DROUGHT EFFECTS ON BIOMASS PRODUCTION AND RADIATION-USE EFFICIENCY IN BARLEY

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 reductions in radiation-use efficiency when drought was imposed from emergence. In these treatments radiation-use efficiency was depressed even after drought was relieved. In contrast, in treatments where drought was imposed from two weeks before anthesis or later, the primary cause of reduced biomass production was a decrease in the amount of radiation intercepted, mostly associated with more rapid leaf senescence. For the later drought treatments, the radiation-use efficiency was stable and near the maximum value for unstressed crops. However, final biomass was sensitive to drought timing and, in particular, was more sensitive to maximum potential soil moisture deficit for the early than the later drought treatments.