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In a 2-year field experiment, the efficacy of five composts prepared from on-farm wastes lresidues of Calotropis procera (Willd) Dryland, Prosopis juliflora (Swartz) DC, Azadirachta indica A. Juss, Acacia nilotica (Linn) Willd ex. Del. and on-farm weeds on severity of dry root rot caused by Macrophomina phaseolina in relation to microbial population dynamics, microbial activity and on seed yield of guar was ascertained. In general, during crop growth compost amended plots retained 16 % higher soil moisture than non-amended plots. Populations of total fungi, bacteria and actinomycetes increased in the amended plots during the crop season. The maximum population of total fungi, actinomycetes and bacteria were recorded in A. nilotica, P. juliflora and weeds compost-amended treatments, respectively. Microbial activity was also 26.1 % higher in amended compared to non-amended plots. Amendment of soil with composts resulted in increases in the concentration of micronutrients and significant reduction in plant mortality due to dry root rot. Beneficial effects of composts were also discernible in yield promotion where 40 % increase in the seed yield was recorded in P. juliflora compost-amended plots. These results suggests that in arid regions of India, certain on-farm wastes can be effectively utilized for managing Macrophomina induced diseases besides enhancing crop productivity.