Drought stress status of corn in Kansas
Drought stress conditions remain a serious concern in the western region of the state, and now drought stress is gradually moving eastward in the state as the crop growing season progresses.
Recent weather has been hot, with scarce and very erratic precipitation patterns. Precipitation in many areas of Kansas has clearly been insufficient for sustaining the evapotranspiration demand of the corn, soybean, and sorghum (Fig. 1).
In some areas of the state, corn is approaching the mid-point of the growing season -- flowering time. At this stage, intense and severe drought stress can dramatically compromise the formation of grain and the final yield. The U.S. Drought Monitor from July 9, 2013 for Kansas is showing “Exceptional” and “Extreme” drought conditions from the central to the western part of the state. In addition, more than 90% of the state is currently classified as “Abnormally Dry” or worse. Only a small area in the eastern part of the state is classified as with no drought stress (<10%).
Overall, the July 9 Drought Monitor for Kansas breaks down like this:
Exceptional drought: 24%
Extreme drought; 23%
Severe drought: 14%
Moderate drought: 15%
Abnormally dry: 14%
Specifically for corn crop, the main questions are:
How much of the yield was or will be affected by the intensity of the drought stress in the next coming weeks? The answer is not straightforward, but for dryland corn if the weather conditions persist or get worse, severe loss of grain yield potential should be expected, depending on the stage of growth and development of corn. The crop is getting, in parts of the state, close to flowering time.
Why “flowering time” is critical or important for the final grain determination? Two weeks before and after pollination is when the final grain number will be determined through a sequence of processes taking place in the female reproductive structure of the corn plants. Before this stage, ear size has already been determined. At the five-leaf to fifteen-leaf stage interval) that will play a critical role in defining the final yield, the ear size.
Why “ear size” is an important component for the yield determination in corn? The size of each individual ear is set during the 5- to 15-leaf stage of growth. This will define the maximum potential number of grains per plant (if the plant carries only one ear) through the determination of the number of ovules that can be fertilized. Thus, the “potential kernel number” is determined before the pollination occurs. The final kernel number will be physically restricted -- small ears have less space for bearing grain.