Efficiency of organic manuring and mineral fertilization regimes in potato brown rot suppression and soil microbial biodiversity under field conditions.

Microbial biodiversity in soil following different fertilisation regimes and their impact on potato brown rot suppression was studied. Evaluation was made at four naturally infested locations in Egypt. Fields with low components of organic matter (OM) and low carbon nitrogen (C:N) ratio were conducive to the disease caused by Ralstonia solanacearum. Contrary to fields rich in antagonistic actinomycetes and microbial biodiversity. The effect of different regimes on disease control varied from location to another according to difference in edaphic factors. The effect of NPK (nitrogen, phosphorous and potassium) suppression was remarkable as related to increase in eubacteria biodiversity, endospores bacteria and actinomycetes in alkaline soils. Replacement of potassium with magnesium (NPMg) significantly suppressed infection and was associated with soil oligotrophism and antagonistic actinomycetes. Replacement of potassium with calcium (NPCa) significantly suppressed infection, increased fungal biodiversity and antagonistic actinomycetes. Composted chicken manure increased suppression and accompanied with a clear shift in soil biodiversity and increased antagonistic bacteria and fluorescent pseudomonas ratios. Decrease in soil biodiversity was recorded in some cases. Plant animal compost showed disease suppression which accompanied with an increase in microbial biodiversity along with high ratio of antagonistic bacteria. On the other hand, an increase in OM dissociation and reduction in C:N ratio was recorded in one area, characterised with natural high soil OM content, which enhanced soil conduciveness. In conclusion, the recommended fertilisation regime to suppress potato brown rot disease vary from soil to another according to different soil edaphic factors. [ABSTRACT FROM AUTHOR]