Carbon sources and dynamics in afforested and cultivated corn belt soils

Authors: HERNANDEZ-RAMIREZ, GUILLERMO - New Zealand Institute For Crop & Food Research; Sauer, Thomas; Cambardella, Cynthia; BRANDLE, JAMES - University Of Nebraska; James, David

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2010
Publication Date: 2/4/2011
Citation: Hernandez-Ramirez, G., Sauer, T.J., Cambardella, C.A., Brandle, J.R., James, D.E. 2011. Carbon sources and dynamics in afforested and cultivated corn belt soils. Soil Science Society of America Journal. 75:216-225.

Interpretive Summary: How land is used, whether it is used for crops or pasture or forest, has a large impact on soil organic matter content. Soils that are tilled every year to grow crops usually lose much of their organic matter. This study looked at how planting trees on crop land affected the amount of organic matter in the surface soil layers. Two field sites were studied. The first site was in eastern Nebraska where two rows of trees were planted for a windbreak with cropped fields on both sides. The second site was in northwestern Iowa where pine trees were planted in a field with fields on each side, one that was tilled every year and one that had not been tilled for ten years. The trees at both sites were about 35 years old when soil samples were collected and analyzed. The results showed greater soil organic matter in the soil under the trees than in the cultivated soils at both sites. Analysis of the fine particles in the soil (bits of needles, leaves, and roots) indicated differences in how fast organic materials from the trees or crops were being decomposed in the soil. Generally, trees can produce more organic material each year and it tends to decompose more slowly than most crop residues. This study also found that most of the increase in soil organic matter beneath the trees came from the tree sources. The results of this study are of interest to growers, scientists, and policy makers as it shows that planting trees on degraded agricultural land can sequester a lot of carbon. This would not only reduce the amount of carbon dioxide in the atmosphere but also improve the quality of the soils.

Technical Abstract: Afforestation of degraded cropland can sequester atmospheric carbon (C), but soil organic C (SOC) sources in such ecosystems are not well-characterized. This study assessed SOC dynamics and sources in two 35-yr-old, coniferous afforestation sites [i.e., a forest plantation and a shelterbelt situated at northwestern Iowa (Sac) and eastern Nebraska (Mead) on Galva silty clay loam and Tomek silt loam soil series, respectively] and the adjacent agricultural fields. Composite soil samples were collected at both sites to determine SOC and total nitrogen (TN) contents, and stable C isotope ratios (d13C, natural abundance) in both whole soil and fine particulate organic matter (fPOM; 53 – 500 µm size). In these fine-textured soils, afforestation of cropland carried out through either shelterbelt or forest plantation caused substantial increases in SOC accrual (= 57%; P< 0.05) at surface soil layers (to 7.5 or 10 cm deep) relative to conventionally-tilled cropping systems confirming the direct benefits of tree planting on soil C sequestration. Soils exhibited a marked gradient of d13C signatures from near constant values in cropped fields (-17‰) to much depleted in afforested soils (-22‰) indicating a gradual shift in C sources. Source-partitioning assessments revealed that tree-derived C contributed roughly half of the SOC found directly beneath trees suggesting that the additional SOC accrued in these afforested sites can be fully explained by tree-derived inputs. In afforested surface soils, fPOM accounted for a large portion the existing SOC (21%) with 79% being derived from tree inputs, thus supporting POM as a significant sink for recently sequestered SOC in these ecosystems.