How Do Fertilizer Additions Change the Soil Biology of Biofuel Switchgrass (Panicum virgatum)?.

In agricultural systems, the addition of fertilizers can change the soil community and its role in regulating soil nutrients. Switchgrass (Panicum virgatum) is a potential biofuel crop because it requires only low levels of nitrogen fertilizer to maximize yields because of its mycorrhizal associations. We ask how mycorrhizal colonization, soil microarthropods, and extractable soil nutrients associated with biofuel switchgrass change due to nitrogen fertilizer applications in both field and greenhouse settings. Our hypothesis is that over the projected life of a switchgrass field (10-20 years), fertilizer applications will change the soil community compared to an unfertilized field. An established switchgrass research field at Adelphia farm in New Jersey was sampled in 2013, 2014 and 2015 to test whether nitrogen fertilizer additions (100 lbs/acre) affected unmanipulated soil communities. Two greenhouse experiments directly tested the impact of additions of fungal-feeding nematodes, mycorrhizal inoculum, and nitrogen fertilizer to sterilized soil taken from Adelphia farm.

There were significant results in the field study but not in the greenhouse studies. Results from Adelphia farm showed significant differences between fertilized and unfertilized plots in Sminthuridae collembola, Hypogastruridae collembola, large predatory mesostigmatic mites and mycorrhizal structures, though multivariate analysis did not show a significant difference. Above-ground biomass yields were significantly different at the p= 0.1 level. Greenhouse results showed that the three treatment factors did not change the soil microarthropod community that developed during the experiment. Additionally, there were no differences in above- and below-ground biomass yields between fertilized and unfertilized treatments. These results suggest that nitrogen fertilizer has a small effect on the soil communities in the field, though this effect is not present in short term greenhouse studies. In addition, nitrogen fertilizer is not producing huge differences in biomass yields. Our results can inform best-management practices for sustainable production of biofuel switchgrass.