Take a quick course in chemistry for your gardening needs

Published 11:00 am Friday, February 14, 2020

Chemistry was my nemesis in school. I hated chemistry and shamefully didn’t put in much effort on the subject.

Chemistry alone would have kept me off any dean’s list anywhere. But had I known the future bore the need to comprehend the basics of soil and fertilizer, I might have taken better notes or studied the book more often.

Long ago on-the-job training taught me about the 16 essential elements for plant growth. Plants get three from air, three from water and the rest from tiny mineral bits from former rocks plus decayed stuff in soil.

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Now I see some university folks claiming 17 elements, some going with 18 and others sticking with 16. The additions, legit or not, are cobalt and nickel.

We don’t fret with adding cobalt or nickel to fertilizer for farming or gardening just like we don’t add most of the other seven minor elements that are needed by plants in very tiny amounts. We bank on the natural mineral makeup of soil having enough of them. 

The element carbon is everywhere. Plants get oxygen and hydrogen from air and water. The rest come into plants from soil via roots. Well, roots carry the elements, aka nutrients, from below ground up to plants, but it is the much smaller root hairs that bring nutrients into roots.

These hairs actually increase the root surface area that can absorb soil water with its diluted minerals. Obviously roots do not take in solids like granular fertilizer, compost or natural organic matter. It all has to get to a liquid form for uptake by plant roots.

A typical healthy plant’s roots only come in direct contact with less than two percent of the soil within its root system. Therefore, absorption directly from soil is not the main way a plant is fed.

There are two other ways nutrients get into roots for upward transfer. The first is due to the upward pull of water by plants as they transpire and send water out of leaves into the air. This pull is the force that draws soil water into roots from the 98 percent of soil not touching roots.

The other natural process important in the soil-to-root movement of nutrients is a seeking of equilibrium of the concentration of elements and their compounds.

Nature makes it such that higher concentrations of these nutrients gravitate to areas of lower concentrations. Since roots are steadily sending nutrients up and away, concentrations are lower right at root surfaces. So nutrients, be they natural or added by us as fertilizer, move to roots to balance themselves out in soil. 

There are certainly other factors that determine how soil fertility is available to plants. Soil pH is a major one as is soil structure.

While none of us wants to till a pure clay soil, a certain amount of clay particles is important to hold silt and sand particles and their nutrients together for plant use.

Remember, plant roots don’t absorb solids and fire ants don’t swallow solids like grits. 


Terry Rector writes for the Warren County Soil and Water Conservation District.