Organic Matters (cont)
By: Carrie Chalmers
Testing Your Soil's Health
Laboratories now use the knowledge of the dynamic qualities of soil fertility and organic matter described here in their tests. Woods End Laboratory stresses the living nature of the soil and the value of tests to gauge soil health. Tests measure respiration in soil and compost samples, which indicates the rate of biological activity.
Woods End now markets a kit to determine compost maturity, and this spring, a kit is available to test garden-soil microbial activity. Wallace Laboratories of California and other labs test for heavy metals and salt levels as well as for nutrients and organic matter. Contaminated organic residues can cause high levels of the kinds of heavy metals that municipal sludge sometimes contains. Such metals accumulate over time and can be toxic to microorganisms, plants, and people. Good management of organic matter will ease these problems. Alan York, a market-grower in California who uses organic methods, encourages testing to develop "visual confidence." Establishing a baseline measurement for your soils allows you to identify deficient or excess nutrients and metals and gauge the results of your later soil-building efforts. Regular testing and evaluation of the results over several growing seasons allow you to rely more on observation and less on frequent testing.
Labs report wide variations in the quality and content of bagged compost and manure. When possible, buy from local sources and from manufacturers that label the ingredients. If you plan to use large quantities of compost or manure, test samples to see if the product is appropriate for your planned use. If they're to be used in a seed-starting or potting mix, large amounts may kill plants that need a mature soil amendment. Retesting may be necessary in the future if you're unsure whether the manufacturer has consistent criteria for its finished product.
Whether you buy organic amendments or use the ones in your garden, you must manage them the same way. Building organic matter in soils is a slow process, and it may be easier to maintain it than to replace it. The results are clear: using good amendments and growing practices enhances biological activity and conserves organic matter in your soil for the future.
Carrie Chalmers is a professional gardener in Weston, Vermont.
Photography by the National Gardening Association.