Document Type

Dissertation - Open Access

Award Date

1986

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Science

Abstract

The purpose of this research was to determine optimal soil storage methods for soils used in carbofuran and terbufos degradation studies. The effect of soil microbes on degradation was also observed. An LD50 study, using 22 day old crickets (Acheta domestica), was undertaken to establish the appropriate LC dose for carbofuran in the soil storage studies. A carbofuran use history failure soil and a noninsecticide use history soil of the same type were collected from the SDSU experimental farm in Centerville, South Dakota. After initial degradation and microbial analysis, the soils were stored air-dried and with a moisture level of 18% at 2°C and 26°C. Aliquots were removed from storage at various time intervals and treated with 30 ppm technical grad carbofuran and 5 ppm technical grade terbufos. Degradation studies were performed by cricket bioassay methods, and bacterial, actinomycetal, and fungal levels were established using pour plate technique. Technical terbufos exhibited a latent period in most time 0 and stored soil analyses, suggesting microbial degradation. Carbofuran did not exhibit a latent period. The presence of fungi enhanced the degradation of terbufos in the time 0 soils, and in some of the stored soil samples. Bacterial presence enhanced carbofuran degradation in the LC50 ­analysis of the time 0 soils. Actinomycetal activity did not influence the degradation of terbufos or carbofuran, and bacteria did not influence the degradation of terbufos. Carbofuran exhibited greater cricket mortality in the soil lacking a history of insecticide use, while terbufos had greater mortality levels in the soil having a carbofuran use history failure. Microbes exhibited some influence on the differences between the history and nonhistory soils. Carbofuran exhibited more dependable degradation curves in soils that were stored moist. Terbufos degradation curves were less sensitive to soil moisture level. Soils should be stored moist, or at near the wilting point (-15 bars), if experimentation with fresh soil is not convenient. Soil storage temperature level and limited influence on degradation.

Library of Congress Subject Headings

Soil degradation
Soils -- Density
Soils -- Testing

Format

application/pdf

Publisher

South Dakota State University

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