Drought stress is a common occurrence in maize production in sub tropical growing regions and is defined as the time point at which soil moisture is not adequate to meet the needs of the growing crop. Drought stress can lead to decreased yields, enhanced susceptibility to insects, diseases, and aflatoxin(link to other page).
Hybrid Selection – choose and adapted hybrid that is rated as drought tolerant for both irrigated and dryland acreage as water supply could fail.
Pre-irrigation (if possible) – ensure adequate moisture is available for full germination as plants per acre is a large component of yield. Thoroughly soak all rows, to the top of the bed if possible, of furrow irrigated land approximately a week and a half before planned planting date to allow for drying. For pivot irrigated fields, apply water immediately after planting sufficient for full germination.
Population – too many plants per acre creates too much competition for limited water resources and can reduce profit margin. For Texas: ~18,000-20,000 on highly productive dryland and 24,000- 30,000 for irrigated depending on geographic locale and type of irrigation. Follow recommendations on seed bag and make informed decisions!
Tillage – use minimum till/no-till/strip-till where possible to minimize moisture loss of soil.
Cultivation – with advent of herbicide tolerance this practice should be limited. Can be used as a method to close up cracks in the soil to avoid water loss.
Nitrogen – over application of nitrogen to drought stressed corn can cause foliar damage from lack of water to break down nitrogen in the leaves.
Timing – if possible, crop should be kept wet at all times. In cases where irrigation is limited, timing of irrigation is crucial. (Adapted from Texas AgriLife pub. http://amarillo.tamu.edu/files/2010/11/Vietnam-Corn-Development-and-Key-Stages.pdf) See Figure (adapted from http://www.extension.umn.edu/distribution/cropsystems/components/DC1322a.pdf) for average daily water use for an estimate of how much water is needed for precision applications. Keep in mind some water is lost to evaporation, wind, and some cannot be recovered by the plant.
Important Developmental Stages Sensitive to Water Stress
- Early Vegetative – plants can handle some stress at this time, but will be vulnerable to pests and disease. Water use is low, but increasing as seen in figure.
- ~V7 – number of kernel rows being determined – field should be wet, or being irrigated. Water use is increasing as seen in figure.
- V12 – number of kernel rows determined, number of kernels per row being determined – field should be wet, must begin irrigation, especially if it takes multiple days to cover the acreage. Water use continues to increase as seen in figure.
- Tassel emergence – any drought stress now will cause delay in silk emergence possibly leading to barren ears. If field is not saturated then an attempt should be made to minimally irrigate to keep silks developing. Water use is almost at seasonal maximum as seen in figure. Water is also needed here for sporulation of atoxigenic strains of Aspergillus flavus applied to field (link to aflatoxin page).
- Silking – CRUCIAL POINT FOR WATER STRESS – field should be saturated for maximum yield, and if possible should be maintained at a high moisture level to keep silk growth rate at maximum. Silks grow starting with the ovaries closest to the base and move toward the tip. It takes approximately 2-3 days for all silks to emerge. Water use is at maximum.
- The 2 Weeks After Silking Especially Milk Stage – 2nd most crucial point for water stress – drought stress now will cause kernel abortions, decreasing the number of full kernels that develop on the ear. Water use is decreasing. Keep fields moist, but avoid over application as fungal growth will thrive in these environments.
- Dent – water stress now will cause lighter kernels which slightly affects yield. Water use continues to drop.
- Black Layer and Maturity – water stress post black layer will not affect kernel yield, but if the crop is allowed to die too soon lodging and dropped ears can become an issue. Apply minimal amounts of water until plant naturally matures and begins to dry down.
Irrigation Systems – know your system and how long it takes to properly irrigate the entire field so that you can plan accordingly.
- Overhead sprinkler systems (center pivots and linears) should be equipped with LEPA systems to maximize quantity of water entering the soil. Multiple small quantities of water may be needed to fully saturate the profile if compaction is an issue causing runoff. AVOID OVERWATERING CAUSING RUNOFF, monitor fields as close as possible as runoff erodes soil and carries nitrogen out of the field.
Furrow irrigation should be conducted in a way to maximize saturation while minimizing time and runoff. Surge valves provide a good soak while minimizing runoff and allow for more ground to be covered per set.
Soil type – know your soil types as sandier soils don’t hold as much water as clay or silt. Caution, heavy clay soils will retain more moisture than the plant can absorb. Monitor your plants carefully for signs of stress, even if the ground is a little moist.
Combine Settings – drought stressed plants will likely have smaller stalks, smaller ears and aborted kernels.
- Adjust ground/rotor/fan speed to maximize clean grain in the hopper. Shoe sieve settings should be monitored as cobs might shatter and fall through and grain will be variable in size.
- Deck plates (if not adjustable) should be adjusted to make sure maximum number of ears are picked. To check deck plate setting, run combine ~100 yards and stop. Check to see if there are any kernels/ears on the ground between the header and the drive wheels. If there are then the grain is being shelled in the header and adjustments should be made.
Written by Gerald De La Fuente