Having the soil dry at harvest not only saves money, but can be beneficial to soil conditions by reducing compaction from heavy equipment.  Crop water usage decreases a little bit each day the last month before maturity, but August and September can still have some very hot days and shorting plants water too soon can be detrimental to the crops’ final yield.

Knowing the exact crop growth stage and the days until maturity are necessary to apply timely irrigation late in the season.  When conditions are hot and dry in mid to late August, crops may mature faster than expected, shutting down prematurely when soil water is depleted.  Irrigation in earlier, smaller increments before depleting the soil of plant available water has shown some benefits, but you must still avoid over application to leave storage space for rainfall.  Watering within 5-7 days before maturity is not recommended.  Irrigating crops advanced in maturity is usually money wasted.  Final irrigation in corn should not be determined until ½ milk line is visible on the kernel at the middle of the ear.  Final irrigation on soybeans should not be determined until seeds are fully enlarged and leaves begin to yellow.  Accurate estimation of plant available water needs to be determined using a hand probe or remote sensing device.  The chart below displays the average water use of corn and soybeans by growth stage.  Water use estimates to maturity will need adjusted for early maturing crops and above/below average ET crop water usage.