ABSTRACT
Moisture stress is one of the most important factors limiting crop yields worldwide. This is because water is an absolute necessity for plant growth and development. As such, water availability is one of the environmental factors with a profound effect on plant growth. In fact, water is the most used substance among all the substances absorbed by plants (Chapman and Carter, 1976). Water performs a myriad of functions in plant growth. These functions can be categorized as follows: an electron source for carbon fixation; a cell constituent; a universal solvent allowing chemical reactions and transport of essential nutrients; and the maintenance of cell turgidity and elongation. These important and critical functions of water in plants suggest that inadequate water (i.e., moisture stress) can greatly affect plant growth and development. Plant moisture stress occurs when plant water status is reduced sufficiently to affect normal plant functioning (Gimenez et al., 2005). Plant moisture stress is a complex function of interaction among plant, soil, and atmospheric factors. Thus, an absolute value of plant moisture stress cannot be defined unless these complex interactions are taken into account (Gimenez et al., 2005). Water requirement may differ among crop species or even cultivars of the same crop species (Ibrahim, 1995). Among the major food crops, rice (Oryza sativa L.) requires the greatest amount of water, and sorghum (Sorghum bicolor L.) requires the least (it is the most drought tolerant) (Chapman and Carter, 1976). However, moisture stress affects plant growth, development, and productivity regardless of crop type. Understanding plant response to moisture stress is thus critical for increasing crop productivity while ensuring efficient use of water. This is particularly important in non-food crops grown for biomass, such as forages. This is because non-food crops are often grown under water-limited conditions (Barbanti et al., 2015). This chapter is therefore focused mainly on moisture stress in forage production systems.
