High daytime temps not a big concern in corn
The available water supply is not as certain for later-planted crop which won’t pollinate until late July or early August. These plants are in mid-vegetative stages and are showing mid-afternoon drought stress symptoms (leaf curling) in areas where recent rainfall has been limited. “This crop has not grown enough to have used up the available soil water to 3 or 4 feet deep. Rather, the root system is simply not as deep or as well connected as it would be had planting been done earlier or if soils had not been so wet earlier,” Nafziger explained.
Another concern with wet weather earlier in the spring is nitrogen supply for the crop. While leaf color remains good in areas with adequate soil water and where the crop has continued to grow well, in areas where soils have dried and some drought effects are starting to appear, leaf color has lightened some. Nafziger said rainfall in these areas should return leaf color to normal green. However if plants have been under stress from lack of nitrogen during the pollination period, he cautioned that success of kernel set can be lowered.
“It is possible that nitrogen loss in some lower-lying parts of fields may mean shortages for the crop, even after root systems recover. Supplemental applications of nitrogen have been made in some such areas, usually as urea, and sometimes with urease inhibitor. Such applications might produce enough added yield to provide a positive return if they are made before or even during pollination, but are likely to be effective only when rain moves the nitrogen into the soil,” he said.
As crops move through pollination and into the grain filling stages, the major concern will be how well the leaf canopy holds up in providing maximum amounts of photosynthate (sugars) to fill kernels.
Soil water supply will be the major factor, followed by leaf health and nutrient supply, Nafziger said. “We expect the crop to take about 8 weeks to reach maturity after pollination is complete, and maintaining green, healthy leaves through this period is the only way to maximize kernel fill and yield. If the crop takes less time from pollination to maturity, it will have stopped filling prematurely and will produce lower yields,” he said.