Water use by sheltered kiwifruit under advective conditions

Abstract

Abstract The transpiration of 2 kiwifruit vines grown within sheltered orchards in the Nelson locality was estimated in late summer by measuring their water uptake for 2 days following excision. Total daily transpiration by vines with vertically projected canopy areas of 16–17 m2 varied between 80 and 100 liters of water per day (4.8–6.1 mm/day) and ranged from 1.6 to 2.4 times the equilibrium evaporation rate. Stomatal conductances on excised vines were lower than those of adjacent uncut vines after the first day. Since transpiration estimates using the Penman-Monteith formula agreed well with the measured water uptake by cut vines, this equation was used to predict the transpiration of adjacent intact vines. Advective enhancement of evaporation contributed between 21 and 49% of the daytime water use despite the presence of multiple, closely spaced shelterbelts. Transpiration continued throughout the night as a consequence of incomplete stomatal closure, so that in total, advected energy was responsible for between 0.44 and 0.59 of the total water consumption over 24 h. Because of the mountain ranges and draughted pastoral lands upwind of the orchards, together with the very windy conditions at the time of the experiments, these measurements are likely to provide a practical upper limit for the advective contribution to water use by kiwifruit grown under New Zealand conditions. A pragmatic approach to providing evaporation estimates for irrigation scheduling under advective conditions is discussed.