The blessings of El Niño notwithstanding, the Southwest remains a drought-prone region, subject to long, devastating drought, interrupted by occasional rainy seasons that cause different but equally serious hazards for farmers and ranchers.
“We see a lot of variability in water,” says Ronnie Schnell, assistant professor, soil and crop sciences, Texas A&M AgriLife Extension, College Station.
Speaking at the Texas Plant Protection Association annual conference in Bryan, he said water stress — either too much or not enough — encourages uneven crop development and may result in lost yield.
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“The plant growth stage when moisture stress occurs is an important factor,” Schnell says. “Early drought will affect plant size, for instance. Flooded, saturated soils for an extended period also reduce plant growth.”
He says dry conditions may affect ear size in corn, as well as kernel numbers and weight. Saturated soils may also result in lighter grain weights. “In sorghum, flooding or drought may have significant effect on plants, especially early. Damage from boot through bloom may not be as severe.
“The young seedling stages of corn and grain sorghum are more susceptible to flooding and saturation and often result in stand loss,” he says.
Moisture stress also affects plant physiology and nutrition. “During drought, water is not moving through the plant, and neither are nutrients. Flooding reduces respiration, damages roots, and impairs nutrient movement.”
IMPACT OF STRESS
Either extreme also affects plant size. “Both drought and flood can reduce leaf size and leaf area and limit the plant’s ability to conduct photosynthesis. Stress reduces plant height and thickness of corn stalks. Moisture stress delays tillering in sorghum and delays development.”
In corn, moisture stress reduces yield potential. Ear or head size may be smaller and kernel and grain numbers may be lower. Photosynthesis will be limited and nitrogen deficiency will limit yield potential.”
Schnell says moisture stress disrupts flowering and pollination.
Uneven growth may create problems with pest management. Different growth stages in the same field mean pests will appear at different times, creating a dilemma in scheduling efficient and effective pesticide applications.
He acknowledges that farmers can do nothing to control the weather, but says they do have options available to improve their odds against either moisture extreme. Variety choice is one. He recommends farmers look at varieties with improved photosynthesis under either heat or moisture stress. Stay green and delayed senescence characteristics are important traits, he says.
Leaf rolling, he says, conserves moisture and encourages drought tolerance. Root architecture is another consideration. Root systems should go deeper and be able to extract moisture from deeper in the soil profile. Early maturity is another advantage.
Cultural practices also play a role, Schnell says. Tillage methods, including reduced till or no-till, may help conserve soil moisture. Eliminating, as much as possible, soil compaction can also improve moisture management. Both roots and moisture can penetrate into the soil profile. Sidewall compaction and traffic can create problems. Proper drainage moves excess water away from susceptible plants.
“Timing and duration of water stress will determine the ultimate impact on crop production,” Schnell says. He notes that crop and hybrid selection, seeding rates, plant population, soil management, and soil fertility are all important factors in working through drought and flood conditions.