Effects of selected insecticides on microbial numbers,leucaena decomposition and biological nitrogen fixation
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Date
1997
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Publisher
Sokoine university of Agriculture
Abstract
The effects of Lannate and Karate on the decomposition of leucaena green manure and nitrogen fixation by cowpea were evaluated, after establishing their inhibitory effects on the decomposer microorganisms and their toxic effects on the bradyrhizobia in vitro.In the decomposition experiment,manure the in in the perforated plastic litter bags was buried (10 cm) soil contained in wooden troughs and the insecticides were applied on the soil at final concentrations of 0.5 and 1.5
ppm for lannate or and 0.51.0 ppm for decomposition process was monitored at 0, after weeks matter, and incubation by measuring residual organic carbon,inorganic-N heterotrophic content
microbial of count karate.1, the 5 and 73,residual dry residual total nitrogen was the soil.The
determined total at each sampling time.The effects of these insecticides each at 0.5 and 1.5
ppm on the covrpea-Bradyrhizobium symbiotic relationship were assessed in potted soil.
Cowpeas were grown and harvested after 35 days. Nodule numbers and dry weight,shoot dry weight and nitrogen content were assessed.Results of these studies indicated that lannate and
karate had an apparent depressive effect on the growth of the heterotrophs at the 0.5 ppm concentration but not at higher concentrations. The bradyrhizobial proliferation invitro was more affected by lannate than karate. However, nodulation and nitrogen fixation was not affected by
any of the insecticides at significantly any of the the two concentrations tested.It was concluded
from this study that insecticides, when applied even up to ten times the field recommended rate
have no profound effects heterotrophic microorganisms, their ability to on the decompose leucaena green manure and on biological nitrogen fixationin cowpeas. However, the very severe depressive effect of lannate on the cowpea-bradyrhizobia in vitro, may warrant further studies in soils.
Description
Dissertation
Keywords
Soil fauna, Soil microflora, Biological nitrogen, Soil decomposition, Leucaena green manure