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.

Reclamation of oil and gas disturbed soils is challenging due to diminished function (i.e., soil physical, chemical, and biological properties) from the loss of soil organic carbon (SOC) and potential mixing of topsoil and subsoil. Biostimulants are agroproducts applied to soil to improve SOC formation, microbial nutrient cycling, and crop yields, suggesting their potential use in reclaiming oil and gas disturbed soils. However, studies on the ability of biostimulants to enhance reclamation in disturbed soils are limited. Therefore, research was conducted to determine if biological properties were affected by biostimulant products in soil collected from an active pipeline installation project. The study was conducted in a greenhouse using pots consisting of the following soil treatments: TS100 (100% topsoil), TS50 (1:1 by-weight subsoil/topsoil), TS25 (3:1 subsoil/topsoil), TS12.5 (7:1 subsoil/topsoil), and TS0 (100% subsoil). Blended soil either received a liquid inoculant or biotic mulch biostimulant and were planted with hard red spring wheat (Triticum aestivum) later on. Soil biological properties were generally influenced by topsoil concentration where TS50 consistently produced similar results to TS100, however, nitrogen (N) and phosphorus (P) were also influenced by biostimulant treatment. Additionally, wheat biomass was significantly greater in the liquid treatment, whereas the biotic mulch stimulated greater microbial abundance and activity. Overall, increased topsoil improved biological recovery in the short term, and the addition of biostimulants in blended soils can also enhance recovery regardless of topsoil content. However, it is unclear whether the recovery is sustained into the long-term without additional biostimulant application.