While many corn and soybean fields have held up amazingly well despite the shortage of soil moisture, the long term prognosis for optimum yields is not promising. The long range weather forecasts do not predict much precipitation and our typically hottest and driest months are just ahead.
 

To gain a better perspective on how widespread dry conditions are, check out the U.S. Drought Monitor at http://droughtmoni

tor.unl.edu/DM_midwest.htm after 8:30 a.m. EST on Thursday mornings. The data cutoff for the Drought Monitor is 7 a.m. on Tuesdays. The Midwest version includes the states of Ohio, Indiana, Illinois, Michigan, Kentucky, Iowa, Minnesota, Wisconsin and Missouri. Last week’s color map showed nearly all of the lower two-thirds of the area as either abnormally dry, or ranging from moderate to extreme drought.

A couple of weather fronts moved through our area recently over a 10-day period that provided some moisture relief in limited areas. Temperatures moderated a little, late last week, which allowed corn and soybean fields to perk up a bit on cooler mornings. Afternoons brought back the rolling of corn leaves and wimpier appearance of soybean plants.

So, where are we as far as yield prospects? Seed companies have come a long way in building some dry weather tolerance into our corn hybrids and soybean varieties. 2012 may show us how much genetics have progressed in helping crops endure long periods of moisture stress.

For corn, stem and leaf cell expansion is reduced when plants are moisture deprived during vegetative development, resulting in less plant height and leaf area. With drier conditions early, we likely have some corn roots reaching 5-8-feet deep depending on soil texture and compaction. Early drought stress does not generally affect yields significantly up to the V10-V12 stages. Since much of our early seeded corn is now beyond the 12-leaf stage, abnormally dry conditions can reduce yield potential 2-4 percent per day up to tasseling.

Lack of adequate moisture around flowering and pollination may delay silking, reduce silk elongation, and inhibit embryo development after pollination. Potential yield loss: 3-8 percent per day of stress. Inadequate moisture or hot temperatures interfere with synchronization between pollen shed and silk emergence. Silk emergence may be delayed until pollen shed is nearly or completely finished. Periods of high temperatures, low relative humidity and parched soils may result in desiccation of exposed silks, making the silks non-receptive to pollen germination. If dry weather persists, yield loss becomes progressively worse.

For the soybean plant, as long as the plant roots are reaching some moisture during the vegetative growth stages, yield impact of dry conditions is limited, as long as weeds and/or insects are controlled.  When the soybean begins to flower, or enter the reproductive stage, insufficient water can cause flowers and young pods to abort, reducing the number of seeds per plant. Moisture stressed plants will also reduce the size of their leaf pore openings to reduce the loss of water vapor. This reduces the intake of carbon dioxide and the production of photosynthates, slowing plant growth. When rainfall relieves the stressed plant, normal growth is resumed. The ability of the soybean plant to reduce metabolic activity, allows plants to tolerate dry spells without dying or harming their ability to resume growth if adequate moisture is received.

Readers with questions or comments for Roger Bender may write to him in care of this publication.