Soil Types for Growing Soybeans

By Dr. Harold Willis

Ensuring your soil is ready to grow soybeans is usually an early step when determining the type of crop you want to grow.

The first thing we need to think about before doing any field work is the soil and its fertility, for without good soil it is impossible to grow a good crop. And a good soil will actually give the plants protection from adverse weather—cold, frost, drought, excess water—as well as protection from pests and diseases.

Fortunately, the soybean is a hardy, not-too-particular plant and can do reasonably well in a variety of soils and soil conditions, but to produce high yields of top quality soybeans, you need to get your soil into really good condition.

Weeds are not a problem when soybeans are planted in the right soil type.

Weeds are not a problem when soybeans are planted in the right soil type. Courtesy How to Grow Super Soybeans

The ideal soil. Ideal soil for peak soybean production is a loose, well-drained loam. All too many fields these days have tight, crusty soil that becomes waterlogged when it rains. More than likely, such soil is low in humus and

has an imbalance in mineral nutrients. Probably there are few beneficial soil organisms (certain bacteria, fungi, algae, protozoa, earthworms and others). In short, the soil is “dead.”

The advantages of loose, well-aerated soil with adequate humus and abundant living organisms include the following: (1) Loose, aerated soil allows air to get to roots and nitrogen-fixing root nodules, plus it soaks up rain and lessens erosion, and it discourages many of the worst weeds; (2) Humus and soil organisms provide steady, balanced nutrition to roots, soak up and hold moisture (provide “drought-proofing”), and protect roots from harmful nematodes, insects and disease pathogens; And (3) Organic matter also tends to buffer soil from extremes in pH (acidity and alkalinity).

Modern Agriculture & Diseased Soil

Yet many of today’s agricultural practices tend to degrade soil and produce the tight, crusty, lifeless conditions mentioned ear­lier. The overuse of synthetic salt fertilizers and anhydrous ammonia tends to reduce soil life and humus, leading to hard soil. Some of the herbicides and pesticides also do the same thing. Too much field traffic and heavy machinery compact soil. Even using the wrong kind of lime may in some cases lead to soil degradation.

The pioneer of composting, Sir Albert Howard, calls erosion a soil disease in his book, The Soil and Health, p. 85: “Perhaps the most widespread and most important disease of the soil at the present time is soil erosion . . . ”

He states that the keys to the solution of soil erosion are humus and soil microbes, p. 86: “The fragments of mineral matter derived form the weathering of rocks [soil particles] are combined by means of the specks of glue-like organic matter supplied mostly by the dead bodies of the soil bacteria which live on humus . . .

“Provided, however, that we keep up the bacterial population of the land . . . the supplies of glue for making new compound soil particles [soil aggregates] and for repairing the old ones will be assured.

“It will be seen from this how fundamentally important is the role of humus. It is the humus which feeds the bacterial life, which, so to say, glues the soil together and makes it effective.”

Howard calls soil erosion a “man-made disease” and says that it is “always preceded by infertility” (p. 87). He then places the blame: “Soil erosion is nothing less than the outward and visible sign of the com­plete failure of a farming policy. The root causes of this failure are to be found in ourselves.”

Sick soil does not have to be a casualty. The patient can recover if the principles of eco-agriculture are applied.

Loose, well-aerated soil is extremely important in growing healthy, high-producing crops. In the classic text, Soil Conditions and Plant Growth (by E.J. & E.W. Russell, 8th ed., p. 335), we read:

The soil pores that are not filled with water contain gases . . . the rate of transfer of carbon dioxide from the root zone to the atmosphere and of oxygen from the atmosphere to the root zone is a soil property of fundamental importance to the crop, and in humid soils the rate of oxygen penetration probably limits root growth more often than the rate of carbon dioxide re­moval; the oxygen supply is as important in humid soils as is the water supply in arid.

Low oxygen and high carbon dioxide in the soil’s pores can cause a multitude of problems, ranging from damaged roots to toxins released from harmful soil organisms to loss of soil nitrogen to insect attack to low crop yield and poor quality. More details are given in The Coming Revolution in Agriculture, Chapter 3.

How can soil be kept loose and well-aerated? The best long-term solution is to maintain adequate levels of organic matter and to foster beneficial soil life, including earthworms, whose burrows add greatly to soil aeration (see The Rest of the Story, p. 62).

Organic matter makes soil loose and holds water. It is also a food supply for the beneficial soil organisms. The microscopic soil organ­isms, including bacteria and fungi, also help loosen soil because their by-products, sticky materials called polysaccharides, glue tiny soil par­ticles together to form larger clumps called crumbs or aggregates.

Ways of increasing soil organic matter and improving the soil’s crumb structure include incorporating animal manure (or better, rotted manure or compost) and plowing under a green manure crop. Leaving a surface cover of plant residue also helps by reducing erosion and keeping soil moist (as long as it is not wet, waterlogged soil). The application of lime along with manure or other organic matter hastens the process of soil loosening. Leaving a field fallow with a cover crop of grasses and/or legumes will also greatly improve soil structure and fertility.

Source: How to Grow Super Soybeans

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