Changes in deep soil organic carbon and soil properties beneath tree windbreak plantings in the U.S. Great Plains

Abstract

Agroforestry systems such as tree windbreaks became a common practice in the U.S. Great Plains following a large tree planting program during the Dust Bowl of the 1930s. Tree windbreaks combine the potential to increase biomass and soil carbon (C) storage while maintaining agricultural production. However, our understanding of the effect of trees on soil organic carbon (SOC) is largely limited to the upper 30 cm of the soil. This study was conducted in the Great Plains to examine the impact of tree plantings ranging in age from 15 to ~ 115-years on SOC storage and relevant soil properties. We quantified SOC stocks to 1.25 m depth within eight tree plantings and in the adjacent farmed fields within the same soil map unit. Soil samples were also analyzed for inorganic carbon, total nitrogen, pH (in water and KCl), bulk density, and water stable aggregates. Averaged across sites, SOC stocks in the 1.25 m were 16% higher beneath trees than the adjacent farmed fields. Differences ranged from + 10.54 to a – 5.05 kg m⁻² depending on the site, climate, and tree species and age. The subsurface soils (30-125 cm) beneath trees stored 7% more SOC stocks than the surface 30 cm (9.54 vs. 8.84 kg m⁻²), respectively. This finding demonstrates the importance of quantifying C stored at deeper depths under tree-based systems when tree SOC sequestration is being assessed. Overall, our results indicate the potential of trees to store C in soils and at deeper depths.