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

Authors: KHALEEL, ALA' - Iowa State University; Sauer, Thomas; TYNDALL, JOHN - Iowa State University

Submitted to: Agroforestry Systems
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2019
Publication Date: 7/31/2019
Citation: Khaleel, A.A., Sauer, T.J., Tyndall, J.C. 2019. Changes in deep soil organic carbon and soil properties beneath tree windbreak plantings in the U.S. Great Plains. Agroforestry Systems. 94:565-581. https://doi.org/10.1007/s10457-019-00425-0.
DOI: https://doi.org/10.1007/s10457-019-00425-0

Interpretive Summary: Tree windbreaks are planted on the edges of crop fields in dry areas to conserve moisture and protect the plants from hot, dry winds. Windbreaks became common in the U.S. Great Plains following the drought years of the 1930's. The objective of this study was to determine how tree planting affects soil properties, especially soil organic matter, in four Great Plains states. Soil samples were collected at two locations in North Dakota, South Dakota, Nebraska, and Kansas. At each location soil pits were dug to 1.25 m under the trees and in the adjacent crop field and samples collected for analysis. There was 16% more carbon in the soil beneath the trees than in the crop fields. There was also 7% more carbon in the deeper layers (30 to 125 cm) than in the surface layer (0 to 30 cm). The differences between tree and crop soils and carbon distribution with depth were influenced by climate, soil type, and tree species and age. These results indicate the potential for tree windbreaks to improve soil health and that sampling beyond 30 cm is needed to accurately assess soil carbon under the tree plantings. This information is of value to farmers and ranchers, agency personnel, policymakers, and scientists interested in improving soil health and increasing storage of soil carbon.

Technical 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 1930’s. 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 >90 years on SOC storage and relevant soil properties. We quantified SOC stocks to 1.25 m 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 to 1.25 m were 16% higher beneath trees than the adjacent farmed fields. Differences ranged from +10.54 kg m–2 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.