Cover Crop Mixtures: Does Adding More Species Change Soil Structure?.

Cover Crop Mixtures: Does Adding More Species Change Soil Structure? Bobby McPherson and Mark Coyne University of Kentucky Cover crop use is a common management practice promoted to improve soil structure for soil quality. Growing cover crops in species-rich mixtures has been suggested to improve agroecosystem functions like weed suppression, biomass production, and yield of a subsequent crop compared to monocultures of component crops. Increasing the number of species in cover crop mixtures could be a useful practice in sustainable agriculture, but successful adoption requires full understanding of the mechanisms by which cover crops use to improve soil quality. For example, the potential for cover crop mixtures to provide benefits in relation to soil structure are not known. This greenhouse study evaluated the effect of cover crop mixtures on soil quality parameters related to soil aggregation: soil polysaccharide content, glomalin related soil protein (GRSP), and wet aggregate stability. The experiment consisted of ten treatments. Crimson clover (Trifolium incarnatum), cereal rye (Secale cereale L.), Austrian winter pea (Pisum sativum L.) and hairy vetch (Vicia villosa) grown as monocultures; mixtures of rye-clover (RC), rye-vetch (RV), rye-clover-vetch (RCV), rye-vetch-pea (RVP), rye-clover-pea (RCP); a four way mix (RCVP) that included all species. Plants were harvested after 90 days and soil samples were collected. Total plant biomass, roots and shoots increased as more species were added to the system: highest amount in a four way mix. It was hypothesized that the soil polysaccharide content would increase as more crop species were added to the system. Although polysaccharide production increased in the RV mixture compared to rye monoculture, in general we observed a decrease in polysaccharide production as more species were added to the system. This study suggests that under a short term rye treatment, labile polysaccharides was a potential soil binding agents. It has also been observed that glomalin related soil protein increased as more species were added in a mixture. However, a higher percentage of water stable aggregates was observed on rye alone treatment which corresponds to the highest amount of labile polysaccharide content contributed in the rye treatment alone.