Agronomy Degree Practice Exam

Select the correct order for most to least sensitive crops to injury from fertilizer burn.

1. Sorghum > Soybeans > Small grains > Corn

2. Soybeans > Sorghum > Corn > Small grains

3. Corn > Small grains > Sorghum > Soybeans

4. Small grains > Corn > Sorghum > Soybeans

The correct answer is: Soybeans > Sorghum > Corn > Small grains

The answer indicates that soybeans are the most sensitive to fertilizer burn, followed by sorghum, then corn, and finally small grains as the least sensitive. This ranking is based on the physiological responses of these crops to nitrogenous fertilizers, particularly when they are applied in excessive amounts or under dry conditions. Soybeans are leguminous plants that are particularly sensitive to high concentrations of fertilizer, primarily because their root systems can be more easily damaged by chemical burn. This makes them highly susceptible to injury, as their roots are sensitive to osmotic imbalances caused by high salt concentrations from fertilizers. Sorghum, while also sensitive, has a somewhat more robust root structure that enables it to cope with minor injuries from fertilizer application. This means it can withstand slightly higher fertilizer rates compared to soybeans before showing signs of damage. Corn, being a grass, is more tolerant of fertilizer applications than both soybeans and sorghum. The structure of corn's root system allows it to better absorb moisture even when some of the roots may be affected by fertilizer toxicity. Finally, small grains (such as wheat and barley) are generally the least affected by fertilizer burn. Their physiological attributes and developmental traits make them capable of recovering from potential fertilizer injury without significant yield loss.