Lebanon Crop Management Video

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27 June 2012

Early Season Drought

Del Voight - Agronomy Extension Agent
                The recent drought has caused much concern for producers and urban dwellers as well.  This article will discuss some basic information related to the drought.  First of all the meaning of drought has two definitions.  A hydrological drought is one by which potable water is depleted to the point that the local governments or state declare an official drought using different indexes.  This differs to an agricultural drought in that an agricultural drought is one which the crops are the indicator of the stress. 
                Signs of  drought stress are poor growth, wilting during the day or complete desiccation of tissue.  The severity of the drought depends on the plant and its rooting depth and growth habit.  In addition, the soil type will determine the severity of the drought.  The water holding capacity of the soil (organic matter, clay content) and soil depth to bedrock will also determine the availability of water in the soil.  In Lebanon, soils located in the northern part of the county are prone to drought due to the soil limitations.  Even in a ideal soil types other factors such a soil fertility, tillage method, and compaction may limit root growth and therefore cause drought effects.  This drought year the extreme northern and southern ends on the county received rainfall while the middle sections were suffering for moisture.
                Crops prone to drought are the shallow rooted crops such as a pastures which different species of grasses that make up the pasture differ in rooting depth.  For instance a highly drought tolerant pasture grass is reed canary due to its 18 inch rooting depth.  In contrast, Kentucky bluegrass is poor in drought due to its 4 inch root system.  Many perennial grasses have the ability to go dormant in times of complete water stress and will turn brown.  This is a critical stage to manage the pasture by removing animals and supplemental feed to prevent permanent injury to the dormant plant. 
                Annual crops such as corn and soybeans also depend on the depth of rooting.  Corn roots will like any other root follow moisture in the soil.  This is to say that when the water recedes the roots grow with the water unless the water recedes more quickly than the roots can grow which is the case with much of the late planted corn and corn after Barley.  Soybeans are more tolerant to drought because of its rapid root growth and tap root system than can penetrate compaction zones to get to water rich areas.  Corn however has a fibrous root system and many times cannot reach all available water.  Corn sends roots down 5- 6 feet with most of the roots in the upper 18 inches of the soil.  There is not much a producer can do right now to counter act the affects of drought.  But, by leaving crop residue on the surface of the soil, above all avoiding soil compaction, maintaining optimum fertility in the soil and planting early much of the drought affect next year may be reduced due to increased root growth and mass.  In 1970 Agronomy Journal a research thesis indicated that corn in vegetative stages is less prone to drought than during anthesis( Table 1).

Table 1. Effect of drought on corn yield


Stage of development
Percent yield reduction
(from 4 consecutive days of visible wilting)
Early vegetative
5-10
Tassel emergence
10-25
Silk emergence, pollen shedding
40-50
Blister
30-40
Dough
20-30
Classen, M.M., and R.H. Shaw. 1970. Water deficit effects on corn. II. Grain components. Agron. J. 62:652

   We are far from chopping at this point however producers should not consider chopping corn for silage until the plant has failed to unroll its leaves at night.  This indicates that the plant is dead and is losing moisture.  Once this occurs chopping should start quickly to ensure proper moisture for ensiling.         Avoid green chopping drought stricken plants due to the concern for nitrate toxicity in the silage or plan to have the silage tested for nitrates before feeding.  Properly fermented drought silage will be safe to feed and it is critical to take the silage at the right moisture.  Chop and test for the correct moisture level.   In either case producers are urged to keep checking fields so that the crop does not get to dry to ensile and silo fires will be avoided which occurred on several farms two years ago.
                Another concern with corn is during the pollen silking interval.  Before the tassel emerges corn that visibly wilts will lose @ 2-3% of the total grain yield per day.  Once the tassel emerges  the loss can be @10-25% per day for grain yield.  Most of the corn in the county has not started to silk.  Once the silks emerge a loss of 40 -50% of the grain yield may take place due to the possibility of barren ears.  This happens because the pollen grains fail to travel through the silks to the kernel and the kernel remains inactive and does not fill.  Corn should be checked for pollination by stripping the husk back and looking for small blisters to determine the need for harvest or to let the stand mature for grain.  Additional information related to handling drought concerns is available in the Extension Office. 
                Alfalfa is very drought tolerant partly due to its origination in the Iran/Iraq area which is droughty by climate.  Reduced growth has pushed producers to wonder whether or not to cut the alfalfa.  Penn State recommends that producers let the alfalfa go to 30% bloom and then cut.  If there is not enough forage there to bale or chop then simply clip the crop to allow the plant to go into a vegetative state and with more rainfall may mean a better fourth cutting. 
                Drought affects many aspects of our lives but causes much financial stress for producers.  Recent rainfall has not brought about desirable results around the county.  Certainly some crops will respond, but some are already lost.  Many others are also affected by an agricultural drought such a golf courses, vegetable producers and even certain wildlife species that survive in areas near rivers etc. like the woodcock which depends on moist soils to probe for earthworms with its long bill.  Fish kills in small streams that dry up and loss of aquatic life all are affected by dry conditions.  In addition many insects such as spider mites, grasshoppers and many other insects are prolific during a drought and may need to be managed which is a whole other area of interest for a future column.  A weekly observation of droughted fields may turn up insect pest spikes and it is critical that the insects be monitored. Forecasted rains will certainly be welcome sooner than later.

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