Carbon and nitrogen accumulation within four black walnut alley cropping sites across Missouri and Arkansas, USA

Authors: THOMAS, ANDREW - University Of Missouri; KALLENBACH, ROBERT - University Of Missouri; Sauer, Thomas; Brauer, David; Burner, David; COGGESHALL, MARK - University Of Missouri; DOLD, CHRISTIAN - Orise Fellow; ROGERS, WENDI - University Of Missouri; BARDHAN, SOUGATA - University Of Missouri; JOSE, SHIBU - University Of Missouri

Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/16/2019
Publication Date: 1/26/2020
Citation: Thomas, A.L., Kallenbach, R., Sauer, T.J., Brauer, D.K., Burner, D.M., Coggeshall, M.V., Dold, C., Rogers, W., Bardhan, S., Jose, S. 2020. Carbon and nitrogen accumulation within four black walnut alley cropping sites across Missouri and Arkansas, USA. Agroforestry Systems. https://doi.org/10.1007/s10457-019-00471-8.
DOI: https://doi.org/10.1007/s10457-019-00471-8

Interpretive Summary: Foresters have developed equations to predict the total weight of trees based on the tree's diameter. These relationships work well in forests but not so for trees grown at wide spacing. In this study, ~ 10-year-old eastern black walnut trees planted at wide spacings at four locations in Missouri and Arkansas were measured, cut, and weighed to develop equations to predict mass from tree diameter. Roots were also harvested and the surrounding soil was sampled. Analysis of the trunks, branches, and roots indicated different amounts of carbon and nitrogen in the different tree parts. Soil analyses showed small differences in carbon and nitrogen with distance from the trees, probably because they were quite young. The data was used to develop equations to predict biomass, carbon, and nitrogen content for eastern black walnut in agroforestry plantings. This research is of interest to researchers, policymakers, and land managers interesting in estimating tree growth, carbon accumulation, and nutrient uptake.

Technical Abstract: Agroforestry and alley-cropping systems that integrate useful long-lived trees with crops or livestock have been proposed to help mitigate the accumulation of fossil fuel-derived carbon in the Earth’s atmosphere. Black walnut (Juglans nigra) is frequently planted and cultivated in North America both for its valuable lumber and its unique edible nuts, and is highly amenable to the introduction of understory crops or livestock in well-managed agroforestry systems. However, little is known about carbon assimilation in black walnut trees, including the amounts and locations of carbon assimilated into lignocellulosic tissues. Forty black walnut trees from four sites across the midwestern U.S.A. were destructively harvested, and biomass, % carbon (C), and % nitrogen (N) quantified. Soils surrounding the harvested trees were also sampled and analyzed for C and N. A growth model for C assimilation into black walnut trees across diverse locations was developed. Total tree biomass (dry weight) for the ˜ 10-year-old trees ranged from 27 to 54 kg. Woody tissues contained an average of 46.4% C and 0.44% N. Percent C differed among various woody tissues, with trunk sections containing more assimilated C compared with root tissues. While soil C and N varied consistently at increasing depths, they did not vary in distance from the trees, likely because the trees were not yet old enough to have impacted the C and N dynamics in the surrounding soils.