EFFECT OF COVER CROP MANAGEMENT ON ORGANIC MATTER PRODUCTION AND SOIL FERTILITY IN AN ABIES FRASERI PLANTATION

Fraser fir (Abies fraseri) is traditionally produced in a high input intensively managed cropping system for Christmas tree production in the Midwest and Eastern United States of America. The goal of the project is to investigate the effect of three ground covers (alfafa [Medicago sativa], Dutch white clover [Trifolium repens] and perennial rye [Lolium perenne]) on the sustainability of Fraser fir Christmas tree production system. This paper reports on the effect of ground cover species and management practices on organic matter production, soil organic matter, and soil mineral nitrogen. Intercropped ground covers were mowed every 21 days, and the cut vegetation returned to the ground as green mulch. The effect of cover crop species and management practices were evaluated by quantifying the cover crop above-ground biomass production. The total amount of mineral nutrients including nitrogen, phosphorus, potassium, calcium, and magnesium were determined by chemical analyses of subsamples of materials from the cover crop biomass. The effect of cover crop on soil fertility was evaluated by monitoring changes in soil organic carbon and soil mineral nitrogen. The results indicate that cover crop species affected the amount of green manure produced and its total nitrogen and macronutrients content. Soil organic matter content was stable in the upper soil profile due to the relatively small quantities of organic matter added with the cropping system compared with the total stock of soil C. Mineral nitrogen decreased over the season due to the synchrony of cover crop decomposition, mineralization and nutrient uptake by trees in the upper profile. These results indicate that intercropping cover crops can improve soil nitrogen fertility and organic matter; however, there is strong competition for other nutrients that need to be carefully considered.