Preliminary investigation of water use efficiency of Avocado varieties, irrigation and intra-canopy variation.

Abstract

This project has identified a relationship between foliar δ13C and foliar δ18O suggesting that Avocado water use efficiency (WUE) (as indicated by foliar δ13C), grown in nursey conditions, varies with transpiration. This result has not been previously been identified in avocado in the literature and may be a useful to explore in avocado and other horticultural crops breeding programs in Australia.
 We have also shown that management influences long-term water use efficiency where the avocado variety Shepard had very different foliar δ13C with the two different irrigation treatments (Sprinkler and drip irrigation). Although not conclusive, the foliar δ13C was higher under the sprinkler irrigation which was likely in response to increased growth or water stress at this site.
 The relationship between foliar N, chlorophyll and the chlorophyll SPAD meter indicates that the N could be monitored with the SPAD meter in avocado orchards. This may be used to supplement dry matter analysis and help improve N use efficiency in North Queensland catchments draining into the Great Barrier Reef, increasing sustainable horticultural outcomes.
 The relationship between foliar N and δ13C (less negative δ13C), indicates that the north facing canopy had a greater variation in N and WUE compared to the south facing and the shoot function site.
 There was variation in nitrogen (N) within the canopies particularly when the shoot function and canopy sampling position samples were pooled, indicating a potential response in the canopy to N cycling at the different sites. This is suggested as a response to Nitrogen management at the different sites. Further work would be required to better understand the mechanisms behind this relationship.
 Finally, the correlation between δ15N and δ13C at the pooled sites indicates how increasing foliar δ15N was related to increasing WUE (less negative δ13C), showing potentially how N availability across sampled orchards influences growth. Again further work would be required to better understand the mechanisms behind these relationships.