(Editor’s Note: This article is an excerpt, slightly
modified, from the new K-State publication Efficient Crop Water Use in Kansas,
NF-3066, available at: http://www.ksre.ksu.edu/library/crpsl2/mf3066.pdf
-- Steve Watson)
By Kansas State
basic principle of efficient crop water use is shifting as much of the total
water use, or evapotranspiration (ET), to crop transpiration and away from
evaporation. One way to reduce evaporation is to increase and maintain crop
also can be minimized by adjusting crop intensity, and by selecting crops and
crop management practices that shift timing of crop growth to occupy portions
of the growing season that are most susceptible to evaporation; that is,
growing a crop when precipitation is greatest.
crop intensity can reduce evaporation. This can be achieved either by increasing
intensity of grain or forage crops or by using cover crops. Either practice can
result in greater amounts of residue, helping reduce evaporation.
crop intensity depends on balancing crop water use with available soil water.
In water-limited areas, there is a point where cropping intensity is too great
and not enough water can be stored during fallow periods to successfully grow a
subsequent crop. A cropping system that is too intense may result in crop
failure. A system that is not intense enough results in inefficient water use.
rainfall amount and distribution, as well as experience with particular soils
and crops, will influence which crops to plant and in what sequence. This can
involve alternating summer and winter crops, or planting a double crop or cover
crop between two crops -- such as wheat and corn in a wheat-corn-fallow
rotation. Dynamic rotations that base crop selection and management decisions
on actual soil water conditions and realistic precipitation expectations have
the greatest probability of success, both in terms of profitability and
water-use efficiency. This type of crop rotation, often referred to as
“opportunistic cropping,” takes maximum advantage of water when the conditions
are right for success.
differ in total amount of water use and in their pattern of water use (see
table below). For example, sorghum requires less water to produce the first
bushel of grain, but corn produces more grain for each additional unit of water
after the threshold requirement has been met. Within
a crop, specific varieties or hybrids will have different water use patterns
depending on the length of maturity. For example, a short-season corn hybrid
produces a smaller plant, reaches maturity sooner, and uses less total water than
a full-season hybrid. This same trend is true for other crops as well.
Growth and water use for corn
hybrids of different maturities
Days to physiological maturity
Grain yield (bu/acre)
Biomass yield (tons/acre)
ET, emergence to physiological
WUE (grain), bu/acre/inch of ET
Adapted from Howell et
al., 1998, Agron. J. 90:3-9
factors can also influence the timing of water use and how water use is likely
to correspond to water availability during the season. Typically, corn is
planted earlier than sorghum or soybeans, shifting key periods of water use
earlier in the growing season. Most grain crops are highly sensitive to water
deficits at and around the time of pollination, so it is important to match
this period of crop growth with water availability. The figure below
illustrates that corn pollination typically takes place when expected
precipitation and temperatures at slightly more favorable than when sorghum
pollination occurs in Manhattan.
The solid bars show the timing of pollination for corn
planted April 13 to 23 and grain sorghum planted May 11 to 24. The lines are
the normal maximum temperature and normal precipitation amounts for Manhattan.
dates can be manipulated to shift silking and pollination to a different part
of the growing season, when expected precipitation and temperatures may be
slightly more or less favorable. The figure below shows that corn silking can
take place anywhere from mid-June to mid-August, depending on when the corn was
planted. Planting a month later does not result in a month’s delay in silking
because corn develops faster when temperatures are higher, reducing the number
of days required to reach silking and eventually maturity.
Bars indicate the timing of corn pollination for different
planting dates. The lines are the normal maximum temperature and normal
precipitation amounts for Hutchinson.
-- Kraig Roozeboom, Cropping Systems Agronomist
-- Johnathon Holman, Southwest Research-Extension
Center, Cropping Systems
-- Josh Jennings, CCA – Graduate Research Assistant,