Long term optimum apple orchard density and shape

Winter months are a great time for planning and you may be considering your orchard planting plans for the next 2-3 years. Apple trees have been ordered and you have an area planned on where to plant and you may be considering what densities would be optimum for the cultivars you will be planting. Perhaps you've been thinking to experiment with a higher density or V-trellis system to maximize productivity but not sure if the benefits will be worth the added cost of production. Researchers from Cornell University in New York State have recently published a 20-year, long term study of orchard performance of 'Gala', 'Fuji', 'McIntosh' and 'Empire' in densities ranging from 240 trees/acre up to 2200 trees/acre in an upright conic shaped system, similar to most orchards in Ontario, or a V-shaped system, which have been widely adopted in Washington State (Lordan et al. 2018 a, b). This article will be summarizing the research by Lordan et al. (2018 a,b,) which looked at both orchard productivity and economic profitability.

Methods

Lordan et al. (2018 a,b) established a replicated field trial using 8 different densities in two different tree shapes on a non-irrigated sandy clay loam site. Trees were on a M.7 rootstock at 240 trees/acre and on a M.26 rootstock at 340 trees/acre. At the higher densities, trees were planted on M.9T337. The conic shaped trees that were planted at densities between 240 to 910 trees/acre were supported by a single wire trellis with a conduit steel pole. At higher densities, conic trees were supported by a three wire trellis. For annual tree pruning, 2–3 large diameter limbs were pruned off with a beveled cut to encourage new growth. Lateral branches were simplified and not headed except for at the highest density of 2200 trees/acre with which branches were shortened to a spur less than 50 cm from the trunk.

For the V-shaped canopy plantings, trees planted at densities between 240–670 trees/acre were supported by a 6 wire trellis, with 3 wires on each side. Trees at this density had a divided canopy which was divided by training half of the branches to one side of the trellis and the other half to the other side of the canopy. Enough branches were tied over so that there was a branch every 20 cm along the trellis. Branches were simplified every year and starting in year 6, one branch was removed per year and a new replacement shoot was tied to the wire. At the higher densities, the canopy was divided by leaning trees, alternating, to either side and were supported by a 2 wire trellis with conduit pipe leaned out 15? on each side. Trees were pruned similarly to the conic shaped trees with renewal cuts except for the branches that grew in the middle of the tree which were pruned right off, cutting close to the trunk.

Yield, growth and fruit quality parameters were all measured. Net present value (NPV) was calculated using the net income from the yielded fruit, total investment costs and discounting the future value of money at a rate of 5% (interest and inflation). Income was calculated from collected yield, number of fruit and pack-out grade. Investment costs were calculated from recorded tree training and pruning costs, establishment costs, management costs and other costs were calculated from averages from New York State apple growers.

Results and discussion

Upright, conic shaped trees compared to v-shaped canopies

Overall, conic-shaped canopies performed better than V-shaped canopies in the research of Lordan et al. 2018 a,b). The conic shaped canopies had higher cumulative yields than the V-shaped canopies in 'Empire', 'McIntosh' and 'Gala' and similar cumulative yields in 'Fuji'. Fruit quality parameters were similar in both shapes of canopy with the following exceptions: in 'Empire', there was significantly higher brix in a conic shaped canopy; in 'McIntosh', the V-trellis produced larger apples; in 'Fuji' and 'Gala', the firmness was greater in a V-shaped canopy.

Lordan et al. (2018b) calculated the cumulative NPV over the span of the orchard's 20-year life. The conic tree shape had a higher cumulative net present value in 'Empire', 'Gala' and 'McIntosh' and there was no significant difference in tree shape in 'Fuji' trees.

V-trellis orchards are much more common in Washington state to maximize light interception. The results from the research of Jordan et al. (2018 a,b) is a good example of what works for Washington in their high sunlight environment may not work as well with us with our cloud cover. The cost to establish a V-shaped canopy is also greater than a conic-shaped canopy which greatly impacts the NPV, especially with no yield benefit with a V-shaped canopy

Planting density

Optimum planting density for maximum cumulative yield was calculated for each canopy shape by Lordan et al. (2018a). For a conic-shaped canopy, the optimum planting density was calculated to be 2200 trees/ acre for 'Gala' and 'Fuji' and 1500 trees/ acre for 'McIntosh' and 'Empire'. For a V-shaped canopy, the calculated optimum planting density for highest cumulative yield was 2200 trees/ acre for 'Gala', 'Fuji' and 'Empire' and 1400 trees/ acre for 'McIntosh'.

Fruit size was affected by density in the research by Lordan et al. (2018a). In conic shaped trees, fruit size tended to be greater in conic shaped trees planted at lower densities than at higher densities for 'Gala', 'Fuji' and 'Empire'. There was no significant difference amongst densities of 'McIntosh' conic trees. In V-shape trees, fruit size was greatest at 910 trees/ acre for 'Fuji', 'Gala' and 'Empire' trees and greatest at 1300 and 2200 trees/ acre for 'McIntosh'.

The percentage of red colour was also affected by density in all cultivars (Lordan et al. 2018a). In 'Empire' conic trees, the greatest percentage of red colour was at the lowest density of 240 trees/acre. In 'McIntosh' conic trees, the greatest percentage of red colour was in densities 340–908 trees/acre. With 'Fuji' in a conic shape, the colour percentage was greatest at 420 trees/acre and declined at higher densities (650-2200 trees/acre) and at the lowest density (240 trees/acre). This trend was similar in 'Gala' conic-shaped trees, colour was greatest at 520 trees/acre and declined with higher densities (910–2200 trees/acre) and at the lowest density (240 trees/acre). In V-shaped canopies, the effect of density on the percentage of red colour was similar to conic-shaped canopies except for at the highest density (2200 trees/acre) which had a lower percentage of colour than apples from lower density plantings of 'McIntosh', 'Fuji' and 'Gala'.

The economics of different planting densities was researched by Lordan et al. (2018b), both cumulative NPV over 20 years and the break-even year were affected by density. Optimum tree density planting for net present value was determined for each cultivar and tree shape (Table 1). Break-even years, for when the costs of establishment and production are recouped, were also determined using NPV (Table 1).

Final thoughts

The optimum tree planting density for yield was greater than the optimum density for NPV in these two papers. This was due to the costs continuing to increase, linearly, as tree density increased; while the extra yield benefit from higher densities starts to level off as density increases (Lordan et al. 2018b) The reason for the optimum density of 'Fuji' for NPV being so low in a conic-shaped orchard was that the biennial bearing habit lowered cumulative yields compared to other varieties and took much longer to break even at high densities which have greater establishment costs (Lordan et al. 2018b)

References

Lordan, J., P. Francescatto, L.I. Dominguez, T. L. Robinson. 2018a. Long-term effects of tree density and tree shape on apple orchard performance, a 20 year study - Part 1, agronomic analysis. Sci. Hortic 238: 303-317

Lordan, J., M. Gomez, P. Francescatto, T. L. Robinson. 2018b. Long-term effects of tree density and tree shape on apple orchard performance, a 20 year study - Part 2, economic analysis. Sci. Hortic 238:435-444