Understanding soil fertility

By Dan Eskelson
Reader Columnist

Every garden season brings new insights and knowledge, so I hesitate to call myself a “master gardener”.  Presumed expertise is often shocked into submission by surprises and failures in the garden. One thing we can do to minimize problems and level out the bumps and valleys of our garden season is to understand and apply the principles soil fertility.Soil-fertility-bw

In a very fertile soil with plenty of organic matter, excellent drainage and perfect structure, additions of fertilizer would not be necessary. Unfortunately this perfect balance of soil fertility and plant food soil is seldom found, and even if found, will not remain perfect because of the loss of fertility through leaching, vaporization and use by plants.

So we need to amend our soils with ingredients that supply specific nutrients which can become available to plants. Plant nutrients in fertilizers are classified as major nutrients, secondary nutrients and micronutrients. The most important major nutrients are nitrogen (N), phosphorus (P) and potassium (K). Plants require these nutrients in relatively large amounts, and these are the nutrients most likely to be deficient for plant growth.

Other major nutrients, called secondary nutrients, are calcium (Ca), magnesium (Mg) and sulfur (S). They are also required in relatively large amounts but are less likely to be deficient. Micronutrients are essential for plant growth, but plants require relatively small amounts of them. They include boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn). These elements may also be referred to as minor or trace elements.

The debate continues to rage over which form of fertilizer is better, synthetic or natural. Proponents of synthetic fertilizers claim that all the essential elements can be supplied in greater quantity and at less cost than their natural counterparts.

Proponents of the natural organic fertilizers counter that indeed the synthetic fertilizers supply the chemical forms of the essential nutrients, but these materials, actually derived from crude oil, lack the necessary beneficial soil microorganisms that help to break down the nutrients into plant available forms.

It’s also been pointed out that the common overuse of chemical fertilizers has resulted in the buildup of harmful salts in the soil, excessive tissue growth resulting in weak plants susceptible to disease and insects, reduced drought tolerance and increased dependence on foreign oil.

Natural fertilizers like compost, manure, blood and bone meal, kelp, etc. all contribute to the quantity and health of beneficial bacteria, fungi and algae, which in turn benefit plant growth. An old adage among organic gardeners is “feed the soil, not the plants”.

In recent years a number of companies have developed granular, easily applied natural fertilizers consisting of mixtures of the traditional organic fertilizers listed above. These can be used in place of the “traditional” chemical or synthetic fertilizers.  Local nurseries carry a good selection of these products.

Yes, natural fertilizers are more expensive because the raw ingredients are not as plentiful and preparation is more involved. An analogy is useful to explain the difference: you can get a burger and fries at the fast food place, or enjoy a well prepared meal of fresh ingredients at a quality restaurant. You’ll save a bit of money at the fast food place, but you may not be happy with the long term effects of regular meals there.

The prepared products mentioned above should not be used as a substitute for general soil improvement. Bulk compost and manures should be used as soil amendments when planting new gardens and landscapes and when mulching established plantings. In addition to supplying essential nutrients, these materials will add to the store of beneficial organisms, increase soil humus and improve the structure of both clay and sandy soils.

I’ve used natural fertilizers since the 1960’s and have found no reason to do otherwise. It’s good to know that I’m feeding my soil without  adverse effects to our planet.

Garden Questions? Visit http://clearwaterlandscapes.com/questions.

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