Summary of Awards to Date

Remediation and recovery measures to expedite planting or replanting of vegetables following soil contamination by Salmonella enterica

Date

Jan. 1, 2014 - Dec. 31, 2015

Award Number

2014-325

Funding Agency

University of California, Davis

Amount Awarded

$376,225.00

Investigator

Trevor Suslow, Ph.D.
University of California, Davis

Co-Investigator(s)

Robyn McConchie

Summary

Layperson's Summary

Producers of fresh fruits and vegetables need practical and sustainable methods to minimize the survival of human pathogens, such as Salmonella, in production soil. Much of the research effort to date has focused on long intervals following manure application and process controls for composting and thermal pasteurization treatments during pelletizing. Despite best intent in setting composting standards, contaminated compost applied to production fields remains a significant problem. Contaminated soil has resulted in hundreds of acres of abandoned crop due to Salmonella in consecutive years, especially with lettuce and salad greens. Remediation and soil recovery treatments are needed to effectively shorten the time interval before replanting of such high value vegetables without fear of losing another crop to preventable sources of contamination. This research, conducted in Australia and California will focus on optimizing the existing knowledge in low‐residue cover cropping, solarization, and field flooding for remediation of soils contaminated with chicken manure known to harbor Salmonella. The anticipate outcome is a set of grower options for integrated management of contaminated soil that may be extended to other pathogens and sources of contamination such as flooding, domestic animal grazing of crop residues, and large numbers of animal intrusion to croplands.

Technical Abstract

Producers of fresh fruits and vegetables need practical and sustainable methods to minimize the survival of human pathogens, such as Salmonella, in production soil. Contaminated soil has resulted in hundreds of acres of abandoned crop due to pathogens such as Salmonella enterica, especially with lettuce and salad greens. Destruction of multiple fields per year, occasional hundreds of acres, is damaging economically but also may negate initiatives of sustainability for the operation. The proposed research, conducted in parallel and coordinated efforts in Australia and California, will focus on optimizing existing agricultural practices and knowledge for predicting both inherent characteristic survival and options for remediation of soils contaminated  with chicken manure known to harbor Salmonella.  The central hypothesis is that single or sequential strategies involving short‐duration, low‐residue cover crops, field or seed‐bed solarization, and flooding will be effective in the practical elimination of residual Salmonella enterica contamination. Soil contamination by Salmonella enterica will be remediated by the allelopathic potential of cover crops, the physicochemical properties and suppressive microbial community that results from the C:N ratio within each system.

Replicated 5 x 5 m plots in Year 1 and 2 will be managed to repeat a sequence of (1) chicken manure‐ litter amendment, (2) baby lettuce‐baby spinach crop, (3) ’contaminated’ crop incorporation, (4) 30 d and 45 d cover crop screening, and (5)/replant baby lettuce‐baby spinach. A targeted subset of plant (cover crop) and soil samples will be used to estimate the concentration of glucosinolates and phenolic compounds present at time 0, 30 and 45 days from cover crop planting and 15 days after disking. A similar targeted subset of samples will be used for microbial community analysis using Next Generation Sequencing technologies to describe soil microbial communities. Additional replicated plots will follow a sequence of (1) chicken manure‐litter amendment, (2) baby lettuce/baby spinach crop, (3) ’contaminated’ crop incorporation, (3a) field and bed solarization for 6‐10 weeks or (3b) flooding for 3‐5 weeks, and (4) replant baby lettuce‐baby spinach. While not the primary focus of the research, we feel it will be critical to determine the potential for the target remediation treatments to elevate populations of Listeria monocytogenes in soil.

The primary purpose of the proposed research is, ultimately, to provide alternative solutions for soil remediation of human pathogens that growers across the United States and Australia could use irrespective of the size of the operation. Furthermore, the outcomes of this research will provide science‐based information that could be used to modify current public health regulatory and enforcement laws mandated through the respective country agencies and authorities.