Does Crop Rotation Influence Soil Microbial Function?

Crop rotations, which increase plant diversity through time, are considered key to sustainable agroecosystem management.  Crop rotations have been shown to alter soil carbon (C) and nitrogen (N) cycle biogeochemistry; however, the specific mechanisms through which rotational diversity alters soil C and N dynamics remain uncertain.  We used two laboratory-based approaches to investigate the effects of crop rotational diversity on soil microbial functioning in soils from the Crop Biodiversity Gradient (CBG), which is located at the W.K. Kellogg Biological Station LTER.  This experiment includes replicated (n = 4) agricultural treatments ranging from 0 to 10 total plant species, and we tested crop rotations varying in length and diversity from a monoculture Corn, Corn-Soy, Corn-Soy-Wheat, Corn-Soy-Wheat(Red Clover cover crop), Corn-Soy-Wheat(Red Clover+Rye cover crops).  Our first approach utilized a laboratory incubation to test whether crop rotation diversity influences the processing of plant litter ranging in quality and diversity.  The second approach used community-level physiological profiling (CLPP) with 31 C substrates to determine the functional diversity of soils under crop rotations of increasing diversity.  

The litter incubation experiment showed that litter quality was the primary driver of respiration, and that soils decomposing lower quality litters showed more of a crop rotational diversity effect (P = 0.006).  However, there was little effect of rotational diversity on the ability of soils to utilize diverse litters (mixtures).  The CLPP showed crop rotational diversity affected catabolic profiles (P = 0.026), but had no effect on catabolic evenness.  Overall, our results indicate that increasing aboveground biodiversity through time alters soil microbial functioning and that more diverse crop rotations have microbial communities that are better suited to utilize poor quality substrates.