Effect of organic amendments on microbial biomass of a tropical soil treated with some herbicides

Abstract

Studies were carried out on the impact of organic amendments on microflora of soils treated with 2,4- dichlorophenoxy-acetic acid, atrazine, atrazine + metolachlor and paraquat herbicides applied at one and half doses of the recommended rates. Poultry manure-0.05%, urea-0.1 M and glucose–0.1 M of herbicide-treated soils resulted in significant (P<0.05) increases in microbial biomass and highest significant increases in microbial counts for all the treatments, with maximum counts of 12.1x107 cfu/ml for 2,4–D, 10.2x107 cfu/ml for atrazine, 10.4x107 cfu/ml for atrazine + metolachlor and paraquat, followed by urea amendment, while glucose gave the lowest increase in microbial population (P<0.05). Bacillus spp. (39.1%), Pseudomonas spp (30.4%), Flavobacterium spp. (8.7%), Actinomycetes (5.8%) and Proteus spp. (4.3%) were isolated from control soils; while Bacillus (42.3%) and Pseudomonas (50.9%) species were most frequently isolated from herbicide treated soils. Introduction of organic amendments therefore, significantly (P<0.05) resulted in increases in microbial biomass with greater probability for pesticide degradation.