Bob Nielsen, Agronomy Department of Purdue University, says soil moisture deficits have been a concern in Illinois and parts of Ohio since earlier in June. Most of Indiana's corn crop was spared until recently due to more generous spring rainfall plus a good shot of rain from Tropical Storm Arlene in mid-June. Within the past week or so, however, the consequences of mounting soil moisture shortages are becoming increasingly evident in cornfields throughout Indiana, primarily in the form of dramatic leaf rolling during daytime hours.
Top soil and subsoil moisture estimates reported by the Indiana Ag. Statistics Service declined sharply in Monday's report (6/27/05); only 35 percent and 54 percent Adequate to Surplus, respectively, contrasted to last week's estimates of 80 percent and 78 percent Adequate to Surplus. Another indicator of the worsening soil moisture deficits was the decrease in crop condition rated Good to Excellent from 66 percent of the corn acres last week to 56 percent reported Monday (6/27/05). Last year at this time, 73 percent of the state's corn crop was rated Good to Excellent.
Given that leaf rolling is an early symptom of drought stress, how does one assess the yield consequences once it appears in a field? An accurate estimate is difficult to give, but we can identify the high risk situations. Obviously, yield losses are more likely the more hours of a day and the more consecutive days that leaves are rolled tightly because of the overall reduction in photosynthetic energy capture and carbon fixation. Yield losses are also more likely when severe drought stress occurs shortly before, during, and shortly after pollination than at any other time of the growing season.
Dealer & Applicator magazine