Wood Residue and Fertilizer Amendment on Bentonite Mine Spoils: II. Plant Species Responses

Abstract

Abstract Second growing season plant species biomass, composition, and diversity responses to varied wood residue and fertilization treatments on bentonite mine spoils are reported. Two seed mixtures, each with six plant species,, were seeded on four wood residue rates (0, 45, 90, and 135 Mg ha −1 ) and four N fertilization regimes (0, 2.5, 5.0, and 7.5 kg N Mg −1 of wood residue). Some species were poorly established irrespective of treatment (green needlegrass, Stipa viridula ) or became established to a limited extent only under specific residue‐fertilization treatment combinations (slender, crested, and pubescent wheatgrass; Agropyron trachycaulum, A. desertorum , and A. trichophorum , respectively). The remaining species became well established under specific treatment combinations. Western wheatgrass ( Agropyron smithii ) and Nuttall saltbush ( Atriplex nuttallii ) responded positively to increasing residue rate, but were unaffected by fertilization. Smooth brome ( Bromus inermis ), streambank/thickspike ( Agropyron riparium/dasystachyum ), tall ( Agropyron elongatum ) and intermediate ( Agropyron intermedium ) wheatgrass exhibited significant, although varied, interactive responses to residue and fertilization rate. Total plant biomass was responsive to residue rate, but peaked at a lower rate (90 Mg ha −1 ) for the native than for the introduced (135 Mg ha −1 ) mixture. Differences in species and growth form composition occurred among treatments. Maximum diversity occurred at residue rates lower than those for maximum productivity; 45 Mg ha −1 and 90 Mg ha −1 for the native and introduced mixtures, respectively. Diversity was consistently stimulated by fertilization for the introduced species mixture, but responded variably to fertilization for the native mixture.