Water Use in Row Crops
 Crop water use, or evapotranspiration, represents soil water evaporation and the water used by a crop
for growth and cooling purposes.
 Factors that can influence crop water use include: prevailing weather conditions, regional climate, soil
water availability, crop species, and crop growth stage.
 Better planning and management decisions can be made by understanding evapotranspiration.
Evapotranspiration
Crop root systems 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.
The difference between ET and water that is stored in the plant
root zone determines irrigation requirements, so ET estimates
can be used to help determine proper irrigation scheduling.
Factors That Influence Evapotranspiration
Weather conditions, water availability in the soil, crop species,
and growth stage 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 over 0.3 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.
Table 1. Seasonal crop water use across geographies.*
South
Midwest
East
West
Crop
(inches/year)
Corn
10
23-28
20-307
20-241
20-226
Soybean
20-2510
20-254
~255
18-209
*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).
Approximate Water use
days to
to maturity
Growth stage
maturity
(inches)
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
End of pod elongation
Beginning seed enlargement
End of seed enlargement
37
29
18
9.0
6.5
3.5
Leaves begin to yellow
10
1.9
Beginning maturity
0
0.0
Soybean
R4
R5
R6
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 1982-2005 at Clay Center, NE.
Table modified from Kranz, W.L. et al. 2008. Irrigation management for corn NebGuide G1850.
University of Nebraska-Lincoln Extension.
Water Use in Row Crops
Relative Maturity: Seasonal ET can be affected by crop relative
maturity. For example, at the same location, a corn product
with 120 day maturity will use more water than an 85 day
maturity product. While longer season products use more
water, they may also have a higher yield potential if heat units
and adequate water are available.
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.
Crop roots should be checked during the growing season to
determine if soil compaction is an issue. 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.
Water Content: As soil dries, it becomes more difficult for
plants to extract water. 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.
Water Stress
Crops respond to water stress differently depending on the
growth stage. Many grain crops respond to water stress during
the vegetative growth stages with reduced yield and delayed
reproductive or grain fill growth stages. For water use in corn,
the critical growth stages 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.
Figure 1. Evapotranspiration is the combination of the water removed from
the soil through evaporation and plant transpiration.
Summary
Crop water use is dependent upon a variety of factors.
Agronomic practices such as no-till can increase the water
holding capacity and help improve water needs. Research and
advancements in plant breeding can help growers improve yield
potential under water stress by developing corn and soybean
products with water use efficiency characteristics and provide
plant population recommendations for different field situations.
Sources
1
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. Overirrigation 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.
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.
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