Much of Nebraska has had plenty of hot dry winds so far this season, a big change from last year, says Gary Zoubek and Chuck Burr, Extension educators in York and Phelps counties, respectively. In comparing 2012 crop indicators in the York with those from last year, Zoubek found the following increases:
- Average high temperatures for May and June 2012 were almost five degrees (Fahrenheit) higher than in 2011, while the low temperatures were up nearly one degree.
- Humdity for the same period averaged about 6% less than last year.
- Average wind speeds have been slightly higher than last year, about 0.65 mph. I would have guessed it to be more than that.
- Reference evapotranspiration (ET) has averaged about 0.298 inch per day in 2012 compared to 0.254 in 2011. That's an increase of 0.31 inch of potential ET per week, compared to 2011.
The crop is also ahead of schedule compared to last season. "We saw tassels on some of the earliest planted corn in late June," Burr adds. "Last year much of the earliest corn was between knee and waist high at that time. With the earlier growth, the crop coefficients used to estimate crop water use are higher in late June at many sites than they were at that time last season. Many of the early planted corn fields in the area are entering a time of high water use. Water use rates increase with the size of the crop and when air temperatures are high, we have low humidity and windy conditions. Due to high water use rates, it's important to avoid stress during the reproductive stages.
While some water stress during early vegetative stages has little influence on yields, water stress during silking will result in the greatest yield reduction. Irrigation applications should increase to match crop ET, however, it is important to not completely fill the soil profile.
Depending upon the system capacity and soil type, leave some room for potential rainfall events. Don't pay for some water that hopefully mother nature will provide.
Water requirements will remain high during the early reproductive stages until dough stage. During this time kernels are growing as the plant transfers dry matter to the grain. Water use rates decline beginning with dough stage as a result of shorted days, cooler temperatures, and lower solar radiation.
No matter what stage your crop is in, it's important to monitor soil water status with some type of sensor or soil probe. Yield can be reduced by having either too little or too much water at critical growth stages.
For the latest crop ET data, go to CropWatch.unl.edu or Water.unl.edu?NAWMN.