Spatial Variability of Aggregate‐Associated Carbon and Nitrogen Contents in the Reclaimed Minesoils of Eastern Ohio

Abstract

Associations of organic C and N with primary (sand, silt, and clay) and secondary (aggregates) particles result in their storage and retention in the soil. The objectives of this study were to assess (i) the CV of C and N contents in the primary and secondary particles and (ii) the spatial variability of water‐stability of aggregates (WSA), geometric mean diameter (GMD) and mean weight diameter (MWD) of aggregates, and C and N contents in macro‐ (>2 mm), meso‐ (2–0.25 mm), and microaggregate (0.25–0.05 mm) fractions. Forty‐five soil samples were collected at the 0‐ to 15‐cm depth of a 20‐ by 20‐m grid at an unmined (UMG) reference site and sites reclaimed in 1978 (R78G), 1982 (R82GT), and 1987 (R87G). The R82GT was seeded to grass in 1982 and planted with trees in 1987. Other sites were under continuous grass cover since reclamation. Soil samples (<2 mm, four samples per site) were fractionated into primary particles (sand, silt, and clay), and aggregate samples (8–5 mm, 45 samples per site) into macro‐, meso‐, and microaggregate fractions; C and N contents were determined for each fraction. The CV for C and N contents was low in all three primary particles. Carbon contents increased with decreasing size of primary particles and clay‐associated C contents also increased with amount of time since reclamation. Geostatistical analysis showed that dispersion variance for WSA, GMD and MWD, and C and N contents (45 samples per site) was higher in R78G than other reclaimed sites. Interpolation using kriging displayed heterogeneity of properties across experimental sites. The relative nugget for most aggregate‐associated properties was lowest for R78G and became stronger with the amount of time since reclamation. The range for aggregate‐fraction‐associated C contents was similar across reclaimed sites and spatial dependence became stronger with increasing amount of time since reclamation. The unmined site displayed large variability; however, low variability for the relatively newly reclaimed site (R87G) indicated that reclamation initially reduced the variability but as time increased, variability also increased, with simultaneous improvement in soil quality.