Assessing the Potential of a Wireless Solid Set Canopy Delivery System for Mist Cooling

July 27, 2020
BY NYAKUNDI MICHIEKA PH.D.
NMICHIEKA@CSUB.EDU

Economics of Pistachio Production in Kern County and California

Pistachio production in Kern County has grown over the last 4 decades. Between 1980 and 1990, output averaged 14,245 tons, then more than doubled between 1991 and 2000, averaging 35,370 tons. In 2017, output was 143,000 tons compared to 178,000 tons in 2016. Today, pistachios are Kern County’s third top crop contributing 15% or $1.14 billion worth gross value of agricultural products, according to the Kern County Deparment of Agriculture and Measurement Standards (2020). Pistachios are also California’s second most valued agricultural export with a value of $1.52 billion. Roughly 44% of exports end up in China or Hong Kong while 30% end up in Europe (California Department of Food and Agriculture 2018).

Pistachio Development and Temperature Changes

California’s central valley is well suited for growing pistachio trees which thrive in hot summers and moderate winters. Winters, however, need to be cold enough for pistachios to complete their dormancy and produce adequate bloom in the following spring (Herrera 1997). This exposure to cool temperatures is called ‘chilling’. Inadequate chilling can result in uneven pollination which can reduce yield, affect uniformity among mature nuts and require growers to make additional harvest passes (Kallsen 2006, Elloumi, Ghrab et al. 2013).

Kern County has been experiencing higher than average winter temperatures which may effect pistachio production. In fact, the California Department of Food and Agriculture (2016) reported that the 2015 drop in California’s pistachio production was due to warmer climate. Studies have also predicted that the next three to five decades may be too warm to grow tree crops (Luedeling, Zhang et al. 2009). Various technologies have been proposed to mitigate the adverse effects of weather on pistachio production with others treating trees with oil, applying kaolin clay or breeding new cultivars altogether.

Mist Cooling System for Pistachio Production in Bakersfield

California State University, Bakersfield (CSUB) developed an automated low cost solid state canopy delivery (SSCD) system that uses a smart control system to apply mist to pistachio trees based on temperature. The system measures air humidity and temperature, then transmits the data wirelessly to a smart control system. The system was set up on a 0.53-acre pistachio orchard located in Bakersfield, California. The orchard was divided into 8 zones, with 4 trees per zone.

Nozzles were suspended 7.62 meters high to allow for trimming and harvesting (figure 2). Temperature monitoring was managed by 8 wireless transmitters (WSN) and a weather station (WS) which collect weather and crop related data from the field. A web-based application was used to visualize the collected data and wirelessly control the SSCD system. A smart control system (SC) was used to collect data from the WSN and WS, then posted data to a cloud-based database and wirelessly controlled the SSCD system.

Four experiments were carried out between 2017 and 2020. In the first experiment, sprinklers were turned on until branches appeared wet. Time and temperature change were both recorded. In the second experiment, sprinklers were turned on for a set time period, then temperature change was recorded. Zones were paired up in the third experiment then misted for a set period of time. In the final experiment, zones were misted for a much longer period (45 minutes) and temperature change was recorded.

Preliminary Findings

Even at lower temperatures of 50 degrees Fahrenheit, temperature drops were possible. The average drop in temperature across all experiments was 5 °F with 16.67 °F being the maximum temperature drop. The most efficient temperature drop occurred where misting was applied to branches until they became wet – as opposed to misting over fixed times. Using more zones led to larger temperature drops, though water usage may have been more. Temperatures did not drop significantly on windy days.

Funding for this project was made possible by the U.S. Department of Agriculture’s (USDA) Agricultural Marketing Service through grant AM170100XXXXG011. Its contents are solely the responsibility of the authors and do not necessarily represent the official views of the USDA.

References

California Department of Food and Agriculture (2018). California Agricultural Exports 2017 - 2018. Available at <https://www.cdfa.ca.gov/Statistics/PDFs/2017-18AgExports.pdf>.
Elloumi, O., et al. (2013). "Chilling accumulation effects on performance of pistachio trees cv. Mateur in dry and warm area climate." Scientia Horticulturae 159: 80-87.
Herrera, E. (1997). Growing Pistachios in New Mexico, New Mexico State University. Cooperative Extension Service. Circular 532. College of Agriculture and Home Economics. Available at <https://aces.nmsu.edu/pubs/_circulars/CR532.pdf>.
Kallsen, C. (2006). "Pistachios short on chilling hours." Accessed. July, 2020. Available at <https://www.farmprogress.com/pistachios-short-chilling-hours>.
Kern County Deparment of Agriculture and Measurement Standards (2020). 2018 Kern County Agricultureal Crop Report. Kern County Crop Reports. 1001 S. Mount Vernon Avenue, Bakersfield, California 93307. Available at <http://www.kernag.com/caap/crop-reports/crop10_19/crop2018.pdf>.
Luedeling, E., et al. (2009). "Climatic changes lead to declining winter chill for fruit and nut trees in California during 1950–2099." PLoS One 4(7): e6166.