September 23, 2020
David Ramotowski, M.S. Student: SSC; Dept. of Crop & Soil Sciences, NCSU
“The Effects of Nitrification Inhibitors on Nitrification and Associated Microbial Functional Guilds, Diversity, and Function“
Nitrate is a major source of N nutrition for plant production, yet it is prone to losses from the soil via leaching and denitrification. Chemicals that inhibit biological NO3 production, known as nitrification inhibitors (NIs) or N stabilizers, can be used to minimize soil NO3 accumulation; however, their efficacy and non-target effects vary. This experiment aimed to gauge the effectiveness of two NIs (VLS, an experimental NI from Verdesian Life Sciences and Instinct II, a commercially available NI from Corteva Agriscience) in inhibiting soil nitrification as well as influences on target and non-target microbial diversity and composition . Two Hastings silt loams of different acidities from southern Seward County, NE, were evaluated in a microcosm incubation experiment over 63 days. There were six treatments: control soils; soils plus (NH4)2SO4 at 4 µg g-1 soil; soils with one of the two NIs; and soils with (NH4)2SO4 soil plus one of the two NIs. Soil samples were taken at Days 0, 7, 14, 28, 42, and 63 to determine soil NH4 and NO3 concentrations. Potential rates of nitrification were also measured at each interval. At the end of incubation, soil DNA was extracted, and population sizes of microbial guilds involved in nitrification and denitrification were measured by quantitative PCR. Marker-gene high-throughput sequencing was also conducted to probe bacterial and fungal community composition. The efficacy of VLS was comparable to Instinct II, as both retained about 80% of inorganic N in the form of NH4. Based on the N mass balance, it seems that VLS might promote soil organic N mineralization or N loss via gaseous emissions, because NH4 was found to be greater in soils with VLS addition, and NO3 was very similar for both NIs. Quantitative PCR and next-generation sequencing data are being processed and will contribute to comprehensive evaluation of the impacts of NIs on soil processes and sustainability.