Soil Health Assessment in Reclaimed Mine Soils

SOIL HEALTH ASSESSMENT IN RECLAIMED MINE SOILS Katie Stutler West Virginia is one of the top coal-producing states in the nation, which has resulted in over 500,000 acres of highly disturbed, anthropogenic mine soils caused by surface mining. Mine soils are often rocky and contain low organic matter content, low plant-available nutrients, and toxic metals, which could result in poor soil health and low productivity. Soil health has been defined as the continued capacity of soil to function as a living ecosystem that sustains plants, animals, and humans. It is assumed that with time since reclamation, mine soil properties and related functions may change, and soil health will improve due to the process of soil development. The objectives of this study were to evaluate and compare NRCS Soil Quality Test Kit measurements to standard laboratory and field methods; to assess and compare soil health related properties also called indicators, plant diversity and productivity in reclaimed mine soils of different ages; and to assess mine soil health related to time since reclamation. The hypotheses were that NRCS Quality Test Kit measurements would yield comparable results to standard methods; that time since reclamation would positively influence soil properties related to soil health as well as plant productivity; and that response to fertilization management would be an indicator of soil health. Four West Virginia reclaimed mine soils were selected for this study based on age: WV32 -32 years, WV16 -16 years, WV11 -11 years, and WV2 -2 years. Three experiments were designed to test the hypotheses: Experiment I compared NRCS and standard methods in assessing soil health indicators on reclaimed mine sites; Experiment II compared the soil health indicators between WV16, WV11, and WV2 sites using 50 soil sampling points per site; Experiment III compared the effect of management (fertilization) on different mine soil health indicators and biomass production. For Experiment I, soil bulk density (BD), wet aggregate stability (WA), slaking, pH, electrical conductivity (EC), soil respiration, and saturated hydraulic conductivity (saturated water infiltration, Ks) were measured using the NRCS Soil Quality Test Kit and standard laboratory procedures on all sites. The results indicated that measurements made with the NRCS Soil Quality Test Kit compared to those obtained with standard research laboratory methods, yielded statistically comparable results for saturated hydraulic conductivity (NRCS: 0.117 cm min-1; Standard: 0.114 cm min-1), for pH (NRCS: 6.4; Standard: 6.4), and for soil respiration (NRCS: 40.4 lb CO2-C ac-1 day-1; Standard: 50.6 lb CO2C ac-1 day-1). However, NRCS measured BD (NRCS: 1.30 Mg m-3; Standard: 1.46 Mg m-3), and NRCS measured EC (NRCS: 0.113 dS m-1; Standard: 0.227 dS m-1) showed similar trends to the standard methods, but tended to underestimate values. There was an effect of time since reclamation on the performance of NRCS Soil Quality Test kit as compared to standard methods. For Experiment II, soil health indicators (BD, aggregate stability, pH, EC, bioavailable nutrients) and vegetation surveys conducted using standard field and laboratory methods showed significant differences on surface soil (0-15 cm) health indicators. Wet aggregation and BD improved with time since reclamation, with higher water-stable aggregates and lower BD observed for WV16 (6.1 mm; 1.46 Mg m-3) and WV11 (5.8 mm; 1.47 Mg m-3) compared to WV2 (5.7 mm; 1.51 Mg m-3). Soil pH was lower on WV11 (5.8), which related to lower SOM (42.2 mg kg-1) compared to WV2 (52.8 mg kg-1) and WV16 (55.1 mg kg-1). Vegetation varied between sites, with WV2 containing more forbs (36%), WV11 containing more grasses (50%), and WV16 containing less variation between legumes (31%), forbs (18%), and grasses (39%). Experiment III (with or without urea fertilization) was conducted using a completely randomized factorial block design (time of application x urea application rate x replications/blocks). Results indicated that urea application positively affected biomass production on the youngest (WV2) and oldest sites (WV16), with a continuous increase in biomass with each harvest (regrowth). Site WV16 had the highest amount of biomass accumulation (4.14 Mg ha-1) compared to WV2 (2.86 Mg ha-1) and WV11 (2.54 Mg ha-1) by the end of the study in fall 2018, as expected with increased soil development with time since reclamation. In summary, this study increased our knowledge of suitable methods to be used in the assessment of soil health in mine soils by determining that the NRCS Soil Quality Test Kit methods can be suitable in mine soils with adjustments to some measurement processes. This study also increased our knowledge in the effect of time on disturbed soils, and the potential for productivity on these reclaimed areas. The results of this research will expand understanding on reclaimed mine soil health and will aid in determining best future land use post-mining.