Evapotranspiration. Crop roots come into contact with water from precipitation or irrigation that enters the soil. Evapo
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
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
*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.
Approximate Water use days to to maturity maturity (inches)
Growth stage Corn R4 R4.7 R5
1/4 milk line
1/2 milk line (full dent)
3/4 milk line
End of pod elongation
Beginning seed enlargement
End of seed enlargement
Leaves begin to yellow
*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.
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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.
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