Maximizing almond yield potential in both the long and short term requires understanding pomological concepts. Research updates presented at The Almond Conference provided growers with those concepts—keys for a successful relationship with their trees with the goal of achieving high sustainable yields.
Intercepting the maximum amount of light by the maximum number of trees per acre will determine yield potential, said Roger Duncan, University of California (UC) Agriculture and Natural Resources (ANR) advisor in San Joaquin County. The reality of production, he pointed out, is that many orchards have a range of soil variability, missing trees and other factors that can affect their yield potential.
Bruce Lampinen, UC Davis, who is known for his work in determining light interception in orchards, correlates almond production with light interception or photosynthetically active radiation (PAR). His studies show that in well managed orchards production increases by 50 kernel pounds for every percent light interception after about five years of age. At 50 percent light interception the orchard has the potential to produce 2500 kernel pounds per acre. At 80 percent the potential for 4,000 kernel pounds is reached. Lampinen said above 80 percent is not recommended due to food safety concerns
Pruning and within tree row spacing also influences yield potential, Duncan said.
High Density Plantings
A pruning and spacing trial he conducted in Stanislaus County showed that the closer the in-row tree spacing, the higher light interception. Light interception tended to peak at year 11 at all in-row tree spacings. Duncan also looked at super high density plantings on dwarf rootstock, which is one of the considerations for off-ground harvest.
Duncan compared spacing at 18 by 21 feet with five by 11 feet spacing and determined the tighter planted trees PAR at mid day was 44 percent compared to 83 percent for the 18 x 21 planting. Yield potential for the higher density block was 2200 with an actual yield of 1,324 kernel pounds per acre. The 18 x 21 block had the potential for 4150 kernel pounds per acre and actual yield was about 3,600.
Duncan also noted that repeated hedging cuts in high density plantings could lead to increased disease potential and lots of big wood that can cause damage to harvest machinery.
Higher density plantings do not necessarily result in higher yields at some point as row spacing gets closer together since more space is devoted to drive rows. There is a possibility of getting decent yields with high density plantings, Duncan said, if effective dwarfing rootstocks can be developed and all orchard operations can be conducted with over the row equipment or smaller tractors.
Research on food safety implications in high density plantings is also needed.
Pre-plant evaluation and modification to address the physical, chemical and biological challenges at the orchard site is another important aspect of maximizing yields. Choosing a rootstock, variety, and tree spacing; proper planting and post planting management also determine the success in an orchard.
One of the barriers to good orchard establishment is stratified sandy loam soil. Stratification restricts water movement and impedes root development and water infiltration.
Stratified soils can also impede root movement and water infiltration. Soil modification or deep ripping should be as deep as possible to create a ‘root friendly” root zone. Biological challenges are soil nematodes that can affect vigor of young trees. Soil analysis can determine pathogen levels and an appropriate fumigation response.
Rootstock choice can also determine long-term health. Duncan calls choosing the right rootstock for an orchard site a defense against problems that can challenge yield potential. Specific conditions where rootstock choice can help determine yields are soils high in pH, salts, alkali, soils with high levels of ring nematode or bacterial canker, or heavy soils. Duncan said peach/almond hybrids, Viking or Empyrean ® 1 are recommended for soils high in salts, alkali or with high pH. Viking, Lovell, Guardian and Empyrean ® 1 are recommended for sites infested with ring nematode or bacterial canker. For heavy soils, Krymsk 86, Rootpac® R and Marianna 2426 are recommended.
Duncan showed field trials that determined in-row tree spacing that provided higher yield potential. Although the trial with Nonpareil on Hanson found no significant difference between trees spacings for first 10-11 years, over the 20-year trial, 10-14 foot tree spacing provided the highest long term yields. Moderate spacing may be best for large variety on vigorous rootstock, Duncan said.
Duncan broke down the costs of higher density plantings, noting for every one foot reduction in row width—for example from 22 feet to 21 feet, many costs are increased by five percent. Those costs include strip fumigation, mowing, spraying, herbicides, irrigation hoses and sprinklers. Planting trees closer down the rows does not increase most on-going costs.
To realize yield potential of an orchard, Duncan advised spending for pre-plant soil modification and disinfestation and choosing the right rootstock and planting configuration for the site. If in doubt, he said, go with more vigor and higher density.
Almond tree training for the first three years of an orchard’s life is another important aspect of maximizing yield potentials.
Katherine Jarvis-Shean University of California Cooperative Extension (UCCE) Orchard Systems advisor Sacramento, Solano and Yolo counties said the goal for those first three years is to create a structure that will support long-term weight of the crop. Minimizing cuts that will affect early yields is advised.
Heading at planting is the most important cut in a tree’s life, Jarvis-Shean said. If the trees are fall planted, growth should be allowed then topped like a new bare root when dormant. If trees are winter or spring planted, they should be tipped if untipped, allowed to grow and then scaffold select at first dormant season. The goal is for room for four to six scaffold branches above about 22 inches for shaker head accommodation.
Scaffold selection goal is for well anchored branches that won’t break or split from trunk with future crop weight. Cross branches, shaker blockers should be removed, then pick the best of what is left for the scaffold, noting angles, spacing and orientation.
By the third dormant season, minimal pruning is required, only removing crossed limbs or tractor smackers. Most pruning at this point will delay early yields.
Consistent production is the goal in maintaining an established orchard, said Franz Niederholzer, UCCE farm advisor in Colusa, Sutter and Yuba counties. The objectives are adequate pollination and nut set, careful irrigation and nutrition and protecting the canopy.
Good bee activity and adequate boron should equal good nut set, but growers and managers should not assume all hives are equal in strength.
Once the crop is set, it must be fed. The focus is on nitrogen, Niederholzer said, but potassium (K) should not be ignored. Leaf K target is 1.4 percent. Levels should be checked in spring and summer. Multiple small applications are better than big shots, he noted.
Maintaining a healthy canopy in the orchard will keep the ‘motor’ running smoothly, Niederholzer said. Irrigations to meet demand, disease and pest control with adequate coverage and monitoring are needed to ensure a healthy canopy.