Soil microbial community structure under perennial bioenergy crops treated with different nitrogen fertilization rates

Authors: Rana Dangi, Sadikshya; Sainju, Upendra; Allen, Brett; Calderon, Rosalie

Submitted to: Soil Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/11/2024
Publication Date: 7/15/2024
Citation: Rana Dangi, S., Sainju, U.M., Allen, B.L., Calderon, R.B. 2024. Soil microbial community structure under perennial bioenergy crops treated with different nitrogen fertilization rates. Soil Systems. 8(3). https://doi.org/10.3390/soilsystems8030081.
DOI: https://doi.org/10.3390/soilsystems8030081

Interpretive Summary: Perennial bioenergy crops help improve soil health by sustaining soil biology as a result of their extensive root systems and the continuous ground cover they provide. Nitrogen fertilization rate of perennial grasses may impact the amount of biomass produced and its N content thus affecting soil microbial communities. ARS researchers at Sidney, Montana, evaluated effect of two perennial grass species grown with varying nitrogen fertilizer rates as well as an annual crop with recommended N rate over 11 years on soil microbial communities in the northern Great Plains. The research evaluated intermediate wheatgrass (IWG) and switchgrass (SG) grown with nitrogen fertilization rates ranging from 0 to 84 kg N ha-1 and annual spring wheat (WH) with 80 kg N ha-1. A specialized type of fungi called arbuscular mycorrhizal fungi (AMF) forms a symbiotic association with plant roots that enhances the plant’s access to water and nutrients. Using a procedure that quantifies these microbial groups, study found that adding more nitrogen decreased AMF and increased the proportion of bacteria that are correlated with carbon degradation. Both perennial grass species enhanced both AMF and the type of bacteria related to greater carbon storage compared to WH and that SG promoting these beneficial microbial groups more effectively than IWG. Soil microbial communities mediate many soil functions and results from this study will help growers select bioenergy perennial grass species and nitrogen rates that will optimize soil biological health and enhance sustainable production.

Technical Abstract: Perennial bioenergy crops may enhance microbial community structure and soil health due to extensive root system compared to annual crops. However, long-term effect of perennial bioenergy crops receiving different N fertilization rates on microbial community structure is not well defined. We evaluated the 11-year effect of perennial bioenergy crops with various N fertilization rates as well an annual crop with recommended N rate on soil microbial properties in 2019 and 2020 in the US northern Great Plains. Perennial grasses were intermediate wheatgrass, IWG (Thinopyrum intermedium [Host] Barkworth and Dewey) and switchgrass, SG (Panicum virgatum L.); N fertilization rates were 0, 28, 56, and 84 kg N ha-1, and annual crop was spring wheat, WH (Triticum aestivum, L.) with 80 kg N ha-1. The proportion of total fungal phospholipid fatty acid (PLFA) and fungal to bacterial ratio were significantly lower under annual spring wheat than perennial grass (SG). Increased N fertilization rate linearly increased Gram positive and Gram positive/Gram negative bacterial ratio for IWG in 2020, but decreased PLFA proportions of arbuscular mycorrhizal fungi (AMF) for both perennial bioenergy crops in all years. The AMF neutral lipid fatty acid (NLFA) and Gram negative bacteria were greater in SG than IWG, but actinomycetes and Gram positive/Gram negative ratio were greater in IWG. Results indicate that perennial bioenergy crops and N fertilization rates had variable effect on soil microbial communities. The study facilitates selection of bioenergy perennial grass species and N rates that will maintain soil health, and enhance sustainable production in the semiarid region of the US northern Great Plains