Case Study 6.1 Reviving Guayule in Southern Arizona: A Circular Bioeconomy & Water Saving Crop
By Haiquan Li, Assistant Professor, Department of Biosystems Engineering, University of Arizona
Kamel Didan, Professor, Department of Biosystems Engineering, University of Arizona
Peter Waller, Associate Professor, Department of Biosystems Engineering, University of Arizona
Dennis Ray, Distinguished Professor, School of Plant Sciences, University of Arizona
Diaa Eldin Elshikha, Assistant Professor & Irrigation Specialist, Department of Biosystems Engineering, University of Arizona
Private industry and universities partner to develop bio-based products for desert environments
Guayule (Parthenium argentatum) is a perennial, low-water-use, drought-tolerant, heat-resistant, woody shrub that grows natively in the desert of southern Texas and Mexico. It is now considered for producing commercial-grade rubber tiles and latex, resin adhesives, and biofuels, among other applications. There is an increasing demand for natural rubber. For instance, US imports of natural rubber increased by 13% in the first half of 2022, making guayule- based rubber production an economically appealing alternative industry.
The United States Department of Agriculture (USDA) funded a National Insitute of Food and Agriculture (NIFA) research partnership between the University of Arizona, Bridgestone Tire Company (American, Inc), Colorado State University, the USDA, and New Mexico State University. This research program entitled ‘The Sustainable Bioeconomy for Arid Regions Center of Excellence’ (SBAR; https://sbar.arizona.edu/) from 2017 to 2023 aimed amongst other things to study the value of guayule to the region’s economy with a focus on sustainability, water use under the looming climate change.
The SBAR project explored and tested systematic approaches to developing a guayule bioeconomy pipeline for the region that includes technologies of guayule planting, management, irrigation optimization of growth and yield of natural rubber biomass (Elshikha et al., 2021 & 2022), genetic improvement (Abdel-Haleem et al., 2019) and genomic characterization (Nelson et al., 2019), rubber extraction and processing (Luo et al., 2019), co-product identification (Cheng et al., 2020), logistics optimization (Vazquez et al., 2021), economic analysis (Moreno et al., 2022), precision management with drones and remote sensing (Combs et al., 2022), and environmental and cultural studies (Mealing et al., 2021). The project considered a series of optimization and study results and developed an economic Break-Even for New Crop Options Model (BENCO) (Omotayo 2022) to help growers estimate the economic risk and benefit of adopting guayule based on water and machinery availability and usability (Vazquez et al., 2021). The SBAR project industrial partner Bridgestone contributed through germplasm development, seed increase, development of cultivation technologies, including planting and harvesting equipment, and development of a rubber processing pipeline toward commercialization of guayule-based rubber and by-product production.
Although rubber production is the main profit stream, recycling and reusing the processing residue can add value to the industry and improve economic efficiency, which promotes the circularity of this bioeconomy. Two types of residues result from rubber extraction and processing. The first biproduct is the woody bagasse, which can be converted into biofuels for heating (Sproul et al., 2020), and generate nutrients and organic matter for soils. The other co-product is guayule resin (Luo et al., 2019), which can be used to make adhesives and other value-added metabolites, fatty acids, steroids, triterpenoids, and sesquiterpene esters (Cheng et al., 2020). Of note, triterpenoids are promising anticancer agents (Xu et al., 2021), among other applications.
Guayule can also serve as an effective cover crop in situations of severe water scarcity and possibly in solar farms and can reduce greenhouse gas emission when its byproduct is used as biofuels (Bayat et al., 2021, Moreno et al., 2022). Other benefits also include soil conservation as guayule has deep (1 to 2 meter), coarse taproots to collect water (Rousset et al., 2021).
Water conservation remains one of the most notable potential environmental benefits for our region, as guayule is a low water-use and drought tolerant crop (Sproul et al., 2020), potentially replacing other crops in areas where available water is limiting. Dennis Ray, a scientist with the SBAR project investigated a six week irrigation scenario, and found that it stimulates extra rubber production in comparison to other irrigation scenarios, while saving water.
Growers are able to farm guayule on 2.4 ft (0.7 m) water per year, well within the normal allocation of water in Central Arizona now that Colorado River water delivery has been reduced. The SBAR team has developed an irrigation scheduling application named WINDS (Water-use, Irrigation, Nitrogen, Drainage, and Salinity) (Waller and Yitayew, 2015), that has since been calibrated with five years of guayule irrigation data to be used for irrigation scheduling of Guayule. Bridgestone plans to invest $40 million in the first phase of a processing plant (in Phoenix), with an additional $200 million investment later and has been recruiting farmers in Central Arizona to grow guayule. This emerging bioproduct is fostering higher education by supporting graduate students in the Sustainable Bioeconomy and Bioenergy Emphasis within the Applied Biosciences GIDP program at the University of Arizona. It provided for training elementary, middle school and high school science teachers, created educational materials for classroom in different levels, and helps with preparing workforce for this industry.
