ORGANIC BY-PRODUCT EFFECTS ON SOIL CHEMICAL-PROPERTIES AND MICROBIAL COMMUNITIES

Soil management practices that contribute to increased soil productivi ty and long-term sustainable agricultural production have been neglect ed over the last four decades. The need to increase soil productivity led to the evaluation of a system of disposing of large quantities of organic by-products and poultry litter on agricultural land. Our objec tives were to evaluate the effects of applying noncomposted municipal solid waste (MSW), amended with either poultry litter (PL) or NH4NO3 t o adjust C:N ratios in the soil surface in either the spring or fall. Changes in soil chemical properties, bacteria population shifts, chang es in species richness and evenness of indigenous soil bacteria, and r esponse by cotton (Gossypium hirsutum L.) were evaluated. Soil P, K, C a, and Mg were increased in the surface 0-15 cm by a factor of three o r four times by application of organic by-products. After two annual a pplications, soil Cu increased slightly, Zn doubled, Co and Cr decreas ed, while Pb increased by a factor of two. Soil organic matter content increased on average by 89 percent for treatments containing newsprin t, yard trimmings, and cotton gin trash. Newsprint plus NH4NO3 resulte d in a shift to more Gram positive bacteria, while newsprint plus poul try Litter resulted in a shift to more Gram negative bacteria. Both N sources resulted in a reduction in Bacillus sp. Shifts in the bacteria l populations and changes in species richness (number of species detec ted) and evenness (relative abundance of each species) were induced by organic by-product additions. These shifts appear to be the result of increased substrate for C mineralization rather than any properties o f biological control. Shifts in the microbial community structure towa rds Gram negative organisms may benefit plant growth and may be useful as an indicator of soil quality.