter, especially for smaller-scale farm and gar-
den systems. Fresh, wet organic matter, especially food
waste, is consumed by worms specifically known for their
composting ability (redworms such as Eisenia foetida are
especially good), and systems have been developed, where
a small household vermicomposting chamber can produce

Manures

Alfalfa leaf meal Feedlot beef cattle manure

Apple and grape pomace Dairy cattle manure

Blood meal Broiler chicken litter

Bone meal Laying chicken litter

Cottonseed meal Turkey litter

Feather meal Swine manure

Almond and walnut hulls Horse manure

Coffee pulp Sheep manure

Cocao pulp Goat manure

Soybean cakes
Rice hulls
Green garden and yard wastes

up to 25 kg of worm castings a month. These castings are
known for their high levels of phosphate, nitrogen, and
other nutrients, and also contain polysaccharides that glue
soil particles together and aid in soil organic matter devel-
opment. Cuban researchers have recently developed farm-
scale vermicomposting systems that are designed to
replace difficult-to-obtain imported fertilizers. Further
development of larger-scale systems could aid greatly in
improved soil management.

FIGURE 8.7 Farm wastes being turned into compost on a farm on the central coast of California. The breakdown of vegetative
matter by microorganisms releases significant amounts of energy in the form of heat.