Cow-Calf Certification Practice Exam

Under drought conditions, where in the corn plant are nitrate concentrations likely to be highest?

1. Upper leaves

2. Mid-stalk

3. Lower 1/3 stalk

4. Roots

The correct answer is: Lower 1/3 stalk

Nitrate concentrations in corn plants are likely to be highest in the lower third of the stalk under drought conditions due to the plant’s physiological responses to water stress. During drought, a corn plant may experience reduced water availability, impacting its ability to take up nutrients efficiently from the soil. As drought stress intensifies, the plant may exhibit a decrease in photosynthesis and overall growth, leading to a breakdown of chlorophyll and a reduced ability to produce carbohydrates. This stress causes the plant to mobilize nutrients from the older tissues—particularly from the lower parts of the plant. Consequently, the lower part of the stalk becomes a reservoir for nitrogen, which may be more concentrated there as the plant reallocates resources to survive in unfavorable conditions. Higher nitrate concentrations in the lower portion can also be attributed to the accumulation of nitrogen from decaying roots and soil organisms, particularly under conditions where the rate of nitrogen uptake is considerably affected by water stress. Therefore, drought can lead to a notable buildup of nitrates in the lower third of the stalk, emphasizing the plant's adaptation against nutrient deficiencies during challenging environmental conditions.