Friday, April 3, 2009

Landscape and Turf - Soil Health

The following is information on soil health, a term used to describe those biological, chemical, and physical characteristics of soils that promote good plant growth.

According to the Cornell Soil Health group, “soil health describes the capacity of a soil to be used productively without adversely affecting its future productivity, the ecosystem or the environment.” Soil health emphasizes the integration of biological with chemical and physical measures of soil quality that affect plant growth and the environment.

From a biological standpoint, soil health relates directly to the root environment and organisms that inhabit the soil. A healthy soil will be one that has few limits to root growth; supports high numbers of beneficial soil organisms such as earthworms; supports a diverse microbial community with high levels of beneficial bacteria, fungi, actinomycetes, protozoa, and nematodes and low levels of plant pathogens (such as root rot fungi, bacterial and fungal wilt organisms, soft rot bacteria, and plant parasitic nematodes). In a healthy soil, plant root systems explore a large portion of the soil volume, plants are under reduced stress, and pest problems are minimal. A healthy soil will also support mineralization or organic matter by soil microorganisms at levels appropriate to the climate.

From a chemical standpoint, healthy soils will be at a proper pH (6.0-6.8 in most soils); have a high cation exchange capacity; have optimal levels of calcium, magnesium, and potassium held on exchange sites; contain optimal but not excessive levels of other mineral nutrients needed by plants, have high levels of organic matter in various levels of decomposition and high levels of stable humus; support aerobic mineralization processes; and be free of toxic minerals from natural sources (such as high free aluminum levels) or from toxic chemical contaminants.

From a physical standpoint, healthy soils will have high levels of stable aggregates in the topsoil (creating a stable granular structure); an optimal mix of pore sizes (macropores and micropores) so that it is well aerated in root zone, well drained, but also has a high available water holding capacity; and a low bulk density relative to the soil texture. They will be free of compaction which limits root growth. Healthy soils are highly permeable to water and not prone to crusting.

Gordon Johnson, Extension Horticulture Agent, UD, Kent County.

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