This article appeared in the July/August 2001 issue of Horticulture Update, edited by Dr. Douglas F. Welsh, and produced by Extension Horticulture, Texas Agricultural Extension Service, The Texas A&M University System, College Station, Texas.
Humus - It's The Dirt !
It is easy to take soil for granted. After all, soil is almost everywhere. It literally comes with the territory when you buy a home or property. Soil may be largely dense sticky clay, thin gritty sand, or powdery silt. (Only the truly fortunate discover loose woodsy loam in the yard.) Whichever type, this existing soil constitutes the planting medium for the garden on the property. To improve its ability to support and nourish plants gardeners strive to improve its structure and boost its fertility. Fortunately, there is an abundant, inexpensive magic ingredient that makes this job a lot easier - humus (often referred to as just plain ‘organic matter’).
HUMUS CREATES SOIL.
It is not a coincidence that the word “humus” is part of every gardener’s vocabulary and that compost piles, one source of humus, are part of their gardens. Humus transmutes sterile dirt into fertile soil. Derived from organic matter of all kinds, humus is the life support system of soil. The presence of humus among mineral particles and air spaces enables soil to nurture plants two ways. Humus creates a loose structure that simultaneously holds moisture and drains well. Humus also creates an environment that supports living organisms that convert soil nutrients into a form plant roots can use, building soil fertility. In short, humus brings soil to life.
In nature humus is constantly introduced into soil as plant debris, dead animals, and other organic matter that decomposes on the ground. Through the alchemy of bacteria, fungi, and other resident micro-life activity, this organic material is reduced by degrees to its soft, spongy essence, called humus. It permeates the top few inches of the soil through rains and the good offices of earthworms and other macro-organisms, where it continually revitalizes the soil around plant roots. This natural cycle is repeated over the seasons out in the wild, sustaining the great forests and other natural areas. Where there is lots of vegetation to decay and enrich the soil, such as in woodland areas, the soil is rich in humus and very fertile. Where there is little or no vegetation to provide the organic debris, such as at the seashore or in the desert, the soil has little or no humus and is lean, infertile.
In developed areas, such as residential yards and gardens, where the natural vegetation has been removed or disturbed, this natural decay cycle is disrupted. Organic matter such as leaves, dried plant parts, prunings, animal remains, manures, and other debris is routinely removed before it can recycle into the soil. Intensive planting of crops, turf grasses, and ornamental plants rapidly depletes soil of its existing humus content. Bare soil in garden beds is exposed to the harsh effects of sun, wind and hard rains, which further reduce its humus content and destroy its structure and fertility. To grow plants successfully gardeners must emulate nature and constantly renew the soil by adding the depleted ingredient, humus.
HUMUS SOLVES SOIL PROBLEMS.
There is no such thing as perfect soil. Every soil has problems in structure, texture, and/or chemistry that compromise its ability to nurture plants. The best way to confirm suspected soil problems is to submit a soil sample for laboratory analysis through the local agricultural cooperative extension office. Their computer printouts profile the soil content and structure, pinpointing deficiencies. Fortunately, the addition of organic matter, or humus, can mitigate many of these problems. Here are six soil problems that can be addressed by adding humus.
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