Assessment of Soil Health throughout an Organic Potato Rotation and Potential use of the Bioindicator, Folsomia candida.

Soil health is a central concept of sustainable agriculture affecting the “capacity for a specific soil to function within natural or managed ecosystem boundaries”. Organic field crop production in Eastern Canada utilizes extended rotations to sustain soil fertility and maintain soil health. The aims of this study were to evaluate changes in soil health for each phase of a 5-year potato/grain/forage rotation at four organic potato production sites in NB and PEI. Total and available soil C and N, microbial biomass C (MBC), light fraction (LF), bulk density, pH, earthworm abundance and biomass were assessed in 2006 and 2007. Long-term permanent pasture sites adjacent to field sites were also sampled as reference fields to determine the influence of the rotation on soil health. The potential of the soil Collembola, Folsomia candida, was also assessed as a bioindicator of changes in soil health by examining its development on sand, sand and yeast, forest soil and pasture soil. Results indicated that the number of years in rotation after a potato crop had a significant positive effect on mean overall earthworm numbers (m^-2) and biomass (gm^-2) (p< 0.0001), and on the MBC/TOC in 2006 and 2007 (p=0.002 and <0.0001, respectively). The number of years in rotation had no significant effect on pH, total soil carbon and nitrogen concentration, bulk density, and LFC at the p= 0.05 level. These results suggest that biological indicators are more responsive to extended rotations than soil physical and chemical properties. Initial results for the use of Folsomia candida as a soil bioindicator were promising with body growth significantly correlated (<0.0001) to pH, organic matter, and C/N ratio values of the four soil substrates. Body growth was a more sensitive indicator of soil health than survival and reproduction.