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¶ Introduction
Dry weather can stress corn during it’s early growth Limited water before the V12 (12-leaf) growth stage usually results in minimal yield loss if adequate water is then available at the V12 stage and beyond.
Early season dry conditions may not significantly impact the final corn yield, but other impacts can or will occur. Each of the following issues assumes that water stress lasts for about two weeks and the field conditions that follow the stress period will let the crop recover.
¶ 1. Rolled Leaves
Corn leaves will roll during the heat of the day to try to conserve as much water as possible. Photosynthesis is reduced when leaves roll, causing corn plants to produce less biomass during drought stress.
¶ 2. Scout the Root System
Soils usually dry from the surface downward. The depth of dry or wet soil can affect root development. Corn roots grow about 0.25 to 0.30 inches per day up to stage V4 or V5, then grow at about 1.0 to 1.3 inches per day until they reach maximum depth at silking. Root growth through the season averages about 2.75 inches per leaf stage to a maximum depth of about 60 inches (see Figure 1).
¶ Figure 1. Corn Root Growth From V4 to V20
¶ 3. Potassium Deficiency
Potassium (K) deficiency is a common indicator of drought stress on young corn plants. Potassium is the primary nutrient associated with transpiration and water relationships in the plant. Potassium deficiency may result from drought stress alone, which limits root uptake and potassium availability.
Plant tissue samples at V3 to V6 growth stages may be likely to show potassium deficiency even if the soil test K is adequate. The corn plant needs water to take up soil potassium, so adding more potash fertilizer will have no effect if the crop does not have water.
¶ Figure 2. Tillage-Induced Potassium Deficiency
¶ 4. Other Nutrient Deficiencies
The corn roots require water take up several nutrients, not just potassium. Potassium might be the most obvious deficiency, but a tissue test may reveal other deficiencies as well. A soaking rain is the best remedy for these temporary or “transient” deficiencies. Soil nutrients are mobilized and corn growth resumes, so deficiencies disappear.
¶ 5. Nutrient “excess”
Some nutrient levels that are reported in a plant analysis report may be high or excessive in drought-stressed or stunted plants. The actual amount of a nutrient taken up may be low, but can be disproportionately high compared to the amount of above-ground growth. Nutrients concentrate in the plant tissue in this situation and result in high plant analysis results.
¶ Figure 3. Corn Radicle Damage
¶ 6. Compaction Becomes Evident
Soil compaction becomes more obvious in dry soils. Corn that twists or curls along a single row or in a section of the field before other corn suggests compaction problems. Compaction may occur along seed furrow sidewalls and/or at the subsurface operating depths of “vertical tillage” implements or discs.
Compacted soil restricts or stunts root growth. It becomes impossible for roots to penetrate these compacted zones in dry soils. These stunted roots only have access to a limited volume of soil so water and nutrient uptake is also limited, which limits above-ground growth.
¶ 7. Fertilizer Injury
Root injury may occur from fertilizer that is in direct contact with seed as an “in-furrow” or“ pop-up” application. Damage is often most noticeable as damaged radicles (first root to emerge from seed) or damaged mesocotyls (white, root-like tissue between the seed and base of the plant). These structures may be stunted, have brown/black discoloration, and have a burned appearance.
The damage results from excess fertilizer “salt” or from free ammonia formed in the seedling root zone from certain fertilizers. Damage can occur even with so-called “low-salt” fertilizers if applied at higher rates. Damage can also occur with fertilizers that are applied a distance away from the seed, including starter (e.g., 2x2 placement) and preplant anhydrous ammonia, urea, or UAN fertilizers.
Damage potential is greater in dry soils, sandy soils and/or at higher application rates. Rates or placement methods that do not damage seedlings under normal conditions may injure seedlings under prolonged dry conditions.
¶ 8. “Rootless” or “Floppy” Corn Syndrome
All of the roots from one or more nodes may desiccate (dry out) and die from dry weather and hot temperature stress. Desiccated roots appear shriveled and discolored. This symptom is unlike that of any other lethal root stress, including salt injury from fertilizer. These symptoms are NOT like any associated with herbicide injury or insect feeding.
A strong wind at this point can knock the plants over. Corn plants from about V2 to V3 will be most susceptible. Corn planted at shallow depths more susceptible. The best remedy is a soaking rain or irrigation that allows new root growth before any strong winds occur.
¶ Figure 4a. Early Stage of "Rootless" or "Floppy" Corn
¶ Figure 4b. Absence of Established Nodal Roots
¶ 9. Loss of Row Number or Kernel Number:
The dominant ear and tassel formation starts at the V6 growth stage. Corn plants are developing nodal root systems at stage V6, the final stage before exponential growth. Water stress from stages V7 to about V12 could reduce the total biomass of stems and leaves.
Water stress at the V12 growth stage starts affecting kernel development and ear size. Drought stress at V12 and beyond will reduce kernel rows and then kernel numbers per row.
¶ 10. Less Disease Risk:
Dry conditions means foliar disease pressure is lower. Fungicides are not needed in a drought.
¶ 11. Reduced Residual Herbicide Activity
Most soil residual herbicides need rainfall to activate. Dry weather may allow weeds to escape residual herbicides, but slows their growth as well. Identify which weeds are escaping and plan a treatment once rain occurs and weeds resume active growth and root uptake.
Weeds will need moisture to resume growth and be receptive to the herbicides. Using the full label rates of adjuvants or conditioners may be more important to assure successful weed control.
¶ 12. Nitrogen Management
Volatilization poses the greatest risk for nitrogen losses in dry weather. Surface-applied urea fertilizers begin to actively volatilize within about three days after application. Urea treated with an adequate rate of NBPT[1] or NBPT plus duomide[2] will not volatilize for about 14 to 21 days. Sidedressing with liquid 28% or 32% UAN may be preferred over broadcast fertilizer application. There is less risk of volatilization because half of the nitrogen is in the urea form. The liquid material also soaks into the soil, reducing surface exposure for volatilization to occur.
Injecting fertilizer into the soil essentially eliminates volatilization potential. Movement of surface-applied or injected nitrogen within the soil will be limited until water from rain or irrigation recharges the root zone. Corn roots will not take up the nitrogen from dry soil, so uptake will be delayed until soil moisture is available.
Spray booms with streaming nozzles or drop tubes in between each row can be used to apply some of the nitrogen requirement close to the plant. Avoid applying nitrogen directly to the corn plants. Leaf spotting or burning may occur following direct contact of the undiluted nitrogen fertilizer with the corn leaf tissue. This leaf burning is typically cosmetic and does not affect plant health and yield. If the corn crop is already under stress (e.g., leaf rolling, stunted growth), there is no need to add additional stress from leaf injury. Use dry urea if it is the only option available. If other options are available, use them.
¶ References
Archontoulis, S. and M. LichtHo. 2017.How Fast and Deep do Corn Roots Grow in Iowa? ICM News, 14 June 2017. Iowa State Univ. Ext. and Outreach. Ames IA. https://crops.extension.iastate.edu/cropnews/2017/06/how-fast-and-deep-do-corn-roots-grow-iowa accessed 06Jun2023.
Lee, C. 2023. Dry weather effects on corn at early growth stages. KyGrains.info blog, 06Jun2023. Univ. of Kentucky Coop. Ext. Svc., Lexington KY. https://www.kygrains.info/blog/dry-weather-effects-on-corn-at-early-growth-stages-2?s=03 accessed 27June2023.
Nielsen, R.L. 2022. “Rootless” or “Floppy” Corn Syndrome. Corny News Network. Purdue Univ. http://www.kingcorn/news/timeless/FloppyCorn.html accessed 27Jun2023.
Quinn, D. 2023. Corn Root Damage Caused by Fertilizer. The Kerne, 26 June 2023.l. Purdue Univ., West Lafayette IN. https://ag.purdue.edu/news/department/agronomy/kernel-news/2023/06/2023-corn-root-damage.html accessed 27Jun2023.
[1] NBPT: active ingredient in Agrotain™ and other products
[2] duomide: active ingredient in Anvol™