Sustainable Gardening

Using Corn as an Example

By Robert Kourik

In a sustainable garden, the ultimate goal would be to eliminate all imported nutrients. Horse manure, cow manure, sacks of bone meal, blood meal, green sand, bat guano, phosphates, etc., all add additional fertility and qualify as “natural” or organic. However, each comes with various environmental costs attached, such as mining, transportation, energy use, and wasted bulk. Corn, as an example, needs lots of nitrogen in one form or another.

Blood Meal

Some gardeners use blood meal to increase the soil’s nitrogen. Here’s an example of the energy invested in making blood meal.

According to the Food and Agriculture Organization’s regulations, blood is introduced  into the processing tank as a coagulated mass, previously obtained by a steam-action process. (Not to mention the energy required to “grow” the blood.) Ideally, as much liquid as possible should be squeezed from the coagulum. Heating is initiated at 82°C (180°F) and progressively raised to 94°C (200°F) for about three hours, then elevated to 100°C (212°F) for 7 hours. (That’s a LOT of energy.) Drying is complete when the final moisture level in the dried product is about 12 percent.

[John Weaver dug up and drew countless roots in the early 1930s. He said that corn roots (Pictured here as the upper six inches of the root system as seen from above.) absorbs nitrates at all levels of the root system. Weaver thus deduces that localized application of fertilizers also localizes roots and prevents them from naturally ramifying (exploring) a larger volume of soil. The more soil explored by the roots, the greater the plant has the ability to absorb nutrients without concentrated fertilizers. Using green manures can fertilize the entire root system.

Green manuring means growing a legume crop such as fava beans, clover, and other legumes solely for the accumulation of nitrogen gathered from the atmosphere’s nitrogen in nodules located on its roots. One of the few legumes that produces enough nitrogen for hungry corn roots is alfalfa, at 250 pounds per acre. Till under the foliage before planting will increase this yield. Cut the green manure off before 10%-20% of the blossoms open. Wait several weeks for the soil’s microbes, root exudates, fungi, organic acids, and other compounds to digest the additional nitrogen. Before that the soil’s nitrogen is bound up in the bodies of the soil’s critters. Planting too early produces yellow foliage and poor growth. [NOTE: Could use this other illustration of the green manure content.]


Purplish strips at the edges of corn leaves usually indicates a deficiency in phosphorus. Some organic gardeners use colloidal phosphate as the solution to this deficiency, but consider this: colloidal phosphate is often strip-mined in Florida, washed with water (and Florida has a big problem with supplies of fresh water), loaded on train cars, and shipped to places as far away as California and Washington, where it’s sacked up and shipped to your local garden-supply store. Furthermore, only 20% of the bulk has available phosphate only 2-3% of soluble phosphate is available the first year.

Florida mines 75% of the phosphorous used by American farmers and about 25% of the entire world’s production. Phosphate ore must be chemically processed with sulfuric acid. When sulfuric acid reacts with the phosphate it produces a slightly radioactive byproduct known as phosphogypsum. According to the Florida Department of Environmental Protection, there are a billion tons of phosphogypsum stacked across the state and 30 million tons are generated each year.

Unnecessary water use, exploitation of limited resources, and wasted energy-all wrapped in a single bag. Add to this the fact that there is a limited supply of easily mined colloidal phosphorus. It’s much like oil: will we have enough in the future? Will we be able to find enough new supplies if the current mines are exhausted? Some say the U.S. supply will be gone by 2035.

Choosing to buy commercial colloidal phosphate and blood meal really means making a very important environmental decision. This is especially clear when one compares the environmental cost of imported amendments to the energy-efficiency of  growing nitrogen and phosphorus at home with green manures. Thus the gardener has two choices:

(1)      Import nutrients such as manure, blood meal and colloidal phosphate to force intensive yields.

(2)      Or, use wider spacing when planting and/or rotate heavy-feeder crops with a season of legumes to cut down on the competition for available nutrients.

Whatever you choose, don’t grow corn in the same spot every year, as it will exhaust much of the nitrogen. Instead, alternate corn crops with green manures-that also increase available phosphorus.

The thoughtful gardener makes a careful choice between vertical (intensive, using additional fertilizers) versus horizontal cultivation (wider spacing with green manures and no purchased fertilizers.)  It of course depends on whether or not you have a large enough garden. Intensive cultivation may be your only option. Then you’ll need to import more resources and/or produce more compost.

Based on the book: Roots Demystified, Change Your Gardening Habits to Help Plants Thrive. 2008, Metamorphic Press, Robert Kourik. See

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