A new approach for predicting the water balance of hops
More frequent drought spells, such as those during 2003 and 2015, and predictions of climate change raise the question of whether supplementary irrigation is needed in the hop-growing regions of Germany. For hop-growing regions such as the Yakima valley in the United States and Saaz in the Czech Republic, it is well established that irrigation stabilizes and increases the yield and quality of hop. However, such knowledge is scant for the hop-growing region of Hallertau. To understand the underlying water fluxes of hop, we quantified its water loss by gas exchange measurements. Transpiration was measured on several days at various heights of four hop plants being either irrigated or non-irrigated, respectively. For this purpose, the plants were subdivided into three segments (bottom, middle, and top) from which the exact leaf areas were known, and the measured transpiration rates were extrapolated and averaged across the entire plant. The irrigated and non-irrigated plants did not differ in their assimilation and transpiration rates. The extrapolation indicated a high rate of water loss, with water consumption amounting for over 50 L plant-1 day-1. In combination with evapotranspiration rates calculated by the Penman-Monteith equation, based on the weather information of a nearby station, new correction factors for the irrigation scheduling of hop were deducted. These correction factors require further verification and implementation within irrigation scheduling.
Graf, T., Beck, M., Portner, J., Baumgartner, A., Mauermeier, M., Ismann, D., Maier, M. and Schmidhalter, U. (2019). A new approach for predicting the water balance of hops. Acta Hortic. 1236, 63-74
evapotranspiration, gas exchange, hop, Humulus lupulus, irrigation control, Penman-Monteith