Capacity of biochar application and nitrogen fertilization to mitigate grass competition upon tree seedlings during stand regeneration

Abstract

Background and aimsThis experiment examined early competition dynamics of a tree-grass intercropping system. We hypothesized that (1) the effects of competition would outweigh those of facilitation in this system and (2) soil amendment-induced fertility would alter competitive relationships between these species. MethodsWe intercropped loblolly pine and switchgrass seedlings at three rates of density-induced interspecific competition (high, low, and pine only) and amended soils with biochar (0, 5, and 20Mgha−1) and nitrogen fertilizer (0 and 56kgha−1N). We measured soil properties, foliar N concentrations, and plant productivity over two years. ResultsSoil temperatures decreased and total soil N increased in intercropping treatments relative to the pine only control treatment. Competition reduced soil moisture and inorganic N concentrations as well as tree productivity and switchgrass yields. Biochar amendments increased total soil C, C:N ratios, and soil moisture. Fertilization acidified soil pH and decreased total soil C and N pools. Switchgrass yields were increased and soil moisture was decreased with N fertilization. ConclusionsThe net effects of competition outweighed those of facilitation within this system. Competitive relationships amongst these species were altered by soil amendment-induced fertility. Favorable switchgrass responses to soil inorganic N suggests its competitive ability is increased on nitrogen-rich or fertilized sites.