What is compost?

com•post | ‘kåm-,pøst (noun)

: the product manufactured through the controlled aerobic, biological decomposition of biodegradable materials. The product has undergone mesophilic and thermophilic temperatures, which significantly reduces the viability of pathogens and weed seeds, and stabilizes the carbon such that it is beneficial to plant growth. Compost is typically used as a soil amendment, but may also contribute plant nutrients.

(US Composting Council)

How is it made?

Similar to putting together a recipe in your kitchen, compost is made by combining a specific mixture of feedstocks to create a biological reaction.

COMBINE FEEDSTOCKS

CARBON & NITROGEN

Commonly referred to as the “browns” and “greens” in a compost pile, carbon feedstocks such as wood chips, small limbs and branches, and decayed leaves are combined with nitrogen feedstocks such as manures and food waste. The combination of these two ingredients provide the necessary food source for microbes to break down. The recommended initial Carbon:Nitrogen Ratio (C:N) of a compost recipe is 25:1 - 40:1.

WATER

Water helps transport and support the functions of the microbes and is essential to maintaining moisture content targets for finished compost.

OXYGEN

Pile aeration is vital to the proper production of compost and can be controlled by pile porosity, compaction, moisture content, and mechanical forced air. Microbes consume oxygen within compost piles so new oxygen must constantly be introduced, otherwise bacteria can switch to anaerobic respiration and produce odors. Properly aerated piles allows for optimized composting and creates a final product with an earthy smell.

PILE SIZE

Compost piles must be sized properly in order to accommodate for a 1/2 to 1/3 reduction in volume during the compost process. Pile volume decreases as the feedstocks are broken down and the heat that is created by the microbes needs to continue to work its way through the pile in order to reach temperature requirements. In order to achieve the recommended temperature ranges for safe compost production, large volumes of feedstocks are required.

MICROBES GET TO WORK

MAGICAL MICROBES

The most active microbes in the composting process include bacteria, fungi, actinomycetes, protozoa, and rotifers, and there are around 3 trillion present in every handful of compost! These microbes consume feedstocks to obtain energy and nutrients, and the bi-product is heat.

MESOPHILIC, THERMOPHILIC, AND BACK AGAIN

During the composting process, piles reach three temperature stages. The first mesophilic phase will produce temperatures in the 68 - 104 degree F range while bacteria break down the available sugars, protein, and starches. This process continues to raise the temperature of the pile in to the thermophilic range with temperatures ranging between 105 - 150 degrees F so the fungi can take over. Heat-tolerant microbes go dormant, pathogens and weed seeds are destroyed, and complex carbohyrdates, fats, and proteins are fully broken down. Finally, the second mesophilic phase results in a drop in temperatures during the curing and maturation phase of the process while actinomycetes and fungi attack the most resistant compounds and stabilize the finished product.

THE FINAL STEPS

TIME

The appropriate amount of time required to create finished compost is dependent on many variables including the feedstock recipe, type of pile, and environmental conditions. Compost can take anywhere from one month to one year to be created, and it is the one factor of the composting process that can not be manipulated.

SCREENING

Screening compost allows for the creation of a consistent particle size. Not only does screening compost provide a more consistent particle size for the finished product, it also helps remove incidental contaminants or foreign material - such as trash and rocks - from the finished product.

ANALYSIS

Lab analysis of finished product will ensure high product quality, stability, and the absence of pathogens.

Why use compost?

Building healthy soils is a vital part of our food chain and ecosystem, and compost can play an integral role in that process when used correctly. Here are just a few of the benefits of using compost :

• Improves soil structure, porosity, and density, thus creating a better plant root environment.

• Increases water infiltration and retention thus reducing water use, erosion, and buffering the effects of drought.

• Supplies soils with significant quantities of organic matter, micro/macro nutrients and microorganisms to give plants all the nutrients they need to thrive.

• Suppresses weeds and pathogens, can bind and degrade pollutants and contaminants, and buffers soil pH.

What is the science?

PHYSICAL

IMPROVES SOIL STRUCTURE

Compost can greatly enhance the physical structure of soil with both immediate and long-term benefits. It helps stabilize soil density, reduces compaction, and improves workability. The soil-binding properties of compost due to its humus content help hold soil particles together, making them more resistant to erosion and reducing runoff.

IMPROVES MOISTURE MANAGEMENT

Increased drought resistance and more efficient water utilization are two major benefits of using compost. Heavy soils (such as Virginia red clay) amended with compost can see a major improvement in the ability for water to infiltrate and permeate through heavy soils, and sandy soils can facilitate moisture dispersion by allowing water to more readily move laterally from its point of application.

CHEMICAL

IMPROVES AND STABILIZES pH

In addition to altering soil pH (depending on the original pH of the native soil and compost), compost has the ability to buffer and stabilize soil pH, whereby it will more effectively resist pH change.

PROVIDES NUTRIENTS, BINDS CONTAMINANTS

A considerable variety of macro and micro nutrients are included in finished compost and are essential for plant growth. Compost is rich in a relatively stable source of organic matter and a large microbial population and provides these nutrients to soils in a slow-release form. Compost also has the ability to bind heavy metals and other contaminants, reducing their potential to leach or be absorbed by plant material. The same binding affect allows compost to be used as a filter media for storm water treatment in biofilter media and has been shown to minimize leaching of pesticides in soil systems.

INCREASES CATION EXCHANGE CAPACITY

Compost improves the cation exchange capacity of soils, enabling them to retain nutrients longer. Soil fertility is often tied to its organic matter content, and using compost allows plants to more effectively utilize nutrients while reducing nutrient loss by leaching.

BIOLOGICAL

PROVIDES SOIL BIOTA

Active soil organisms are essential to productive soils and healthy plants, and are largely based on the presence of organic matter. Microorganisms such as bacteria, protozoa, actinomycetes, and fungi play an important role in organic matter decomposition which leads to humus formation and nutrient availability. Sufficient levels of organic matter also encourage the growth of earthworms that further increase water infiltration and aeration through tunneling.

SUPPRESSES PLANT DISEASE

Disease incidence on many plants may be influenced by the level and type of organic matter and microorganisms present in the soils. Research has shown that increased populations of certain microorganisms may suppress specific plant diseases such as pythium and fusarium as well as nematodes.

[adapted from the United States Composting Council Factsheet]