Mississippi studies indicate corn requires about 1.5 inches of water per week during the peak growing period. Rainfall is normally insufficient to meet this requirement. When rainfall is insufficient, good yields depend on water stored in the soil. This is why early plant development and the water-holding capacity of the soil are so important. Corn pollinating in late May and June will have a better moisture relationship in most years than will corn flowering in July and August.
Temperature also affects yield.
Temperatures in these ranges begin in early to mid-July in Mississippi. High temperatures can cause death of pollen and also kernel abortion. A combination of water stress and high temperatures at pollination can be disastrous. Under these conditions pollen shedding is accelerated and siling is delayed, resulting in ear barrenness because of contrast in development timing. Stress during grain filling results in severe competition for photosynthate between vegetative and reproductive components, leaving less for grain filling, thus greatly reducing yield.