Understanding Drought and Heat Stress in Crops

Despite significant technological advancement in modern agriculture such as improved genetics, modern chemistries to control pests, equipment to aid in efficiency, and several other up-to-date management strategies, we still largely depend on nature to maximize crop production and profitability. Weather conditions (both short- and long-term) significantly affect major crop production. Crop producers are concerned with precipitation and temperature on a day-in-day-out basis.

Drought & Heat Stress: Impact on crops
South Dakota has seen higher than average temperatures in the last few weeks and the current U.S. drought monitor (June 6, 2017) shows that almost 80% of the state is facing moisture deficit conditions with Central and North Central region facing the worst—other parts of the state even though not as severe still show large areas of dry conditions. Producers generally think this is too early in the season to be in such situation. Weather conditions are highly variable within a small geographical area and so can the soil moisture depending on the growing region and the type of crops planted on any given time.

Winter Wheat & Small Grains
Generally, fields with winter wheat and other spring small grains can show less moisture in the soil profile than corn and soybean fields as small grains start growing and using moisture earlier in the season. Moreover, winter wheat growing regions such as Central and Western S.D. are showing more moisture deficit conditions because soils were already dry last fall when the crop was seeded. Crops in these fields were showing typical drought symptoms such stunted plants, rolled up leaves, and in some cases highly dried leaves as early as late May. Many producers in these Regions, especially those with livestock, were even considering harvesting the crop as hay rather than grain.

Corn & Soybeans
The soil in corn and soybean fields can sometimes reveal a different picture—since plants are fairly small and may not have used as much moisture like small grains. However, they may still show stress, which could be due to drying up of the top 1-3 inches of soil as a result of consecutive warmer temperatures during the last few weeks. There could still be enough moisture deeper in the profile for plants to utilize as they develop their root system.

Assessing Soil Moisture
The best way to assess soil moisture is to use a soil probe and “feel” the extracted soil from deeper profile for moisture. In this situation, plants can show drought-like symptom such as curled leaves in the morning, which could be entirely due to extreme heat rather than soil moisture deficiency. Although drought and heat stress can go hand-in-hand most of the times on a production system, they can have different outcome depending upon the soil type and crop growth stage. In the current SD situation young corn and soybean plants showing heat stress may recover quickly and efficiently when compared to small grain crops which are more advanced in their growth stage.

Source: David Karki, iGrow

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