R.L. (Bob) Nielsen
Agronomy Dept., Purdue
Univ.
West Lafayette, IN 47907-1150
Email
address: rnielsen@purdue.edu
uch of Indiana has received less
than normal rainfall since mid-summer 1999. Soil moisture reserves are
currently very low, especially in the northern half of Indiana. Some
forecasters are predicting widespread drought for this coming growing season.
What plans, if any, should Indiana corn and soybean farmers develop to manage
the effects of a possible drought in 2000?
As of 22 February, the National Drought Mitigation Center's Drought Monitor site characterized much of the northern half of Indiana (Fig. 1) as being in a Level 2 or severe drought stage (level 4 being the worst). Numerous reports have been received (post hole digging, grave digging, tile repair) testifying to the dryness of the subsurface soils throughout much of the area. Precipitation for the past nine to twelve months has been below normal.
Fortunately, current long-range weather forecasts from the NOAA Climate Prediction Center are not particularly dry in their predictions for precipitation for our area of the Corn Belt through early to mid-summer (Fig 2). Granted, none of the monthly forecasts are predicting above normal rainfall, but few are calling for significant chances of below normal rainfall either. Nonetheless, some private forecasters are predicting strong probabilities for a major drought occurring somewhere in the Corn Belt this coming crop season. Those forecasts plus the current dry subsoil situation throughout northern Indiana are making quite a few farmers nervous about the prospects for drought stress on corn and soybeans in 2000.
Planning for drought stress is not necessarily a smart move for Indiana corn and soybean growers. Historically, the odds are in our favor for sufficient rainfall to grow crops. Planning for drought is somewhat like planning to fail. Nonetheless, there are a few agronomic options available for those bent on planning for a drought.
Minimize the number of tillage operations you plan on performing on your fields yet this spring. Reducing tillage trips will lessen the opportunity for further evaporative soil moisture loss. An added benefit is that your overall fuel expense will also decrease. Where soils are suitable or adaptable (moderate- to well-drained), consider foregoing tillage altogether and implementing a no-till cropping system instead. Crops will benefit later in the season from conserved soil moisture.
By now you should have been working closely with your seed dealer to identify high-yielding varieties with excellent drought tolerance, early season vigor and stable yield performance. High population tolerance is often related to drought tolerance and thus can be used as an indirect indication of drought tolerance in a hybrid. Early season vigor is important for encouraging healthy, vigorous stands of corn or soybean that will better tolerate stresses later in the season. Stable yielding ability means the ability to yield at a relatively constant level no matter the growing conditions. Corn hybrids that are bin-busters in excellent weather, but fall apart under stress are not the hybrids of choice if drought is looming in your future.
Many factors influence the choice of the "correct" seeding rate for corn hybrids. Generally speaking, hybrids with small crop canopies, good to excellent stalk health characteristics and little ear size flexibility perform best at higher seeding rates. Conversely, hybrids with large crop canopies, average to poor stalk health characteristics and significant ear size flexibility do not require as aggressive a seeding rate.
To a large degree, seeding rate selection can be based on the historical production level for a given field and/or hybrid. Where yields are consistently greater than about 125 bushels per acre, optimum seeding rates range from about 28,000 to 33,000 seeds per acre. For conditions where 100 to 125 bushels are the norm, optimum seeding rates are about 24,000 seeds per acre. Where historical yields are less than 100 bushels per acre, seeding rates should be closer to about 20,000 seeds per acre.
Obviously, if one is confident that a major drought will occur this year that will drop yields below 100 bushels per acre, then one may consider dropping the seeding rate to 20,000 seeds per acre in anticipation thereof. HOWEVER, if your historical yields are greater than 125 bushels per acre and the drought does not develop, then you have pretty well guaranteed that you will not attain the maximum yield potential of that field if you drop your seeding rates.
Furthermore, most of today's hybrids are much more tolerant of stresses in general than the hybrids of ten to fifteen years ago. Hybrids that perform well with final stands in the upper 20's will likely perform well at the same populations under dry conditions. So, my advice is to not stray far from your usual choice of seeding rates even if you are concerned about a possible drought in 2000.
If seedbed conditions are dry at planting time, then your main objective should be to place the seed in uniformly moist soil. If necessary, corn can be planted as deeply as 3 inches if that is the depth where seedbed moisture is uniform. Soybean, on the other hand, should not be planted much deeper than 1½ inches deep because of the difficulty created for the emergence of the hypocotyl or "shepherd's crook" of the seedling.
If soil is bone-dry at planting, but you anticipate rainfall in the near future, go ahead and plant. Recognize that seed stores as well in a dry seedbed as in a dry seedbag! Those of you that experienced the "Great Drought of 1988" should remember those fields planted in late April that finally germinated and emerged perfectly in late July once enough rainfall occurred. Insect and disease activity are generally less in dry soils. Having the seed already planted also avoids further planting delay after rain does occur.
Early planting helps avoid the usual summer heat and dry stress conditions during flowering, especially for corn. In fact, this factor was one of several that helped the 1999 corn crop in Indiana yield as well as it did given the dryness and several hot spells that much of the state endured. So, be well prepared to head for the fields as soon as the soil is fit and temperatures are reasonable. Historically, those conditions occur from about early April in southern Indiana to late April in northern Indiana.
If you feel strongly that a major drought is imminent and your corn crop will suffer severely, then consider hedging your nitrogen bets by foregoing pre-plant nitrogen fertilizer in favor of sidedress N applications. Apply 20 to 40 lbs. N in your starter fertilizer. Assess crop condition prior to sidedress time. If the crop is struggling with drought stress, you may opt to apply less N at sidedressing if you anticipate significant yield decreases due to drought. In the worst case scenario, you may opt to not apply any further N if the crop is heading toward total disaster. On the other hand, remember that a rainy June may create problems for you in terms of covering all of your corn ground at sidedressing time.
Corn requires from 16 to 25 inches of water (rain, irrigation, & soil) to produce a crop of grain. Critical times for avoiding water deficits are stand establishment (emergence to knee-high), determination of potential ear size (knee-high to shoulder-high), pollination and the grain filling period. Of these time periods, drought stress at pollination can impact grain yield the most. Maximize irrigation efficiency by matching irrigation use with rainfall and crop demands. Minimize costs and maximize yields by implementing formal irrigation scheduling procedures. A comprehensive Web site on numerous irrigation issues is available at the University of Nebraska-Lincoln ( http://www.ianr.unl.edu/pubs/irrigation/ ).
Historically, drought is not something folks should generally plan for in the eastern Corn Belt. Implement sound agronomic strategies to encourage a vigorous crop and aim for "normal" yields, but adjust for soil and crop conditions where feasible.
For other information about corn, take a
look at the Corn Growers Guidebook on the World Wide Web at
http://www.kingcorn.org