Impact of different doses of deltamethrine on soil microbial density and crop growth

Abstract

The effects of agrochemicals pollution on soil nutrients, soil microbes as well as plants cultivated on the soil were studied. Insecticide and herbicide were used to impact on the soil samples across concentration gradients. Bean and maize seeds were planted in separate experiments to monitor the effects of the agrochemicals on the plants. The microbial diversity and the physicochemical characteristics of the soil before and after pollution were determined using standard methods. Chlorophyll contents of the leaves were also determined after planting. Results indicated that bacterial isolates such as Enterococcus sp 54(40%), Staphylococcus sp 8(13%), Bacillus sp 46(34%) and Micrococcus sp 15(11%) and fungal isolates such as Penicillium sp 41(34%), Saccharomyces sp 67(56%), Yeast sp 4(3%), Geotrichum sp 6 (5%) and Aspergillus sp 1(1.8%) were recovered from treated and untreated soil with the percentages representing after planting. From the results, the herbicide treated soils indicated that the Total Heterotrophic Bacterial Count (THBC) increased after cultivation while the Total Heterotrophic Fungal Count (THFC) decreased after cultivation. On the other hand, the insecticides treated soils recorded a general decrease in THFC and THBC after cultivation. The total nitrogen (TN) and available phosphorus (AP) had no significant differences before and after planting while the exchangeable potassium (EP) had significant increase recorded after planting. Plants generally had poor growth characteristics recorded by stem girth and length, as well as chlorophyll content.