Soybean (and dicot crops) response to heat and limited soil-water

Dry conditions continue to plague large areas of the Central US crop production areas and extremely hot daily temperatures across an even wider area have been common. Both high temperatures and soil-water deficits can negatively affect crops particularly when they are in the reproductive growth stages. In general most temperate region crops prosper with moist soils, ample sunlight, and a day temperature of around 86 F. Night temperatures are also important. Night temperatures in the 70s and 80s (F) can increase respiration (the undoing of photosynthetically produced sugars) and decreasing seed weight

Soybeans can tolerate some moisture stress in the vegetative growth stages but like most crops, water supply during the reproductive stages is most important. As discussed several articles ago, earlier-planted soybeans have a better chance to develop deeper root systems before hot dry weather commences thus availing the crop to more subsoil moisture. Early planting accompanied by a successful PRE herbicide application will lead to earlier canopy closure, another helpful asset when trying to get through dry spells. A closed canopy not only promotes better weed control but virtually eliminates soil surface evaporation thereby routing most of the soil-water into the plant, driving photosynthesis.

In early stages of drying soils soybean leaves may go vertical exposing the lighter-coloredcolored underside of the leaf and align parallel to solar radiation

Double-crop soybeans have additional challenges as they are often planted into dry soil that can experience elevated temperatures. Germination may be spotty and the young plants growing in hot soils may experience suppression of nitrogen fixation.

If hot dry conditions occur after blooms appear (R1) the soybean responds by dropping blossoms. The period of bloom production can last for 4-6 weeks and drought ending rain that does occur will allow the most recent blossoms to successfully pollinate and produce a pod. As pods begin to form (R3) temperatures in the high 90's can cause both small pods and blooms to abort. In the later stages of the reproductive period, moisture stress and high temperatures can continue to cause pod abortion and at this time the possibility of new blooms is ending thus capping the number of pods per plant. When blossoming ends the number of pods is capped (and can only get lower) and any yield compensation must be done through increased seed size if growth conditions improved. Poor growth conditions during pod fill will reduce seed size and reduce yields.

In more advanced drought soybean leaves may droop and show a wilted appearance.

Peanuts tolerate drought and heat better than soybean, an obvious factor that defines the production regions. Because of the unique harvest needs peanuts are typically grown on sandier soils that when non-irrigated are more prone to drought. Although moderately high temperatures are not injurious, sustained temperatures of 100 F can destroy over 30% of pollen (Prasad et al. 2003 Global Change Biology).

Cotton is generally well-suited to hot dry conditions but not immune to negative effects at the highest levels of temperatures (> 100 F) or soil-water deficits. Dry matter accumulation, plant height, node number, and photosynthetic rate may all be reduced under drought stress. Cotton varieties have been developed with thicker cuticles, smaller leaves, and smaller stomata to help defend against drought. As with most dicots cotton will eventually droop leaves and close stomata, and cease photosynthesis to survive under adverse conditions

Coming next: Critical yield determining periods for corn

BASF provides the information in this article as a service to its customers; however, the views expressed by guest writers are their own and do not necessarily reflect the views of BASF.