Soil organic carbon and nutrients affected by tree species and poultry litter in a 17-year agroforestry site

Authors: AMORIM, HELEN - University Of Arkansas; Ashworth, Amanda; ZINN, YURI - Universidade Federal De Lavras; Sauer, Thomas

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2022
Publication Date: 3/5/2022
Publication URL: https://handle.nal.usda.gov/10113/7711854
Citation: Amorim, H., Ashworth, A.J., Zinn, Y.L., Sauer, T.J. 2022. Soil organic carbon and nutrients affected by tree species and poultry litter in a 17-year agroforestry site. Agronomy Journal. 12(3). Article 641. https://doi.org/10.3390/agronomy12030641.
DOI: https://doi.org/10.3390/agronomy12030641

Interpretive Summary: Agroforestry (AF) provides multiple benefits to the ecosystem and society by diversifying food production, increasing biodiversity, and preventing land degradation. The choice of tree species and fertilization source may affect the ability of AF systems to provide ecosystem services, such as soil organic carbon (SOC) storage and reduction of greenhouse gas emissions (e.g. CO2). Thus, researchers investigated how plantings of two different tree species (red oak and pecan) and fertilizer type (mineral vs. organic) affected soil health and nutrients after 17 years of establishment. Between 2001 and 2007, the eastern part of the site received poultry litter (PL), a mixture of manure, urine, and bedding material, and the west half received an inorganic nitrogen fertilizer. Researchers evaluated soil structure, SOC, and nutrients in 2001, 2008, and 2016 at two depths: 0-15 cm and 15-30 cm. After 17 years, applications of PL reduced soil acidity and increased phosphorus levels. Applications of PL under pecan stands increased SOC and soil nitrogen. Poultry litter applications were more beneficial than inorganic nitrogen fertilizer, since the observed greater soil nutrient concentrations likely increase biomass yield and pecan production. These findings may serve as a guideline for improving the productivity of temperate AF systems, as well as their ability to provide ecosystem services.

Technical Abstract: The choice of tree species and fertilization source may affect soil organic carbon (SOC) and fertility in agroforestry (AF) systems, mostly due to distinctive leaf litter and nutrient inputs. This study assesses changes in SOC and major nutrients in a 17-year AF site established on a Ultisol in Fayetteville, AR. It was evaluated how management [tree species red oak (Quercus rubra L.) and pecan Carya illinoinensis (Wangenh.) K. Koch. and fertilization type (mineral vs. organic)] affected soil physical and chemical. Between 2001 and 2007, the eastern part of the site received annual applications of 3.9–6.7 Mg ha-1 poultry litter, and the west half received 50–76 kg ha-1 N as NH4NO3 (control). Soil samples were collected in 2001, 2008, and 2016 from 0-15 and 15-30 cm depths. Bulk density, SOC, and major nutrients (N, P, K, Ca, Mg, and S) were assessed. Stocks (Mg ha-1) of SOC and N were calculated per soil depth for 2016. Analysis of variance and mean comparisons of the main effects (year, tree species, fertilizer source, and soil depth) and their interactions were performed. Tree species establishment in an AF system led to distinctive trends in nutrient concentrations during 17 years of management. Applications of poultry litter led to an overall increase in pH, whereas Mg and S concentrations decreased when compared to initial levels (1999). Poultry litter applications also increased soil P concentration in 53% compared to baseline levels (1999), and reduced soil C:N ratio. After 17 years, increased Ca, SOC, and N concentrations were observed in soils under pecan stands that received poultry litter. Positive correlations were found between SOC and N (r = 0.96), Ca (r = 0.71) and P (r = 0.61) at the 0-15 cm soil depth. Results demonstrate that changes in SOC and fertility in AF soils vary with tree species and fertilization, and that organic matter accumulation increased SOC retention and nutrient availability in temperate AF systems.