Corn water use will fluctuate throughout the season depending on weather conditions and crop growth stage (Figure 1). Factors that will affect ET and irrigation decisions include:Crop growth stage. Crop Crop water use, or evapotranspiration (ET), is the movement of water through evaporation (E) from the soil and plant surfaces and transpiration (T) through the plant. Transpiration is the movement of water from the soil into plant roots, through plant stems and leaves, and back out into the atmosphere. Transpiration is an important concept because yield is related to the amount of water a plant transpires. An understanding of when corn requires water the most for maximum yield potential can help guide more efficient irrigation applications.
Corn water use will fluctuate throughout the season depending on weather conditions and crop growth stage (Figure 1). Factors that will affect ET and irrigation decisions include:Crop growth stage. Crop water requirements vary depending on growth stage. Young plants transpire less than larger plants due to a smaller leaf surface area. Corn requires the most water just prior to and during the reproductive growth stages.
Relative maturity. Longer-season corn products will require more water over the growing season than short-season products. While longer-season corn products use more water, they may also have a higher yield potential if heat units and adequate water are available.
Weather conditions. The ability of the atmosphere to evaporate water is the driving force for soil water evaporation and transpiration. Daily ET is influenced by solar radiation, air temperature, relative humidity, and wind. High air temperatures, low humidity, clear skies, and high winds cause a large evaporative demand.
Soil water holding capacity and soil water content. A soil’s water holding capacity indicates the maximum amount of water that will be available for plant use when the soil water profile is full (field capacity). Fine textured soils can hold more water than coarse textured soils. As the 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.
Residue management / Tillage system. Minimizing soil disturbance from tillage and increasing surface crop residue can reduce soil water evaporation. Reduced tillage practices, particularly no-till and strip-till, can help the soil capture and retain more moisture. Tillage increases the exposed surface area of the soil for evaporation and increased runoff, destroys crop residue that can catch rain and snow, and may reduce water infiltration because of compaction that can be created during the tillage process. Surface residue helps increase infiltration rates by limiting the amount of surface sealing created by rainfall and irrigation droplets.
Surface residue also helps reduce runoff by creating obstructions that limit water movement and allow more time for water to seep into the soil profile
Seasonal water requirements for high-yielding corn range from 20 to 30 inches per year depending on planting date, maturity group, location, and weather.1 Corn requires the most water during the early reproductive growth stages (Table 1), which are also the most sensitive stages to water stress. When corn does not receive enough water to meet ET demands during this critical water use period, significant reductions in yield can occur.
Planting. Corn uses very little water during the seedling stage. Irrigation is not recommended immediately following planting in regions where earlyseason precipitation and stored soil moisture are adequate for seedling emergence and early plant development. Without the plant canopy to shade the soil surface, much of the irrigation would be lost to evaporation. Farmers should rely on stored soil moisture and natural precipitation as much as possible during the early growth stages.
Vegetative stages. The vegetative stages of corn are often considered the least sensitive stages to water stress. If irrigation supplies are limited, the vegetative stages may provide an opportunity to reserve irrigation for the reproductive stages where it will have the most impact on yield potential.
Early reproductive stages. Water stress should be avoided during the reproductive stages (tasseling, silking, and pollination). Water stress during silking can have the greatest impact on yield potential due to desiccation of the silks and pollen grains, which will result in poor pollination.2 It is important to know when crop water demands will become greater than precipitation, which often occurs during the critical reproductive periods. Plan ahead by knowing the capacity of the irrigation system to ensure that adequate water is available to the crop through these stages.
Dough through dent stages. Corn water use rates steadily decrease from the dough stage through maturity due to a lower evaporative demand (shorter days, lower temperatures, lower solar radiation), a loss of transpiring leaf area as lower leaves begin to die, and changes in plant physiology.2 At the beginning of the dough stage, corn will still require roughly 1/3 of its seasonal water requirement (Table 2). For optimal grain development and maximum yield potential, corn requires water right up until physiological maturity. Water stress during the dough through dent stages can accelerate maturity, prohibiting kernels from reaching their full potential size and weight.3
Maturity. After physiological maturity (black layer), water is no longer needed for kernel growth and no yield benefits can be achieved with additional irrigation. Allowing soils to dry at maturity is a good strategy for avoiding compaction that can be caused by harvesting machinery on wet soils.
1 Schneekloth, J. and Andales, A. Seasonal water needs and opportunities for limited irrigation for Colorado crops. No. 4.718. Colorado State University Extension. www.ext.colostate.edu.
2 Kranz, W.L., Irmak, S., van Donk, S.J., Yonts, C.D., and Martin, D.L. 2008. Irrigation management for corn. NebGuide G1850. University of Nebraska-Lincoln Extension.
3 Lamm, F.R. and Abou Kheira, A.A. 2009. Corn irrigation macromanagement at the seasonal boundaries – initiating and terminating the irrigation season. Proceedings of the 2009 CPIC. Colby, Kansas, Feb 24-25.
Other sources: Yonts, C.D., Melvin, S.R., and Eisenhauer, D.E. 2008. Predicting the last irrigation of the season. NebGuide G1871. University of Nebraska-Lincoln Extension. Web sources verified 3/31/15. 140421060305