Irrigation Sanitizers and Soil Health: A Survey of Romaine Production Systems in Arizona

Abstract

Purpose. Romaine growers in the Desert Southwest have connected with the University of Arizona’s Cooperative Extension to investigate whether or not sanitizer application is affecting soil health. This study was designed to determine if sanitizer treated sprinkler irrigation water impacts soil health in romaine production systems of Arizona, and to identify soil health indicators that are sensitive to these changes. Background. As outbreaks of foodborne illnesses are on the rise, the California and Arizona Leafy Greens Marketing Agreements were developed from extensive research findings that promoted the use of antimicrobial agents, or “sanitizers,” in sprinkler-irrigated leafy vegetables production systems. The main hypotheses were twofold: first, there are deleterious soil health changes caused by the implementation of irrigation sanitizers in US Southwestern sprinkler-irrigated romaine production systems; secondly, certain soil parameters could be used to guide interpretations of these soil health changes after sanitizer application. Methods. A subset of five fields from an initial survey population of 14 were analyzed. Forty samples were collected, and 39 soil properties were measured. The full suite of soil health assays included indicators of carbon dynamics, nitrogen dynamics, and additional physical and chemical properties. Statistical analyses were then conducted to determine sanitizer impacts on individual soil health indicators, as well as multivariate soil health profiles of collected samples. Results. Results showed sanitizers significantly impacted several indicators of carbon and nitrogen dynamics, including total soil carbon, soil organic carbon, total nitrogen, and potentially mineralizable nitrogen. Additional soil physical and chemical properties were not impacted. Sanitizers had no effect on multivariate soil health profiles, which were mostly determined by preexisting site conditions. Conclusions. This study does not provide convincing evidence to diverge from the use of irrigation sanitizers, though land managers should work with experts to monitor soil health and manage soil carbon and nutrients when determining management practices like fertilizer rates. Additionally, growers should consider utilizing strategies like cover cropping, application of organic amendments, and diverse crop rotations to ensure effective carbon and nitrogen cycling in the agroecosystem.