You just can’t escape Liebig’s Law of the Minimum in crop production, says Mitchell. This concept was originally applied to plant or crop growth when it was found that increasing the amount of plentiful nutrients did not increase plant growth. Only by increasing the amount of the limiting nutrient was the growth of a plant or crop improved.

“Whatever is the most yield-limiting factor, in whatever field you’re managing, you have to take care of that first before you can reach your yield potential,” says Mitchell.

Rarely are nutrients the most limiting factor, although they can be, he adds. “Fifty years ago, it definitely was nutrients, and that’s when soil testing began. We can throw nutrients out there, and in some cases, there’s even too much nutrient.”

Researchers, including Mitchell, conducted a cotton survey in central Alabama about 10 years ago looking at various growers’ fields.

“We took soil samples and leaf samples from about 300 fields of cotton. Rarely were nutrients not in the range that we like to see. Soils tested high in most nutrients and there was hardly ever a problem with tissue analysis. Our farmers are doing a great job soil-testing and managing nutrients.”

The research, however, did find that 67 percent or two-thirds of the fields had a hard pan or a traffic pan, says Mitchell. “Fifty-percent of the fields had soil organic matter less than one-half of 1 percent. That’s not a soil, that’s dirt. By definition, soil must contain some organic matter. And that’s why they had hardpans — they didn’t have the structure there to maintain that in-row subsoil slit whenever it was cut.”

At that time, he says, about half the growers were planting a cover crop. “But they were killing the cover before it made any substantial growth in the spring, so they weren’t putting back any organic matter.

“But at least they were planting a cover crop. If we went back today, I think it would be a different situation. We’ve learned the value of organic matter to soil quality.”

As far as nutrients, there are about 16 to 18 elements that all plants need and three of them come from air or water, says Mitchell. “Water is critical, making up 80 percent of a plant’s green weight. Without water, you can forget everything else. That’s why irrigation is a key to high yields.”

If you believe in it, global warming actually is helping in the production of carbon dioxide or C02, says Mitchell.

“We know C02 is increasing, and that can only help plants. Some of the high yields we’re seeing today could be due to some of the increased C02 in the atmosphere. We’re taking care of the carbon, hydrogen and oxygen — the rest of them come from the soil or must be added as fertilizers.

“Plants need relatively large amounts of nitrogen, phosphorus, and potassium. These nutrients are referred to as primary nutrients and are the ones most frequently supplied to plants in fertilizers.”