Plant growth, soil properties, and microbial community four years after thermal desorption

The effects of thermal desorption (TD) on soil physical and chemical properties after crude oil contamination are recently well studied. However, there are limited field-scale studies on long-term soil biological property recovery such as microbial communities and plant growth, which are vital for meeting global agrosystem demands and restoring ecosystem health. This study describes the status of soil biological properties after 4 yr of crop production on oil-contaminated cropland remediated via TD and a modified land farming technique. Plots were constructed in 2015 with native, uncontaminated topsoil (A); TD-treated subsoil (TDU); untreated land-farmed subsoil (SP); TDU + A (TDA), and SP + A (SPA) where soil ratios were 1:1 by volume, and composted manure (CM) was applied at 40 Mg ha(-1). After 3 yr of crop production (2019) grain sorghum [Sorghum bicolor (L.) Moench] was planted. Soil microbial community characteristics were assessed through phospholipid fatty acid analysis and by estimating mycorrhizal root colonization. Notably, inherent soil chemical and physical properties influenced the recovery of microbial communities in remediated soils. However, sorghum biomass production in TDU was 50 +/- 9% greater than SP while the microbial abundance in these treatments remained similar. Mycorrhizal colonization variation likely reflected rhizosphere nutrient scarcity and not the interactions of either remediation strategy. Based on these results after 4 yr of cropping, TDU does not diminish soil microbial recovery, and when possible, blending TDU materials with topsoil provides the greatest level of recovery relative to topsoil only.