Can we enhance soil services in agroecosystems through rotational diversity?
Increasing plant biodiversity in non-agricultural systems has been experimentally linked to increases in productivity, nutrient availability, ecosystem stability and resource use efficiency, but the consequences of crop rotational diversity in agroecosystems remains uncertain. In particular, the positive benefits of plant biodiversity on belowground processes have mostly been observed in natural systems. Mechanistic insights into belowground responses to rotational diversity are needed to predict how the global expansion of monocultures and simple rotations are influencing important soil and ecosystem functions. This information is also critical for developing more productive low-input agricultural systems, which rely on plant-soil interactions to sustain soil fertility. Using a combination of analytical and experimental approaches we help elucidate rotational diversity effects on belowground processes that lead to enhanced soil services in agroecosystems.
We conducted a meta-analysis of published studies that showed rotational diversity increases soil organic matter (SOM) on average by 3.6 % and microbial biomass by 20.7 %. In a lab based study we found positive rotational diversity effects on microbial activity that lead to more rapid crop residue decomposition and greater N mineralization. In a field study at the Kellogg Biological Station LTER, we manipulated rotational diversity in isolation from other management practices by adding crops sequentially, from monoculture to a five species rotation that included two cover crops, or non-harvested crops. At this site we observed strong, positive correlation between crop rotational and microbial diversity. Increases in rotational diversity also enhanced microbial activity with positive impacts on aggregate formation and SOM accrual; water stable aggregates were increased by up to 103 % in high diversity rotations while soil C and N were increased by 35 % and 47 %, respectively, in the highest diversity rotation compared to monoculture. Overall, our results highlight the importance of rotational diversity for sustaining and improving soil services in agroecosystems. With these insights, increasing crop rotational diversity should be considered an important management strategy in the context of agroecosystem sustainability and food security.