In organic agriculture, crops and the farmers who grow them depend on soil microbial communities to decompose organic forms of fertilizer to make nitrogen (N) available for plants to use. Farming practices, such as crop rotations and use of cover crops, influence microbial community development over time. We used soils from farms in southwestern Wisconsin to take the pulse on how organic farming practices impact soil quality and microbial communities over time. Additionally, we conducted a greenhouse experiment to examine how differences in soil microbial communities among farms influence corn, soybeans, and rye growth/yield. To test for differences in functionality among microbial communities, we provided every plant x microbial community combination four different forms of organic N to decompose and then measured plant responses.
Results/Conclusions
Our results illustrate how soil microbes both respond to long-term soil management and influence current nutrient cycling and crop growth. In the greenhouse experiment, corn and rye responded similarly to the N types, and N types had predictable effects on plant growth. The N type that was predicted to be the most difficult to decompose (sorghum sudangrass) resulted in significantly larger corn plants when grown with microbial communities from farms that had been under organic management for the longest time. No such trend was found for plants grown with the more labile forms of N, suggesting that high C:N litter may be incorporated into the N cycle more quickly over time. Furthermore, microbial community inocula from individual farms impacted photosynthetic activity of the three crop species differently, suggesting that active management of soils for a particular crop species may lead to trade-offs for other crops in rotation in the same soil.