As the weather warms up, it’s safe to say most of us are excited to go out and get to work in the field. Although recent precipitation has relieved some parts of the state, we are still experiencing various levels of drought across the region. Recently, a group of colleagues put together an article highlighting the agronomic considerations for moisture deficit conditions in South Dakota. I’ll be summarizing some of their points this week.
The most current U.S. Drought monitor map was released on March 11. It shows the entire state of South Dakota in some type of drought, ranging from abnormally dry to extreme drought with a majority of the state in moderate to severe drought. Although weather patterns can change quickly, I feel it doesn’t hurt to plan for a drought, and be able to loosen the reins if plenty of precipitation falls. Here are a few pointers to keep in mind as we enter the growing season into a potential drought:
• Soil nutrients/yield goal – Soil testing is the best approach to determining fertilizer needs that reach optimum yield goals. Be sure to follow sound farming practices and reasonable yield goals. A yield goal is not a wish for the future, it’s actually an average based upon yield history for the field or zones of a field that excludes obviously high and low outlying yields. You can take your average yield factor times a range from 1.03 to 1.07 to account for increasing yield potential, but omit using such a factor if drought and other outlying major crop stressors are predicted to occur.
• Insects – Weather highly influences insect populations in growing crops. If our conditions continue to be hot and dry, keep an eye out for grasshoppers. They tend to hatch early during a warm spring, which can create a larger population than typical. Grasshoppers tend to follow green areas by moving from less favorable hosts to those that are still green and growing. Spider mites can also be a risk during drought periods and are important to watch for. In addition, soybean aphids do well in dry conditions but population growth is often limited due to excessive heat. Keep in mind that insecticides are not selective and often using one during hot, dry periods may kill beneficial insects that serve as natural enemies of other pests.
• Nitrates in forages – Nitrates, when converted to nitrites in forage crops can cause toxicity to livestock. If nitrogen fertilizers were applied to forages and drought conditions exist, nitrate build up is very possible, especially in the lower parts of the plant. It is best practice to test for nitrates when forage crops (especially grasses) are grown under drought conditions.
• Nutrient deficiency – If dry conditions persist, crops may begin to show moderate nutrient deficiency symptoms, regardless if adequate fertilizer was placed on the field. During drought, plants can experience difficulty extracting potassium. If potassium deficiency symptoms appear in your fields, we recommend soil and plant tissue sampling from affected and unaffected areas. In addition, top-dressed dry N fertilizer may not be readily available to plants as it sits on the soil surface (potentially volatilizing) while plant roots reach deeper into the soil profile to find moisture.
• Weed control – When drought happens, weeds tend to show more tolerance to herbicides than when growing under optimal conditions due to thicker wax layer development on the leaf surface. In addition, herbicides applied under drought conditions can conversely cause crop injury and not effect intended weeds as planned.
This is just a short list, to bring drought issues to mind as we enter planting time for small grains and eventually warm season row crops.
Reference: Karki, D., A. Bly, J. Davis, G. Shaffer, and A. Varenhorst. Agronomic Considerations for Moisture Deficit Conditions. SDSU Extension. 2021. https://extension.sdstate.edu/agronomic-considerations-moisture-deficit-conditions
• SDSU Crop Hour Webinar Series- March 16-19: Water, Weather, and Climate. March 23-26: Regulatory Information and Pesticide Education. Webinars run from 10-11a.m. CT. Free registration can be found at https://extension.sdstate.edu/agriculture/crops.
• 2021 Ag Economic Dialogues (virtual)- March 19: Drought planning and decision making indicators. 10 a.m. CT. Free registration can be found at https://extension.sdstate.edu/events.