|Dangi, Sadikshya -|
|Ajwa, Husein -|
|Cabrera, J -|
Submitted to: International Conference on Methyl Bromide Alternatives and Emissions Reductions
Publication Type: Proceedings
Publication Acceptance Date: September 30, 2012
Publication Date: November 6, 2012
Citation: Dangi, S., Gerik, J.S., Ajwa, H., Cabrera, J.A. 2012. Response of soil organisms to dimethyl disulfide fumigation. International Conference on Methyl Bromide Alternatives and Emissions Reductions. p. 17. Interpretive Summary: Soil fumigants are applied to control key diseases, weeds and volunteer crops. After the phase out of methyl bromide (MeBr), other replacements such as dimethyl disulfide (DMDS) are now in use. Much of the studies have focused on MeBr but the effects of other recently used fumigants on both target and non-target organisms are unknown. Soil microorganisms play an important role in ecosystem function and significantly contribute to nutrient cycling, organic matter decomposition, plant nutrient uptake, and maintenance of soil structure. Fumigant application can change the microbial community composition which may lead to changes in the overall soil quality. Therefore it is important to know the impact of fumigant on microbial communities in soil. The aim of this study was to determine the effectiveness of different rates of DMDS on both target and non-target organisms in soil.
Technical Abstract: After the commonly used soil fumigant methyl bromide (MeBr) was phased out in the United States, alternatives to MeBr such as dimethyl disulfide (DMDS) which is known to have broad pest control spectrum, is increasingly used. However, effectiveness of DMDS has been mainly investigated to study target soil borne pathogens and nematodes but their effect on microbial community structure are largely unknown. Soil microorganisms are essential in sustaining health of agricultural soil and hence, it is very important for them to recover after treatment with fumigants for the development of healthy soils. DMDS was applied at 32, 64, 128, or 256 mg a.i./L air space per vine. One treatment remained without DMDS fumigation and served as control. Immediately after fumigation, 3.7 L water was applied to each vine in a 2 h period to seal the soil surface. One soil sample per vine at 1-60 cm soil depth was taken 15, 45 and 60 and 90 days after fumigation with a 2.5 cm diameter auger. From the top soil samples phospholipid fatty acids (PLFA) were extracted from 10-g soil samples using a modified Bligh–Dyer methodology. Fatty acids were directly extracted from soil samples using a 1:2:0.8 chloroform/methanol/phosphate buffer mixture. Phospholipid fatty acids were separated from neutral and glycolipid fatty acids in a solid-phase extraction column. After mild alkaline methanolysis, PLFA samples were qualitatively and quantitatively analyzed using an Agilent 6890 gas chromatograph with autosampler, split-splitless injector, and flame ionization detector. The system was controlled with Agilent Chemstation and MIDI Sherlock software. Individual PLFA signatures were used to quantify the abundances of specific microbial groups in soil samples. Treatments were arranged in a complete randomized block design. Each treatment had six replicates. The experiment was conducted twice. The primary objective of this study is to examine and compare the impact of different rates of DMDS on target (Citrus nematodes, Pythium spp., Fusarium oxysporum etc.) and non-target soil organisms (fungi, gram positive bacteria, gram negative bacteria, actinomycetes, Arbuscular Mycorrhizal Fungi (AMF), protozoa). Effects of DMDS on target and non-target soil organisms will be discussed.