ReCon Soil Project: Dataset for Identification of Soil Health Indicators in Construction

This dataset represents experimental results from Work Package 4 of the ReCon Soil Project: https://www.plymouth.ac.uk/research/institutes/sustainable-earth/the-recon-soil-project Soil health indicators for maintenance in a construction context, are less about soil fertility and more about maintaining those indicators identified, to minimise loss of carbon (C) and nitrogen (N), maintain soil microbial activity and to ensure stockpiled soils are maintained to a point where they can be reused effectively in the future. To this end, an experiment was designed in order to identify and monitor key soil health indicators for construction, and to investigate methods to mitigate against carbon losses in stockpiled soils. The main questions that were addressed were: 1. Will sowing grass and other plant species in stockpiled soils reduce losses of C and N from the soil? 2. What effect does soil stockpiling have on microbial communities? 3. What effect does wood chip application on stockpiled soils have on C and N stocks and microbial communities? 4. How do rapid in-field methods for carbon and microbial analysis compare with established lab methods? The experiment was established at the end of August 2022. Any vegetation was cleared from the study site by using a digger to scrape away the top 5cm of soil. Diggers were used to take soil from an area adjacent to the study site which had been undisturbed for 3-4 years, vegetation was cleared from this area and the topsoil was formed into 12 stockpiles (6m length x 4m width x 2m height). The stockpiles were then randomly assigned one of three treatments; amenity grass seed mix, herbal ley seed mix or control. For the seeded treatments, each stockpile was sown by hand to an application rate of 70g/m2. After seeds were sown, wood chip was applied by hand to half of each stockpile (randomly assigned), to a depth of covering of approximately 2cm. This resulted in 4 replicates of each combination producing 24 sample plots. Soil samples were collected using a soil sampling auger to collect samples at 0-30 cm and 90-100cm. One sample was taken from each replicate at both depths, these were taken at baseline (T0), and intervals of 1 week (T1), 2 weeks (T2), 4 weeks (T4) and every 4 weeks after that. The soil cores were sealed in sterile plastic bags and transported to the laboratory for processing. At each time point, soil was analysed in the laboratory at Eden Project Learning for the following parameters: non-purgeable organic carbon (NPOC), total nitrogen (TN), soil organic matter (SOM), gravimetric water content, pH, and microbial activity using a fluorescein diacetate assay. All remaining bagged soil samples were then transferred to a freezer and stored at -18°C. These were later defrosted and analysed for total organic carbon (TOC), available iron, ammonia, nitrate and nitrite at a subset of time points. Using in-field equipment, soils were analysed for CO2 emissions at every time point, fungi:bacteria ratio and for soil carbon every 4 weeks. Samples for soil eDNA were taken from each replicate at T0, T8 and T20.