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Compost: There's More to It than Meets the Eye

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I've fielded many questions pertaining to composts and composting over the years. The demand for information on these topics has never been greater than today.

There are a few factors fueling this interest including a ready availability of feedstocks, the rising cost of synthetic fertilizers and an escalating demand for all things organic.

Wood fiber, animal manures and municipal biosolids constitute the primary feedstocks for commercial composting. All three are in abundant supply in the region. The carnage to trees caused by the recent ice storm in central and eastern Oklahoma resulted in countless tons of wood chips, much of which is being composted. The number of municipal composting facilities and the volume of waste composted by these facilities continue to increase in response to an ever increasing population. Millions of pounds of chicken litter are generated in eastern Oklahoma and western Arkansas each year, a significant amount of which is composted. The I-35 corridor between Oklahoma City and Dallas is home to one of the largest populations of horses in the world. Numerous piles of stall cleanings are composted on site and available to area residents.

Perhaps the major factor driving the interest in the use of compost as a soil conditioner and fertilizer is organics. Motivated out of a concern for the environment and/or personal health, many hobby gardeners and market gardeners are going organic.

Understand that there is more to compost than meets the eye and that not all composts are created equal!

Unlike chemical or synthetic fertilizers that are consistent industry-wide, composts vary greatly in terms of quality and consistency due to the wide range of feedstocks used and techniques employed in their manufacture and handling. To avoid problems, you will want to take a few precautionary measures prior to purchase.

Start by asking who, what, when, where and how. Who produced the compost? Do they have a good reputation? What feedstocks were used to make the compost and where did they come from? How was the compost managed?

One problem associated with compost generated from horse bedding is picloram contamination. Picloram, a component of Grazon herbicide, is routinely used to control broadleaf weeds in bermudagrass pastures. This chemical concentrates in the manure of horses fed contaminated hay. Picloram is resistant to degradation in the composting process and can cause damage when the compost is applied to vegetable crops even when detected in very low (parts per billion) concentrations. If there is a question about herbicide contamination, you can submit a sample of the compost to a lab for analysis (an expensive option), test the response of a tomato plant seeded or transplanted into a pot filled with the compost, or simply look for another source.

Visually inspect the compost. If feedstock materials are identifiable, then the compost has not been properly aged. When incorporated into the soil, the presence of debris such as twigs and roots can interfere with seedbed preparation and planting.

Identifiable weeds or weed parts, including bermudagrass rhizomes and stolons, mixed with the compost may indicate that weeds were allowed to grow on the surface of the pile or windrow prior to distribution. Weed-contaminated composts can also be contaminated with weed seed and should be avoided.

Last, but not least, you will want to submit a sample of compost to a lab for analysis. Ideally, the pile or windrow should be mixed prior to taking a sample to insure better uniformity. To collect a representative sample, take 12-18 sub- samples throughout the pile and mix thoroughly in a plastic bucket to form a composite sample. Submit a pint of the sample to a lab for analysis. Most labs equipped to analyze manure can analyze compost. Expect to pay around $40 for a complete analysis. For assistance in interpreting test results, refer to the U.S. Composting Council publication Field Guide for Compost Use. This publication also contains guidelines for using compost to produce vegetables and ornamental crops.