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Cropping Strategies for Limited Irrigation
Management
4/23/2002
Ron F. Meyer
Area Extension Agent
(Agronomy)
Colorado State University Extension
Golden Plains
Area |
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Authored by: J. Schneekloth and R.F. Meyer, CSU
Extension
The cropping year for 2002 is beginning with much below-normal
precipitation. However, even best weather predictions indicate that the rest of
the growing season has equal chances for below normal, normal, or above normal
precipitation. Therefore, the amount of precipitation during the coming growing
season is anyone’s guess at this point. However, three weeks into the
wettest portion of the year has resulted in little or no moisture. As a result,
producers with limited-capacity irrigation systems will be forced to make
difficult decisions as to which crops to plant, how much of those crops to
plant and agronomic practices associated with the crop choice. Corn generally
is the most widely irrigated crop because of its greater response to water than
many other crops. Much of this article will discuss management decisions to
maximize irrigated corn with a limited irrigation capacity. For producers with
surface water facing the possibility that irrigation water may be shut off
early, other options must be explored.
When working with a limited
capacity irrigation system, a common idea is to reduce corn plant populations
drastically in hope of reducing crop water use. However, research suggests that
to significantly reduce crop water use, plant populations must be reduced to
less than 18,000 plants per acre. At that population, potential maximum corn
yields are also highly reduced. Research from Kansas State University at Colby,
Kansas looked at the impact of varying plant populations at different
irrigation capacities. Although this data is from Kansas and the work was done
with sub-surface drip irrigation, it is the best and most complete information
available. Research results found that increases in corn populations increased
grain yield even at low irrigation capacities. Plant populations below 28,000
plants per acre had lower yields than populations above 28,000. However, plant
populations above 28,000 plants per acre offered only small increases in corn
grain yield when irrigations were limited.
Low-capacity irrigation wells
producing in the range of 400 to 600 gallons per minute are common within some
Colorado locations and will have a difficult time keeping up with a high
population corn crop’s water demand. Corn yields of below 150 bushels per
acre were common in 2001 where less-than-normal rainfall occurred with these
types of well capacities. As a result, producers who have fields that fit the
above-mentioned scenario, should reduce corn populations to approximately
28,000 plants per acre, but not much less.
Another option for low
capacity wells is to reduce the acres of high water use crops such as corn (and
alfalfa) and include crops that have different peak or critical time periods
for water and those that use less water. Splitting the center pivot with
different crops works well. Summer crops that have different critical
irrigation time periods than corn include soybean, dry bean and sunflower. The
critical time period for corn is from pre-tassel to milk stage. This time
period is generally from early July to early August depending upon growing
conditions and planting date. The critical time period for soybean is from pod
elongation thru early pod fill and is generally during the month of August.
Sunflower’s critical time period is from early flower through grain fill
and is generally during August and early September. A further option on the
remainder of acres is a late season forage crop. With dry weather, range and
forage production may be reduced and the price for forages may
increase.
By reducing irrigated acres of an individual crop, the
available water can be concentrated on those acres. An example is that
irrigated corn acres under a single pivot are reduced by half. The net effect
is that irrigation capacity is doubled and water applications more closely
represent crop water use. When the corn crop is past its critical time period,
the water can be used on the crop planted on the other half of the pivot during
that crop’s critical time period. Work at Colby, Kansas shows that corn
grain yields increase by 28% when the irrigation capacity is increased from 1.9
to 3.8 gallon per minute per acre which can be accomplished by cutting
irrigated acres in half for portions of the irrigation season. Although
irrigated acres were decreased, the net return of those irrigated acres
increased four-fold. Work from western Nebraska shows similar results in
increasing net return by changing the crop mix with limited irrigation water by
mixing crops that have different critical water timing and needs.
For
more information, feel free to contact Joel Schneekloth at (970) 345-0508 or
Ron Meyer at (719) 346-5571. |
Page Created and Maintained by: Perry D. Brewer, Area
Extension Agent (Technology Education/Youth)
1/16/2003 |
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