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Drought-tolerant corn in the United States: Research, commercialization, and related crop production practices
Mar. 15, 2019
Highlights:
Genetically engineered (GE) and non-genetically engineered (non-GE) drought tolerance became broadly available in corn varieties between 2011 and 2013.
By 2016, 22 percent of total U.S. corn acreage was planted
Droughts are among the most frequent causes of crop yield losses, failures, and subsequent crop revenue losses across the world. Due to the complex ways in which plants respond to heat and water deficits, the physical effects of drought on crops can take many forms. In corn, a major U.S. row crop with significant water needs, the leaves typically roll under and turn yellow-gray as growth slows and the plant struggles to fuel itself. Depending on the timing and severity of the drought, water stress can lead to fewer and smaller kernels, and ultimately lower yields.
Farmers have few widely available tools or strategies to significantly lessen the physical effects from drought within the span of a single growing season. Planting dates, the space between crop rows, and seeding rates can be adjusted to try to more efficiently match the amount and timing of water available—but these are limited by farmers’ growing environments and field characteristics. For example, many farmers cannot plant corn early in the spring because of cold, hard soils and the potential for late-spring freezes. Soil organic matter (decomposing plant and animal residue) can help soils retain moisture, but this matter takes several growing seasons to accumulate. Irrigation is among the most effective means of drought mitigation, but it is only practical in areas with ample sources of irrigation water that can be cost-effectively applied.
Farmers can mitigate the financial losses from drought by enrolling in a number of Federal programs. Most major row crop production in the United States is eligible for protection through federally supported yield or revenue insurance, which disburses indemnity payments under certain conditions, including losses from drought. Disaster assistance payments tend to be ad hoc Government responses to floods, droughts, and other natural disasters. In addition, past USDA, Economic Research Service (ERS) research has shown that USDA’s Conservation Reserve Program and Environmental Quality Incentives Program can aid drought risk adaptation. However, Federal crop insurance and disaster assistance programs typically do not fully compensate farmers for financial losses.
New technologies or management practices to avert or reduce the drought damages that lead to lower profitability would increase the resiliency of U.S. agricultural production, while also reducing farmers’ reliance on Federal financial assistance. Newly available drought-tolerant (DT) corn is one such technology.
Field trial research indicates that DT corn exhibits small yield advantages over non-DT corn in growing conditions with limited water, somewhat similar to certain drought conditions farmers might experience on their fields. However, some studies suggest they are not effective in severe droughts. Data from USDA’s 2016 Agricultural Resource Management Survey (ARMS) show that non-irrigated DT corn yields averaged six bushels per acre (or 4 percent) higher than non-irrigated non-DT corn yields. This difference was not statistically significant, however. DT corn varieties were not designed to produce significantly higher yields than non-DT varieties under drought-free growing conditions—the kinds of conditions that prevailed across most major U.S. corn-producing areas in 2015 and 2016.
Development and Commercialization of DT Corn in the United States
DT corn varieties became available to U.S. farmers between 2011 and 2013. Decades of research on drought tolerance by crop breeders and plant scientists preceded the national commercialization of these varieties. Scientific gains in drought tolerance have been made in other crops, but corn has been a major focus of research because of its significant acreage and sensitivity to drought.
Since the 1960s, national average corn yields have been increasing by just under 2 bushels per year as a result of many factors, including the development of corn varieties that are hardier and more resilient to biological stresses (such as plant diseases and pests) and environmental stresses (such as freezes and droughts). The DT corn varieties currently available have benefited from this type of basic research. However, most DT varieties are the direct result of applied private-sector research and breeding that selects plants based on their yields in growing conditions with limited water.
Private seed companies have taken two broadly different approaches to seed development—using either genetic engineering (GE) or conventional (non-GE) methods. GE drought tolerance relies on insertion of a gene from the soil bacterium Bacillus subtilis into the plant. This gene activates a protein that helps mitigate the damaging effects of drought. In contrast, non-GE drought tolerance has mainly resulted from molecular breeding research. This type of research uses genetic analysis and extensive computer modeling to predict corn varieties optimized for drought, though the corn plants themselves are conventionally bred. Regardless of development method, DT varieties are designed to help check the plant’s natural tendency to divert energy from reproduction to survival in droughts.
In 2012, the first year after the limited release of DT seeds to farmers, only about 2 percent of total U.S. corn acreage was planted with DT varieties. Five years later, in 2016, just over 22 percent of total U.S. corn acreage was planted with DT varieties.
To better understand this growth rate, ERS researchers compared it to the adoption of genetically engineered herbicide-tolerant (HT) and insect-resistant (Bt) corn. HT corn is immune to specific weedkillers, while Bt corn protects the corn crop from specific insect pests. Because of these valuable pest management traits, farmers began planting HT and Bt corn after their introduction in 1996, despite the fact that genetically engineered seeds were a novel and unfamiliar technology. Between 1996 and 2000, HT corn acreage increased from 3 to 7 percent of total U.S. corn acreage. Over this same time period, Bt corn acreage increased from 1.4 percent to 19 percent. In the following years, corn farmers gained much more experience choosing, planting, and managing GE varieties, and adoption levels continued to rise. By 2012, nearly 75 percent of U.S. corn acres were planted to varieties with at least one GE trait.
Most of the DT corn varieties currently sold in the United States have drought tolerance developed through conventional breeding rather than genetic engineering. Yet, 91 percent of DT corn fields in 2016 were planted to corn that is also herbicide tolerant and insect resistant. Combining DT with one or more of these GE traits could be a result of many factors, but some evidence suggests these pest management traits are complementary. For example, a corn crop will generally be less vulnerable to drought if it is not competing with weeds for water, and if its roots and leaves are not damaged by insect pests.
The relative prices of corn varieties also influenced the adoption of DT corn. Data from the 2016 ARMS indicate that the average cost of a bag of corn seed with DT, HT, and Bt traits was $264. In contrast, the average cost of a bag of corn seed with only the HT and Bt traits was $254. This implies a national DT price premium of $10 per bag, on average. However, variability exists in farmers’ willingness to pay premiums for drought tolerance across the United States, leading to some variation in market prices of DT corn seeds.
Geography of Drought-Tolerant Corn Adoption
DT corn adoption is highly correlated with the frequency and severity of drought, as well as how recently farmers experienced drought. In 2016, States in the western Corn Belt—including Nebraska, Kansas, Texas, Colorado, and South Dakota—had the highest adoption rates of DT corn. Over 42 percent of Nebraska’s corn were planted with DT varieties (4 million acres), similar to the 39-percent adoption rate in Kansas (2 million acres). Adoption rates in South Dakota, Texas, and Colorado were somewhat lower, ranging between 20 and 27 percent.
DT corn adoption rates in 2016 were lower in the eastern Corn Belt—Iowa, Illinois, Indiana, and Ohio—than the western Corn Belt. Between 16 and 21 percent of these States’ corn acres were drought tolerant. However, farmers in Iowa and Illinois planted the greatest quantity of DT corn in the United States, roughly 2.2 and 2.1 million acres, respectively. This is partly because of the sheer volume of corn planted in these two States, which tend to be the top contributors to annual U.S. corn production. Geographical trends were less clear outside the Corn Belt. In regions where corn is commonly irrigated (e.g., the western Corn Belt and Georgia), adoption is affected by farmers’ perceptions of irrigation and drought tolerance as substitutes or complements.
Many of the private companies currently selling DT corn varieties performed late-stage testing in the western Corn Belt—where these varieties were first commercially available. Initial marketing was concentrated in the western Corn Belt because droughts are typically more frequent and more severe in this region than other U.S. corn-growing areas. For example, 89 percent of Texas counties experienced a severe-or-worse drought (as measured by the U.S. Drought Monitor) in 2011. In 2013, 37 percent of Texas counties experienced a severe-or-worse drought.
Drought-Tolerant Seed Choice and Use of Other Crop Management Practices
Drought-tolerant corn works, in part, by improving the plant’s ability to take water up from soils and convert water into plant matter. This creates a natural link between DT corn adoption and use of water management practices in corn production. Among the most common of these practices are conservation tillage and irrigation, which are widely used in the western Corn Belt.
Minimal disturbance of soils through tillage—such as through conservation tillage—makes more water available to the crop by reducing evaporation. No-till management—a conservation practice in which farmers do not disturb soils from tillage operations—was used on 41 percent of DT corn fields, but only 28 percent of non-DT corn fields. Similarly, conservation tillage, including no-till, was used on 62 percent of DT corn fields in 2016, compared to 53 percent of non-DT corn fields.
Although farmers in certain regions can increase soil moisture through irrigation, the use of irrigation does not preclude the use of DT corn as well. For example, nearly 31 percent of Nebraska’s irrigated fields were planted with DT varieties. Farmers’ decisions to irrigate their DT corn fields may be influenced by many factors, including the extent of soil moisture deficits (if any), amount and timing of rainfall throughout the growing season, and irrigation expenses. However, such regions generally have higher levels of DT use on dryland fields. For example, 60 percent of non-irrigated fields in Nebraska were planted with DT varieties.
Although farmers in certain regions can increase soil moisture through irrigation, the use of irrigation does not preclude the use of DT corn as well. For example, nearly 31 percent of Nebraska’s irrigated fields were planted with DT varieties. Farmers’ decisions to irrigate their DT corn fields may be influenced by many factors, including the extent of soil moisture deficits (if any), amount and timing of rainfall throughout the growing season, and irrigation expenses. However, such regions generally have higher levels of DT use on dryland fields. For example, 60 percent of non-irrigated fields in Nebraska were planted with DT varieties.
Beyond Current Adoption: Implications and Prospects
Use of DT corn varieties, especially when combined with other soil moisture conservation practices, can play a significant role in farmers’ risk management strategies. Under mild-to-moderate drought conditions, there will be differences in yield losses between DT and non-DT corn fields. Increasing variability in yield losses could lead to changes in the number of farms receiving certain Federal crop insurance indemnity and/or disaster assistance payments, as well as payment amounts.
In the short term, adoption of DT corn is likely to increase. Yet DT corn adoption increased less swiftly than HT and Bt corn adoption during their major growth period between 2000 and 2009. There are two main reasons for this. First, many areas of major U.S. corn production, like the Corn Belt, experience pest infestations each year. These same regions, especially States in the eastern Corn Belt and upper Midwest, do not experience severe drought each year. Second, it may be difficult for farmers to determine the efficacy of drought tolerance in the short term. For example, a farmer could plant DT and non-DT corn and see little to no difference in yields under a very mild drought. In the next season, the same farmer could grow both DT and non-DT corn, experience a very severe drought, and suffer crop failure on all fields. That may lead the farmer to incorrectly conclude that DT corn does not work under any drought scenario.
In the long term, the pace of DT corn adoption could increase if private seed companies increasingly combine drought tolerance with HT and/or Bt traits—at prices farmers are willing to pay. Increased “stacking” could result from companies selling additional varieties with all three traits, or through a gradual market withdrawal of HT and/or Bt varieties that are not drought tolerant. The latter type of marketing strategy has been used for some types of farm machinery, whereby new technologies—initially introduced as options—gradually become standard equipment.
Source: USDA
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