Crop Water Use in Corn and Soybean
 Crop water use, or evapotranspiration (ET), represents soil water evaporation and the water used by a
crop for growth and cooling purposes.
 The amount of water used by a crop can be influenced by: prevailing weather conditions, regional
climate, available soil water, crop species, and growth stage.
 By understanding ET, better planning and management decisions can be made.
Evapotranspiration
Crop roots come into contact with water from precipitation or
irrigation that enters the soil. Evapotranspiration (ET) is the
water removed by soil evaporation and plant transpiration.
Transpiration is the movement of water from the soil into plant
roots, through plant stems and leaves, and back out into the
atmosphere. Evaporation is the water evaporated or lost from
wet soil and plant surfaces. Significant evaporation can only
take place when the top 1 to 2 inches of soil is wet or the plant
canopy is wet. Once the soil surface is dry, evaporation
decreases sharply. Therefore, significant evaporation occurs
after rainfall or irrigation.
Table 1. Seasonal crop water use across geographies.*
West
South
Corn
23-28
8
20-307
20-241
20-226
Soybean
20-258
20-254
~255
18-209
Crop
Weather conditions, water availability in the soil, crop species,
and growth stages can all influence crop water use.
Weather/Climate: The ability of the atmosphere to evaporate
water is the driving force for soil evaporation and crop
transpiration. Weather factors that have a major impact include:
solar radiation, temperature, relative humidity, and wind. These
all increase the amount of water the plant must transpire to
keep cool and produce biomass. Seasonal crop water use may
vary across geographies as shown in Table 1.
Crop Growth Stage: Crop ET also depends on the crop
growth stage (Tables 2). ET is related to crop surface area, so
small plants transpire less than large ones. In general, row
crops like corn and soybean reach maximum ET just prior to
the reproductive growth stage. For example, a corn plant will
require the most water during the 4 to 5 weeks surrounding
silking. During this time, a corn plant can use as much as 0.28
inches of water per day. Any moisture stress around the time of
silking may cause the pollen to shed from the tassel before
silking occurs, resulting in poor or no pollination. The amount of
water row crops require is also dependent on temperature. As
temperatures increase, more water is needed.
AsgrowandDEKALB.com
East
(inches/year)
*Crop water use varies across geographies and these values represent a range
depending on several factors including region and soil type.
Table 2. Average crop water use (ET) by growth stage for
113-day maturity corn (Western region).
Irrigation requirements are determined by the difference
between ET and water that is stored in the plant root zone, so
ET estimates can be used to help determine proper irrigation
scheduling.
Evapotranspiration Factors
Midwest
Approximate Water use
days to
to maturity
maturity
(inches)
Growth stage
Corn
R4
R4.7
R5
R6
Dough
34
7.5
Beginning dent
24
5.0
1/4 milk line
19
3.75
1/2 milk line (full dent)
13
2.25
3/4 milk line
7
1.0
Physiological maturity
0
0.0
Soybean
R4
End of pod elongation
37
9.0
R5
Beginning seed enlargement
29
6.5
R6
End of seed enlargement
18
3.5
Leaves begin to yellow
10
1.9
Beginning maturity
0
0.0
R6.5
R7
*Long-term average number of days since planting required to progress from the previous
growth stage to the next. For example, to go from the blister kernel stage to the beginning
dent stage requires approximately 15 days (day 89 to day 104). Days to each growth
stage were determined using the Hybrid-Maize Corn Growth Model for the period 19822005 at Clay Center, NE.
Table modified from Kranz, W.L. et al. 2008. Irrigation management for corn NebGuide
G1850. University of Nebraska-Lincoln Extension.
Asgrow and the A Design® and DEKALB and Design® are registered trademarks of Monsanto Technology LLC.
Crop Water Use in Corn and Soybean
Relative Maturity: Seasonal ET can be affected by the relative
maturity (RM) of a crop. For example, at the same location, a
corn product with 120 day RM will use more water than an 85
day RM product. While longer season products use more
water, they may also have a higher yield potential if heat units
and adequate water are available.
Planting Population: Recommended populations for dryland
production are less than those for irrigated production.
Populations are lowered below 18,000 plants per acre to
reduce the transpiration component of ET by the crop and to
better match precipitation and stored soil moisture in dryland.2
On ground with higher plant populations, research would
suggest populations above 18,000 plants per acre will transpire
similar amounts of water regardless of the population.
To determine if soil compaction is a problem, crop roots should
be checked during the growing season. Subsoiling may help
increase water use in droughty, shallow soils by breaking up
hardpans that have formed.3 Fall subsoiling may help with
infiltration and storage of winter moisture.
Figure 1. Evapotranspiration is the combination of the water removed from
the soil through evaporation and plant transpiration.
Water Availability: Plants will have more difficulty extracting
water from soil as it dries. At field capacity, plants use water at
the maximum rate. Plants use less water as the water content
of the soil drops close to the permanent wilting point. When
crops do not receive enough water to meet their ET demands,
grain yield potential can be reduced.
ET, water should be saved for the reproductive stages where it
will have the most impact on yield potential, or irrigated acres
should be reduced. Agronomic practices such as no-till can
increase the water holding capacity and help reduce irrigation
needs. Research and advancements in plant breeding can help
growers improve yield potential under water stress.
Researchers are working on developing corn and soybean
products with water use efficiency characteristics and
continued work on best management strategies will help
provide plant population recommendations for different water
availability situations.
Water Stress
1
Crops will respond differently to water stress depending on the
growth stage. Many grain crops respond to water stress during
vegetative growth stages with reduced yield and/or delayed
reproductive or grain fill growth stages. For water use in corn,
the critical growth stage timeframe are from tassel until grain is
fully formed. For soybeans, the critical growth stage begins at
full pod (R4) and continues until seed set. Shortages in water
supply during these growth stages may cause a reduction in
yield potential.
Sources:
Wright, J. 2002. Irrigation scheduling checkbook method. University of Minnesota.
http://www.extension.umn.edu/agriculture/water/irrigation-scheduling-checkbook-method/
#amount. 2 Is a population change warranted in irrigated corn due to water constraints?
2013. University of Nebraska—Lincoln. Crop Watch. http://cropwatch.unl.edu/ 3 Tacker, P.
and Vories, E. Irrigation. Arkansas Soybean Handbook. M197. University of Arkansas.
4
Thomas, J.G. and Blaine, A. Soybean irrigation. Pub. 2185. Mississippi State University
Cooperative Extension. 5 Irrigation. Corn Agronomy. 2015. University of Wisconsin
Extension. http://corn.agronomy.wisc.edu/Management/L026.aspx. 6 Barker, D. et. al. Ohio
Agronomy Guide. 14th edition. Bulletin 472. The Ohio State. 7 Espinoza, L. and Ross, J.
Corn Production Handbook. MP 437. University of Arkansas Extension. 8 Martin, C., Burr, C.,
and Olson, B. 2015. Irrigation handbook for the great plains. 9 Irrigation. Ag 101. 2012
Environmental Protection Agency Ag Center. http://www.epa.gov/oecaagct/ag101/
cropirrigation.html. 10 Klocke, N.L., Hubbard, K., Kranz, W.L., and Watts, D.G.1990. G90-992
Evapotranspiration (ET) or crop water use. University of Nebraska-Lincoln Extension. Paper
1197. http://digitalcommons.unl.edu. Web sources verified 7/28/15.140504060312
Excess Water
Excess moisture can negatively impact crop growth and yield
potential, as well as increase nitrogen leaching and runoff.
Waterlogged soils can be due to poor irrigation management,
above-normal rainfall, and/or poor drainage conditions.
Over-irrigation can result in reduced root oxygen, increased
toxicity build-up, increased negative microbial growth and root
disease, and a reduction in root mass due to lower soil
temperature.
Summary
When water is limited, changes in irrigation and agronomic
management practices can help improve water use efficiency
and yield potential. If irrigation allocations cannot meet full crop
For additional agronomic information, please contact your local seed representative.
Developed in partnership with Technology, Development, & Agronomy by Monsanto.
Individual results may vary, and performance may vary from location to location and from
year to year. This result may not be an indicator of results you may obtain as local growing,
soil and weather conditions may vary. Growers should evaluate data from multiple locations
and years whenever possible.
ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Asgrow and the A
Design® and DEKALB and Design® are registered trademarks of Monsanto Technology
LLC. All other trademarks are the property of their respective owners. ©2015 Monsanto
Company. 072815CRB