Impact of Organic and Conventional Systems of Coffee Farming on Soil Properties and Culturable Microbial Diversity

A study was undertaken with an objective of evaluating the long-term impacts of organic (ORG) and conventional (CON) methods of coffee farming on soil physical, chemical, biological, and microbial diversity. Electrical conductivity and bulk density were found to increase by 34% and 21%, respectively, in CON compared to ORG system, while water holding capacity was found decreased in both the systems. Significant increase in organic carbon was observed in ORG system. Major nutrients, nitrogen and potassium, levels showed inclination in both ORG and CON system, but the trend was much more pronounced in CON system. Phosphorus was found to increase in both ORG and CON system, but its availability was found to be more with CON system. In biological attributes, higher soil respiration and fluorescein diacetate activity were recorded in ORG system compared to CON system. Higher soil urease activity was observed in CON system, while dehydrogenase activity does not show significant differences between ORG and CON systems. ORG system was found to have higher macrofauna (31.4%), microbial population (34%), and microbial diversity indices compared to CON system. From the present study, it is accomplished that coffee soil under long-term ORG system has better soil properties compared to CON system.

The effects of varying moisture and nutrient levels on the transfer of a conjugative plasmid between Streptomyces species in soil

Biparental crosses were established in sterile silt loam between a plasmid-free Streptomyces parvulus strain (recipient) and a recombinant Streptomyces lividans strain (donor) bearing the recombinant, conjugational plasmid pIJ303 which codes for thiostrepton resistance. The crosses were established in autoclaved portions of soil adjusted to approximately 60, 40, and 20% water-holding capacity. The soil was amended with either CaCO3 alone (limed), or CaCO3 along with cottonseed flour, chitin, and cellulose (nutrient amended). After a month or longer incubation at 30 °C, the number of transconjugants in each soil treatment was determined by spread-plating on thiostrepton–agar selective medium. The heterotrophic microbial activity of each soil was also assayed with fluorescein diacetate. Nutrient amendment resulted in two to three times more fluorescein diacetate activity than for the unamended, limed treatments of equivalent moisture content. The nutrient-amended, low moisture treatment resulted in the greatest frequency of plasmid transfer. In comparison, plasmid transfer frequencies for the nutrient-amended, higher moisture treatments and for the limed treatments were approximately 5 to 73 times lower. The results suggest that nutrient-amended, relatively dry soils possess frequent microsites where mycelial growth and conjugationally mediated plasmid exchange between streptomycetes occur readily.Key words: Streptomyces, plasmid, conjugation, soil, gene transfer.