Fertile Soils Lessen Insect Injury

Recent soils research suggests that a more carefully balanced soil fertility may reduce plant pest and disease losses, says W. A. Albrecht, chairman of the University of Missouri soils department.

In many instances, the research indicates that the responsibility for disease and insect control should be with the person managing crops and their nutrition. In the past, the responsibility has been given to the chemist manufacturing poisonous drug compounds to fight vermin and disease.

Corn grown on soil with a low fertility level is more susceptible to insect damage while in storage than is corn grown on more fertile soil, says W. A. Albrecht, chairman of the University of Missouri soils department. 

In the picture above, the small infested ear of corn was grown on a soil with a low level of fertility and was an easy mark for the grain borer. The ear at the left was grown on the same soil but with added nutrients and was undamaged except for a few borer holes where the two ears were in direct contact for a period of time. The open pollinated ear at the right was in contact with the infested one five months but showed only one sign of borer injury.

 

Nature grew most of the present-day crops in a healthy condition before they were taken over by the human race, Albrecht points out. Generally, plants in their natural state were in a pure stand, had been growing at the same location for many years, had accumulated much of their own residues as soil organic matter, and were free from diseases and pests.

Albrecht says these facts are in direct contradiction to present-day references that state in one way or another that “it’s impossible to overemphasize the importance of crop rotations to control diseases, maintain fertility, prevent erosion, and maintain soil structure.”

This contradiction again suggests there is much to be learned about nature’s success in growing crops with a high survival rate and without wars on diseases and pests.

Plants, as found in nature, were growing in soils where no fertility was removed. In present-day agriculture, far more fertility is removed than is returned. According to Albrecht, this is the basis for the theory that depleted soils and the consequent poor plant nutrition results in plant disease and insect attacks.

If this theory is correct, then it’s logical to believe that properly balanced fertility levels would prevent such troubles and yield healthier plants.

In tests with fungus diseases of soybeans, research clearly demonstrated that attacks were highest on soils with low calcium levels. These attacks weren’t evident where there were higher levels of exchangeable calcium in the soil.

More recently, improved research methods indicate that the presence or absence of leaf-eating insects varied with the levels of nitrogen and exchangeable calcium. These two fertility elements are usually connected with the production of protein-producing legume crops.

When small supplies of nitrogen were present in the soil, thrips attacked the plants. When nitrogen levels were higher, thrips were no problem, Albrecht notes.

And, when nitrogen supplies were low but calcium was plentiful, there was less damage from the leaf-eating insects than when both fertility elements were at low levels.

In still more recent work, corn grown on soils with high fertility levels was better able to withstand grain borer attacks in storage than corn grown on poorer soils. Corn, fertilized with nitrogen only, was much more susceptible to borer damage while in storage than was corn getting both phosphorous and nitrogen in the form of a soil treatment.

Ear samples from these two soil treatments were under observation for a three-year period following their harvest, Albrecht says. The corn getting only the nitrogen was badly damaged while the same hybrid fertilized with both nitrogen and phosphorus was virtually undamaged.

This is good evidence that nature was able to produce crops without destruction from diseases and pests. It’s also evidence that while soils may be managed to give larger yields, there’s still much to learn about a soil management that nourishes plants so well that they can protect themselves from diseases and pests without poisons or medications.

Also, it raises the question of whether crops too deficient in their nutrition to grow antibiotics needed for self defense would contain enough nutrients to produce healthful livestock.

Albrecht says this poses a serious challenge for soil researchers. The challenge lies in the possibilities of formulating a balanced fertility as guarantee of less plant diseases and fewer crop pests as well as a means of producing more vegetative bulk per acre.