. Bacteria in relation to soil fertility. Soil microbiology; Bacteriology, Agricultural. 2o6 BACTERIA AND SOIL FERTILITY. Metallic Poisons.—Copper, lead, and arsenic at times occur naturally in native agricultural soil and at times are added to soils by sprays and from smelter smokes. Hence, the question nat- urally arises as to what influence they are going to have upon the microflora of the soil. Moreover, it is of economic impor- tance as any factor which modifies the bacterial flora must of necessity influ- ence the crop. Extensive studies have been made on the influence of various arsenic


. Bacteria in relation to soil fertility. Soil microbiology; Bacteriology, Agricultural. 2o6 BACTERIA AND SOIL FERTILITY. Metallic Poisons.—Copper, lead, and arsenic at times occur naturally in native agricultural soil and at times are added to soils by sprays and from smelter smokes. Hence, the question nat- urally arises as to what influence they are going to have upon the microflora of the soil. Moreover, it is of economic impor- tance as any factor which modifies the bacterial flora must of necessity influ- ence the crop. Extensive studies have been made on the influence of various arsenic compounds upon the bacterial flora of the soil with the result that arsenic was found to be a stimulant in low concentration and toxic only in larger quantities. The extent of stimulation and toxicity varies greatly with the specific type of microorganism and the form in which the arsenic is applied. Ammonifiers.—Experiments on ammoniiiers demonstrated that this class of bacteria are not at first injured by the arsenic, but their speed of action is increased. The actual results showed that whereas the untreated soil produced in unit time lOO parts of ammonia, soil to which sixty pounds of arsenic in the form of lead arsenate an acre was applied produced 103 parts of am- monia in the same length of time. And it was not until 2,500 pounds of arsenic an acre was applied to the soil that the produc- tion of ammonia was reduced to one-half normal. The Paris green, on the other hand, retarded the action of this class of bac- teria even in the lowest concentration added, and by the time 600 pounds an acre had been applied the ammonia produced in unit time had been reduced to one-half normal. The poisonous action Fig. 41.—Arsenic obtained from various Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Gr


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Keywords: ., bookcentury1900, bookdecade1920, booksubjectbacteriologyagricult