Nitrogen Accumulation and Form over Time in Young Mine Soils

Abstract

Nitrogen deficiency is a common problem during reclamation of mine soils, and limited comprehensive information is available concerning the forms and characteristics of N in Appalachian mine soils. This chronosequence study was conducted to investigate the accumulation, distribution, and component change of N in mine soils over time. Fresh spoil, coal, natural forest soil and 10 mine soil sites with ages ranging from 1 to 30 yr were sampled and analyzed for N components. Young mine soils (> 10 yr) were dominated by seeded grass‐legume vegetation, while the older sites supported native mixed hardwoods. There was a considerable amount of indigenous N in the fresh spoils (250–475 mg kg −1 ), consisting primarily of fixed NH + 4 (Fix‐N) held in micas and nonhydrolyzable organic N (NoHyOM‐N) bound in coal. Both the Fix‐N and NoHyOM‐N fractions were geologic N, stable in chemical character, and unavailable to plants. With time, N accumulation occurred primarily in the surface 0 to 5 cm, associated with A horizon development. In this layer, soil total N and active N [Act‐N, consisting of hydrolyzable organic N (HyOM‐N) and exchangeable N (Exch‐N)], were significantly correlated with site age. The corrected‐N (Corr‐N), which was obtained by subtraction of soil total N at 10 to 20 cm from soil total N at 0 to 5 cm at each site, had a much higher correlation coefficient with site age ( r = 0.95, P < 0.0001) due to its correction for variation in soil indigenous N content among sites. The annual rate of N accumulation estimated by the Corr‐N method was 60.5 mg N kg −1 in soil (<2mm) or 23.4 kg N ha −1 in the top 0 to 5 cm. The total C content of the mine soils was correlated with site age ( r = 0.65, P < 0.05), while pH, N availability index, Fix‐N, and NoHyOM‐N were not.