By John Wilton
A sustainable orchard business needs to have a planned orchard redevelopment programme in order to maintain its variety mix and plantings at a profitable level of production and returns. This planning needs to be long term, at least five years out and preferably longer.
Good orchard performance data should be the basis of orchard redevelopment decision making. Limiting factors to performance in each orchard block should be noted and possible solutions carefully assessed. Our OrchardNet™ tool is capable of benchmarking orchard blocks by variety against industry performance and this makes a good starting point for putting block performance into perspective.
Well managed orchards can remain at their peak performance for many years, often well past the 20-year life that is generally considered the average orchard life span. The variety becoming obsolete and therefore uneconomic is the most frequent reason for orchard redevelopment.
The next most likely reason for decline in profitability is a drop in yield and fruit quality. Pest and disease, or site related limiting factors, are the main reason for declining orchard performance. In this situation, it is critical that reasons for decline are fully investigated otherwise the next orchard on the site will suffer the same problems as the present one. As this is now a replant site there is a fair chance that the new planting performance will be even worse than the one it replaced due to specific replant disease unless the site has been treated to overcome it.
Obsolete planting systems and the inability to get labour willing to work them is probably the third main reason for orchard redevelopment. Once easily managed, simple, intensive planting systems that are labour friendly become well established, it becomes more and more difficult to entice labour into older orchards with large trees that are difficult to work in.
There is also movement these days towards more mechanisation for many orchard husbandry tasks, notably pruning, hand thinning and harvest. Older, extensively planted orchards do not readily adapt to mechanisation. It is difficult to forecast how far this trend will proceed but there is sufficient evidence to indicate that platforms rather than ladders will be widely used in future orchards and it is probable that mechanical hedging may replace some of the pruning role.
Orchard topography will probably become a limiting factor to efficient or cost effective mechanisation as it is unlikely that machines will easily adapt to sloping orchard terrain. So we may see a move to shifting orchards away from hilly country onto flat or gently sloping sites.
Beware of planting system fashions
The fruit growing scientific journals and the popular press are littered with many different systems and variations around established growing systems. Not many of these have stood the test of time and often an orchard can be dated by the orchard planting fashion that was in vogue at the time of planting. Some of these planting systems were unduly complicated and expensive to establish. Some overlooked fundamental plant physiology leading to excess vigour problems. Others, particularly the so called ‘pedestrian’ orchards planted in bed systems failed to recognise the need for easy access for both men and machinery. These were popular in Europe around 30 to 35 years ago but are now seldom seen.
In general, planting systems have steadily evolved towards slim, well-supported hedge row systems that are either an upright vertical canopy based on a spindle bush style tree or narrow V-trellis systems. Narrow V-trellis systems tend to be popular in hot climates where there are large problems with sunburn.
Along with the trend to slim canopies there has been a movement away from single leaders towards multi-leaders in a two dimensional row. This can lower tree densities and can therefore reduce orchard establishment costs and make vigour management easier because tree vigour is dissipated along the row. The catch with these multileader systems is that relative to the central leader configuration the tree structure is weakened so more robust tree support is required.
In the modern orchard, particularly in mainland Australia, net protection is becoming the norm so robust net support is required which, with careful design, can also provide tree support.
Orchard life is much simpler if planting systems, particularly in regard to between-row spacing, are standardised across the whole orchard. This is easy on flat land but becomes more difficult on sloping land because of machinery crabbing and differential tree vigour up and down the slope.
Incidentally, where there have been marked vigour differences along the row, these should be mapped prior to removal of the existing orchard and strategies implemented to overcome this vigour variation in the new planting. Strategies can include wider in-row spacing with multileader tree form to dissipate the excess vigour in high vigour parts of the block, reverting back to single leader and close in-row spacing where previous tree growth has been poor.
Young orchard performance critical to success
Redeveloping orchards is capital intensive so these establishment costs load new plantings with a high level of fixed cost. In order to service the debt and pay it off over the orchard life, high yields of top quality fruit are necessary. We estimate that between 70 and 75 per cent of an orchard’s costs are fixed, so the higher the saleable yield, the lower the unit cost.
Data on young orchard performance from OrchardNet™ shows that average yields commence at around 35 to 40 per cent below the upper quartile average in year two, rising to 50 to 55 per cent in years three and four, then stabilising at around two thirds of the upper quartile average. Achieving upper quartile yield and quality performance, therefore results in a huge lift in profitability, often around double of the average.
Within block tree uniformity is the key factor responsible for high yield and quality. This is much more important than planting densities, training systems or pruning methods. Every tree should be pulling its weight evenly across the block.
The second most important factor lies in developing a canopy that captures more than 60 per cent of the light coming into the orchard. Many orchards now use reflective mulches to bounce light, which gets through to the inter row area, back up into the canopy allowing considerably more than 60 per cent of light to be utilised. Yield and fruit quality correlates closely with the amount of light captured by the canopy.
Canopy uniformity is the key to high orchard yield and quality. This has to be the objective of any orchard planting. Before removing existing plantings, their tree size and vigour behaviour needs to be carefully mapped and reasons for these vigour differences investigated.
Usually vigour differences will be due to soil profile variation. The first thing to investigate is top soil depth and soil texture differences. For tree fruit crops, potential rooting depth, even with dwarfing rootstocks, needs to be greater than 60cm and preferably a metre.
Deep ripping should be standard practice for pre-planting soil preparation but will not replace the need for adequate drainage. Its main role is to break up hard pans which impede the downward movement of surface water or provide easier pathways for roots to explore the soil. In the absence of good drainage, deep ripping can sometimes make soil drainage problems worse. It is best carried out in dry soil to get maximum shattering effect.
Winter water tables need to be at least 60cm deep or deeper to avoid waterlogging. Checking drainage is therefore, an essential part of block redevelopment. Be very wary of light textured top soils because these have low moisture holding capacities and therefore vulnerable to drought stress problems and can become easily water logged as well.
Where sub soils are heavy and relatively impervious, such as the duplex soils around Shepparton, drains need to be close and if the sub soils will hold a mole drain well, then a mole drain/tile system can be a good option. On these soils, planting on the ridged top soil along the rows also improves tree performance and has become standard practice.
Specific replant disease
Where an orchard block is being replaced by a new planting of the same species there is often a problem in getting the new trees to grow well.
Working in Tasmania, Dr Gordon Brown investigated apple tree replant growth on ten different sites. Average percentage growth reduction was 58.5 per cent and ranged from 30 to 70 per cent compared to fumigation treatments. Relative to the total costs involved in replanting, the cost of fumigation for specific replant disease is very small so it should be an essential treatment when orchards are being replanted. To be effective, specific replant disease treatment needs to follow other soil preparation such as drainage and soil ridging because the effect of treatment can be nullified if untreated soil re-contaminates the treated area.
Details of Dr Brown’s work on specific replant disease can be found in the Future Orchards® library.
During ground preparation it is important to address soil pH and fertility status within the rooting zone. Pre-planting ground preparation is the only chance you have to add lime, dolomite or gypsum to the sub soil. Excessively low pH in the sub soil can lead to aluminium and manganese toxicity both of which seriously reduce potential tree performance.
Some Australian soils can have soil salinity problems. These can only be successfully dealt with prior to planting, primarily by improving drainage and adding gypsum to displace and leach sodium out of the soil. High sodium is bad news for pome fruit because of the adverse effect it has on calcium uptake and predisposing the fruit to pit and blotch problems.
The initial young tree spring growth flush in their first season is largely dependent on the level of stored nitrogen reserves they come with so it is questionable whether or not it is necessary to apply general fertilisers such as nitrogen before planting.
Where soils have poor structure and low organic matter, applying compost or animal manures as part of the pre-plant preparation is well worth considering provided that it is not going to adversely affect drainage in the root zone.
General soluble fertiliser applications are best done after planting once root growth is underway, say four to six weeks after bud break. This is best addressed through fertigation.
Incidentally, putting soluble fertilisers in the planting hole is not recommended because of the risk of root injury. I have seen more young trees killed from fertiliser than any other cause.
The safest way to apply pre-planting soluble fertilisers is to broadcast them along the row then incorporate them into the soil during final ground preparation. Mono ammonium phosphate is often used for this purpose because newly planted trees are very responsive to a good supply of soluble phosphates.
Provision for irrigation
Newly planted trees have very confined root systems that rapidly exhaust their accessible soil moisture supply once growth begins. When moisture stress occurs in trees during their early establishment, their growth may slow down and, once terminal buds form, are very difficult to get growing again.
It is necessary to have the irrigation system commissioned by the time spring growth commences.
About the author
APAL’s Future Orchards® program is funded by Horticulture Innovation Australia Ltd using the apple and pear industry levy funds from growers and funds from the Australian Government. AgFirst is a key Future Orchards partner.