Jack Hughes, Fruition Horticulture (First seen in The Orchardist Magazine)

Plant and Food’s Future Orchard Production System (FOPS) research programme is working on a step change in new orchard design. Drs Stuart Tustin, Ben van Hooijdonk (see photos) and their team are developing and testing systems aimed at raising the utilization of incoming light energy from the 60-65% typical for current apple plantings to something approaching 90% use efficiency.

These creative initiatives have got the industry thinking and have sparked fresh debate about tree design and orchard management. So with some trepidation, I thought I’d wade into the discussion with a few thoughts on the subject.

Prototype 1 trial plantings at Havelock North use unique combinations of tree layout, design and crop management. Row widths are substantially narrowed (1.5-2.0m) to increase light interception while tree spacing is increased (3.0m) to accommodate two permanent leaders. Twin leader trees have been custom grown in the nursery to speed up canopy establishment. These leaders are trained down to near horizontal and produce vertical fruiting branches.  Tree density of the block shown is 1,600-2,200 trees per hectare which is within the range commonly used for intensive plantings (Figure 1).

Crop loading will be managed using the spur extinction technique where bud numbers are adjusted manually. Chemical thinning won’t be used. The new system seeks to close the energy efficiency gap by using more and wasting less incoming light energy and to raise productivity without sacrificing fruit quality.

Yield a function of light interception

It has well well established by researchers that the productivity of orchards is a function of their light interception. So maximising the amount of light intercepted and seeking uniform light distribution within the canopy is widely accepted as the name of the orchard systems game.

Luca Corelli-Grappadelli who visited New Zealand recently and spoke to summerfruit growers and Alan Lakso who recently retired from Cornell University wrote a thought provoking paper entitled ‘Is maximising orchard light interception always the best choice?¹. In it they asked whether the principle of maximum light interception necessarily holds for all environments.

They observed that most of the research and systems development work has been done by folk in places like Europe and upstate New York where direct radiation and evaporative demands are relatively low. The currently popular training systems developed there and adopted worldwide are based on thin, shallow canopies which expose most leaves and fruit to high light levels. They are suited to those conditions which could be called “low stress” in terms of the demands on the photosynthetic apparatus (leaves) and risks of sunburn damage (fruit).

It could be that in hot and saturated light environments, the productivity of small, well exposed canopies is compromised because the photosynthetic machinery is often pushed into a stress zone.

Coping with stress

Trees have a coping mechanism for high light intensities and temperatures called photorespiration. This is an alternative metabolic pathway to photosynthesis where leaf chloroplasts repair oxidative damage. Energy is used in this process so there is likely a cost in terms of carbon gain and hence productivity. In hot climates, fuller canopies that provide intervals of intermittent shade may give exposed leaves and fruit some respite and allow better overall performance?

Nevertheless, I guess that NZ conditions are pretty kind on a world scale and normal losses to sunburn and heat stress are not usually severe enough to stop us from using the “low volume, high efficiency” canopies being FOPS tested.

Made in the shade

Excess shade is probably a bigger enemy for us. Early work on light interception with apple found that at least 30% of incident light was needed to ensure fruit colour and flower bud differentiation.  Luca Corelli-Grappadelli found that shading to 30% light caused a shift in carbon flows in favour of extension growth shoots within a fruiting branch ie too much shade creates even more shady shoot growth!

Its interesting that these growing systems were developed before the arrival of reflective cloth. We now have reliable ways to “top-up” the orchard light environment to improve fruit value. Cloth is used pre-harvest in NZ to increase fruit colour. Trials by the Washington Apple Commission have shown significant yield improvements with season long use. Admittedly, the dry Washington climate means fewer tractor passes and less wear and tear to the cloth so full season use may be more feasible there.

Thunder years, blunder years

The phrase “thunder years, blunder years” pokes fun at a common pattern for high performance in the early years of intensive plantings followed by major hiccups when shade and/or crop load induced problems kick in. The risk of blunder years may be higher with intensive systems but it does raise the challenge of achieving consistency – even with familiar and established systems.

How often do blocks get the correct pruning over the years? Blocks often suffer from phases of over / under pruning as fashion, ideas and implementation changes. It all comes at a cost and takes time to fix. Of course, thats no reason not to try something new but the FOPS tree form may make for some difficult pruning decisions – when and if to replace upright fruiting branches?

Complicating nursery production

I don’t mean to climb on the beat-up nurserymen bandwagon. Yes, trees are expensive in NZ but we lack the economies of scale and competition of the big industries overseas. NZ nurserymen face a number of challenges with fluctuating demand and ever changing variety rootstock preferences. Adding in another variation with bi-axis or twin trunk tree form would only further complicate things at the tree supply end.

Spur extinction

Stuart is a tad controversial when he describes chemical thinning as “yesterdays lunch”. Granted he has a point that some chemical thinning cocktails become flavour of the month only to disappear without trace in later years (read, fail). And sure, a stress induced kink early on in the fruit growth curve may come at a significant cost of smaller size at harvest. Its a big call to say that chemical thinning technology should be ditched for being too unreliable!

Spur extinction, the manual removal of spurs to targeted densities, does achieve some predictable responses – fruit set per bud is increased, fewer buds fail to set fruit and December drop virtually disappears. The combined effect is a significant increase in fruit size.

Trial work² in 2008-9 compared manual and chemical thinning singly and combined in three commercial Jazz orchards. Admittedly results were variable and showed that both methods worked some of the time. The common ingredient was early crop load adjustment and when that was suitably achieved, the outcome was very financially beneficial.

In the block where bud thinning was most successful, 1 year flower buds at branch tips and underneath spurs were removed by (gloved) hands at the popcorn bloom stage at a cost of $2/tree. Bud thinning did not affect the percentage of sites setting fruit but it did increase the average number of fruit set per cluster from 1.9 to 2.1. Fruit was also significantly larger (2.2mm) at harvest at the same crop load as the other treatments.

In the same orchard, chemical thinning with a fruitlet thinner reduced average fruit set per cluster from 2.2 to 1.8 with a lesser improvement in size of 0.7mm. So on this orchard, bud thinning gave a bigger gain (+$27k/ha) than post bloom chemical thinning (+$16k/ha) compared with normal pruning and hand thinning. In another block, significant gains were achieved with chemical thinning at bloom while none were detected from bud thinning. In the third block , tree to tree variability was too great to measure any treatment responses.

Perhaps the need for and benefits from manual or chemical thinning have to be assessed on a variety by variety basis. I’d venture to say that recent and valuable gains to improve regular cropping of Pacific Queen and Rose, have largely come from effective chemical thinning right at the outset ie bloom time.

Seeking nett gain

In the late 1980’s there was a Red Delicious systems trial at DSIR, Goddards Lane. In its final years, the V shaped canopy of the Tatura trellis yielded the most, free standing central leaders were second, Ebro trellis was third and the single horizontal trellis of the Lincoln canopy a distant fourth.

The Tatura trellis probably intercepted the most light. It was certainly a scary tractor ride down the sagging, narrow rows. The trial ended up begging a question – did the extra yield of the Tatura trellis more than cover the cost of the structure? History suggests the answer was “probably not”.

The same types of questions will be asked of the FOPS system and especially if the rows are too narrow for conventional tractors and bins. If thats the case, there will be the added need to develop specialised equipment along with solutions to post/harvest fruit handling. Now theres a challenge.

References

1          Luca Corelli-Grappadelli and Alan Lakso (2007) Is Maximising Orchard Light Interception Always the Best Choice, Acta Hort 732, pp 507-518.

2          Jack Hughes, Greg Dryden and Ulf Kerer,  Research Report to Enza (2009) Centrifugal training, chemical thinning and crop loading to optimise the value of  Jazz™