The biological basis of soil fertility: Microbial community response to organic transition strategy

Background/Question/Methods

The ability of soil microbes to mediate nutrient supply while potentially building soil fertility is critical for sustaining plant nutrient demands while conserving soil reserves under organic management. At the Windsor Organic Research Trials (WORT) in Urbana, IL, different farming system treatments (ley fallow/low intensity, row crop/intermediate intensity, vegetable production/high intensity) were randomized to evaluate soil chemical and biological implications of transitioning from conventional to organic production. We examined total bacterial community composition based on DNA fingerprinting to determine if changes in the bacterial community composition were correlated to different farming system treatments. 

Results/Conclusions

Organic management intensity (low – ley fallow, intermediate – row crop, and high – intensive vegetable production) accounted for the most variation in bacterial community composition across all years and management strategies (PERMANOVA, Intensity: R² = 0.063, P < 0.001). Variation in bacterial community composition was significantly different between all management intensity types (PERMDISP, P < 0.001). Within the farming system treatments, we observed the highest variability in bacterial community composition among samples from the low intensity treatment (ley fallow). Bacterial communities tended to be less variable among the samples collected from the high-intensity treatment, suggesting that disturbance due to management may homogenize soil bacterial assemblages. Microbial communities in the less intensively managed plots show more differences between samples, suggesting that less frequent disturbance may lead to a more heterogeneous soil environment for soil organisms. Variation in bacterial response to organic management strategies can directly influence maintenance of soil nutrient supplies.