No abstract

This study is the first to demonstrate an increase in fruit abscission in an evergreen tree in response to pruning. The effect appeared to be related to competition for carbohydrates between post-pruning shoot growth and fruit development and was local, with shoot growth on pruned branches having no effect on fruit abscission on unpruned branches.

Orchard crowding in the macadamia industry is common and there has been concern that it reduces yield and quality. To investigate this we monitored yield, nut quality, tree volume, and light interception in macadamia orchards (Macadamia integrifolia Maiden and Betche) that represented a range in crowding. The predicted rate of change in yield/ha with time remained positive, i.e. yield increased over time, for orchards with crowding levels up to a tree volume of 43 500 m3/ha and light interception of 94%. There was a trend for the rate of yield change to decrease with increasing tree volume/ha. For orchards with tree volume >43 500 m3/ha the rate was negative, indicating a slight decline in yield over time. There was no evidence of a detrimental effect of orchard crowding on percentage kernel recovery, unsound kernel, or grade 1 kernel. It appears that macadamia, unlike many other orchard crops, can maintain yield and quality up to a high level of orchard crowding. The implication of this is that timing of canopy management and optimum canopy dimensions will be dictated by management requirements for machinery access and effective spray coverage before yield decline becomes an issue.

Macadamia (Macadamia integrifolia Maiden and Betche, M. tetraphylla Johnson and hybrids) orchards in Australia are typically hedged around anthesis (September). Such hedging reduces yields, largely through competition for carbohydrates between early fruit set and the post-pruning vegetative flush, but also through a reduction in photosynthetic capacity caused by the loss of canopy. We examined whether hedging at other times might mitigate yield losses. Hedging time was found to affect yields across four cultivars: ‘A4’, ‘A38’, ‘344’ and ‘816’. Yield losses were lower for trees hedged in November–December than for trees hedged in September. Yields for trees hedged in June were higher than for trees hedged in September in one experiment, but were similar in a second experiment. Yield losses for September and October hedging were similar. Hedging time changed the pattern of fluctuations in stem water-soluble carbohydrates (WSC). WSC declined shortly after hedging in September, October or November, and the declines preceded increases in fruit abscission relative to unpruned control trees. The increase in fruit abscission was less pronounced for the trees hedged in November, consistent with the idea that fruit become less sensitive to carbon limitation as they mature.

No 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.

No abstract

Horticultural tree crop yields tend to be linearly correlated with the percentage of photosynthetically active radiation (PAR) intercepted by the canopies, at least for part of the PAR interception range. Models of PAR interception by hedgerows have been used in the design of orchards for temperate tree crops, especially apples, but not for subtropical tree crops, such as lychee and macadamia. Subtropical crops need special consideration because of the latitudes at which they are grown, the specific shapes and dimensions of the hedgerows, and the evergreen habit, which requires an understanding of the entire annual cycle. We present outputs from a PAR interception model for solid rectangular and tapered hedgerows, based on a model of irradiation beneath blue skies. Annual PAR interception tends to decline as row orientation rotates from north–south to east–west, but with some exceptions for particular tree geometries, and declines slightly with decreasing latitude. Daily PAR interception is also affected by row orientation, with little seasonal variation for north–south rows but large fluctuations for east–west rows, including very high interception in winter and low interception in summer. Row orientation and tree shape greatly affect the distribution of PAR over the surface of the canopy. For example, the side faces of evenly spaced, symmetrical, identical north–south hedgerows are equally irradiated throughout the year, but there can be large seasonal differences in the relative irradiance of the north and south faces of the same hedgerows aligned east–west. The solid tapered hedgerow model tended to overestimate measured PAR interception by ~6% overall, but the percent overestimation seemed to vary with PAR interception, being greater at lower levels of PAR interception. A curvilinear relationship was found between the yield of macadamia in the Northern Rivers area of NSW in 1997 and the measured PAR intercepted by the trees, with an explained variance of 50%. Maximum yield occurred at ~86% PAR interception. Using modelled PAR interception the explained variance of the yield was 34%. Model estimates of PAR interception were close to those measured and might be used to address a range of physiological questions concerning the canopy development of subtropical hedgerows.