Soil texture is measured using a combination of the Hydrometer method and wet sieving. The hydrometer method is used to calculate the clay fraction; the wet sieving is used to calculate the sand fraction, and the silt fraction is calculated by difference. The soil is initially tested for organic matter and pretreated with hydrogen peroxide if organic matter content is greater than 1.5%. After pretreatment (if needed), soil is dispersed with a solution of sodium hexametaphosphate to then measure the clay content by the Hydrometer method. Once the clay fraction is measured, the dispersed sample is wet sieved to 53µm to collect and dry the sand fraction in an oven at 105 Celsius degrees. With the sand fraction calculated, the silt fraction can be calculated by difference. Fine root biomass (defined as roots < 2mm in diameter) is estimated by picking from the soil and placing the soil in a sieve. After that, the roots are rinsed and dried in an oven at 65 Celsius degrees. Once roots are dried, they are weighed.

The soil water retention curves (SWRC) were measured using two instruments to best represent both the wet and dry ends of the SWRC. 1) Saturated soils were put onto METER Group HyProp and water was allowed to slowly evaporate while measuring soil tensions and soil mass. Measurements spanned two- fourteen days depending on soil texture. 2) Unsaturated soils were removed from HyProp and two subset samples were selected and transferred to WP4C sample containers where they were measured repeatedly until soils reached -15 MPa. Data from WP4C and HyProp were compiled to form SWRC spanning entire spectrum of soil moisture conditions. Previous curves were generated using a nonlinear least squares model. This Version 2 utilized a Bayesian approach, with a confidence interval of 90%.

The soil saturated hydraulic conductivity (KSAT) is measured from samples that have been saturated for 24-48 hours. Saturated soils samples were put into METER Group KSAT and measured using falling head approaches. Each sample was measured 3-7 times aiming to capture consistent measurements for each sample. These replicated measurements were summarized for analysis of KSAT. Soil bulk densities were estimated using soil mass (g) inside the 250 mL rings. The estimates of KSAT are inherently noisy as roots, rocks, and macropores produce preferential flow pathways, we have aimed to reduce this uncertainty by only using the best measurements for analysis. We have used Grade A measurements in all summaries and analysis. Grade A measurements are defined as cores meeting the following QAQC criteria: sample bulk density within 1.5 standard deviations of the median bulk densities for each soil depth, measurements reaching a 0.99 R2 correlation, and individual observations within METER Group’s listed measurement ranges (i.e., 0.01 < KSat [cm d-1] < 5000).

## [1] "List of samples meeting A criteria being within 1.5 standard deviations from the median bulk density"

##  [1] "US-NR1_Site1_010" "US-NR1_Site2_000" "US-NR1_Site2_010" "US-NR1_Site2_025"
##  [5] "US-NR1_Site3_000" "US-NR1_Site3_010" "US-NR1_Site3_025" "US-NR1_Site4_000"
##  [9] "US-NR1_Site4_010" "US-NR1_Site4_025"

## [1] "List of samples meeting B criteria being outside 1.5 standard deviations from the median bulk density"

## [1] "US-NR1_Site1_000" "US-NR1_Site1_025"

All measurements used in the tables are defined as cores meeting QAQC criteria, i.e., “Grade A” within 1.5 standard deviations of the median bulk densities for each soil depth, measurements reaching a 0.99 R2 correlation, and individual observations within METER Group’s listed measurement ranges (i.e., 0.01 < KSat [cm d-1] < 5000). Saturated hydraulic conductivity of clay-rich soils is often outside the measurement range of the lab-based KSAT sensors.