Abstract
A field experiment was conducted to investigate the effect of some pesticides on soil microorganisms numbers including bacteria, fungi and actinomycetes. The land was chosen , prepared ,leveled and divided into plots 1x1.5m. Each experimental unit was replicated four times, five seed potato (HZPC from Holland) were placed in a hole at the depth of 6-10 cm , with 25 cm spacing between holes. After planting, potato plants were sprayed with pesticide as recommended by manufacturals source including insecticide (Fatec), herbicide (Grastop) and fungicide (Phostrol).
Results showed that the effect of pesticides on soil microbial communities was varied with pesticides types and microbes which had different response to the used pesticides.
The toxicity effect of Fatec on soil bacteria was more at third and eighth day after spraying and had a significant difference in comparison with control with about 0.7x106, but the maximum effect on fungi occurred at the third day differing from control with about 0.5x104 ,but its effect on actinomycetes was less with about 0.2x103 from control at the first day only.
The effect of Grastop was less which caused reduction of the number of soil bacteria at the first, third and eighth day ,but its effect on soil fungus and actinomycetes occurred on( first & third) and eighth day respectively. Phostrol was more effective on soil actinomycetes which caused reduction of these microbes on eighth day after spraying followed by fungus and then bacteria which affected by this fungicide at first and third day with the difference with control by 0.3x106 and 0.7x106 respectively.
