Fact, fashion or fiction?
Keeping it simple is always best.
The industry must be flush with money at the moment. Looking at the way land values have skyrocketed and the complex, expensive, untested growing systems being adopted, sure gives this impression.
In my younger days, I was involved in Jaycees and one of our mantras was “KISS – keep it simple stupid”. In general, this rule still applies. When it comes to growing fruit trees, this principle certainly applies. The closer your training system is to the tree’s natural growth habit, the easier it will be to establish a profitable orchard and the lower the capital outlay involved.
THE INTENSIFICATION MYTH
In recent years we have seen tree planting densities rise well above optimum planting densities for our climatic conditions and soil tree vigour potential. Relative to many parts of
the world where apples are major crops we have a long growing season with relatively mild summer temperatures, so there are few days in our summer with temperatures high enough to shut down efficient leaf photosynthesis. Apple leaf photosynthesis efficiency tends to fall off rapidly once temperatures rise much above 28°C. In continental climates, such as Washington or warmer lower latitude growing areas, such as the central valley in Chile or South Africa, tree growth and fruit sizing shuts down for the hottest part of the growing season.
With our longer, effective growing season here, tree vigour is generally stronger than found in most apple growing areas around the world. Our high levels of relatively uninterrupted photosynthesis means that young trees have both good vigour and the capability of sizing significant crop loads. Usually, these are at cropping levels well above those quoted in published scientific literature from elsewhere in the world.
The objective of obtaining early yields is often quoted as the driver for intensive planting. This being so, one would expect to see significant production as early as the year of the planting and certainly in the next year. This is the case in many northern European plantings. The nurseryman there grows a big, well-feathered tree capable of fruiting in the year of planting and at the densities they plant these big trees at, they would be in big trouble with excess vigour if they did not crop them as soon as possible.
Yet, when I look at some of our higher density plantings, cropping will be several years away because most of the potential fruiting wood for these early crops is promptly pruned off to make the tree grow and conform to the proposed intensive tree-training system.
Earlier this year we had a staff conference out of Hawke’s Bay where we were shown different planting systems, most more intensive than the Hawke’s Bay norm. When the question was asked, why the trees were not being cropped in the first couple of years, we were told cropping them would hinder tree development. What is the point of planting high tree
“Trees with adequate room to accommodate their vigour will settle down to regular cropping without huge manipulation.”
densities if you are not going to crop them as soon as possible to start getting a return on the extra capital outlay required for planting trees at high density?
Some years ago, I ran regression analysis on young tree yields against tree development expressed as percentage increase in trunk cross sectional area using data presented by Dr John Palmer at fruit grower seminars. I cannot remember the exact R² result of this analysis, except that it was well under 0.1, so crop load had a very minor effect on tree growth. Crop load is therefore, not the main cause of poor young tree performance. The notion that you should not crop young trees because it will inhibit their development is obviously fiction.
As well as crop load, there are many factors that limit young tree growth. These include the three W’s; water, weeds and wind, inhospitable soils for root development, excessive blossom levels and too many growing points caused by insufficient pruning out of laterals along the leader, as well as laterals bunched together and choking the leader. We have found that the tree is quite capable of carrying the crop that remains on a young tree after a heavy hit with an aggressive postblossom thinner and at the densities we plant at today make satisfactory canopy development with that crop level.
Optimum planting densities depend on soil quality, rootstock, scion vigour and tree canopy form. Crop load is your best vigour control agent. Because it usually takes two to three growing seasons for a branch to carry sufficient crop to achieve a good vigour/crop balance, trees need to be far enough apart to allow at least two years of annual shoot extension growth before running into canopy density problems in the next tree.
MATURE ORCHARD PERFORMANCE
One of the problems with orchard system trials is that in many the trial is terminated after five or six years, so there’s not a lot of data about on how the various planting systems perform after full canopy is reached. Most orchards do not cover establishment costs until at least four to eight years after planting, depending on establishment costs and tree growth in the establishment period. Most data indicates that breakeven on direct operating costs will occur sooner, often three to five years after planting. Canopy development and yields by this stage have barely reached half way towards full potential when breakeven on direct operating costs occurs.
The real success of the planting is determined by the full canopy yield and quality performance achieved and how long this level of production can be maintained. The longer you can maintain high yield and quality in an orchard planting, the better the internal rate of return will be. Provided the variety is not superceded and the orchard is maintained well and does not suffer any major disease problems, a productive life of 20 years or more should be possible.
We have an extensive database on orchard block performance covering a number of years. I investigated mature orchard performance for Scifresh over the 2016 and 2017 harvests and the 2017 and 2018 harvests. In generating the data, two consecutive years of production was combined to remove any biennial-bearing influence. Regression analysis of yield and profit against tree density was carried out. The dataset for the 2016 and 2017 seasons was more complete than that of the 2017 and 2018 seasons so the R² for the 2016 and 2017 seasons was better than for the 2017 and 2018 seasons.
The table below shows the R² results. The trend lines all showed both profit and yield were maximised at around 1500 trees per hectare and were similar for both sets of data.
The conclusions we can draw from the data is that in the real commercial world differences in tree density influences only around 15 percent of the huge range in orchard yields and contrary to popular belief, and most short term systems trial data optimum planting densities are lower than the 2500 to 3000 trees per hectare usually recommended.
Fig 2. This Scilate block is on the same rootstock as the block in Fig 1 but planted at 2381 trees/ha. Cumulative packed yield by the third leaf was only 3.99T/ha, partly because of lower than optimum crops in years two and three and as a result, poor export fruit recovery in the third leaf. Orchard management rather than planting density determines young orchard performance.