Healthy soil and sustainable growing

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Soil Fertility Basics: Organic Matter by Steve Peters
http://www.seedsofchange.com/enewsletter/issue_20/issue_20.asp


The key to growing healthy, nutritious plants is maintaining fertile soil. 
Much more than dirt, garden soil is a richly complex ecosystem that is as 
dynamic and diverse as a tropical rainforest. Most soil activity, however, is 
invisible to the human eye so we tend to think of soil as merely a medium for 
holding up plants. Nothing could be further from the truth. A single gram of 
soil can host billions of living organisms!

Soil The most important component for sustaining a healthy, living soil is 
organic matter (OM). OM comprises all organic substances in varying stages of 
decay including plant roots, stems, and leaves, microorganisms, and added 
organic materials such as compost, manure, and straw. When organic matter 
reaches its most mature and stable form it is called humus, a dark and 
fragrant, nutrient rich substance essential for long term soil fertility. OM, 
and in particular humus, serves many vital purposes. It attracts and holds 
essential plant nutrients. It acts much like a sponge by retaining moisture. 
It produces vitamins, hormones, and other growth substances important for 
plant health. It is also critical for maintaining good soil structure by 
binding the mineral portion of the soil into loose aggregates. This permits 
air to reach the roots, allows for capillary movement of water, and enables 
roots to penetrate the soil.

Finally, and perhaps most significantly, organic matter is the food source 
for soil based organisms, including bacteria, fungi, actinomycetes, yeasts, 
soil-dwelling insects and earthworms. Without these living organisms plants 
would cease to exist. They perform a variety of critical processes including: 
1) Converting organic nitrogen, which is unusable to plants, into inorganic 
nitrogen compounds (ammonia and nitrates) which are available to plants; 2) 
fixing atmospheric nitrogen and making it available to plants; 3) producing 
organic acids that make mineral nutrients soluble and available to plants; 4) 
living symbiotically on plant roots and aiding the plant in the uptake of 
many important nutrients and growth substances; 5) preying on pathogenic 
organisms that would otherwise be detrimental; 6) contributing to soil 
aggregation by producing gum-like polysaccharides; and 7) producing carbon 
dioxide (CO2) which is released into the atmosphere and is essential for 
photosynthesis.

As a home gardener, the best way to increase the organic matter content of 
your soil is to add mature, high quality compost. Composting is that 
seemingly magical process that transforms raw organic residues into a stable, 
sweet-smelling earthy substance that contains a balanced blend of all the 
essential plant nutrients. Compost can be applied to the soil at almost any 
rate without fear of toxicity or loss of nutrients, although more frequent, 
smaller applications are preferred. Compost provides a slow and steady 
release of nutrients throughout the growing season, and can cure a variety of 
problems including high or low pH or a nutrient imbalance. Mature compost is 
particularly important in sandy soils which lack the ability to retain much 
water or nutrients.

Another important source of organic matter is >cover crops, which are grown 
specifically for soil improvement and are incorporated into the soil prior to 
growing vegetables and other garden plants. Cover crops can be grown any time 
of the year. Spring annuals (Oats and Triticale) are planted as soon as the 
soil can be worked in early spring. Summer annuals (Buckwheat, Cowpea, 
Sorghum) are grown only during frost-free months, while winter annuals 
(Austrian Winter Pea, Hairy Vetch, Winter Rye) are planted in late 
summer/early fall, overwinter, and resume growing the following spring. For 
longer term soil-building, biennials (Yellow Blossom Sweetclover) and 
perennials (Red Clover) can be grown. Cover crops are not as effective as 
compost for building humus, but they stimulate a greater amount of biological 
activity. In heavy clay soils, fresh cover crop residues may be preferred 
over compost because they help open up the soil and provide drainage.

Raw animal manures are not generally recommended for direct application to 
the garden because much of the nutrients are lost by leaching. They can also 
introduce unwanted weed seeds and pathogens, and can cause over-stimulated 
leafy growth because of excess available nitrogen. We recommend composting 
raw manures before putting them in the garden.

Steve PetersMany organic residues such as straw, leaves, and sawdust, are 
very high in carbon (C) relative to nitrogen (N). When incorporated into the 
soil, these materials will stimulate biological activity. The problem is, 
however, that because of a lack of N, the soil microorganisms tie up most of 
the available soil N, causing a nitrogen deficiency in plants. Eventually 
these microorganisms will die and release their N, but this could take weeks 
or months. Therefore, it is best not to incorporate these high-carbon 
residues into the soil but rather to use them in pathways, spread them as 
surface mulches, or to add them to your compost piles.

There are soil tests available through many cooperative extension services 
and private soil testing laboratories, which can give you an idea of the 
organic matter content of your soil. However, this is often not cost 
effective for the home gardener. A simple way to measure the biological 
activity in your soil is to measure CO2 respiration, which is associated with 
the breakdown of organic matter by soil microorganisms. Higher levels of 
biological activity in the soil reflect healthier soils, which provide 
essential plant nutrients like nitrogen and phosphorous. The Woods End 
Institute, a leading soil and compost quality laboratory, has developed a 
simple method for the home gardener to test for CO2 respiration in soil and 
compost. Please look for the Solvita Garden Care Test in our product 
offerings below.