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Drought Stress Beginning to Impact Corn Growth (7/5/12)

It has been hot and dry this past week and the US Drought Monitor (www.drought.unl.edu/dm/DM_highplains.htm) characterizes the northeastern and far southwestern portions of the state as being under moderate drought conditions.

If no rain is received soon, undoubtedly the area impacted by drought will expand rapidly as crop demand for water is now quite high. These last few days early planted corn has been using between 0.22 and 0.34 inches of water a day (data on water use can be obtained from NDAWN’s water use application). At these high rates of water use, stored moisture will soon be depleted and the crops will begin to exhibit symptoms of drought stress. In fact, some fields, particularly those with sandy soils are already exhibiting leaf curling during the heat of the day (see accompanying photo) indicating that the crop’s demand for water exceeds that which is available.  Corn is one of the most water efficient crops grown in North Dakota.  Nevertheless, it has a high water requirement because of its high yield potential and large biomass and can be significantly impacted by drought.  The impact of drought on corn growth and yield varies considerably depending on its timing and severity.  Research has shown that there is little impact of short periods of drought on corn growth during early vegetative stages.  During late vegetative development, however, short periods of drought stress (four days of sufficient stress to cause leaves to curl) can reduce yields by 5-10%.  Currently, most of the corn in North Dakota is in the 8 to 12 leaf stage with some just beginning to tassel.  Kernels numbers per cob are being set during this stage until just before silking, so drought stress now can impact the size of the cob.  Drought stress during tassel emergence has the potential to reduce yields by 10 to 25%.  The most sensitive period for drought stress in corn is during the period between silk emergence and the blister stage where yield losses between 40-50% can occur with just four days of severe water stress.  Corn is most sensitive to drought during this stage because the male and female flowers are separated by a considerable distance and pollen and silks are sensitive to hot and dry conditions.  When corn is severely stressed prior to flowering, silk growth is delayed and pollen shed will occur before the silks have emerged, resulting in barrenness.  Silks can also dry before they are pollinated resulting in poor fertilization and missing kernels.  Abortion of developing kernels is common, particularly towards the tip of the ears, with drought stress during early grain fill.  Since the corn plant has the capacity to store considerable reserves in the stem, yield losses when drought stress is delayed until the dough stage usually are in the 20-30% range.  These yield losses discussed above can be additive if stress occurs at more than one growth stage.  With about half the growing season still ahead of us, the potential for yield losses due to drought appear to be quite high for a large part of the state this year unless we get some timely rains.

Leaf curl on cornWater is essential for numerous chemical reactions in the crop plant and provides structure to cells and tissues.  The vast majority of the water that the crop uses, however, is for transpiration.  When moisture supplies are adequate, the transpiration stream brings nutrients and water from the soil via the roots to all parts of the plant, cools the plant, allows stomata to remain open and carbon dioxide to enter the leaves.  When soil moisture is limiting, stomata close, reducing the availability for carbon dioxide, increasing the temperature of the leaf tissue, reducing photosynthesis, thereby slowing plant growth (and in some cases hastening plant development).  Drought stress can reduce crop yields even before the plant begins to wilt, the first visible symptom of water stress.  During the first stage of stress, the upper leaves curl or roll towards the midrib during the hottest part of the day (see photo).  If stress continues, premature leaf death begins at the bottom of the plant and proceeds upward. Leaf death is the first sign of permanent damage to the plant.  With severe stress, the upper leaves roll so tightly that they appear like “onion leaves”.  These tightly wrapped leaves can restrict the emergence of tassels in some cases. With less leaf area capable of photosynthesis, plant growth is slowed even while maturing at an accelerated pace.  After pollination, carbohydrates that had been stored in the stem earlier in the season can be moved to the developing ear.  Not surprisingly, crops that are stressed later in the season are more prone to lodging because of poor stalk health.

Given the high demand for water from now until the end of grain filling (currently running at potentially more than 2 inches per week) and the limited supply of water in the soil in most regions of the state, significant rainfall is needed in order for our corn crop to realize the excellent potential yield that was established earlier in the season. After the last two seasons, it is seem odd to be writing about drought!

Joel Ransom

Extension Agronomist for Cereal Crops

Joel.ransom@ndsu.edu

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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