response of groundnut (Arachis hypogaea L.) to timing of irrigation. I. Development and growth

A timing-of-irrigation experiment was conducted in controlled-environment glasshouses, in which a finite quantity of water was applied to four stands of groundnut (Arachis hypogaea L.) at different stages of the growing season. Irrigation schedules were broadly divided into two periods; sowing to pod initiation and pod initiation to final harvest. Within these periods two levels of soil moisture deficit were imposed by withholding or applying limited amounts of irrigation at regular intervals. Shoot dry matter yields were hardly affected but pod yields were more than 4-fold lower in early- than in late-irrigated stands. Thermal time was used to separate the effects of temperature and water stress on developmental processes. The degree-day requirement for peg initiation was similar in all treatments but late-irrigation delayed pod development by about 200 degrees Cd. The effect of timing of irrigation on pod yield operated mainly through its influence on the duration of pod production, which was closely linked to the rate and duration of canopy expansion late in the season. The insensitivity of pod yield to early moisture deficits reflected the extreme plasticity of growth and development in groundnut, since most processes resumed rates similar to the pre-stress levels in early-irrigated stands once stress was released.