Permanent swards increase soil microbial counts in two Australian vineyards

This study examined the effect of permanent swards and bare soil (by repeated herbicide treatment) on soil microbial counts in Australian cool and warm climate vineyards. In both climates, hot water extractable soil C (HWC) in the vine row was increased by 73% after 3 years of sward development. Most of the soil bacterial counts were greatly decreased by the herbicide treatment and principal components analysis was able to clearly discriminate between microbial populations from the grassed and bare soil. In both the under-vine and inter-row soil, HWC was positively correlated with fungal counts and with cellulolytic, pseudomonad, copiotrophic and oligotrophic bacterial counts. HWC was also negatively correlated with soil bulk density. The grapevine rhizosphere bacterial population was dominated by cellulolytic bacteria in both climates. Many cellulolytic bacteria were slow growing, requiring up to 84 days of laboratory incubation. This study shows that permanent swards can significantly enhance the microbial community in vineyard soil.