Mounting air quality regulations and pressure from urban neighbors in the San Joaquin Valley continue to place pressure on growers to reduce dust and fine particulates emitted from their farming operations.
The valley has been in narrow compliance with federal PM10 (particulates 10 microns or less in size) standards in recent years. While the ag industry can certainly feel good about the voluntary efforts they are making to help meet PM10 standards, growers still need to pay attention to dust, and find ways to further reduce their emissions at harvest.
For the past four years, the Almond Board of California and its Environmental Committee has been supporting research to help better understand and reduce PM10 dust emissions during almond harvest.
A careful look at the different stages of almond harvest by Dr. Robert Flocchini, professor of Meteorology and Resource Science and director of the Crocker Nuclear Lab, and Teresa Cassel, Crocker Nuclear Lab, both of University of California (UC), Davis, and more recently by Dr. Sergio Capareda, assistant professor, Biological and Agricultural Engineering Dept., Texas A&M University, reveals that pickup at harvesting emits the most PM10 dust, followed by sweeping and then shaking.
Pickup machines typically emit four times more dust than sweeping, which is about 10 times dustier than shaking. As a result, efforts have focused more on reducing dust emissions from pickup and sweeping.
Two other UC Davis researchers, Dr. Dan Downey, assistant research engineer, and Dr. Ken Giles, professor, Dept. of Biological and Agricultural Engineering, have measured relative amounts of dust from sweepers and pickup machines with various setups.
As a result of these research efforts, insights and recommendations are now available that allow growers to reduce harvest dust, particularly in sweeping and harvest pickup, without having to purchase new equipment or significantly change their operations. Here are a few examples of what we have learned, and some of the practices growers have adopted:
Set sweeper heads to optimum level. Research shows that sweeper heads set 0.5 inches below optimum levels substantially increased the dust released by the sweepers through contact with the soil surface. Heads set too low can also nearly double the dust released by the harvester.
Reduce blower passes where possible. Making three blower passes doubled the amount of dust released from the orchard during harvest, compared to making a single blower pass.
Use wire tines on sweeper heads. Sweepers with wire tines significantly reduce dust emitted compared to those with rubber sweeper head parts.
Reduce pickup machine speed. Slower speeds of 1.5 mph cut dust emissions by 50 percent compared to speeds of 3 mph.
Lower separator fan speed. Reduce separator fan speeds to the extent possible.
Maintain a clean orchard floor. In almost all these cases, a well-prepared orchard floor prior to harvest will reduce dust produced, and provide an orchard more conducive to each of the previously mentioned steps.
Keep in mind that orchard canopies often act as filters for dust. As a result, as with pesticide spray drift, dust emissions are more likely at the ends of rows during turnarounds and near the edges of orchards.
Paying attention to dust emissions at harvest not only helps promote good air quality, but can also impact food safety. If there does happen to be a pathogen in the orchard, reducing dust helps reduce the chances that pathogen will move around.