Compost Management on Organic Farms
On-farm composting of organic materials is commonly done using the following methods: 1) passive windrow composting method, 2) passively aerated windrow composting method, 3) aerated static windrow composting method, 4) turned windrow composting method, 5) in-vessel composting method, and 5) vermicomposting. The proper approach depends on the time to complete composting, the materials and volume to be decomposed, space available, the availability of resources (labor, finances, etc.), and the quality of finished product required.
Passive Windrow Composting Method
Passive windrow composting is a very low-cost approach requiring more land, but less labor and capital than other composting methods. Generally, material to be composted is collected and promptly piled into windrows, which remain untouched (See Figure 11.1). Farmers who use this method may or may not use a compost recipe, and they usually make no attempt to adjust moisture content, or the carbon-to-nitrogen (C:N) ratio.
Passively Aerated Windrow Composting Method
In the passively aerated windrow method, the pile is aerated with perforated pipes embedded in the bottom of the pile (See Figure 11.2). Aeration occurs as hot gases rise in the windrow—called the “chimney effect.” The pile should be 3 feet (1 m) high by 10 feet (3 m) long, with an insulating layer of finished compost on the bottom and top.
Aerated Static Windrow Composting Method
The aerated static windrow method does not mechanically agitate compost material to achieve the desired level of aeration. The pile is constructed above an air source such as, perforated plastic pipes, aeration cones, or a perforated floor; and aeration is accomplished either by forcing or drawing air through the compost pile (See Figure 11.3). This system of aeration requires electricity at the site and appropriate ventilation fans, ducts and monitoring equipment. The monitoring equipment determines the timing, duration and direction of airflow.
Turned Windrow Composting Method
In the turned windrow method, materials to be composted are laid out in windrows 3- to 12-feet (1 to 3.7 m) high by 10- to 20-feet (3 to 3.7 m) wide. Windrows operate by passive air movement. The rate of air exchange depends on windrow porosity. Thus in a windrow of light, fluffy material, the air exchange can be much higher than in one of a relatively dense material. Windrow size should be optimized to achieve good aerobic composting throughout the windrow. Windrow size is largely determined by the organic substrate to be composted and the turning equipment used for the turned windrow composting method. If the windrow is too large, the center of the pile will be anaerobic and bad odors will be released when the pile is turned. If the windrow is too small, it may lose heat too quickly and the pile will not achieve temperatures high enough to evaporate moisture and kill pathogens and weed seeds. For example, dense materials that allow less passive air movement in and out of the windrow are typically smaller windrows that are made of more porous materials.
In-vessel Composting Method
In-vessel composting combines processes from the turned pile and from the static pile techniques (See Figure 11.5). It overcomes disadvantages and utilizes good points of each method. In-vessel compost systems are high rate controlled aeration systems, which are designed to provide optimal composting conditions involving mechanical mixing of compost under controlled environmental conditions. Although various designs are available, the different systems are similar in that they are both capital and management intensive. In-vessel, or enclosed-vessel systems fall under three main categories:
Vermicomposting uses earthworms to process organic wastes. There are many variations and scales of vermicomposting systems, but they all maintain organic materials in an environment that is highly favorable for earthworms. Thus, the composting materials are maintained under high-moisture and well-aerated conditions and at ambient (less than 95°F, 35°C) temperatures. These composting systems generally operate best if the organic materials have been well macerated and mixed before being added to the vermicomposting system.
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