When it is hot there is a tendency to irrigate more frequently and apply copious quantities of water to emerging crops. However, too much water can cause as much harm to the soil and the crop as too little water. Consider the following points:
Air/water spaces: Between soil particles are void spaces called "pores" that are occupied by air and water. These pores occupy about 50 percent of the soil's volume. If water is filling the pores, then most of the air is displaced. As the water is used by plants, evaporates or drains away, the air returns. If too much water is applied then the pore spaces remain filled with water. This creates an unfavorable condition for plant roots that need soil oxygen to survive. Root hairs start to die and become nonfunctional, restricting the uptake of water and nutrients to the foliage.
Leaching of nitrogen fertilizer: Water is needed to satisfy the photosynthetic needs of plants and to drain salts from the plant root zone. Excessive amounts of water applied increase drainage volume and thus increase the loss of water-soluble nitrate-nitrogen. With fertilizer prices being high, conservation of nitrogen for plant use should be practiced. You only need to apply enough water to meet crop water requirements (evapotranspiration) during the early stages of crop growth. Additional water for leaching should be applied at or toward the end of vegetable crop season. Additional water for leaching is not needed during the growing season (vegetable crops only). For field crops, particularly alfalfa, additional water for leaching may be needed during the year. Leaching is most effective at the end of the growing season after the removal of the crop, working the soil out and applying a leaching irrigation.