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Irrigation can be one of the most critical management needs for silage corn. Adequate water for corn around the time of pollination is most important. Corn water use will remain high through the early reproductive stages. Terminating irrigation too early can reduce yield and silage quality potential.
The relative water use by corn as it grows to maturity is shown in Figure 4. Daily water use rates peak during tasseling and silking or around the time of pollination. Water requirements remain high during the early reproductive stages. When corn reaches the R4 stage, it begins to transpire less and water use declines up through maturity.
Water stress during corn tasseling and silking can result in the greatest yield reduction of up to 50%. Corn yield reductions of up to 40% can result if drought stress occurs after pollination up through the dough (R4) stage. During these early reproductive stages, kernels are growing as the plant transfers dry matter to the grain. Corn uses less water when it reaches the dent (R5) stage, but yields could still be reduced by up to 20% if drought conditions occur during this time up through maturity (R6).
Figure 1. Relative corn water use by growth stage. Adapted from Irrigation Management for Corn, NebGuide G1850, University of Nebraska. .
Silage corn yield potential can be impacted by moisture stress during vegetative growth because stalk internode length and plant height can be reduced. Fiber digestibility and forage quality can also be affected. Irrigation during vegetative growth can have the greatest effect on increasing digestibility. Irrigation during reproductive growth can have the greatest effect on corn starch content. Reducing irrigation during vegetative growth, followed by increased irrigation during pollination and grain fill, can produce shorter plants and a reduced forage yield, along with a greater proportion of grain in the silage.
Research shows no yield or quality advantages when irrigating silage corn at 75% ET (evapotranspiration or water use by the plant) compared to 100% ET. Maintaining available soil water above 60% in the upper 2 to 3 foot depth should occur through the early reproductive growth stages.
Timing of the last irrigation to refill the root zone for silage corn depends on the soil texture, weather conditions, and availability of irrigation water. This could occur between the dough (R4) and dent (R5) growth stages, a week or more before harvest. Irrigation flexibility is important based on the conditions prior to the estimated harvest time.
In summary, to produce high yielding and quality corn silage, irrigate just before the available soil water is depleted to 60%, replenishing available soil water near field capacity in the appropriate root zones.