Vineyard Soil Microbial Communities Shift with Changes in Soil Resources.

Disturbance frequency and intensity associated with vineyard floor management practices are lower than in annual cropping systems that experience multiple tillage passes. Thus, soil carbon and nitrogen dynamics and the respective microbial communities may be distinct in vineyard systems.  This hypothesis was investigated from Fall 2005-Fall 2006 in a Chardonnay vineyard planted in 1997 (Monterey Co.). Vineyard floor treatments included a clean, cultivated treatment and two cover crops [i.e., Trios 102 (Triticale x Triosecale); Merced Rye (Secale cereale)] that had been planted annually for five years prior to the study. Soil microbial community composition and associated nutrient pools and activity measurements were measured in fall, winter, spring and summer. Merced Rye had 1.5-2 fold more aboveground biomass than Trios 102 during the growing season, but it was similar just prior to mowing in April. Root biomass (0-10 cm) at peak aboveground biomass was approximately 2.5 times greater in Trios 102 than Merced Rye. Microbial communities, as determined with phospholipid fatty acids (PLFA), differed among treatments. Soil microbial communities in cover crop treatments were associated with higher labile carbon (C) and nitrogen (N) pools, and greater rates of N mineralization, nitrification and denitrification, and respiration as compared to the tilled treatment. Seasonal shifts in microbial communities paralleled changes in these activity measurements, as well as soil water content and temperature. This suggests that seasonal changes in soil microbial communities were linked to changes in soil resources and environmental conditions. Further, the microbial activity rates were similar among cover crop treatments, despite differences in biomass allocation. These findings indicate that the presence of cover crops enhanced the biological function of the vineyard soils.