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The Basics of Identifying Crop Quality

By Arden B. Andersen

Field trips in agriculture often are more like dog and pony shows than extended classroom experiences. Typically, the circulating tour group is paraded around at a distance, being shown various test plots, tillage systems, and management practices. One very important group experience that is rarely included in traditional field tours is the evaluation of crops, weeds, and soils in a hands-on manner in the field. Keen observation of field and crop details can tell the observer more than any soil or plant-tissue analysis. This is a key point because the farmer and consultant must take note of field observations to determine whether progress is being made and whether soil and plant-tissue tests are providing accurate pictures of the situation.


The Field Trip

Upon approaching any field, notice the overall appearance of the crop. Is it droopy? Rigid? Does it smell fresh? Are there any peculiar odors like methane gas, mold, ammonia, or pesticide? Is the overall color of the crop a deep blue-green? A mild-green or pale-green color? Do the leaves have a glossy sheen or a typical absorbent appearance? Are any birds nearby? Are they singing? How does the field feel to you? In other words, what sense do you get about the field?

As you move into the field, notice what types of weeds are growing and whether they or the crops are being eaten by insects. Ask whether a herbicide was used to control weeds and what type of weeds are most bothersome. Check the refractometer reading of both the weeds and the crop; write down the value of each. As the soil improves, the weeds will decline and the crop will increase in brix readings. Pull some weeds and slice open their stems lengthwise with a knife. Look at the pith of the weed. What color is it? Is the stem hollow? The healthier the weed, the higher the brix reading, the more solid the stem and the more pearly white its pith, and the less insect damage it will have. The same, of course, holds true for the crop. The healthier the weed, the more conducive your fertilization practices are to growing weeds rather than crops unless weeds (herbs) are your crop.

Notice what type of root structure the weed has. Grasses often have shallow, dense root systems that are attempting to loosen compact soil. Broadleaf plant generally have long taproots that are attempting to relieve hardpans and gain access to nutrient reserves at lower depths in the soil, as well as to extend the electrical circuit of the soil/plant complex to greater depths.

Corn

Dig up a corn plant. Notice the amount of root mass present and in which direction the roots grow. Are they pretty much growing out in the top two or three inches, or are they mostly growing down? Are there many or any live roots directly below the middle of the plant? Where does the soil structure change from a loose, crumbly structure to a platey, blocky one? Most soils in America have a crumbly structure for only the top one-half to two inches of the top soil and a platey structure from there on down. This means there is only a one-half to two-inch aerobic zone; the rest is predominately anaerobic, for all practical purposes.

In general, the roots will be concentrated primarily in the aerobic layer. You will notice that the greatest concentration of fine, fuzzy hair roots will be in the aerobic zone; this is because microbes and root hairs need oxygen. The microbes and root hairs make up the rhizosphere, which is the area of greatest nutrient exchange. Notice the color of the corn roots. Are they pearly white and soft, or are they brown and brittle? Pinch the roots slightly and pull to check whether the root bark sloughs off easily. If it does, there is a salt problem. Check for hardpan using a penetrometer, shovel, or brazing rod. This condition can be present in a sandy soil as well as in a clay soil. Notice that the roots pretty much stop at the hardpan.

Cut the corn stalk lengthwise and look at the plant’s plumbing system. Is the bottom of the stalk base, the pons, brown and hard? In general, we find that it is. This is congested or plugged tissue caused by toxins in the soil. These toxins might be pesticides, or they might be metabolic by-products from anaerobic breakdown of crop residue and manures. These could be products like formaldehyde and alcohol. Notice that the corn stalk has sprouted brace roots above this area. This is the back-up or by-pass plumbing system functioning to keep the plant alive. You may find that the node where these first brace roots sprouted is also brown and hard. In this case, a second layer of “by-pass” roots has sprouted. Brace roots are the plant’s rescue response when the plumbing system below gets plugged. If the plant did not sprout brace roots, it would die. In this case, as David Larson and others have reported, covering the brace roots, through cultivation, can increase corn yields by 5 to 15 bushels per acre. This allows the brace roots to contact the soil and, consequently, to interact with nutrients. In some areas the soil conditions are so toxic that the brace roots curl or burn off upon touching the soil surface. Compare the conditions of the plumbing systems of corn stalks between fields and note the differences in corn quality and refractometer readings.

Cut the corn stalk horizontally. The stalk should be round, not oblong or teardrop shaped. Out-of-roundness is an indication of a calcium deficiency. Look at the veins. Ideally, they should be pearly white and packed so tightly that it is difficult to count them. The pith should also be pearly white. Pull off the leaves from the stalk and notice that at each node, on opposite sides as you progress up the stalk, there is a baby or embryonic ear. This represents the plant’s true potential, which will be realized only when the soil is regenerated to the point that the plant’s plumbing system remains clear throughout, and the roots have an aerobic zone of 10 to 12 inches in which to grow.

About the Author

Arden B. Andersen

Dr. Arden B. Andersen apprenticed with Dr. Carey Reams, worked as a research assistant with Dan Skow, D.V.M., and as a field researcher with Philip Callahan, Ph.D. In addition to his B.S. in agricultural education, he holds a Ph.D. in biophysics and a D.O. in medicine. He currently works in general preventative and nutritional medicine while still consulting to some of the largest farming operations around the world.