Investigation of sampling procedures to determine macadamia fruit quality in orchards

Abstract

Summary. Macadamia kernel quality estimates are of fundamental importance to understanding tree responses to many experimental treatments and orchard management protocols. Experimental measures of macadamia kernel quality, collected under field conditions, traditionally rely on the average of 100 fruit, sampled from the estimated peak in fruit drop. To detect changes in kernel quality over a single season, we measured variation in fruit quality of macadamia cv. 344. To sample this variation we measured 10 fruit from 6 blocks of 3 trees at each of 7 sites, over 4 harvests made at monthly intervals. For all fruit collected we determined: husk, shell and kernel dry weights; kernel recovery (the percentage of kernel to kernel and shell weight); and kernel specific gravity from which oil content was estimated. A split-plot analysis of variance model was used to determine variance estimates for each of the fruit quality parameters measured. The percentages of partitioned total variance of the quality parameters were lowest for sites (3.6–6.7%), intermediate for harvests (3.3–41.1%) and highest for fruit (32.9–71.2%). Using these estimates, we investigated the influence of varying the number of replicates per site and fruits per replicate on kernel quality estimates. The analyses indicated that samples of 5 fruit, from each of 6 randomly located blocks within a site, represent the minimum replication required to detect commercially relevant changes in the kernel quality parameters measured. Larger sample sizes and increased replication did not significantly increase the precision of estimates.