Impact of Some Pesticides on Total Counts of Soil Non-Symbiotic Nitrogen-Fixing Bacteria, Particularly Azotobacter sp

Abstract

A pot experiment was conducted to evaluate the effect of glyphosate herbicide (n-phosphonomethyl glycine), mancozeb fungicide ([[1,2-ethanediylbis- [carbamodithioato]](2-)] manganese mixture with [[1,2-ethanediylbis- [carbamodithioato]]-(2- )] zinc) anddiazinon insecticide (O, O-diethyl O-[6- methyl-2- (1-methylethyl)- 4-pyrimidynyl]), threesoil orders and two soil moisture contents (50% and 100% of field capacity) and theircombinations on soil total non-symbiotic nitrogen-fixing bacteria particularlyAzotobacter sp. counts. This experiment last for two months from the 6 th of Jun until the8 th of August 2011 with five sampling periods at biweekly intervals. Factorial experiment(4×3×2) with Completely Randomized Design (CRD) and three replications was usedand the means were compared using Revised Least Significant Differences (R.LSD) atthe level of significant of 0.05. Significant results were obtained at the last two scheduledperiod’s sampling of 4 th and 5 th , and the results showed that: Mancozeb fungicidedecreased total Azotobacter sp.; Diazinon insecticide decreased both total non-symbioticnitrogen-fixing bacteria and total Azotobacter sp.; Agholan soil (order Entisols) showedthe greatest increase in soil total non-symbiotic nitrogen-fixing bacteria. 50% soilmoisture content revealed the greatest reduction total Azotobacter sp. while, 100% soilmoisture content showed the greatest increase in soil total Azotobacter sp. count. Thecombinations among: glyphosate, Agholan soil and 100% moisture combination showedthe greatest reduction in total non-symbiotic nitrogen-fixing bacteria and totalAzotobacter sp.