Managing Drought Stress in Soybean

Especially during the reproductive stages of soybean growth, inadequate water supply can significantly impact yield potential. Throw high temperatures into the mix, and your soybean crop will likely experience yield-limiting effects. You can’t predict the weather, but you can make choices that can help reduce plant stress and guard against losses caused by unpredictable weather you may face this season.

Effect of heat and drought stress on soybean 

Drought and extreme heat can ultimately reduce soybean yield by up to 70% if they occur during reproductive stages and nearly 30% when these conditions occur during vegetative stages.¹

Typically, when temperatures exceed 85 F, especially over a span of several days, your crop is at risk for heat stress. Excessive heat and drought often occur simultaneously, doubling down on the damage to yield potential.

Yield-robbing effects of high temperature and drought vary based on the soybean growth stage. 

Impact of heat and drought on vegetative growth stages

Unusually high temperatures combined with a lack of water can reduce the rate of photosynthesis or even stop photosynthesis altogether as the plant closes its stomata to help conserve moisture, subsequently limiting CO2 uptake within the plant. Additionally, temperatures above 86 F can reduce nodulation and N-fixation in soybean.

Impact of heat and drought on reproductive growth stages

Soybean water requirements peak when a full canopy forms. This typically coincides with the reproductive growth stages, including pod elongation (R4), early pod fill (R5), and mid-pod fill (R5-R6). On average, the R4 through R6 growth stages require almost double precision the water use that occurs in the earlier growth stages. Additionally, limited soil-water supply and high heat stress can cause “aborted flowers, aborted small pods, aborted seeds in larger pods, and production of smaller seeds” according to Dr. Rachel Vann, Assistant Professor and Extension Soybean Specialist at NC State University. 

Optimal water supply during these stages is critical to achieve the highest grain yield, so if irrigation is available in your fields, make sure you are sufficiently irrigating your crop during these stages.

Soybean water usage chart

📸: BASF internal graphic/ Featuring a soybean water usage chart

Symptoms of heat and drought stress in soybeans

• Stunted vegetative growth: Before the leaf flipping symptom (see below) becomes apparent, you may notice plants are undersized.

📸:@saraTM via Canva/Featuring an example of a soybean field with leaves flipping due to drought 

• Leaf flipping: Drought conditions cause soybean leaves to flip upside down, exposing their silvery undersides, which reflect more light and reduce transpiration (the process of water movement through a plant and its subsequent evaporation from leaves, stems and flowers). 

• Leaf curling/clamping: In severe drought conditions, soybeans may exhibit leaf curling/clamping, a stress response used to conserve water by reducing the amount of leaf area exposed to the sun. Leaf trifoliates close, clamping the center leaflet between the outside leaflets, hindering further growth and productivity.²

How to prevent and manage heat and drought stress in soybeans

Mitigating the damage of heat and drought stress in soybeans involves a mix of preventive measures and in-season management practices. 

Select drought-resistant seed 

In areas where drought stress is common, consider selecting seed that has been developed to tolerate drought and remain productive under stress. 

Selecting seed that works well with earlier planting schedules should also be a consideration, as early planting is another tactic to help prevent yield loss from drought stress.

Plant early

Early-planted soybeans typically can develop deeper root systems before hot, dry weather hits, allowing the crop to more effectively absorb subsoil moisture throughout the season. 

Planting soybeans early and in narrow rows also helps the crop canopy close sooner, effectively shading the soil surface and reducing soil moisture loss due to evaporation. 

Reduce other stressors

Reducing other types of stress, whether from disease, weeds or pests, can help your crop navigate a drought scenario. 

For example, early-planting soybeans and implementing a successful pre-emergence herbicide application will provide better weed control and promote earlier canopy closure. Canopy closure is key to outlasting dry spells since it essentially eliminates soil surface evaporation, leaving more soil water available for use in photosynthesis.

📸: @DCWcreations via Canva/Featuring an image of a lush soybean field

Additionally, using a fungicide like Priaxor® can provide more than just disease control. This fungicide has received the Plant Health label from the EPA. This label designates products that go above and beyond disease control, encompassing benefits that include improved host plant tolerance to yield-robbing environmental stresses. Plant Health benefits include stress tolerance, growth efficiency and disease control from the bottom up, helping soybeans stay greener longer by preserving bottom leaves, maintaining middle leaf growth and conserving top leaves.

Learn more about how fungicides can reduce plant stress:

• Is a fungicide just a fungicide?

Experts are available to help you navigate and manage the detrimental effects of heat and drought in soybeans. Reach out to your seed retailer, a nearby extension office agent, or a seed company professional like your regional BASF representative.

Learn more at Grow Smart® Live:

Discover more about heat and drought stress impacts soybean production.

• Soybean (and dicot crops) response to heat and limited soil-water
• Seasonal changes in crop water needs

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Endnotes

1. Poudel, Sadikshya, et al. "Resilience of soybean cultivars to drought stress during flowering and early-seed setting stages." Nature, 23 Jan. 2023, www.nature.com/articles/s41598-023-28354-0. Accessed 29 May 2024.
2. Licht, Mark, and Sotirios Archontoulis. "Influence of Drought on Corn and Soybean." Integrated Crop Management, 21 July 2017, crops.extension.iastate.edu/cropnews/2017/07/influence-drought-corn-and-soybean. Accessed 29 May 2024.

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