Submitted to: Biodiversity of Soil International Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/24/2007
Publication Date: 9/29/2007
Citation: Arevalo, G.E., Helling, C.S., Marquez, D.K., Zuniga, C.L., Baligar, V.C. 2007. Fungus index and residual effects of pesticides in acid and alkaline soils. Biodiversity of Soil International Conference Proceedings. 9.29.2007. Interpretive Summary:
Technical Abstract: Soil applied pesticides have profound effects on the population density and diversity of fungi, however, such information is lacking in tropical soils of the Amazon region. Field experiments were implemented at two experimental farms ("El Choclito", "Bello Horizonte”) of Tropical Crop Institute (ICT) Tarapoto, San Martin, Peru. Soil of "El Choclito” is acidic, where as soils of “Bello Horizonte" is alkaline in reaction. The objective of the study was to determine the residual effects of pesticides in acid and alkaline soils on population density and diversity of fungus. The pesticides tested were: Atrazine, Butaclor, Chlorpyrifos, Metamidophos, Tebuconazole and a control plot without pesticide was also included. Each plot perimeter was surrounded with a plastic curtain of 60 cm tall to prevent pesticide from drifting into adjacent plots. In each plot a site was selected at random for sampling and soil was sampled at two depths (0-20 and 20-40 cm). Initial soil samples were collected before the application of pesticides and second soil samples were collected 90 days after application of pesticides. The mycological analysis (population and diversity) of soil samples was carriedout at the ICT-Phytopathology laboratory. The quantification and identification of fungi was done by serial dilutions and growing on Potato-Dextrose -Agar (PSA) with inverted plate technique. With the microscope and adequate keys, fungus genera were identified and quantified as colony forming units per gram of soil (cfu/gsoil). Total of 45 fungal genera were identified. The genara Trichoderma sp., Penicillium sp., Fusarium sp., and Aspergillus sp. represented 88% of the total fungal populations in the acid soil; where as in the alkaline soil they represented 83% of the fungal population. Overall, in both soils pesticide application decreased fungal diversity by 37.04% to 42.65% with respect to the initial evaluation. The reduction of population and diversity of soil fungus was also influenced by the depth and type of soil. The Atrazine (Azodrin) showed a negative effect against to the micofauna in both soils.