Assessment of changes in soil health throughout organic potato rotation sequences

The use of extended rotations to maintain soil health and overall sustainable agricultural practices were evaluated under commercial organic potato (Solanum tuberosum L.) production systems in Atlantic Canada. A 2-year study quantified the changes in soil health for each phase of 5-year potato/grain/forage rotations at four organic potato production sites. Changes in soil (0–15 cm) physical and chemical (bulk density, light fraction organic matter (LFOM), pH, total organic C (TOC) and N), and biological properties (microbial biomass C (MBC), microbial quotient (MBC/TOC), mineralizable C, metabolic quotient (qCO2), earthworm (abundance and biomass)) were assessed. Long-term permanent pastures at each site served as reference fields. Rotation phase was found to have had no significant affect on soil physical and chemical properties. In contrast, soil biological properties were negatively affected by the potato phase but recovered to reference field levels over the rotation length in both years. The potato phase significantly decreased the MBC (297.4 and 217.9 μg C g−1 soil), microbial quotient (1.48 and 1.28%), earthworm abundance (73.5 and 31.2 m−2) and biomass (32.15 and 12.15 g m−2) in 2006 and 2007, respectively. MBC in 2006 returned to levels found in the reference fields (780.7 μg C g−1 soil) after 3 years (627.0 μg C g−1 soil) in the rotation, however was unable to obtain reference field levels (621.6 μg C g−1 soil) in 2007. Microbial quotient reached comparable levels to the reference fields (3.69 and 2.80%) after 3 years (2.85%) and 4 years (2.79%) in rotation in 2006 and 2007, respectively. Mineralizable C was significantly affected by rotation phase in 1 year only, but this was not reflected in the metabolic quotient. Earthworm biomass recovered to reference field levels (215.44 and 158.21 g m2) after 3 years (152.00 g m2) and 4 years (156.93 g m2) in 2006 and 2007, respectively. Earthworm abundance consistently required 4 years (450.30 and 434.29 m2) in rotation to recover (493.5 and 445.8 m2). Overall, results suggest that the extended rotations used in organic potato production systems retain soil organic matter and allow recovery of key attributes of soil health following the potato phase. Soil biological properties appear to be more sensitive indicators of these changes.