Soil Nutrition and Charles Darwin's Experiments

The North Central Louisiana Master Gardeners recently offered one of their spring seminars on Soil Nutrition at the Lincoln Parish Library. Two knowledgeable Master Gardeners and the LSU Agriculture Extension agent explained the fundamentals of soil composition, organic makeup and chemical composition. Now that spring is definitely in the air, it is time to start preparing your vegetable and flower beds for the growing season; it is crucial to remain mindful of the composition, condition and nutrition of your garden soil. Soon, North Central Master Gardeners, Ruston Farmers’ Market and local nurseries will tempt you with all kinds of plants to purchase. Therefore, you must make sure that the soil in your garden is ready to support the new additions that you acquire.

Once you have created a good soil mix with a balanced ratio of sand, clay and organic material, how do you maintain it to support healthy plant systems? Sand, silt and clay determine soil texture, but it is the organic materials consisting of microbes, fungi and decayed plant and animal matter that improve soil structure by forming aggregate. Organic matter also adds nutritional richness to the soil and without adequate nourishment, plants will not thrive. Soil which lacks nutrients will need to be improved by adding compost (decayed plant and vegetable matter). Organic mulch should be layered on gardens twice a year. Mulch doesn’t even have to be mixed in, just spread on the top soil, and it will gradually make its way down. Plants need minerals to grow, so a correct mix of nitrogen, phosphorus and potassium is crucial. Only a proper soil test will tell you exactly what kind of soil you have, be it acidic or alkaline, so the best way to know for sure is to do a test. You can obtain a free soil test kit at the Ag Center, containing detailed instructions on how to get soil samples. Once the lab results come back, the agent will help you interpret them and guide you as to the best fertilizer to use. Caution should be taken when using fertilizers. Too much can burn your plants.

The realization that all rich, composted soils have an abundance of earthworms rekindled my memories of a visit to Kent, England where I toured the country estate of naturalist Charles Darwin. Prior to the 19th Century it was thought that earthworms were largely pests; nuisances, inhabiting the dark underground. Before that visit, I hadn’t realized that it was Darwin who discovered that earthworms were actually creators of soil. Apparently, in the 1830s, he became fascinated by the worms in his extensive gardens at Downe House, where he and his family spent summers in the country away from London.

Darwin initiated a series of on-going experiments to determine what role the earthworm played in soil movement and enrichment. He observed that the worms ingested plant material which passed through their digestive system, eventually forming “casts” on elimination, rich in bacteria, nitrogen, calcium, magnesium, phosphorous and potassium . . .the richest of all humus material. Where the particles stuck together, the soil formed aggregate that aided soil structure as the movement of the worms turned and aerated the soil. One experimental observation area was measured over a thirty-year time period!

It was from these experiments that Darwin wrote The Formation of Vegetable Mould Through the Actions of Worms With Observations on Their Habits, published in 1881. Interestingly, this study sold even more copies than his most notable work, The Origin of Species, (1859)! So, it was actually Charles Darwin who first gave us an appreciation for what earthworms can do to enhance and enrich the soil.

It would be nice to leave it to the earthworms to condition the soil, but unfortunately they need a little help. You must do your part to ensure your garden soil has the structure, texture and nutrients needed to support new spring acquisitions.

This article is submitted by Mary Elleson, North Central Louisiana Master Gardener.

5/17/2019 2:37:20 PM
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