The discomfort level for plants is, therefore, highest on clear, bright days with low relative humidity. This is because on bright, sunny days with low humidity, transpiration may exceed the rate of water uptake by roots causing the plant to wilt. Loss of turgidity in plant cells also results from moisture stress. This loss of turgidity causes stomata to close, which lowers CO2 uptake by the leaf and reduces dry matter accumulation. When humidity is high, crops can tolerate high temperatures because there is little moisture lost through evaporation.
Corn has a relatively high water require-ment.
In the central Corn Belt, the amount of water used by the crop, plus that lost by evaporation from the soil surface, generally exceeds normal season rainfall by 3 to 5 inches. This precipitation deficit is offset by water stored in the soil from early season rainfall. Most Iowa soils will hold approximately 2 inches of available water per foot of depth in the upper 5 feet of soil. During rapid growth in the later vegetative stages of development, a corn plant will use about 0.2 to 0.25 inches of water per day. This may increase to almost 0.33 inches of water per day during pollination.