Effect of Biochar on the Abundance of Soil Bacteria.

A pot experiment was conducted to study the effect of biochar on the abundance of soil bacteria and compare it with the source biomass. Seven different treatments and a control were used in the experimental set-up. Three different types of biomass were selected and three types of biochar were produced from them. Both the materials were applied to the soil at a rate of 5t/ha. All treatments were incubated for 30, 60 and 90 days. Cultural, microscopic and biochemical tests were carried out to identify the bacterial isolates in soils treated with biochar and its source biomass. Bacterial isolates identified in soil and in some of the biomasses before treatments were applied include Bacillus badius, Bacillus krulwichiae, Bacillus siralis, Bacillus sylvestris, Bacillus flexus, Aneurinibacillus aneurinilyticus and Bacillus thuringiensis while after incubation periods, seven new isolates were identified. This was true for the biomass treated soils where additional one to two isolates reappeared. Conversely, in the biochar treated soils, most of the isolates disappeared except Bacillus badius that survived in all soils till 90 days. Because of its tolerant nature, it was further investigated for cellulase enzyme activity. Interestingly, the isolate did not show any such activity. Conclusively, biochar application may exert negative effect on the distribution and proliferation of soil bacteria with possible effect on soil quality and crop production.

Arsenic contamination in food-chain: transfer of arsenic into food materials through groundwater irrigation.

Arsenic contamination in groundwater in Bangladesh has become an additional concern vis-à-vis its use for irrigation purposes. Even if arsenic-safe drinking-water is assured, the question of irrigating soils with arsenic-laden groundwater will continue for years to come. Immediate attention should be given to assess the possibility of accumulating arsenic in soils through irrigation-water and its subsequent entry into the food-chain through various food crops and fodders. With this possibility in mind, arsenic content of 2,500 water, soil and vegetable samples from arsenic-affected and arsenic-unaffected areas were analyzed during 1999-2004. Other sources of foods and fodders were also analyzed. Irrigating a rice field with groundwater containing 0.55 mg/L of arsenic with a water requirement of 1,000 mm results in an estimated addition of 5.5 kg of arsenic per ha per annum. Concentration of arsenic as high as 80 mg per kg of soil was found in an area receiving arsenic-contaminated irrigation. A comparison of results from affected and unaffected areas revealed that some commonly-grown vegetables, which would usually be suitable as good sources of nourishment, accumulate substantially-elevated amounts of arsenic. For example, more than 150 mg/kg of arsenic has been found to be accumulated in arum (kochu) vegetable. Implications of arsenic ingested in vegetables and other food materials are discussed in the paper.