Impact of sodium azide and organic amendments on soil microorganisms

• Main Author: Rivas-Davila, Maria E
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2005
• Subjects: Soil sciences
• ISBN: 9780542109126; 0542109123

Agricultural soils typically have been fumigated with methyl bromide to provide pest control in the production of high-value crops throughout the world. Methyl bromide will be phased-out in 2005 or soon after, and sodium azide has potential as a substitute pesticide. Sodium azide has broad biocidal activity, and may therefore also impact nontarget soil microorganisms. To minimize potential deleterious effects, organic amendments could be incorporated with sodium azide to stimulate recovery of affected beneficial microorganisms. To determine the impact of sodium azide and organic amendments on soil microorganisms a series of greenhouse tests were established. Initially sodium azide was applied to the soil at rates of 0 to 100 mg/kg and squash was planted. The number of culturable soil microorganisms was observed from pretreatment time to 4 weeks after planting (WAP). Populations of total and oligotrophic bacteria remained stable over time, while heat-tolerant bacteria, chitinolitic bacteria and fungal populations decreased. Microbivorous nematode populations were reduced by sodium azide treatments. Additionally, phytotoxicity was observed on squash with rates of 50–100 mg of sodium azide. Because of detrimental effects on non-target bacteria, microbivorous nematodes and squash seed germination, <50 mg of sodium azide was chosen for subsequent greenhouse experiments. The impact of sodium azide-treated soil on introduced microorganisms was studied measuring colonization of soybean seed and root by two rifampicin-resistant PGPR mutants: Bacillus pumilus strain INR7 and B. subtilis strain GB05. Overall, colonization by PGPR strains was not affected by sodium azide. To evaluate the impact of incorporation of organic amendments with sodium azide on the soil microflora five experiments were conducted: three experiments to test two types of amendments, soybean meal (SBM) and cotton seed meal (CSM), at rates from 0–2 g kg/soil in combination with sodium azide at rates from 0–30 mg/kg soil; a fourth experiment evaluated the effects of multiple applications of sodium azide and SBM on soil microflora; and the fifth experiment determined temporal changes in soil bacterial community structure related to application of sodium azide alone and in combination with SBM. Changes in populations of certain groups of soil microorganisms affected by application of sodium azide were initially observed but over time populations did not differ. Populations of soil microorganisms in soils with combination treatments of amendments and sodium azide varied depending on the particular type of amendment and combination rate. (Abstract shortened by UMI.)