Building soil quality, enhancing soil microbial function, and alleviating chlorosis in Concord grapes with inter-row cover crops

Leaf yellowing, or chlorosis, occurs on more than 50% of the Concord vineyards in central WA, resulting in significant reductions in vine size, uniformity, productivity, and eventually vine death. The yellowing of the leaves resembles classic Fe-deficiency chlorosis, however many studies have attempted without success to determine the precise cause and effective treatment of this type of chlorosis. All work, to date, supports the concept that some aspects of soil quality, specifically soil biogeochemistry, are involved in grape chlorosis in central Washington State. Through 2016-2017, we began been testing a panel of four cover crops known to enhance soil quality through a variety of mechanisms, such as siderophore production, nitrogen fixation, or simply building soil organic matter. Through these functions, we hypothesized cover-cropping would enhance soil biological activity and serve as a means to manage beneficial soil microbes. We initiated the study with two different vineyards in 2016.  However, the chlorosis in the second vineyard became so severe, the grower removed the entire vineyard in early 2017 and planted the area to watermelons.  Therefore, we continued work in one vineyard, where we tested five replicate plots of each cover crop and a grower-control (extant vegetation) in a complete randomized block design.  Measures of chlorosis severity, canopy density, leaf tissue nutrient content, soil pH, Fe content, and microbial community functions were undertaken. Initial work focused on developing a method to easily screen whole vineyards for microbial Fe-chelating abilities (siderophore activity).  After this method was optimized, it was successfully applied along with a suite of microbial community functions to determine the success of cover cropping towards increasing soil health and reducing vine chlorosis.  All microbial community activity levels were associated with increased soil health when measured directly under the cover crop.  Additionally, vine rooting zone microbial siderophore activity was significantly associated with increased canopy density.  However, it was unclear if cover cropping and these increased microbial activities led to decreased chlorosis over the course of this short-term study, particularly with only one vineyard.

Grant Information

  • Project ID: 163
  • Project Status: Complete


  • Principal Investigator(s): Sullivan, T.
  • Investigator(s): Davenport, J.
  • Grant Amount: $39,978



Lewis, R., LeTourneau, M.K., Davenport, J. & T.S. Sullivan, 2018. ‘Concord’ grapevine nutritional status and chlorosis rank associated with fungal and bacterial root zone microbiomes.  Plant Physiology and Biochemistry, 129:429-436.

Lewis, R., Islam, A., Dilla-Ermita, J.C., Hulbert, S.H., and and T. S. Sullivan. High-throughput siderophore screening from environmental samples: plant tissues, bulk soils, and rhizosphere soils. Journal of Visualized Experiments (In Press:

Lewis, R., Opdahl, L., Islam, A., Davenport, J., and T. S. Sullivan. Comparative genomics, siderophore production, and iron scavenging potential of root zone soil bacteria isolated from ‘Concord’ grape vineyards. Microbial Ecology (Accepted with minor revisions. Revised and resubmitted Nov 21, 2018).

Islam, A., Davenport, J., and T.S. Sullivan. Cover cropping improves soil health and microbial activity in chlorotic ‘Concord’ vineyards in the alkaline, irrigated grape vineyards in central Washington.  American Journal of Enology and Viticulture (to be submitted Feb 2019).


  • Short-Term: This project has increased our understanding of the importance of rhizosphere siderophore production by root-associated microorganisms and the genetics and genomics of the interactions of these organisms with the grapevine rooting system. We have also increased understanding of the importance of cultivating a cover crop for proper vineyard floor management can lead to increased microbial activities and nutrient turnover in the zone where the cover crop is planted.  The results of this study can be leveraged for future funding from a variety of sources and lay the groundwork for similar studies in other perennial crops.
  • Intermediate-Term: The knowledge generated from this BioAg project will assist organic and sustainable producers to develop economically feasible and long-term solutions to vineyard floor management with cover crops to enhance soil health. Additionally, the genes associated with microbial siderophore production that may be most closely associated with vine health, can be targeted across vineyards and new management strategies developed in order to further enhance the expression of those genes and lead to healthier vines through management of the rhizosphere microbial communities.
  • Long-Term: Increasing crop nutrient uptake and overall vigor and yield by long-term sustainable management of the soil microbial community is technology that can transfer to many different annual and perennial cropping systems. This project takes us one step closer to understanding the mechanisms of metal and micronutrient enhancement in crops.