1Water Management Research Unit, USDA-ARS, Parlier, CA
2Department of Plant Sciences, University of California, Davis, CA
Effects of fumigants on target and non-target
organisms in soil
Recovery of beneficial soil microorganisms
after fumigation
For the past few decades, soil fumigants have been extensively
used to control target soil borne pathogens and weeds.
After methyl bromide phase out, alternatives such as 1, 3
dichloropropene (1, 3-D), methyl isothiocyanate (MITC),
chloropicrin (CP), dimethyl disulfide (DMDS) is increasingly
used.
Effect on non-target soil organisms are largely unknown.
Toxic only to the target organisms.
Biodegradable
Should not leach into the groundwater
A methyl bromide replacement candidate.
Ubiquitous, simple, and natural product.
Key component of biogenic atmospheric cycle.
Registered with FDA as a food additive.
Zero ozone depletion potential, a broad spectrum fumigant.
Critical role in sustaining the health of soil systems
Significant component of nutrient cycling
Changes in soil quality
Soil microorganisms, as a sensitive indicators of soil health.
Very little ecotoxicological information available for chemical alternatives to methyl bromide.
Important to gain broad biocidal activity.
Determine the effects and recovery of target and
non-target organisms under different fumigation
treatments and,
Compare these organisms in fumigated vs. non-
fumigated control sites
Traditionally a time consuming
task
Culturing techniques
Culture-independent method
Essential components of every living cell
Great structural diversity with high biological specificity
A proxy for the ‘living’ and ‘active’ microbial biomass
Not found in storage products
Relatively constant proportion of
the biomass
Laboratory Analysis
- Fatty acids extracted from
soil samples
- An Agilent 6890 gas
chromatograph
- MIDI Sherlock software
Signature PLFAs
Group Signature PLFAs
Actinomycetes 10Me16:0, 10Me18:0
Gram - bacteria cy17:0, 18:1w7c
Gram + bacteria i15:0, i16:0
Fungi 18:2w6c
AMF 16:1w5c
CH3(CH2)4CH=CHCH2CH=CH(CH2)7COOH ω-6 cis, cis-Δ6, Δ9 C18:2
Treatment † Application rates
(gal/acre) Tarp† Application method
Control 0 Bare -
Telone C35 (TFNB) 48 Bare Shank with N2 delivery
Telone C35 (TFNPE 48 PE Shank with N2 delivery
Telone C35 (T2/3NB) 32 Bare Shank with N2 delivery
Telone C35 (T2/3NPE) 32 PE Shank with N2 delivery
Telone C35 (T2/3NTIF) 32 TIF Shank with N2 delivery
Telone C35 (T2/3COTIF) 32 TIF Shank with CO2 delivery
MeBr:CP (MeBrPE) PE Shank
†Abbreviations: MeBr, Methyl bromide; PE, polyethylene film; TIF, totally impermeable film
Populations of Pythium spp. in soil samples collected from plots fumigated with MeBr PE (Methyl
bromide, PE tarp), T2/3COTIF (carbonated Telone C35, 2/3 rate, TIF tarp), T2/3 NB (Telone C35, 2/3
rate, bare), T2/3NPE (Telone C35, 2/3 rate, PE tarp), T2/3NTIF (Telone C35, 2/3 rate, TIF tarp), TFNB
(Telone C35, full rate, bare), TFNPE (Telone C35, full rate, PE tarp) liters per hectare. Error bar indicates
standard error.
Mycorrhizal PLFA from plots fumigated with MeBr PE (Methyl bromide, PE tarp), T2/3COTIF
(carbonated Telone C35, 2/3 rate, TIF tarp), T2/3 NB (Telone C35, 2/3 rate, bare), T2/3NPE (Telone C35,
2/3 rate, PE tarp), T2/3NTIF (Telone C35, 2/3 rate, TIF tarp), TFNB (Telone C35, full rate, bare), TFNPE
(Telone C35, full rate, PE tarp) liters per hectare. Error bar indicates standard error.
Vectors represent standardized canonical coefficients and indicate the relative contribution of each
biomarker group to each canonical variate
Important to know the recovery of non-target
soil organisms after fumigation.
Microplot test
DMDS was applied at 32, 64, 128,
or 256 mg a.i./L air space per vine.
Treatments were arranged in a
complete randomized block design.
Each treatment had six replicates.
Field Trial
Post-plant spot-fumigation was performed
to achieve 112, 224, 448, or 897 kg/ha.
The experiment was arranged in a complete
randomized block design. Each treatment
was replicated six times.
The ability of soil microorganisms improve after treatment with
pesticide is critical for the development of healthy soils.
Application of fumigants results in a decline of soil organisms.
Fungal and AMF biomass tends to significantly decrease in fumigated
soils.
Similar trend was observed for Gram negative and Gram positive
bacterial biomass.
Significant for management decisions as there are numerous benefits
of microorganisms in soil.
Examine the recovery of belowground component of the ecosystem.
Microbial community structure and soil structure redevelopment by
analysis of aggregate size distribution and aggregate stability with
different time frames;
Determine initial impact of different fumigants on both target and
non-target soil organisms; and
Compare the non-target organisms in fumigated vs. non-fumigated
control sites.
Thank you