Drought Effects on Field Crops in 2012

Impact of Drought on Field Crops

  • Corn, soybeans and alfalfa have experienced severe drought stress throughout many areas.
  • Each crop responds differently to drought conditions.
    • What is considered drought stress?
    • What level of damage can be expected?
    • What are management options under drought?

Water Use by Crops

  • Water use is similar among corn, soybean and alfalfa. Each requires more water during reproductive growth (see tables below).
  • Factors that affect the ability of crops to uptake available moisture include:
    • Root development
    • Soil type
    • Nutrient availability for healthy growth
    • Weed competition
    • Disease and insect pressure
  • Field compaction caused during or shortly after planting has not been uncommon in 2012. This compaction, including sidewall compaction, can severely restrict root development and water uptake capability.
  • Coarse-textured or tight clay soils cause additional stress that prohibits availability of moisture as well.
  • Restricted roots or lack of root development due to drought stress increases the likelihood of nutrient deficiency.
  • Competitive stress from weeds, and damage from diseases and insects further restricts plant growth and water uptake.

Drought Effects on Corn Yield

Water Use in Corn by Growth Stage (inches/day)

Water Use in Corn by Growth Stage

Managing Drought-Stressed Corn

Water Use in Soybean by Growth Stage (inches/day)

Water Use in Soybean by Growth Stage

Managing Drought-Stressed Soybean

Water Use in Alfalfa by Growth Stage (inches/day)

Water Use in Alfalfa by Growth Stage

Source: Data estimates full potential of daily ET per week by Killen (1984) and tabulated by Wright (2002).

Managing Drought-Stressed Alfalfa

Estimated corn evapotranspiration and yield loss per stress day during various stages of growth

Estimated corn evapotranspiration and yield loss per stress day during various stages of growth

Derived from Rhoads and Bennett (1990) and Shaw (1988). From: What Happens Within The Corn Plant When Drought Occurs? Joe Lauer, University of Wisconsin-Extension, 8/20/03.

  • As the table above indicates, drought effects on yield are greatest from pollination through early grain fill.
    • Drought at pollination inhibits pollen release, silk growth.
    • Maximum pollen shed is limited to approximately 4 days during a 7- to 10-day period with only 4 hours per day of pollen release.
    • Silks contain more than 90% water; therefore, additional days without moisture reduce pollination.
    • During early grain fill, kernels are filled at the bottom first then progress to the tip of the cob.
  • Lack of pollination can occur at any point and timing of the stress can be identified by gently husking the cob and shaking the silks to see which are still attached (not pollinated), to those that fall away (pollinated).
  • If stress continues through grain fill, the plant will develop kernels near the bottom first and may leave unfilled kernels (noses) on the tip of the ear.
Corn yield expressed as % of well-watered treatment

*Yield expressed as % of well-watered treatment. Adapted from Cakir, 2004

Additional References

  • Chopping corn for silage can be considered if the crop is unlikely to recover, but there are some watch-outs:
    • Yield will be limited due to lack of grain and fodder.
    • Harvest moisture can vary considerably and cause fermentation issues.
    • Nutritional value will vary throughout the field.
    • Nitrate content - high levels can be toxic.
    • Safety - the ensiling process will release nitrates by converting to nitrous gas, which is extremely toxic.
  • Use of a foliar fungicide to protect drought-stressed corn may not be helpful. Diseases present during drought are often bacterial and will be unaffected by fungicides.
  • Monitor plants for silk-clipping insects such as Japanese beetles and corn rootworm beetles.

Managing Drought-Stressed Soybean

  • In addition to irrigation, weed and insect management can help reduce additional stress under drought.
  • Scout stressed soybeans for damage from spider mites; be prepared to take control measures as populations increase.
  • Scout for defoliating insects like bean leaf beetles, Japanese beetles and grasshoppers.
  • Glyphosate may be applied to soybeans through the R2 stage of growth, so make plans to control weeds prior to pod set.
  • Good scouting notes can help determine if fields have issues with low soil fertility, soil compaction or herbicide-resistant weeds. Take detailed notes now to prevent future problems.
  • Soybeans that do recover from drought may have green stem symptoms later in the season.

Managing Drought-Stressed Alfalfa

  • Similar to soybeans, little can be done for alfalfa as it may enter dormancy. Full recovery of a stand that goes into dormancy from drought may not be determined until enough precipitation occurs or at spring green-up.

Additional References

Killen, M. 1984. Modification of the Checkbook Method of Irrigation Scheduling for use in Minnesota. Design Project. Agricultural Engineering Department, University of Minnesota.

Kranz, W.L., R.W. Elmore, and J.E. Specht 2005. Irrigating Soybean. Univ. of Neb. NebGuide G1367.