Investigation of sampling procedures to determine macadamia fruit quality in orchards

Macadamia kernel quality estimates are of fundamental importance to underst anding tree responses to many experimental treatments and orchard managemen t protocols. Experimental measures of macadamia kernel quality, collected u nder field conditions, traditionally rely on the average of 100 fruit, samp led from the estimated peak in fruit drop. To detect changes in kernel qual ity over a single season, we measured variation in fruit quality of macadam ia 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; kern el recovery (the percentage of kernel to kernel and shell weight); and kern el specific gravity from which oil content was estimated. A split-plot anal ysis of variance model was used to determine variance estimates for each of the fruit quality parameters measured. The percentages of partitioned tota l variance of the quality parameters were lowest for sites (3.6-6.7%), inte rmediate 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 re plicates per site and fruits per replicate on kernel quality estimates. The analyses indicated that samples of 5 fruit, from each of 6 randomly locate d blocks within a site, represent the minimum replication required to detec t commercially relevant changes in the kernel quality parameters measured. Larger sample sizes and increased replication did not significantly increas e the precision of estimates.