Cover crop and liquid manure effects on soil quality indicators in a corn silage system
Due to a lack of surface residue and organic matter inputs, continuous corn (Zea mays L.) silage production is one of the most demanding cropping systems imposed on our soil resources. In this study, our objective was to determine if using cover/companion crops and/or applying low-solids liquid dairy manure could improve physical, chemical, and biological soil properties and overall soil quality. Corn was grown for 4 yr on a Bertrand silt loam in rotation with a living mulch of kura clover (KC, Trifolium ambiguum L.) or June-interseeded red clover (Trifolium pratese L.), and continuously with June-interseeded Italian ryegrass (IR, Lolium multiflorum L.), September-seeded winter rye (Secale cereale L.), or no cover crop. Extractable P and K, pH, soil organic matter (SOM), active C, water-stable aggregates, bulk density, penetrometer resistance, and microbial biomass/diversity were measured, and the Soil Management Assessment Framework (SMAF) soil quality index (SQI) was determined. Cover/companion crop treatments generally had more large macroaggregates, greater aggregate mean-weight diameter, and larger quantities of total microbial biomass and most lipid/microbial groups than no-cover treatments. Manure and starter fertilizer additions resulted in significant cover/companion crop treatment effects on extractable P and K. Liquid dairy manure alone did not improve any soil quality indicators. Although soil quality benefits of cover crops and manure are typically attributed to additions of organic C, we found no significant treatment effects on SOM content. However, the active, or labile, C fraction, was significantly increased by cover crops and showed good relationships with aggregate stability and microbial biomass. Overall, use of cover/companion crops appears beneficial for corn silage systems, but it may take more than 4 yr for some soil quality indicators to fully respond.