The effects of artificial spur extinction (ASE) on the water use efficiency of apple tree canopies

This paper presents results from a field experiment to examine the effects of modified 'Cripps Pink' apple tree canopies, through the technique known as artificial spur extinction (ASE), on tree water use (TWU) and water use efficiency (WUE). TWU was measured using sap flow sensors in trees that were subsequently thinned by removing buds using the ASE technique to establish a range of floral bud densities. Sap flow data was used to verify a simple model of TWU based on light interception (LI) and reference crop evapotranspiration (ETo). WUE (g L^-1) was computed from the ratio of tree fresh-weight yield and cumulative TWU over the growing season.

There was a strong positive linear relationship between TWU and ETo. Despite an 9% reduction in simulated TWU, attributable to a reduced leaf area in the early part of the season, WUE was not altered on the ASE trees when floral bud density was set to a level aimed to achieve normal commercial yields (i.e., 70-80 t ha^-1). Results from this study provided initial relationships that will be used in a replicated experiment to further investigate the effects of ASE on WUE.