Influence of fungicide treatment on CaCl2-extractable phosphorus and phosphate-solubilizing micro-organisms in soil

Abstract

An incubation experiment was performed to determine the influence of the fungicides Benomyl, Captan and Thiram on CaCl2-extractable P. Small, but statistically significant increases occurred in treated soils over the incubation period, to reach maxima 20 days after treatment. Insoluble phosphate (CaH4 (PO4)2) was then added to determine the influence of fungicide treatment on phosphate solubilization. With phosphate additions of less than 100 μg/g of soil, less P was extracted from soils treated with 100 μg of the fungicides/g of soil than from untreated soils. At 200 μg/Pg soil, however, increases in phosphate solubilization occurred. Numbers of both bacteria and fungi capable of solubilizing insoluble phosphate increased in treated soils but no evidence was found for an increase in water soluble organic acids. The results suggest that fungicide treatment selectively increased the proportion of micro-organisms capable of solubilizing both native and added insolube phosphate. re]19760713