DROUGHT EFFECTS ON BIOMASS PRODUCTION AND RADIATION-USE EFFICIENCY INBARLEY

Changes in biomass production of a barley crop in response to droughts of various timing and duration were analysed using a simple radiation interception model. Decreased growth rates were caused primarily by r eductions in radiation-use efficiency when drought was imposed from em ergence. In these treatments radiation-use efficiency was depressed ev en after drought was relieved. In contrast, in treatments where drough t was imposed from two weeks before anthesis or later, the primary cau se of reduced biomass production was a decrease in the amount of radia tion intercepted, mostly associated with more rapid leaf senescence. F or the later drought treatments, the radiation-use efficiency was stab le and near the maximum value for unstressed crops. However, final bio mass was sensitive to drought timing and, in particular, was more sens itive to maximum potential soil moisture deficit for the early than th e later drought treatments.