BUILDING SOIL FOR BETTER CROPS

Part 1

Farmers sometimes use the term soil health to describe the condition of the soil. Scientists usually use the term soil quality, but both refer to the same idea — how good is the soil in its role of supporting the growth of high yielding, healthy crops?

How would you know a high quality soil from a lower quality soil? Most farmers or gardeners would say that they know one when they see one. Farmers can certainly tell you which of the soils on their farms are of low, medium, or high quality. They know high quality soil because it generates higher yields with less effort. Less rainwater runs off and fewer visible signs of erosion are seen on the better quality soils. Less power is needed to operate machinery on a healthy soil than on poorer, compacted soils. Soil scientists are working together with farmers and agricultural extension personnel to try to come up with a widely accepted definition of soil health and to determine what factors (pH, bulk density, aggregate stability, etc.) need to be measured to estimate a soil’s quality. The first thing many might think of is that the soil should have a sufficient supply of nutrients throughout the growing season. But don’t forget, at the end of the season there shouldn’t be too much nitrogen and phosphorus left in highly soluble forms or enriching the soil’s surface.

Leaching and runoff of nutrients are most likely to occur after crops are harvested and before the following year’s crops are well established. We also want the soil to have good tilth so that plant roots can fully develop with the least amount of effort. A soil with good tilth is more spongy and less compact than a soil with poor tilth. A soil that has a favorable and stable soil

For soil thou art…

—BOOK OF GENESIS

Structure also promotes rainfall infiltration and water storage for plants to use later. For good root growth and drainage, we also want a soil with sufficient depth before there’s a restricting layer. We want a soil to be well drained, so it dries enough to permit timely field operations. Also, it’s essential that oxygen is able to reach the root zone to promote optimal root health — and that happens best in a soil without a drainage problem. (Keep in mind that these general characteristics do not hold for all crops. For example, flooded soils are important for paddy rice production.)

We want the soil to have low populations of plant disease and parasitic organisms so plants grow better. Certainly, there should also be a low weed pressure, especially of aggressive and hard-to-control weeds. Most soil organisms are beneficial and we certainly want high amounts of organisms that help plant growth, such as earthworms and many bacteria and fungi.

A high quality soil is free of chemicals that might harm the plant. These can occur naturally,

such as soluble aluminum in very acid soils or excess salts in arid region soils. Potentially harmful chemicals also are introduced by human activity, such as fuel oil spills or application of sewage sludge with high concentrations of toxic elements. A high quality soil should resist being degraded. It also should be resilient, recovering quickly after unfavorable changes like compaction.

THE NATURE AND NURTURE

OF SOILS

Some soils are exceptionally good for growing crops and others are inherently unsuitable; most are in between. Many soils also have limitations, such as low organic matter content, texture extremes (coarse sand or heavy clay), poor drainage, and layers that restrict root growth. Iowa’s loess-derived prairie soils are naturally blessed with a combination of silt loam texture and high organic matter contents. By every standard for assessing soil health, these soils — in their virgin state — would rate very high. We can compare them with a person who is naturally very healthy and has great athletic abilities. Many of us are not quite so lucky and Nature has given us qualities that may never make us great baseball players, swimmers, or marathon runners, even if we tried very hard. The way we care for, or nurture, a soil modifies its inherent nature. A good soil can be abused through years of poor management and turn into one with poor health, although it generally takes a lot of mistreatment to reach that point. On the other hand, an innately challenging soil may be very “unforgiving” of poor management and quickly become even worse. For example, a heavy clay loam soil can be easily compacted and turn into a dense mass. Both the naturally good and poor soils can be pro ductive if they are managed well. However, they will probably never reach parity, because some limitations simply cannot be completely overcome. The key idea, however, is the same that we wish for our children — we want our soils to reach their fullest potential.

Copy from : Building Soils for Better Crops 2ND EDITION --Fred Magdoff and Haroldvan Es---