Testing wetting agents for soil drag and bootie swabs and validating them in varied agricultural soils

Testing wetting agents for soil drag and bootie swabs and validating them in varied agricultural soils

Jan. 1, 2024 - Dec. 31, 2024

2024CPS08

University of Illinois at Urbana-Champaign

$141,910.00

Matthew Stasiewicz, Ph.D.
University of Illinois at Urbana-Champaign

Pratik Banerjee, Ph.D., Andrew J. Margenot, Ph.D.

Practical and powerful soil sampling methods can improve microbial quality and safety in produce production. Aggregative sampling methods, such as drag and bootie swabs, have been studied in animal and produce production but have not been fully optimized for produce.  This project optimizes the wetting agent for drag and bootie swabs for use in different agricultural soils. We will first test increasingly practical wetting agents buffered peptone water, neutralizing buffer, and phosphate-buffered saline and compare them with reference methods. We use evaporated milk as a reference for the optimization of wetting agents and soil composite grabs as a reference for the validation of aggregation. The optimal wetting agent should be shelf stable, not animal sourced, not allergenic and should show at least as good, if not better, results for bacteria recovery than reference methods. In addition, this project will validate the best wetting agent testing in varying soils created by various stages of ground preparation for different commodities, using bacteria recovery and diversity as metrics. This project will determine the best wetting agent for aggregative soil sampling across multiple produce-relevant soil types. 

Technical Abstract

Aggregative sampling methods, such as drag and bootie swabs, have been studied in animal and produce production but have not been fully optimized for produce – for example the typical wetting agent is evaporated milk, which is a potential allergen, animal sourced, and not shelf stable. Thus, there is a need to optimize wetting agent composition for drag and bootie swabs of produce soil. In this proposal, we use soil composite grabs as a reference to ensure the aggregation is valid and evaporated milk as a reference to ensure the optimization for wetting agents is valid. Three sample schemes will be used to collect samples, paired steps and scoops, scoping at some steps, and walking a serpentine pattern. In objective 1, we will compare evaporated milk, buffered peptone water, neutralizing buffer, and phosphate-buffered saline wetting agents for organism recovery from soil sprayed with untreated-manure, over up to 6 months of for die-off. Aerobic count recovery, total coliforms, and generic E. coli will be tested for microbial quality and safety purposes. Compared to reference methods, the drag and bootie swabs hydrated with optimal wetting agent could be (i) more practical if it was clean label, easier to use, faster to collect samples, and less labor; and (ii) more powerful if it would show at least as good, if not better, results for bacteria recovery abilities. In objective 2, drag and bootie swabs will be hydrated by the optimal wetting agent and tested on three commodities in sustainable student farms and two commodities in specialty crop farms. For each commodity, we will collect samples on tilled soil, immediately or 1-2 days post-irrigation, and after opportunity events like rainfall or animal intrusion. The bacteria recovery ability will be analyzed by plate counts and enrichment. 16s rRNA sequencing will be used to test bacteria diversity. We will keep track of the soil parameters, such as texture, pH, soil organic carbon, and microbial biomass, every visit for both objectives 1 and 2. The goal of this project is to enable evidence-based changes in produce soil sampling through industry and academia to ultimately allow producers to better protect public health by evaluating food quality and safety indicators.