The Impact of Early Drought on Corn Yield

The early drought that has plagued most parts of eastern North Carolina has caused concern about it’s impact on corn yield. Corn is very susceptible to drought damage due to the plant’s requirement for water for cell elongation and it’s inability to delay vegetative growth. Therefore, there is always the danger of yield loss regardless of the timing of dry weather. In fact, the golden rule of corn production is that Highest yields will be obtained only where environmental conditions are favorable at all stages of growth. The amount of yield loss that occurs during dry weather depends on what growth stage the corn is in and how severe the dry conditions become. The following are some general guidelines for corn yield loss by growth stage.

Emergence to V8 (eighth leaf full emerged or about 4 weeks after planting):

Growth during this period determines the size that the plant achieves and the size of the individual leaves. Dry weather during this period will reduce plant and leaf size. Impact on yield will be based on the reduction in leaf area available for photosynthesis. Minor reductions in leaf size will have little impact on yield while major reductions (all leaves removed from the plant) could reduce potential yields as much as 20 percent. Extended dry weather that results in leaf burning and loss will have the greatest impact on yield. The following chart shows the relationship between leaf area and yield loss during this growth period. Remember that even though there is little or no leaf burn, leaf size can be effected by drought and result in reduction in leaf area.

V8 to V16 (All leaves emerged, start of tasseling; from 4 weeks to 66 days after plant emergence):

Plant growth in this period determines ear size and the number of kernels set. From V8 to V14, ear size is set. Drought during this period will reduce ear size and potential yield. Yield losses will be related to the length and severity of drought. Potential yield losses can range from 10 percent to 30 percent. From V14 to tasseling, the number of kernels that can be fertilized are determined. Drought during this period drought stress can reduce corn yields 10 to 50 percent. Throughout the V8 to V16 period the key question is how long the drought stress is present. The following chart has been compiled from the best information available showing the relationship between the length of drought during the V8 to V16 period and the loss of potential corn yield.

Silking:

This is the most sensitive stage for drought stress. Drought during silking coupled with high temperatures can result in 100 percent loss. This occurs most frequently in the midwest where high daytime temperatures can kill pollen before it can reach the silks. In the southeast, high humidity often results in heavy dew which can help pollinate the corn silk. However, severe yield reductions can occur due to incomplete pollination and the loss of kernel number. There are no good measures of yield loss. Scouting of the corn crop can determine the number of kernels set following pollination and can help determine yield potential. To determine if pollination has occurred, remove the shucks from the ear and take your hand and run it over the surface of the ear. If the silks brush off easily, then the kernel has been pollinated. If the silks stay attached then pollination has not occurred. Another good measure of pollination is to examine the length of the silks. The silk will continue to grow until pollination occurs or until it becomes damaged. The longer the silks the less efficient the pollination process was.

Silking to Maturity:

Drought during this period effects kernel weight. Severe drought can reduce corn yields during this period by 20 to 30 percent. Again, the key factor is how long the drought occurs and how late in this period it occurs. Drought immediately following silking has the largest impact, and can reduce yield substantially. Drought latter in this period is less damaging, but can hasten maturity.

While each stage is important, drought during some stages can be especially devastating. The key stage is silking followed by the V8 to V16 period and then the grain fill period from silking to maturity. The current drought has hit most fields in the V8 to V16 stage. Some yield losses (10 to 30 percent) have occurred depending on the length of the drought and its severity at a given location (see chart above). In most fields there remains the potential for decent corn yields, however, the weather throughout the remainder of the growth cycle must remain favorable. Dry weather that continues during silking and into the grain growth period will have a compounding effect with severe reductions in corn yields. Also, the current dry period will have an effect on delaying silking in relation to the release of pollen by the tassel. This means that the critical period during which the silks can be effectively pollinated has been reduced from 6 to 8 days to 1 to 2 days. Heat and drought during these few days of effective pollination can be devastating to corn yields.