ENHANCING SOIL HEALTH IN MICHIGAN POTATO CROPPING SYSTEMS

Limited rotational crop diversity and frequent mechanical disturbance may promote soilborne disease and limit soil productivity in Michigan potato cropping systems. The objective of this four-year study was to evaluate alternative production practices that may impact soil health and potato production. To examine practices in both a two- and three- year potato rotation, two field studies were established near Clarksville, MI. Treatments within each cropping rotation represented practices hypothesized to impact soil health and include: fumigation (i.e., prior to first-year potato or none), annual applications of 2.2 or 4.4 Mg poultry litter ha -1 depending on crop rotation, and cover crop (i.e., cereal rye following corn/prior to potato). Soil health indicators included standard chemical indicators, 24hr microbial burst CO 2 respiration, permanganate oxidizable carbon, autoclaved citrate extractable protein, water stable aggregates, Potato Early Die (PED) pathogen population densities and soil microbial community composition (16S and ITS sequencing and phospholipid fatty acid analysis). Crop productivity was evaluated by crop yield and tuber quality. Management practices hypothesized to improve soil health did interact in some cases to influence soil health and crop productivity, but in different and at times unpredictable ways. There were no observed changes in soil organic matter under any of the management strategies. Over the four years, annual poultry litter application produced increasingly greater midseason microbial respiration burst and soil test P values as well as greater yields. Adding a rye cover crop inconsistently weakened the positive effect of manure on yields, likely due to the suppressive effect of spring incorporated rye biomass on midseason respiration burst. Despite greater diversity and limited effect on PED pathogen levels, eliminating soil fumigation resulted in greater disease severity and reduced yields in the first year of potatoes. The fumigation effect dissipated by the second year of potatoes in both rotations.