Cover Crops Alter the Soil Microbial Community and Increase Potato Tuber Yield and Quality.

An on-going study at a commercial farm operation in the San Luis Valley, CO is examining the effect of various summer cover crops (mustard, canola, sorghum-sudangrass, and a wet fallow control) on potato tuber yield and quality.  In four of the five years, potato tuber yield and quality has shown significant increases for most of the cover crops, particularly the sorghum-sudangrass.  In this study, we examined the influence of these cover crops on the soil bacterial community abundance (i.e., qPCR) and diversity (i.e., pyrosequencing) over the course of two years.  All four cover crops increased the abundance of soil bacteria (ANOVA, p < 0.001) with the greatest increase following one of the sorghum-sudangrass varieties (Sordan 79), which was more than 3-fold greater than the wet fallow control.  Community composition assessed by pyrosequencing revealed no significant differences in a-diversity associated with the various cover crops; however, b-diversity significantly differed by cover crop and year (AMOVA, p < 0.001).  Partial least square regression suggests that tuber yield and quality is better explained by the shifts in the community composition rather than abundance.  For example, tuber yield was positively correlated with 33 OTUs (10 Acdiobacteria, 7 Actinobacteria, 3 Gemmatimonadetes, 9 Proteobacteria, and 4 unclassified).  A different subset of OTUs was related to tuber yield; such that, 56 OTUs (7 Acidobacteria, 25 Actinobacteria, 2 Chloroflexi, 1 Geammatimonadetes, 12 Proteobacteria, 9 unclassified, 2 Chloroflexi, and 1 Gemmatimonadetes) were positively correlated with the proportion of tubers belonging to the largest size class (i.e., > 10 oz).