Drought conditions have plagued the Southwest, High Plains, Northern Plains, and parts of the Midwest this spring, just as producers are looking to get crops in the ground. For corn, the greatest water needs occur during the later vegetative growth stages, but early-season drought can have negative impacts that are felt throughout the entire growing season due to the effects on plant growth and nutrient uptake. Below is more information about the impact of early-season drought stress on corn:
Germination and Emergence:Dry conditions within the seed zone at planting can lead to uneven germination and emergence across the field. This is particularly true when the seeding depth is variable, and some seeds are not placed in an area of adequate moisture for imbibition to occur. Corn seeds must absorb about twice their weight in water to initiate the germination process. Drastic differences in emergence can lead to later-emerging seedlings to essentially become weeds and be out-competed for resources to the extent that their contribution to yield is significantly reduced.
Root Growth:Soil moisture is essential for proper root growth. Early season drought can cause root tips to dry out and stop growing. The first root system, the seminal roots, do provide early water and nutrient needs, but stops growing once the coleoptile emerges from the soil. The nodal root system is beginning to provide some resources at V3 and is the dominant source for soil resources by V6. Dry soils cause brace roots to grow along the surface rather than penetrate the soils, which leads to standability issues later in the season. Under an extremely dry soil surface, hot air temperatures (above 80°F) can result in the soil temperature reaching a level that causes death of the developing roots. In cases where the entire whorl set of roots is killed, moisture uptake by the nodal system must be delayed until another whorl set becomes established. Roots killed in this manner take on a “roasted” or burnt appearance. This may lead to what is referred to as “floppy corn.” The decrease in root growth limits the surface area available to collect nutrients and water from the soil.
Plant Growth:Early season development, up to V8, determines the size of the overall plant and the size of each leaf. Drought stress at this critical time period will reduce plant and leaf size. A small reduction in leaf size will not have a significant impact on yield, but the more the leaf size is reduced the less photosynthetic area will be available to contribute to yield. Extended drought that results in burned leaves and leaf death can significantly reduce yield potential. A common sight when corn is experiencing drought stress is leaf rolling. Leaf rolling conserves water by decreasing the surface area of the leaf exposed to sunlight and reducing transpiration. Four consecutive days of leaf rolling can result in a 5 to 10% yield reduction.
Nutrient Uptake:Dry soils may temporarily reduce available nutrients in the soil solution. Potassium (K) is vital to several plant functions, including water and nutrient uptake and stalk health. Dry soils can exacerbate the plant’s inability to uptake potassium due to reduced physical mobility and root interception of K. Deficiency symptoms start on the plant’s older leaves and can be identified by yellowing or firing on the leaf margins. Generally, drought will have less of an impact where K availability is adequate in the soil. Adequate K levels within the plant will also help to increase drought tolerance by supporting water uptake.
Ear Length and Kernel Row Number:Drought stress that occurs between V6 to V8 can impact the number of kernel rows. While this trait is genetically controlled, it can be modified by the environment. If the corn product is genetically predisposed to have 18 kernel rows but ends up having less than that, it is most likely due to some stress that occurred between the V6 to V8 growth stages. In an ear that has 16 kernel rows around, one kernel row equates to about 5 bushels per acre with an average plant population. In addition, the kernel number per row is established as early as V5 and continues to be determined through pollination and grain fill. Thus, early-season drought stress may reduce the number of rows and the number of kernels within a row. (Sources: Dekalb, GoldenHarvest, Perdue University)