Though the Southeastern states have received average to above average rainfall this spring, the ever-lingering fear of a reoccurrence of last year’s drought is on the mind of every farmer.
Corn, as farmers in the Southeast learned last year, is one of the most sensitive crops to drought. For many farmers who switched to corn or increased dryland corn acres to take advantage of record high prices, the drought was a sobering reminder of how Mother Nature can cause financial losses even in the best of financial times.
A prolonged period of dry weather (drought) is the most difficult and damaging problem a corn grower faces. Shallow root zones caused by low pH subsoils or hardpans restrict the amount of soil water available to the corn plant.
A significant rain event every 10 to 14 days is required to prevent damage to the corn crop. Unfortunately, summer weather patterns are anything but consistent — a point driven home unmercifully by last year’s drought in the Southeast.
Without irrigation, corn yields will be limited by lack of water. It’s just that simple says North Carolina State University Corn Specialist Ron Heiniger.
The amount of yield lost will depend on when the drought occurs and the amount of available soil water the soil can hold, he says.
Yield is reduced when evapotranspiration demand exceeds water supply from the soil at any time during the corn life cycle. Nutrient availability, uptake, and transport are impaired without sufficient water. Plants weakened by stress are also more susceptible to disease and insect damage.
The keys to managing drought are to understand the effect of drought on corn at different times in the growing season and to find ways to improve drought tolerance either by increasing available soil moisture or through crop management.
Heiniger says 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.
Heiniger says drought in the following stages affects corn yield differently:
• From emergence to about 4 weeks after planting dry weather reduces 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.
• From 4 weeks to 66 days after plant emergence drought 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.
• The number of kernels that can be fertilized is determined from V14 to tasseling and drought during this period can reduce corn yields 10 to 50 percent.
•Silking is the most sensitive stage for corn drought stress. Drought during silking, coupled with high temperatures, can result in 100 percent loss. In the Southeast, high humidity often results in heavy dew which can help pollen reach the corn silk. However, severe yield reductions can occur due to incomplete pollination and the loss of kernel numbers.
For dryland corn producers there is no reliable way to avoid drought damage. However developments in corn hybrid drought resistant traits is encouraging for the future.
Corn hybrids developed for drought-plagued regions of Africa are already capable of producing relatively high yields of corn with only three inches of rainfall or moisture during the growing season.
High yielding, low moisture-requiring corn is no eye-in-the-sky dream, it’s a well financed and researched reality financed in large part by American philanthropists Warren Buffet and Bill Gates.
The African Agricultural Technology Foundation (AATF) today is a public-private partnership established to develop drought-tolerant maize varieties for Africa.
Monsanto and BASF are also partners in the African project and plan to offer drought tolerant varieties to many African nations free of charge.
Monsanto is a world leader in agricultural biotechnology research and drought tolerance is going to be a popular trait in their future crop varieties. Though Monsanto is testing thousands of drought tolerant varieties, one drought tolerant corn variety is moving through the regulatory pipeline and may be ready for commercialization as early as 2010.
Under drought conditions this variety has shown a 20 bushel yield advantage over non-transgenic corn varieties. There is little doubt farmers across North America will be very interested in these new drought tolerant corn varieties once they have passed all the regulatory evaluations required for commercialization.
Clearly there is an economic motivation for corn growers in the Southeast to do a better job of managing drought stress. Choosing the optimum hybrid variety for a combination of drought stress management and yield potential is a good first step, according to Heiniger.
Another proven drought management strategy, he says, is to implement soil and nutrient management practices that improve the soil’s water holding capability.
“One of the best practices for improving the soil's water holding capacity is to increase rooting depth. The major limitation to rooting depth is acidic subsoils. The careful application of lime with incorporation to depths of 8-12 inches can help increase pH in the soil profile and improve rooting depth,” Heiniger says.
Lack of adequate potassium often makes drought management more difficult, he says. Potassium (K) is an important element that affects water movement within the plant and in stalk and root health.
No-till, especially long-term use of this tillage practice, is a good way to help corn survive and thrive in dry conditions. Studies have shown that planting corn into a residue mulch on sandy loam soils has the potential to increase yields 10-20 bushels per acre.
Heiniger cautions before considering the use of no-till practices, the potential for subsoil compaction should be considered. On sandy loam soils with clay subsoils (common in many areas of the Coastal Plain and Tidewater regions), the potential for subsoil compaction is high. In-row subsoiling on these soil types increases nutrient uptake and water use from beneath the compaction layer.
Plant populations can be a critical issue, especially on drought-prone soils. Reducing plants per acre to 18-000-20,000 acres can help growers reduce drought damage.
With corn and the inputs needed to grow corn at near record prices, it is critical to manage drought. Though no one can totally manage weather-related problems, choosing the right hybrid, using no-till planting, and keeping potassium levels at recommended levels can help improve a corn growers chances against drought.
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