Research at California State University-Fresno is focusing on issues that include an ultra-high-density almond orchard system and dust-free harvesting using much the same technology employed in the pistachio harvest.

Gurreet Brar, assistant professor in the Department of Plant Science, talked about that during a field day at the university.

The dust created in conventional almond harvesting has become a significant issue, with critics ranging from irked neighbors to environmentalists to regulators of air quality.

Among the approaches to be tested at Fresno State include the dust-free harvesting of almonds through use of a catch method akin to that used in the pistachio harvest that stops nuts from dropping to the orchard floor.

In addition to looking at the high-density system, Fresno State is also looking at an almond rootstock evaluation trial and pruning responses and tree architecture.

The rootstock evaluation will look at water use efficiency and how trees perform when irrigated or deprived of water.

High-density systems

In conventional orchards trees are pyramid-shaped with a large volume of shaded canopy, and there are dust issues during harvest as nuts are collected from the orchard floor. Conventional cultivars also bear nuts on spurs, while the high-density systems bear them on a dard-type system that bears laterally.

In the high-density trial, two cultivars were planted, Nonpareil is a traditional cultivar that has a strong spur bearing habit and a vigorous growth habit producing strong lateral shoots. Another cultivar is BA2, a self-fertile cultivar which has a predominantly “dard-type” bearing habit with narrow upright growth that provides a different tree architecture

“We are trying to develop narrow slender trees with a central leader and no, or minimal pruning so that when we harvest with shake and catch type harvesters, we have uniform maturity of nuts across the whole canopy of those narrow trees,” Brar said. “The ultra-high-density experiment will help us find out how much density is too much in regards to creating shading, non-uniform maturity and other issues.”

 “They may have better shakeability,” Brar said. “They may achieve better yield with closer planting.”

 “The trees grow in high density and are not pruned,” he said.

The Almond Board of California is among those paying for the research at Fresno State at $50,000 to $60,000 a year. There are also matching funds from the California State University Agricultural Research Institute.

Rootstock research

The rootstock research is on five acres.  Another six acres are devoted to pruning responses and tree architecture and high-density research. Researchers will look at whether there is more yield due to closer plantings and whether trees are suitable for shake and catch free harvest.

One of the challenges will be drying the nuts, which is commonly done on the orchard floor for almonds. That is not the case for pistachios and walnuts.

But it will be two years before researches will have to cross that bridge. And Brar said there are machines that can harvest almonds and catch them in canopies. They’re already in use in dense plantings in Spain. And he believes a way to dry the nuts can be found.

“We plan to get our hands on an over-the-canopy harvester for almonds or perhaps a pistachio harvester,” he said.

Researchers are also looking at arriving at better lighting in the orchard.

The high-density planting plot has 15, 18 and 21 feet between the rows. There are 16, 10 and seven feet between the trees.

A conventional planting is 21 by 16 feet.

Sister trial

A sister trial is going on in South Australia, headed by Grant Thorp, a plant and food researcher.

Brar said the trial in the southern hemisphere means researchers can get “two years’ worth of data in one year because we have alternating seasons.”

The research looks at pruning responses, how tree architecture can be shaped.

It does so with five varieties, Nonpareil, Winters, Wood-Colony and Monterey and BA2.

In Control No. 1, there was a heading cut plus trimming of side branches in the nursery and no further pruning. For Control No. 2, there will be a heading cut plus trimming of side branches in the nursery and a narrow “palmette” prune in the field in year two.

For Central Leader Trial No. 1, there will be no heading cut or trimming in the nursery and no further pruning. For Central Leader Trial No. 2, there is no heading cut, but side branches will be trimmed at the nursery to produce a “bare pole.”

The research looks at, among other things, which varieties lend themselves to the more vertical structure and how they differ in growth habit. An early but preliminary indication is that Winters does not lend itself to having a strong central leader.

Brar’s team of researchers includes Thorp; Robert Willmott, orchard manager at Fresno State; visiting scientist Masood Khezri; graduate students Daniel Syverson, Hardeep Singh and Travis Woods; and undergraduate students Madison Hedge and Georgia Reyes.