Evaluating Inter-Row Cover Crops to Enhance Rhizosphere Microbial Community and Reduce Grapevine Chlorosis.

Evaluating Inter-Row Cover Crops to Enhance Rhizosphere Microbial Community and Reduce Grapevine Chlorosis 

Anjuman A. Islam, Ricky W. Lewis, Taylor N. Bruchet, Joan R. Davenport, and Tarah S. Sullivan

SSSA National Annual Meeting: October 22-25, 2017, Tampa, FL

Poster Abstract:

Grapevine chlorosis, a deficiency in bioavailable iron (Fe) that causes yellowing of leaves and decreased vine vigor, affects vineyards of both wine and juice grapes in alkaline soils around the world. Our work aims to ameliorate chlorosis by improving overall soil health and increasing soil microbial activity through cover-cropping. We hypothesize that because grapevines are Strategy 1 plant species, cultivating cover crops between vine rows with mixtures that include Strategy 2 plant species will maximize overall soil health, increase microbial community activity, and maximize Fe availability in these systems. In fall of 2015, five cover crop treatments were established in a Concord vineyard near Prosser, WA (USA) affected by Fe-chlorosis: wheat, barley, rye, wheat/vetch mix, and a grower-control. Soil and leaf tissue samples, as well as visual chlorosis rankings were taken at bloom in 2016 and again in 2017. Soil samples were collected from both within the vine-row and under the cover crop to characterize Fe availability, soil microbial community, and their relationship to grapevine chlorosis. Also, Plant Root Simulator (PRS®) probe data were collected every two weeks during the growing season. Differences in soil microbial community composition among treatments were determined using terminal restriction fragment length polymorphism (T-RFLP) analysis, and a novel 96-well microplate CAS-Fe (Chrome azurol S-Fe) assay was developed for assessing soil microbial community siderophore activity. As expected, a negative correlation was found between leaf tissue Fe concentrations and visual chlorosis rankings. Significantly greater rhizosphere microbial siderophore production was detected in the soils of wheat/vetch mix cover crops, and the lowest siderophore production was found within the soils of the rye cover crop. Additionally, PRS probes revealed higher concentrations of available Fe under the wheat cover crop. These data indicate wheat as a cover crop has potential to enhance soil Fe availability to grapevines. In summary, inter-row cover cropping, particularly with wheat or a wheat/vetch mix, is an easily adoptable sustainable practice with potential to enhance soil health and microbial community function, while reducing Fe-chlorosis.