What was it all about?

This project investigated the usefulness of taking tree samples to measure non-structural carbohydrate levels as a potential predictor of crop load in macadamia nut trees.

The study began with a literature review of the use of non-structural carbohydrate measurements, and found that they have been widely used in both tree crops and forestry to explain cropping behaviour.

An earlier study of macadamia trees found that non-structural carbohydrate levels increased steeply from nut maturity in late February until flowering, followed by a sharp decrease until nuts were mature. This suggests a cycle where spare carbohydrate is stored by the tree at certain times, then used when demand exceeds supply from photosynthesis.

This project set out to investigate reliable sampling techniques and laboratory methods as well as establish annual patterns of carbohydrate accumulation and depletion in currently grown varieties. Hawaiian and Australian macadamia varieties were incorporated in the study.

The effective sampling technique that the researchers developed involved drilling into the wood of trees to gather shavings. Samples were collected from 50 trees, beginning March 2014. Ten trees were sampled each month for the duration of the project and results collated.

In addition to non-structural carbohydrate measurements, light readings were taken at site in the middle of the day. These showed that within 1-1.5m of the outside of the canopy there is not enough light for photosynthesis.

Results from the research confirmed findings from earlier studies that there is a distinct seasonal pattern in carbohydrate stores. However, the measurements showed that the Australian A varieties had much lower non-structural carbon levels as Hawaiian varieties.

Further work needs to be done to investigate the effects of non-structural carbohydrate levels on yields.