Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/26/2009
Publication Date: 6/2/2009
Publication URL: http://agron.scijournals.org/cgi/reprint/101/4/727
Citation: Jokela, W.E., Grabber, J.H., Karlen, D.L., Balser, T.C., Palmquist, D.E. 2009. Cover Crop and Liquid Manure Effects on Soil Quality Indicators in a Corn Silage System. Agronomy Journal. 101:727-737. Interpretive Summary: Continuous corn silage production, even with no-tillage, can degrade soil quality because of nutrient depletion and minimal organic matter additions. Manure application and the use of different companion or cover crops in corn silage production systems may lessen or prevent soil quality degradation by improving various soil properties. We quantified changes in several different chemical, physical, and biological soil properties after four years of different manure/cover crop combinations in a no-till production system. Cropping treatments included corn grown with a living mulch of kura clover or June-interseeded red clover followed by one year of clover production, and continuous corn grown with June inter-seeded Italian ryegrass, September-seeded winter rye, or no cover crop. Manure was surface-applied annually in April. In this no-till cropping system, most soil parameters - soil test P and K, % organic matter, aggregate stability, and microbial populations - decreased with soil depth. Companion/cover crops, especially clover, led to some improvement in physical conditions, as indicated by increased large soil aggregates. Microbial biomass was increased with companion/cover crops, while no-cover treatments, especially with manure, had a reduced microbial community. Manure application alone showed no improvements in soil parameters, perhaps because of the low-solids nature of the manure applied. Overall soil quality, as indicated by a soil quality index, the Soil Management Assessment Framework, or SMAF, was improved by the use of cover crops in these manured corn silage cropping systems. While some specific companion/cover crops performed better for individual soil properties, none stood out as better than others for the whole range of soil attributes. Our results suggest that companion or cover crops have the potential to improve soil quality in a silage corn system, but it will be a long-term process.
Technical Abstract: 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 (RC, Trifolium pratese L.), and continuously with June-interseeded Italian ryegrass (IR, Lolium multiflorum L.), September-seeded winter rye (WR, 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.