ABSTRACT

The use of atrazine (1-Chloro-3-ethylamino-5-isopropylamino-2, 4, 6-triazine) and paraquat (1, 1’-Dimethyl-4, 4’-bipyridinium dichloride) as alternatives to manual or mechanical weeding in the developing world is becoming inevitable. The frequent application of these two pesticides has led to contamination of soils with dire attendant environmental consequences.A study was therefore, conducted to evaluaate the ability of cocoa and rice husk-derived biochar types to enhance the remediation of atrazine and paraquat contaminated Acrisol (Adenta series) and Vertisol (Akuse series) and to ascertain the effectiveness of the two biochar types in actively supporting the growth of beneficial soil microorganisms to enhance the degradability of the pesticide in contaminated soils. The two soils were amended with each of the two biochar types at 10 t/ha and thereafter contaminated with the each of the two pesticides at three rates of zero, normal application and ten times normal application rates and replicated three times in a completely randomized design. The moisture contentwas kept at 80% field capacity and the samples incubated for 90 days.. Total heterotroph count, microbial biomass C and N and C and N mineralized were determined at 10 day intervals for the entire duration of the experiment. Results showed that biochar amendment stimulated growth of heterotroph counts in both the Akuse and Adenta series with the highest mean counts of 66 x 10⁵cfu/g soil being obtained from the Akuse series amended with cocoa husk biochar and contaminated with atrazine at ten times the normal rate of application. Microbial biomass carbon was also high for the biochar amended soils especially for the cocoa husk biochar amended soil. The use of paraquat had a depressive effect on the total heterotroph counts. Application of paraquat did not significantly depress the microbial biomass carbon especially in the cocoa husk biochar amended soils contaminated with ten times the normal rate of atrazine. Microbial activity was also high in the biochar amended soils compared to the un-amended soils

and contaminated with pesticide. Degradation of atrazine at normal rate of application was faster in both soil series amended with rice husk biochar as compared to the soils amended with cocoa husk biochar and the un-amended. At ten times the normal application rate of atrazine, degradation was fast in the cocoa husk biohar amended Akuse and Adenta series. There was less degradation of paraquat in both soils; however, at normal application rate of paraquat, degradation was faster in the rice husk biohar amended soils i.e. for both Adenta and Akuse series. The high composition of the nutrients in the cocoa husk biohar biochar especially the available P materials make it a suitable material to be used as soil amendment in the highly acid soils in Ghana.