Horticulture Principles and Practices

Moisture Supply
Water is required by microorganisms for decomposition. It is best to keep the moisture
content of the compost heap at 40–60 percent. If too wet, pieces of newspaper or wood chips
may be added to the heap to remove excess moisture. Too much of it may cause anaerobic
conditions to develop in the pile leading to foul odor, while too little slows decomposition.
Efforts should be made to provide moisture uniformly throughout the pile, accomplished by
moistening the material layer by layer as it is being piled and as needed. A well-moistened
compost heap material feels as moist as a wet sponge that has been wrung. Overwatering a
compost pile is a waste of water and also causes leaching of nutrients. Rain water is ideal for
watering since it contains useful microorganisms, minerals, and oxygen.
Size of Pile
An effective pile size is one that is manageable and self-insulating without causing
compaction in the layers. A large pile may cause overheating and anaerobic conditions
to prevail in the inner part, a situation that is detrimental to bacteria. A small pile, on the
other hand, may be overventilated and thus not be able to reach peak temperatures; it may
also require artificial insulation. Since a pile should be turned over regularly, a huge pile
may be unmanageable.
Aeration
A compost heap should be well ventilated for good growth of aerobic bacteria. A pile
may be built around ventilating pipes or a tube of wire mesh. Such a practice may be
necessary in methods where the pile is left unturned or turned infrequently.
Temperature Monitoring Heat is generated as a by-product of decomposition of
organic material by the microbes. The temperature at each point in time depends on how
much heat is being generated by the microbes and how much is lost to aeration. If well
constructed, a compost heap would attain a temperature of 40–45°C within two to three
days and drop as the decomposable material becomes depleted. Be sure to insert the
thermometer deep into the compost pile for a reliable measurement.
pH Compost decomposers operate best at a pH of neutral to slightly acid conditions
(pH = 5.5–8.0). Organic acids form at the start of the process of decomposition,
favoring the growth of fungi and breaking down lignin and cellulose. Once the organic
acids are neutralized, the mature compost heap would have a pH of 6–8. Aeration and
mixing of the heap are two practical ways of achieving a good pH in the compost heap.
Soil test kits may be used for pH monitoring. However, if the heap is moist, a pH paper
may suffice.
Odor A composting process will not be odor free. However, the presence of a foul
odor is an indication of improper composting environment. Ammonia gas indicates a low
C:N ratio, while a musty odor indicates a wet pile. These conditions may be corrected,
as previously suggested.
22.17 CONSTRUCTING OUTDOOR COMPOSTING SYSTEMS
Two critical factors to consider in constructing an outdoor composting unit are location
and container type and design.
Location
The compost site should be near the garden or a place where it is easy to manage. The pile
should not be allowed to dry out, so locating it in the shade in tropical areas is desirable. In
22.17 Constructing Outdoor Composting Systems 665