Abstract
The purpose of this study was to elucidate the effect of cropland conversion to black locust (Robinia pseudoacacia L.) forest on soil organic carbon (SOC) contents within aggregate size fractions on the slopes of the southern Loess Plateau, China. Soil samples were collected from six sites at 0 to 20 cm and 20 to 40 cm in duplicate. Five sites were artificial black locust forests that had been converted from cropland 6 years (FL06), 15 years (FL15), 29 years (FL29), 40 years (FL40), and 56 years (FL56) ago, and one neighboring site was cropland (CK) cultivated with wheat (Triticum aestivum L.). Five aggregate size fractions (>2 mm, 1 to 2 mm, 0.5 to 1 mm, 0.25 to 0.5 mm, and <0.25 mm) were obtained via wet sieving. The sum of the >2 mm and <0.25 mm aggregate was higher than 55% for all topsoil samples of the six sites. The >2 mm and <0.25 mm aggregate fractions in the black locust forests were significantly higher than those in CK. The SOC contents in the >2 mm and 1 to 2 mm aggregate fractions under the locust forests increased by 11% to 192% and 15% to 230%, respectively. The contribution ratio (R) of the aggregate-associated SOC to the corresponding total SOC in <0.25 mm aggregate fraction was the highest both at the 0 to 20 cm and 20 to 40 cm depth. The findings revealed that land use conversion from cropland to forest could increase the macroaggregates and improve soil structure. Additionally, the effect of this land use conversion on SOC contents within aggregate size fractions changed along with different conversion time. Macroaggregates, aggregate-associated SOC, and total SOC can be used as reference factors for evaluating the effect of vegetation restoration on soil quality and erosion control.
- © 2019 by the Soil and Water Conservation Society
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