Browsing by Browse by SEO 2008 "820206 Macadamias"

Macadamia is a subtropical, evergreen tree which flowers in response to cool temperature, producing racemes that originate from axillary buds. The physiology of macadamia flowering, including some new data, and applications to canopy management are discussed. Floral initiation is also reliant on axillary bud release, which is affected by the timing of vegetative growth and characteristics of the stems. Other endogenous signals, including signals from the fruit, may also be involved. The most common form of canopy management in Australian macadamia orchards is mechanical hedging. Well timed autumn hedging or hedging in early winter would ensure the absence of immature vegetative flush that has the potential to suppress flowering. The relationship between flowering and yield in macadamia is largely unknown, so increasing flowering may not necessarily increase yield as with some other subtropical and tropical tree crops.

Early crop yield forecasts provide valuable information for growers and industry to base decisions on. This work considers early forecasting of macadamia nut yield at the individual orchard block level with input variables derived from spatio-temporal datasets including remote sensing, weather and elevation. Yield data from 2012–2019, for 101 blocks belonging to 10 orchards, was obtained. We forecast yield on each test year from 2014–2019 using models trained on data from years prior to the test year. Forecasts are generated in January, for the coming harvest in March–September. A linear model using ridge regularized regression produced consistently good predictions compared with other machine learning algorithms including lasso, support vector regression and random forest. Adding meteorological variables offered little improvement over using only remote sensing variables. The 2019 forecast root mean square error at the block level was 0.8 t/ha, and mean absolute percentage error was 20.9%. When block level predictions were aggregated across the multiple orchards per region, production prediction errors were between 0–15% from 2016–2019. The ridge regression model can be easily implemented in GIS platforms to deliver block-level yield forecast maps to end users.

Macadamia is a subtropical evergreen tree native to the east coast of Australia and grown around the world for its edible kernel. The trees are tall with dense canopies and at maturity orchards are heavily shaded and crowded unless tree size is controlled. This shading has been associated with yield decline but the evidence for this is limited to one site. The shading also limits ground-cover growth leading to increased soil erosion; slows orchard floor drying after rain resulting in harvest delays and reduced nut quality; and increases pest and disease pressure. Crowded orchards are also more difficult to spray effectively. The aims of this study were to further investigate the evidence for yield decline, assess canopy management methods adopted by industry, and investigate the effect of pruning on fruit set to improve outcomes from some of these methods. A yield survey in mature orchards confirmed earlier conclusions that yield decline occurred at high levels of light interception but that it was small compared with inter-seasonal yield variation.

Macadamia ('Macadamia integrifolia' Maiden and Betche, M. 'integrifolia X tetraphylla' Johnson) flowers are borne on racemes that usually originate from axillary buds in response to cool conditions. In this report, we examine the relationship between stem characteristics and the number of racemes produced, to improve our understanding of the control of floral initiation and axillary bud release.Two macadamia trees of each of the cultivars 'A4', '660', '695', and 'A38' were pruned annually for 3 years and the relationships between stem length, stem age, the number of vegetative flushes, stem orientation, and the number of racemes produced were quantified in year 4 (2006). In addition, trees of cultivar '849' were pruned in Autumn and early Summer, and the flowering characteristics of the post-pruning vegetative flushes were monitored the following Spring (2006). There were significant differences in the extent and location of racemes between cultivars. Racemes were produced preferentially on short stems that consisted of few vegetative flushes. In cultivar 'A4', 1-year-old stems were more likely to flower than 2-year-old stems; whereas, in cultivar 'A38', 2-year-old stems were more likely to produce racemes than 1-year-old stems. As stem orientation changed from horizontal to vertical, the likelihood of raceme production increased in cultivar '660' stems consisting of one flush and in '695' stems consisting of two flushes. Stem characteristics, particularly stem age and vigour, indicate the likelihood of flowering, but position within the canopy may be another important consideration. Canopy management practices that promote the production of short stems may increase whole-tree raceme production and, given the variation in the location of raceme production with cultivar, canopy management practices specific to cultivar should be considered.

Whole-tree excavations, root-core and minirhizotron studies indicate that the grafted macadamia tree root system is relatively shallow and spreading, with a short taproot and most of the fibrous root system near the soil surface, while ungrafted trees have a longer taproot. The length of fibrous roots diminished with depth and distance from the trunk. This pattern is consistent with other fruit trees, in that the highest density is generally within 1 m of the trunk. Values obtained in core samples in this study were 4.97 (± 0.43) cm/cm3 and 1.67 (± 0.45) cm/cm³ for 0–10 cm and 10–20 cm at 0.5 m from the trunk, and 2.34 and 1.08 cm/cm³, respectively, at 1 m from the trunk at Clunes. These values were similar to those obtained in separate studies in 1991–93, involving assessments at 5 cm depth increments down to 15 cm, where mean root length densities were 2.0–3.5 cm/cm³ and 1.3–1.9 cm/cm³ at 0–5 cm and 5–15 cm depth, respectively, 1.4 m from the trunk. Root length under old trees in bare soil at Dorroughby and Clunes, using minirhizotrons (0.25–0.40 cm/cm²) and soil cores (1.14 and 3.50 cm/cm³, respectively), was similar to that found at other sites in the study area (minirhizotrons 0.28–0.33 cm/cm²; soil cores 1.25–2.80 cm/cm³). There is an apparent lower rate of decrease in root length density with increasing distance from the trunk at 10–20 cm compared with 0–10 cm. New root growth occurred predominantly in autumn, but some new fibrous roots were produced in early winter and spring. Proteoid roots were found in abundance in soil cores and adjacent to minirhizotron tubes and there were more of them in the root systems of younger trees at Clunes than with older trees at Dorroughby. Proteoid roots were found at a greater depth than previously recorded for other Proteaceae species, and appeared to retain their function in relatively dry conditions for more than a year. Non-proteoid fibrous roots at the minirhizotron surface appeared to be functional for about 1.5 years in relatively dry conditions, before decay after the onset of wet soil conditions. The effects of 2 newly established perennial legume groundcovers on the root systems of younger and older macadamia trees were studied over 2.5 years. In general, the presence of groundcover either had no effect on the growth of the macadamia roots or increased the root length density at some sampling dates and some depths. At Clunes, where the proteoid root length density was higher than at Dorroughby, the presence of groundcover was associated with higher proteoid root length density than that with bare ground. Arachis pintoi cv. Amarillo generally had a lower root length density than 'Lotus pedunculatus'.

In Australian macadamia ('Macadamia integrifolia' Maiden and Betche, 'M. tetraphylla Johnson' and hybrids) orchards, trees are generally side-hedged in early spring to maintain the inter-row for efficient orchard management. Hedging at this time increases fruit abscission and decreases yield due to competition for carbohydrates between fruit and post-pruning shoot growth, and to the loss of photosynthetic area. Girdling increases fruit set in many crops and the possibility that girdling might mitigate the effect of pruning on fruit abscission and yield was investigated in this study. Girdling was also investigated for its potential to control shoot growth and tree size. In the first experiment, in early spring around anthesis, trees were pruned (P), pruned and girdled (PG), or were left as unpruned and ungirdled control trees. Fruit per raceme over time, percent of racemes with fruit at 20 weeks post anthesis, fruit number per tree, nut weight, yield, and the shoot length and number of the post-pruning flush were measured. In a second experiment, trees were pruned (P) or pruned and girdled (PG) in autumn, and the shoot length and number of the post-pruning flush were measured. In a third experiment, trees were girdled at anthesis in 3 years over a 4-year period and shoot growth, tree height, yield, fruit number and nut weight were compared with ungirdled control trees. Girdling mitigated the effect of pruning on fruit abscission and yield but the mitigation was slight with PG trees producing 28% less yield than unpruned control trees. Girdling reduced shoot length and number but more so on unpruned branches (26% and 28%, respectively) than on pruned branches (10% and 14%, respectively). The tree height increment in girdled trees was around half that of ungirdled trees. In the 4-year study, girdling increased yield by around 10% in two out of four seasons, and decreased it in one season. Cumulative yields were similar for girdled and ungirdled trees. This study has shown that girdling was not useful in mitigating the effect of pruning on yield. However girdling was effective in controlling shoot growth and tree size, with no reduction in cumulative yield, and may be useful as a tree size control strategy. Further monitoring of long-term effects of repeat girdling is required to confirm this.

Macadamia, a subtropical evergreen tree, flowers profusely but sheds more than 98% of flowers and fruitlets within 10 weeks of anthesis. This premature fruit abscission is accentuated when trees are hedged in spring, as is commonly practiced in Australian orchards. The aim of this study was to assess the effect of the ethylene inhibitor aminoethoxyvinylglycine (AVG) on fruit abscission in macadamia and if it could be used to mitigate the effect of pruning on abscission. Racemes on '849' trees that had been planted in 2002 were sprayed either pre or post anthesis with AVG at concentrations of 0, 30, 60 or 90 ppm in 2007, and 0, 200, 400 or 600 ppm in 2008. Whole trees that had been tip pruned at anthesis to simulate hedging, were sprayed twice (pre and post anthesis) with AVG at concentrations of 60 ppm in 2007 (10-year-old 'A4' trees) and 400 ppm in 2008 (6-year-old '849' trees). Post anthesis applications to racemes increased set only slightly and the effects of low concentrations in 2007 were similar to those of high concentrations in 2008. Pre anthesis application had a similar effect to post anthesis application in 2007 but decreased initial fruit set relative to post anthesis application and the control in 2008. The increase in fruit abscission associated with pruning was not prevented by AVG application; and whole tree sprays did not increase yield on either pruned or unpruned trees. Overall the response of fruit set in macadamia to AVG in this study was poor even at high rates and with two applications. This may indicate an alternative to ethylene as the primary regulator of abscission of young macadamia fruit.

Accurate yield forecasting in high value fruit tree crops provides vital management information to growers as well as supporting improved decision making, including postharvest handling, storage and forward selling. Current research evaluated the 8 spectral band WorldView 3 (WV-3) with a spatial resolution of 1.2 m, as a tool for exploring the relationship between individual tree canopy reflectance and a number of tree growth parameters, including yield. WV-3 imagery was captured on the 7th of April, 2016, over two Macadamia ('Macadamia integrifolia') and three Avocado ('Persea americana') orchards growing near the Queensland township of Bundaberg, Australia. Using the extent of each block, the WV-3 imagery was sub-setted and classified into 8 Normalised Difference Vegetation index (NDVI) classes. From these classes 6 replicate trees were selected to represent high, medium and low NDVI regions (n=18) and subsequently ground truthed for a number of yield parameters during April and May, 2016. The measured parameters were then correlated against 20 structural and pigment based vegetation indices derived from the 8 band spectral information corresponding to each individual tree canopy (12.6 m2). The results identified a positive relationship between derived vegetation indices (VI) and fruit weight (kg/tree) R2 > 0.69 for Macadamia and R2 > 0.68 for Avocado; and fruit number R2 > 0.6 for Macadamia and R2 > 0.61 for Avocado. The algorithm derived between the optimum VI and yield for each block was then applied across the entire block to derive a yield map. The results show that remote sensing of tree canopy condition can be used to measure yield parameters in Macadamia and Avocado grown in the Bundaberg region.

Many pollinator species visit multiple crops in multiple regions, yet we know little about their pollination service provisioning at local and regional scales. We investigated the floral visitors (n = 13,200), their effectiveness (n = 1718 single visits) and response to landscape composition across three crops avocado, mango and macadamia within a single growing region (1 year), a single crop (3 years) and across different growing regions in multiple years. In total, eight wild visitor groups were shared across all three crops. The network was dominated by three pollinators, two bees (Apis mellifera and Tetragonula spp.) and a fly, Stomorhina discolor. The visitation network for the three crops was relatively generalised but with the addition of pollen deposition data, specialisation increased. Sixteen managed and wild taxa were consistently present across three years in avocado, yet their contribution to annual network structure varied. Node specialisation (d’) analyses indicated many individual orchard sites across each of the networks were significantly more specialised compared to that predicted by null models, suggesting the presence of site-specific factors driving these patterns. Identifying the taxa shared across multiple crops, regions and years will facilitate the development of specific pollinator management strategies to optimize crop pollination services in horticultural systems.

Groundcovers can be useful for controlling erosion in macadamia orchards but they can have adverse effects on tree growth and crop yield. The effects of groundcovers versus bare soil on banana and macadamia were compared in a glasshouse study and on macadamia in the field. A glasshouse trial compared the effect of 3 water regimes with unmown or mown 'Arachis pintoi cv'. Amarillo groundcover versus bare soil, on stomatal conductance and growth of banana and macadamia. Mean stomatal conductance was higher overall for macadamia (178 mmol/m².s) compared with banana (90 mmol/m².s) when data were pooled across groundcover and water treatments. Medium and dry substrate moisture treatments significantly reduced the growth and vigour of banana compared with the wet treatments, as indicated by reduced total dry matter, leaf area, number of live leaves at harvest, and total root length, but had no significant effect on macadamia. Groundcover had a more adverse effect on the growth of banana than macadamia compared with bare soil and, likewise, unmown cover had a greater effect on growth of banana than mown cover, while there was no mowing effect on macadamia. In an unirrigated field trial, mown and unmown groundcover and bare soil treatments were compared for their effect on early morning leaf xylem water potential of young and older macadamia trees at 3 sites where groundcover was established at different tree ages. Water potential was generally <0.2 MPa more negative in the groundcover treatment than bare soil in spring and summer under dry seasonal conditions over 2 years, although there was no apparent effect on tree health. The difference in water potential between groundcover and bare soil was highest in young trees planted in established groundcover. The more adverse effect of groundcover on water status of young trees in established cover correlates with a greater reduction in growth compared with older trees reported separately (Firth et al. 2003 Aust. J. Exp. Agric. 43, 419–423). Soil bulk density under groundcover was slightly reduced (0.028 g/cm³) at 0–10 cm depth, and penetrometer resistance also slightly reduced (<0.3 MPa) at 0–12 cm depth, compared with bare soil. Higher penetrometer readings in the traffic zone (often >4 MPa at 30–40 cm in the initial survey) compared with the tree line indicate the potential long-term benefits to be derived from groundcovers.

The effects of 'Lotus pedunculatus' (cv. Grasslands Maku) and 'Arachis pintoi' (cv. Amarillo) groundcovers on growth and yield of 1-, 4- and 14-year-old macadamia orchards were investigated over 5 years near Lismore in northern New South Wales. Bare control plots were used at all sites, along with an unmown groundcover in the oldest orchard. Vegetative growth was assessed in terms of shoot extension, trunk diameter and canopy volume. The groundcovers had the greatest effect on vegetative growth of the trees when they were established into an existing sward, followed by the 4-year-old trees, and then the 14-year-old trees. Yields were collected from the 4- and 14-year-old trees and were generally similar under bare soil or groundcovers, with smaller or similar canopy volumes. Nut quality was not consistently affected by the groundcovers, whereas nut-drop was delayed. Acceptable yields can be obtained in macadamias with groundcovers, with potential benefits in terms of soil structure, fertility and stability. Mown and unmown plots have similar productivity.

Accurate estimates of tree crop orchard age and historical crop area are important to develop yield prediction algorithms, and facilitate improving accuracy in ongoing crop forecasts. This is particularly relevant for the increasingly productive macadamia industry in Australia, where knowledge of tree age, as well as total planted area, are important predictors of productivity, and the area devoted to macadamia orchards is rapidly increasing. We developed a technique to aggregate more than 30 years of historical imagery, generate summary tables from the data, and search multiple combinations of parameters to find the most accurate planting year prediction algorithm. This made use of known planting dates of more than 90 macadamia blocks spread across multiple growing regions. The selected algorithm achieved a planting year mean absolute error of 1.7 years. The algorithm was then applied to all macadamia features in east Australia, as defined in an recent Australian tree crops map, to determine the area planted per year and the total cumulative area of macadamia orchards in Australia. The area estimates were refined by improving the resolution of the mapped macadamia features, by removing non-productive areas based on an optimal vegetation index threshold.

Tree condition, pruning and orchard management practices within intensive horticultural tree crop systems can be determined via measurements of tree structure. Multi-spectral imagery acquired from an unmanned aerial system (UAS) has been demonstrated as an accurate and efficient platform for measuring various tree structural attributes, but research in complex horticultural environments has been limited. This research established a methodology for accurately estimating tree crown height, extent, plant projective cover (PPC) and condition of avocado tree crops, from a UAS platform. Individual tree crowns were delineated using object-based image analysis. In comparison to field measured canopy heights, an image-derived canopy height model provided a coefficient of determination (R²) of 0.65 and relative root mean squared error of 6%. Tree crown length perpendicular to the hedgerow was accurately mapped. PPC was measured using spectral and textural image information and produced an R² value of 0.62 against field data. A random forest classifier was applied to assign tree condition into four categories in accordance with industry standards, producing out-of-bag accuracies >96%. Our results demonstrate the potential of UAS-based mapping for the provision of information to support the horticulture industry and facilitate orchard-based assessment and management.

We examined the relationship between shoot growth and temperature and solar radiation in macadamia ('Macadamia integrifolia' Maiden and Betche, M. 'integrifolia X tetraphylla' Johnson) as an aid to developing pruning strategies for this crop. Trees growing at Alstonville (28.9°S) in northern NSW, Australia, were pruned at various times to promote vegetative flushing under a range of environmental conditions. Flush development in macadamia is cyclic: bud release and stem elongation followed by a period of dormancy, before bud release of the subsequent flush. The rate of bud release after pruning was best correlated with the product of the mean temperature and solar radiation (r² = 0.75, P < 0.0001), whereas the rate of flush development was best correlated with the mean temperature (r² = 0.76, P < 0.0001). The number of buds released per pruned stem was greater under higher temperatures and solar radiation (r² = 0.37, P < 0.001), but the length of the flush after pruning decreased with increasing temperatures (r² = 0.32, P < 0.01). The descriptive models were combined with long-term weather data to predict the duration and characteristics of flushes following pruning at various times of the year along Australia’s eastern seaboard, from Mareeba (17.0°S) to Coffs Harbour (30.38°S). Flush duration and stem length following June pruning were predicted to be greater than following early autumn or September pruning and to vary from year to year, and with location (latitude). We discuss the implications of the model predictions for productivity and propose pruning times intended to optimise flowering and yield. Further research is required to test these proposed pruning strategies.

Background and Aims: There is good evidence for deciduous trees that competition for carbohydrates from shoot growth accentuates early fruit abscission and reduces yield but the effect for evergreen trees is not well defined. Here, whole-tree tip-pruning at anthesis is used to examine the effect of post-pruning shoot development on fruit abscission in the evergreen subtropical tree macadamia ('Macadamia integrifolia', 'M. integrifolia' x 'tetraphylla'). Partial-tree tip-pruning is also used to test the localization of the effect. Methods: In the first experiment (2005/2006), all branches on trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R treatment) and shoots were removed from others (NR treatment). Fruit set and stem total non-structural carbohydrates (TNSC) over time, and yield were measured. In the second experiment (2006/2007), upper branches of trees were tip-pruned at anthesis, some trees were allowed to re-shoot (R) and shoots were removed from others (NR). Fruit set and yield were measured separately for upper (pruned) and lower (unpruned) branches. Key Results: In the first experiment, R trees set far fewer fruit and had lower yield than NR trees. TNSC fell and rose in all treatments but the decline in R trees occurred earlier than in NR trees and coincided with early shoot growth and the increase in fruit abscission relative to the other treatments. In the second experiment, fruit abscission on upper branches of R trees increased relative to the other treatments but there was little difference in fruit abscission between treatments on lower branches. Conclusions: 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.

For 'Macadamia integrifolia' Maiden and Betche var. 849, we compared four limb removal strategies of varying style and severity over 4 years, in terms of effects on yield, on the distribution of light, and new vegetative shoots, racemes and fruit within the canopy. Limb removal reduced yields. The reduction corresponded with the severity of pruning, not with the style of pruning. Limb removal had little impact in the medium term on light penetration to the orchard floor. Within the canopy, shoot production and raceme production were inversely related. Shoot production was favoured by high light conditions; raceme production occurred predominantly in areas of heavy shade, with 49% of racemes produced at canopy locations receiving less than 2% full daylight, and 94% produced at locations receiving less than 16% full daylight. Most flowering appeared to occur on wood more than 3 years old. The capacity of different parts of the canopy to support fruit set and retention increased with proximity to the more irradiated parts of the canopy, but fruit production was still high deep within the lower part of the canopy, with 50% of fruit produced at canopy locations receiving less than 2% full daylight, and 90% produced at locations receiving less than 16% full daylight.

Yields of macadamia ('Macadamia integrifolia', 'M. tetraphylla', and hybrids) orchards tend to increase with increasing tree size up to ≈94% light interception. Beyond this, there is some indication that crowding leads to yield decline, but the evidence is limited to one site. Increasing tree size and orchard crowding also present numerous management problems, including soil erosion, harvest delays, and increased pest and disease pressure. The aim of this study was to better characterize long-term yield trends in mature orchards and to assess the effects of manual and mechanical pruning strategies on yield, nut characteristics, tree size, and economics. We monitored yield at four sites in mature '344' and '246' orchards for up to seven years and confirmed a decline in yield with crowding for three of the sites. There was a small increase in yield over time at the fourth site, which may reflect the lower initial level of crowding and shorter monitoring period compared with the other sites, and highlights the need for long-term records to establish yield trends. Pruning to remove several large limbs from '246' trees to improve light penetration into the canopy increased yield relative to control trees but the effect was short-lived and not cost-effective. Removal of a codominant leader from '344' trees reduced yield by 21%. Annual side-hedging of '246' trees reduced yield by 12% and mechanical topping of '344' trees caused a substantial reduction in yield of up to 50%. Removal of limbs in the upper canopy to reduce the height of '344' trees had less effect on yield than topping but re-pruning was not practical because of the extensive regrowth around the pruning cuts. Tree size control is necessary for efficient orchard management, but in this study, pruning strategies that controlled tree size also reduced yield. Research into the physiological response to pruning in macadamia is required to improve outcomes.

We take three approaches to more clearly define the role of carbohydrate (CHO) reserves in the development of evergreen trees. First, we examine the lychee and macadamia literature to develop a whole tree carbon budget to show that current photosynthatemakes a greater contribution to the carbon for new growth than CHO reserves. Second, we show that the presence of leaves is sufficient for the production of a functional new shoots on small, girdled branches with few CHO reserves. Third, we use a shade experiment to show that short-term suppression of whole-tree photosynthesis can severely affect new shoot development. Subsequent decapitation of all branches on both the shaded and control trees resulted in faster bud release in the shaded trees, notwithstanding lower CHO reserves. Overall we argue that the main role of CHO reserves is to buffer the pool of current photosynthate. Although such buffering can be quite strong during periods of high carbon demand, even then CHO reserves are a secondary source of carbon.

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.