ABSTRACT
Crops use water for cooling, nutrient transport to the leaves, and photosynthesis. Most of the water used by the crop evaporates from the surface of the leaves. Plants function like an evaporative cooler where large amount of water is used for cooling, which is an integral part of the photosynthesis process. The growth of plant is tied to the ability of leaves to produce carbohydrate via photosynthesis. The carbohydrate is the basis for the accumulation of biomass and growth of the plant. The leaves capture light over the surface area of the leaves exposed to the sun. Upon exposure to the solar energy, the leaves open thousands of tiny pores (stomata) to let in carbon dioxide (CO2) and solar energy to produce carbohydrate. The open stomata and solar energy also result in water evaporation at the same time. The water evaporated through the stomata is referred to as transpiration. The sum of water loss through transpiration and evaporation outside of stomata such as soil surface is referred to as evapotranspiration (ET). The ET is a function of climate condition, plant leaf area, and the stomata behavioral characteristic of the plant. The water that evaporates through ET is supplied from the stored moisture within the root zone of the plant. Thus the success of the crop growth and yield production depends on the climate, the plant, and the ability of the producer to provide the soil reservoir with timely and sufcient quantity of water. Water is the single most important production parameter in irrigated agriculture. This chapter describes how the crops’ water requirement (ET) can be estimated and how the soil moisture reservoir can be managed to achieve successful production.
