Do litter inputs or the microbial community drive nutrient cycling across a cropping rotational gradient?

O’Neill, B., A.S. Grandy, M. McDaniel and T.M. Schmidt.

Presented at the All Scientist Meeting (2013-04-04 to 2013-04-05 )

Most row crop agriculture in the U.S. Midwest consists of limited rotations of few crops, primarily corn, soy and some wheat. Increased demand for these commodities along with a desire for improved environmental benefits has resulted in calls to harness soil ecological processes and reduce external inputs by increasing cropping system diversity. It is well-known that increasing rotational complexity, especially with cover crops, can greatly improve crop productivity. Research at the KBS-LTER Biodiversity gradient has shown that greater productivity in more diverse cropping systems is linked to rapidly cycling fractions of soil organic matter, especially potentially mineralizable N and labile soil carbon fractions. In addition, increasing cropping system diversity altered soil microbial communities and increases their heterogeneity. So while labile litter quality appears to fuel this system, the microbial community is the engine for SOM mineralization. We want to test whether substrate quality or the microbial community has a greater influence on mineralization across a gradient of cropping system complexity. Using a reciprocal inoculation approach we will compare the efficiency of SOM mineralization when sterile soils from simple rotations are exposed to the microbial community from complex rotations and vice versa. We expect no ‘home field advantage’ for the community under simple rotations. Instead, we anticipate microbial communities from diverse crop rotations will be both better and more efficient at mineralizing SOM from less diverse rotations.