Shredding of pruning brush has high promise as an alternative to burning and a way to improve soil microbes and water penetration in California almonds, but debris picked up with nuts raises issues in processing, says a Madera County farm advisor.

Brent Holtz has been investigating shredding or chipping of brush instead of burning the piles of the material near orchards.

He spoke about his findings at the Almond Board of California’s recent 33rd Almond Industry Conference in Modesto and said he believes a sustainable alternative to burning can be found.

Holtz noted that federal and state legislation on air quality control has tightened restrictions on burning. The almond industry’s practice of burning green pruning brush in the fall or winter generates smoke that concerns regulatory agencies.

Pointing to the state’s 2003 almond acreage of 550,000 acres, he said preliminary studies show that nearly 2,000 pounds of green brush per acre, or about 1 billion pounds, must be disposed of each year.

Although “burn days,” as weather permits, are allowed, they are often too few for growers, particularly those in the southern San Joaquin Valley, to adequately dispose of brush.

Opinions differ

“That’s why some growers have tried to chip or shred some of their brush,” he said. Over the past 15 years, several designs of self-propelled or tractor-pulled wood shredding implements have appeared. Some growers leave the debris in the orchard middles to add organic matter to the soil, while others remove it, fearing the decomposing material will draw nutrients away from the trees.

“If wood chips can be shown not to interfere with harvest or take valuable nutrients from trees,” Holtz said, “then growers would be more likely to adopt chipping or shredding as an alternative to burning, especially if advantages to soil health and nutrition could also be demonstrated.”

With funding from the California Almond Board, Holtz did several trials between 2000 and 2004 in Madera and Oakdale. He had analyses done on samples of the particles and soils for effects on soil chemistry, nematodes and microbes in comparison with those from soil without the chips. He also investigated the effects of wood chips on harvest.

“We’ve seen less ring and lesion nematodes and more bacterial- and fungal-feeding nematodes in soil with wood chips. We’ve seen a trend toward higher phosphorus and nitrate levels.

“We’ve also seen significantly more debris in windrows at harvest and in USDA samples of almonds taken from harvest carts,” he said. Some of the debris remained with nuts, even though much of it was blown out during nut pick up.

Improve soil

He recorded more soil-aggregating fungi, which, as they decompose the chips, bind the matter to soil particles to improve soil quality. Soil water infiltration was improved in soils with chips.

Holtz said manufacturers of chippers and shredders have improved the equipment to make smaller chips. “We can still modify pick-up machines to blow out more debris and put de-stickers on harvest carts. Processors may need to adjust or implement new equipment to separate wood debris from almond hulls, and they will have more debris to dispose of.”

It will take an industrywide effort, he said, by growers, processors, equipment manufacturers, researchers, and the Almond Board of California, but “equipment has advanced so that its use should help reduce air pollution and provide a sustainable method of brush removal.”

Measuring PM10

In another project sponsored by the Almond Board, Sergio Capareda, a researcher from Texas A&M University, is working with University of California, Davis scientists to measure the amount of PM10 emissions in dust from almond sweeping operations. Key in the project is air sampling equipment developed by Texas A&M.

The team has determined that these emissions are dependent on weather, soil type, age of the particular orchard, and equipment, Capareda said.

One objective of the trials in Bakersfield and Arbuckle is to arrive at a measurement-based PM10 emission factor for almond sweeping to replace the estimate currently used by air quality control authorities. Another is to provide the emission factor that is most representative of standard industry practices.

Capareda said they have found that by modifying how conventional equipment is used, particularly air flow control, emissions can be reduced by 50 to 60 percent. During the 2005 almond harvest, they measured PM10 emissions, both upwind and downwind from sweeping operations.

While new, unspecified, emission standards are being determined by EPA, he warned it is important that the almond industry continue to work on dust abatement strategies. “Sooner or later, you are going to be asked to eliminate a certain amount of dust from your operations.”

Daniel Downey of the Biological and Agricultural Engineering Department at UC, Davis reported on an ongoing project to evaluate dust generated from almond harvesting.

Cut fan dust

Among other findings, Davis and his fellow researchers have learned that by placing a dirt removal bag on the harvester fan, the dust intensity reading fell to about 12.5 percent, versus 35 percent without the bag.

The project involves measurement by an instrument mounted directly on the pickup machine rather than placed at the end of a row. It is based on how a light beam penetrates the dust in air passing through a plenum.

Various combinations of settings for ground speed, fan speed, and dirt chain speed were compared to find how they influence the amount of dust. Continuing research is planned with different machine designs and orchard cultural practices.