Compost: What Is It? Part 3
By John Ferguson
Fall 1997

Aerobic composting is the most common method of producing compost.  Aerobic compost is produced using two major methods, the windrow and static pile techniques.  Each method has its advantages, depending on one’s goals.

The windrow method was developed in the feedlots of West Texas and later for use in composting very wet material like biosolids (15-20% solids) from city wastewater treatment plants.  A windrow is a compost pile 5-6 feet tall, 8-10 feet wide, and several hundred feet long.  This pile is generally produced on a hard surface (asphalt or concrete) since special expensive machines called windrow turners are required to pass over the material, mixing it, every day.  The piles tend to get very hot (55º-65º C), which produces a lot of gases, resulting in large volume reduction of the material.  The gases include carbon dioxide (C02), water (H2O), ammonia (NH3), and many other compounds, some containing sulfur (S).  As you know, both NH3 and S are important plant nutrients.  Carbon (C) stored in the compost adds energy for beneficial microbes to feed on.  Hence, if these components are lost, the compost can be of lower quality.  This method can produce compost in 4-6 weeks (or less) depending on the type of feedstocks.

The other method, called the “static pile” technique, is to form large piles from the feedstock.  These piles are commonly 12-15’ tall (high as a front end loader can reach) to over 100’ tall, 30-50’ wide to over 200’ wide, and can be any length the operator wants.  These piles are turned only 3-8 times during the production process, which can last from 6 months to 3 years.  The core of these piles can get very hot (55º C +) from the action of thermophilic bacteria, just as a windrow does, with the same gases produced.  However, as these gases move from the hot core of the pile to the cooler outer layers (mesophilic regions) the microbial population changes from bacterial to fungal.  The fungal species “eat” the nutrient-containing gases, converting them into amino acids, proteins, enzymes, etc., enriching the compost and preventing the loss of these beneficial chemicals.

Either method can produce compost that is beneficial for use in horticulture and agriculture.  Millions of people, from backyard gardeners to commercial growers and producers around the country, are now using compost successfully.  Recently we have seen growers like Gallo Winery and Fetzer Vineyards admit that the awards they have won were on organically grown grapes fertilized with compost.  Gallo has become the largest producer of compost in California since it has proven so profitable for them.  A couple of years ago Gary Logon of Indiana, a farmer using compost, won the national corn growing contest for best quality and highest yields.  Last year in Texas, cotton growers had one of the biggest crop failures in history from boll weevils, yet the farmers using compost did not suffer a crop failure and had good yields.

Researchers are now studying how to apply what we have learned about compost usage in field crops to bedding and container media for nurseries.  In the new issue of the journal HortScience (April 1997) the feature article was, Suppression of Plant Diseases by Composts.  This is a summary of research at Ohio State University using compost for disease control in potting media.  In future issues of the newsletter, as we continue our series on composts, we will continue to explore the factors related to compost utilization.