Archive for February 20, 2008

Something we haven’t seen for awhile – soil!

This post is by Master Gardener Dan Rockwell

We often hear that Iowa has some of the best soils in the world. Well what makes a good soil?

Iowa soils are great because of the tall grass prairie that covered much of the state 150 years ago. When we look at a tree, half is above the ground and half is below the ground, but when you look at prairie grass, 10% is above the ground and 90% represents the roots below the ground. That root system extends deep into a strata where the roots can extract valuable nutrients such as potassium and phosphorous and at the same time provide channels for rain water to enter deeply into the soil. As the roots die, they add organic matter to the soil, organic matter that provides nutrients that support a thriving biological community and gives the soil what farmers call tilth

 Tilth is a measure of soil structure.  A soil with good tilth has a structure that resists compaction and works well.  Good tilth is like good art, hard to define, but you know it when you see it.  This organic material in the soil represented a major storage of carbon.  In the last 100 years, we have plowed our soil eliminating the tall prairie grasses and significantly reducing the organic matter in the soil.  Plowing destroyed the organic matter by increasing the aeration of the soil, thereby increasing the rate of organic matter oxidation.  Some scientists believe that the destruction of soil organic matter has been a major contributor to the increase in carbon dioxide in the atmosphere.

So how can we make a good garden soil? One way is to incorporate organic matter into our garden and a good source of organic matter is compost. Compost is created by biologically converting our organic wastes (for example food scraps, grass clippings, and tree leaves) into a soil-like material. Compost mirrors the soil building properties of the tall grass prairie, and compost acts as a reservoir for nutrients, improves soil tilth, stores water and acts as a storage sink for carbon dioxide.  What a good way to improve your garden and decrease your carbon footprint! 

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