By Angela McClure, Extension Corn and Soybean Specialist
Dry weather has already plagued some parts of the state. We do have some likely rains in the forecast, but for those who miss rain once again this weekend and are thinking about turning on the irrigators, included are some basic irrigation amounts for corn, soybeans and grain sorghum.
Corn water use using the checkbook method of irrigation (It is important to start on time, don’t get behind and try to supply most of demand between V-9 to 3/4 milk line stage.)
| Growth stage | Importance | Est. crop water use |
Seedling corn | Early vegetative growth | <1″ per week |
V9 – V12 | Rapid vegetative growth | 1.75”/wk |
V12 – V17 | Ear length determined | 2.0”/wk |
VT – R2 (blister) | Ear size potential | 2.3”/wk |
| R3 (milk) – R6 (black-layer) | Grain filling period | 1.75-0.7”/wk*(declining) |
* Irrigation amounts may be reduced in latter part of grain fill. Under hot, drought conditions producers may benefit from watering until black layer. In wetter years, producers may stop irrigating after 3/4 milk line stage.
Soybean water use using the checkbook method (It is important to not overwater soybeans. Critical water needs are between R3 and R6 stages.)
| Growth stage | Importance | Est. crop water use |
| V3 – R1 (begin bloom) | Rapid vegetative growth | 1.0”/wk** |
| R1 (begin bloom) – R3 (begin pod) | Pod count set | 1.4”/wk** |
| R4 (full pod) – R6 (full seed) | Seed size set | 2.0”/wk |
** Rainfall is usually adequate for soybeans until R2 and early season irrigation shows little benefit other than to ensure seed emergence and activate preemergence herbicides. The important thing to remember with soybeans is less is best during the early part of the season.
Grain sorghum water use using the checkbook method. (Grain sorghum is our most drought tolerant crop but does respond to water when weather turns dry. It is important to not overwater early season but try to irrigate prior to and at boot stage and at bloom if needed. Late season irrigation is usually not recommended.)
| Growth stage | Comments | Est. crop water use |
| | | |
| Early growth | First 30 days after planting | < 1 “ per week |
| Rapid vegetative growth | 30 to 60 days after planting | 0.7 to 1.4” per week |
| Preboot and Boot | Water preboot and at boot stage if dry | 1.5”/wk |
| Bloom | Water during bloom if dry | 1.75 to 2.1”/wk |
| Grainfill | | 1.75 to 0.7”/wk (declining) |
Click here to see more...