ldquo;We know more about the dark side of the moon than we do about the Earth beneath our feet,” according to a new exhibit that opened at the Smithsonian's National Museum of Natural History in Washington, DC, last month.
The interactive exhibit, called Dig It! The Secrets of Soil, shows many reasons why soil is essential to life on earth. For instance, a great diversity of microorganisms live in it, comprising the soil food web; it is used to make everyday products; it filters water; and it stores and releases carbon dioxide, which influences climate. Included in the exhibit are soil profiles from all fifty states.
The exhibit will remain at the Smithsonian until January 2010, then it will travel to selected locations for several years.
And, for those of us enthralled by the mysteries of soil and the new science of ecological soil management that is helping to explain what organic gardeners have been doing for ages, it's about time for a major exhibit devoted to soil.
The conventional way to garden has been to get your soil tested, find out which major nutrients are lacking, and buy fertilizers with the required NPK (nitrogen, phosphorus, potassium) ratios. But this approach neglects the contributions of the soil microorganisms, which play such a large role in growing healthy plants.
It is the microorganisms in the soil that make nutrients biologically available to plant roots. The research of Roland Bunch and others has shown that roots need constant access to low levels of all nutrients, as provided by compost, rather than spikes of high-nutrient fertilizers. Moreover, high concentrations of nutrients may be harmful to the soil food web.
Compost, which is decomposed organic matter, has traditionally been regarded as a soil amendment so low in nutrients that its NPK (nitrogen, phosphorus, potassium) ratio is negligible. But in fact, a generous top dressing of compost, or an application of aerobically activated compost tea, delivers nutrients that soil microorganisms can use. The organic gardener's mantra “feed the soil, not the plants” reflects an understanding of the soil food web.
Of course, it's still a good idea to get your soil tested if you think it may have been contaminated with heavy metals such as lead, arsenic, or mercury, or to find out if your soil is deficient in significant minerals.
And you may want to use a balanced organic fertilizer with low NPK numbers to jump-start a new planting. But proponents of ecological soil management say that feeding the soil a balanced diet of compost will help your garden withstand stresses such as temperature swings better, help your plants become less susceptible to pests and diseases, and even make your vegetables more nutritious.
Along with compost, other important elements of Bunch's approach mimic the way a forest manages soils: using cover crops, intensive planting, and intercropping to increase production from a given space, keeping soil covered with mulch, and not tilling the soil.
© 2008 Tanya Kucak