Water usage by potato plants at different stages of growth

Three groups of single-halm potato plants were tested for water usage at different stages of growth under growth chamber, greenhouse and field conditions by conducting 24-hour uptake studies at weekly intervals. Although the water usage was higher and more variable in the greenhouse and field than in the growth chamber because of varying environmental conditions during the 24-hour test periods, similar patterns were obtained. From emergence, the potato plant appeared to have four growth stages based on morphological development and water use. The young plant stage from emergence to tuber initiation is characterized by rapid growth, high transpiration rate per unit of plant material (essentially foliage), transpiration significantly correlated with the amount of foliage and a higher percentage of moisture being retained in the plant. The second stage is essentially a short transition stage of tuber initiation where top growth continues, transpiration levels off and a lower percentage of moisture is retained in the plant. The third stage is the tuber bulking stage where transpiration and water use remain relatively static because of non-expanding top growth and a lower percentage of moisture being retained in the plant during the bulking process. The final stage of senescence and tuber ripening is characterized by a marked reduction in water use primarily because of lower transpiration and loss of functioning foliage.