Assessing Post-Irradiation Effects of Neutron Gamma Analysis on Soil Microbial Activity

Abstract

Pulsed fast-thermal neutron-gamma analysis (PFTNA) is used in a new method of assessing soil elements by measuring gamma rays that appear when soil is irradiated with neutrons. Impacts on soil microbes of PFTNA irradiation at levels used with this method have not been examined. We investigated PFTNA effects on aspects of microbial communities in three soil types (loamy sand, silty clay, and clay) over time using a stationary 1 hr irradiation period (dose of 3.2 × 10−5 Gy). This represented a worst-case scenario, since radiation exposure when operating in the mobile scanning mode for soil mapping would be 500 to 1000 times less. Microbial biomass N and dehydrogenase activity showed a few effects after soil irradiation within the first 24 hr with none noted at 2 wk post-irradiation; there was no impact on microbial diversity based on the use of Biolog Ecoplates at any time period. This suggests that PFTNA should have no effect on soil biota at radiation levels used for measuring and mapping soil elements. This methodology could be useful in precision agriculture to account for temporal and spatial heterogeneity in soils, which would help improve resource use efficiency and agricultural productivity.