Organic matter returned to the soil replenishes nutrients, and improves or restores soil structure. It also feeds organisms that are food for many beneficial reptiles, birds, and mammals. Kitchen and garden waste, with natural recycling methods, can be converted into organic rich compost.
Essentials of Composting (1)
Air and Moisture Interactions (1)
Organic waste can be added directly to soil. Assuming there is a healthy soil biome, the organic matter will eventually breakdown. However, microorganisms consume nitrogen when digesting organics. Direct application can deplete nitrogen necessary for growing plants. Organics containing green or fibrous matter should therefore be added in the fall. The material will continue decomposing over dormant periods when temperatures are above freezing (see Figure 1) without competing with plants for nitrogen.
Direct applied mulches can include shredded leaves, partially composted materials from compost piles or bins, green cover crops tilled back into the soil, or kitchen scraps, such as coffee grounds and crushed eggshells.
Figure 1: Relative activity bacteria/fungi with 25 C° as baseline ratio 1 (4)
Large quantities of organic matter are best composted in a bin or pile (see Figures 2 and 3). Higher pile temperatures will develop, increasing rates of decomposition, which will assisting in destroying pathogens and weed seeds. The end result is fully or partially composted organics.
The level of decomposition achieved depends on the type and level of microbe activity. Aerobic micro and macro-organisms are preferred, to avoid noxious smells. Therefore, aeration is important. Aerobic organisms include both detritus feeders that break down the organics, and predator microbes, that feed on the detritus feeders. The microbe’s body wastes also become part of the compost.
Figure 2: Open compost pile, with adjacent enclosure for turning over (mixing and aerating) pile.
An open pile shown in Figure 2 allows mixing, promoting aerobic activity. It is open to precipitation, but the pile should be kept damp, not saturated.
A static pile uses an enclosure (Figure 3). Layering is essential as mixing cannot be done. Water must also be added. Layering promotes aeration in the composter, and balances carbon, supplied by brown matter, and nitrogen, supplied by green matter. Manure or garden soil is added to add microbes.
Figure 3: Enclosed compost bin. Note bottom access and air holes.
See Figure 4 for layering techniques.
Figure 4: Layering a Static Pile (2)
The ideal carbon to nitrogen ratio for composting is 30:1 (Figure 5). If carbon is higher, nitrogen fertilizer is added to feed the microbes. If nitrogen is higher, nitrogen can be lost through ammonia gas production, and anerobic activity can develop. More brown materials should be added in that case.
Material C:N ratios are shown below for various materials.
Figure 5: Carbon:Nitrogen effects on composting (3)
Table 1: Materials to Compost, Carbon Nitrogen Ratio and Limitations Associated with Each Material (3)
Composting is one thing we each can do to nurture our soil and to help the environment within our own back yards. Composting is also an important step towards future no-waste households, and sequesters carbon in the soil, an important tool towards limiting carbon emissions to everyone’s benefit.
Diana Westland
Mississauga Master Gardeners
Sources:
1 University of Arkansas Division of Agriculture Research and Extension, ‘Compost and Composting Resources’, https://www.uaex.edu/yard-garden/vegetables/compost.aspx
2 Healthy Home and Garden (April 21, 2019), ‘Backyard composting for a better, faster-growing garden’, https://www.northcarolinahealth.com/backyard-composting.php
3 Suzanne Smith Hirrel, Tom Riley, Dr. Craig R Andersen, ‘Composting’, University of Arkansas Division of Agriculture FSA2087-PD-1204R, https://www.uaex.edu/publications/pdf/FSA-2087.pdf
4 Janna Pietikainen, Marrie Pettersson, Erland Baath (March 2005), ‘Comparison of Temperature Effect on Soil Respiration and Bacterial and Fungal growth rates’, REMS Microbiology Ecology, Volume 52, Issue 1, March 2005, https://academic.oup.com/femsec/article/52/1/49/483427