A Riparian Buffer at 10 Years: The Effect of Black Plastic Mulch on Soil Variables, Nutirent Stocks and Tree Biomass

Abstract

Riparian zones are the interface between terrestrial and aquatic ecosystems. Riparian buffers are an important component of this interface environment because the vegetation of the buffer can provide many ecosystem services. Establishing riparian buffers on agricultural land can help reduce agricultural pollutants such as excessive nitrogen and phosphorus, but also provide opportunities to sequester carbon and produce biomass. Sampling was done after 10 years of growth in a riparian buffer of five tree species, hybrid poplar (Populus × canadensis), red ash (Fraxinus pennsylvanica), bur oak (Quercus macrocarpa), red oak (Quercus rubra) and white pine (Pinus strobus) to measure the long-term effects of black plastic mulch on soil variables, tree growth, tree nutrient sequestration and biomass production, as well as the species effect on these variables. Specifically, this study measured: (1) the physical, chemical and biological soil properties, and the fine root biomass of soils in the buffer to determine the long-term effects of black plastic mulch, and; (2) tree biomass production and the carbon and nutrient sequestration potential of the five tree species, as well as to determine if black plastic mulch can cause an increase or decrease in these variables. After 10 years, the use of black plastic mulch decreased soil organic matter, total soil carbon, total soil nitrogen, earthworm biomass and abundance. Soil NO3 concentration was three times greater under the mulch, despite higher tree growth in this treatment. This study shows the importance of the total pool of fine roots on the maintenance and enhancement of soil carbon and earthworm biomass. White pine growth was only slightly enhanced by the black plastic mulch, while red oak was the tree species that ii benefited the most from the mulch treatment, especially for survival. The mulch treatment produced a greater average tree height, survival and basal diameter than the control treatment. Foliage, branch and stem biomass were significantly higher in the mulch treatment, as were the sequestration of carbon, nitrogen, potassium, phosphorus, sulphur, magnesium and calcium. Hybrid poplar accumulated the greatest biomass of all species in all its compartments and had the highest quantity of carbon and all measured nutrients. Hybrid poplar was the best species to produce rapid tree biomass. Alternative mulching options that do not degrade important soil properties and other native tree species should be investigated in other studies to determine their value for future use in riparian buffers. The results from this study will help in designing agroforestry riparian buffers that will maximize nutrient capture and sequestration, and tree biomass production. Such riparian buffers will deliver more ecosystem services (reducing agricultural nitrogen and phosphorus input to watersheds; creating new habitats for flora and fauna) and produce wood biomass for timber or bioenergy.