How can you know if your soil is healthy? With all the different types of soils, from sandy to heavy clays, it’s not easy to determine the quality of any given soil without a laboratory analysis.

However, one almost universally good sign of a healthy soil can be easily seen with just a little digging—an abundant population of earthworms, said Peter Tomlinson, K-State Research and Extension environmental quality specialist. Taking steps to maintain and increase earthworm populations is one good way to celebrate Earth Day 2012 year-round, he said.

“The beneficial effects of earthworms on soil physical, chemical and biological properties have been observed for a long time by those who have studied and observed nature. For example, in 1881 Darwin published his observations on the importance of earthworm activity in the formation of vegetable compost,” Tomlinson said.   

Earthworms improve soil structure, which in turn improves soil porosity, aeration, water-holding capacity, the rate of water infiltration, and soil carbon accumulation, the K-State scientist explained. This helps prevent the soil from being eroded and degraded while protecting water quality, plant productivity, and the earth’s climate, he added.

How, exactly, do earthworms improve soil quality?

“The physical movement of soil as earthworms move through the soil creates an interconnected network of burrows. This is one way that soil porosity and aeration are improved. Earthworms also excrete a mixture of soil and organic matter, and these casts can develop into stable soil aggregates. Depending on the species the cast material may be deposited in the burrow or on the soil surface,” Tomlinson said.

The activity of earthworms accelerates decomposition of plant material and mineralization of soil organic matter, increasing the availability of plant available nutrients, he added.

There are some steps people can take to maintain or even increase earthworm populations, he said.

“Try to keep from disturbing the soil as much as possible. In agricultural fields, earthworm populations generally become reduced in cultivated fields,” he said. “When tillage practices are reduced or eliminated as a result of conversion to a minimal or no-till system, earthworm populations generally begin to increase.”

Other ways to encourage earthworm populations include soil testing and liming as needed to maintain optimal soil pH, and ensuring that sufficient organic matter is being returned to the system by minimizing plant residue removal and utilizing crop rotations, Tomlinson said.

It should be noted that as beneficial as earthworms are in most situations, they are not a panacea in all cases, however, he said.

“For example, where drain tiles have been installed to move water from poorly drained soils, earthworm burrows can actually become a problem by increasing the movement of fertilizer and chemicals more readily through the soil to the tile drains,” he noted.

In the vast majority of situations, earthworms can do much of the heavy lifting in improving soil quality and help you celebrate Earth Day in a meaningful way, he concluded.

There is a wide diversity of earthworms found in Kansas and the U.S, said Peter Tomlinson, K-State Research and Extension environmental quality specialist.

“There are nine families of earthworms found in North America. Of the nine families, three consist only of species native to North America, three consist only of non-native species, and three consist of both native and non-native species,” Tomlinson said

About 31 percent of the earthworms in North America are estimated to be non-native, he said.

“Earthworms native to North America are generally found only in soils south of the Wisconsinan glaciation, which is an area roughly south of a line from Montana through Iowa and the Midwestern states and into southern New York. In those areas, soils may have only native, only non-native, or a mixture of native and non-native species depending on land management. North of that line, the earthworms are non-native and primarily of European origin,” he explained

According to previous studies, where non-native earthworms are introduced into ecosystems inhabited by native earthworms, native species remain dominant or coexist in natural conditions, such as native prairies and forests, he said. However, non-native species became dominant as management intensity increased, such as managed pastures, or after soil disturbance occurs, he added.

The well-known “night crawler” (Lumbricus terrestris) is a non-native species introduced from Europe, he said. The discarding of earthworms used for fishing bait has introduced non-native earthworm species into forest ecosystems that either developed in the absence of earthworms (northern hardwood forests) or with the presence of native earthworms (Appalachian Mountains), Tomlinson said.

Earthworm species are generally grouped into three functional categories (epigeic, endogeic, and anecic) based on habitat, feeding, and behavior, he explained.

•Epigeic species live at the interface of plant residue and the mineral soil, do not form permanent burrows, and consume plant residue.

•Endogeic species inhabit mineral soil, do not form permanent burrows and consume organic matter associated with the mineral soil.

•Anecic species form and inhabit permanent burrow structures that extend from the soil surface into the mineral soil and feed on both plant residue and organic matter.

Endogeic and anecic species have been linked to improved soil structure and porosity, the K-State scientist said.

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