Alfalfa water relations and irrigation

Morphological and physiological features allow alfalfa to adapt to a wide range of soil moisture conditions. Alfalfa water use is often considered extravagant, since seasonal evapotranspiration is large compared to other crops, primarily because of long periods of transpiration. This chapter discusses the pathway of water movement, physiological and morphological effects of soil moisture deficits, water requirements for seed and forage production, and irrigation scheduling criteria. Alfalfa nitrogenase activity decreases 85% when plants are subject to a water deficit, but activity recovers to 70% of pre water deficit rates when turgor was restored. Water movement occurs along a water potential or pressure gradient from the soil to the atmosphere through the roots, stems, and leaves. Historically, water requirements have been regarded as lower for seed than for vegetative production. Water use during daytime hours usually constitutes the largest daily proportion.