Soil C and N stocks of Alfisols under native tallgrass prairie in the mid-Southern, USA

Abstract

The objective of this study was to evaluate the effects of soil moisture regime (i.e., aquic and udic) and physiographic region (i.e., Ozark Highlands of northwest Arkansas and Grand Prairie region of east-central Arkansas) on the change in soil carbon (C) and nitrogen (N) storage and other soil properties over a 15-year period. Soil samples were collected from the top 10 cm in 2001/2002 and again in 2016/2017 and the change over time was directly quantified for numerous soil properties. Averaged across soil moisture regime, TC content and concentration, C:N ratio, and TC fraction of soil organic matter all increased (P < 0.05) over time in the Ozark Highlands, as well as the Grand Prairie region, with the exception of total C (TC) content and concentration, which both decreased in the Grand Prairie. Despite the Grand Prairie region losing soil C at a rate of 0.23 Mg ha−1 yr−1 or 0.02% yr−1 over the 15-year duration of this study, soil C storage in 2016 did not differ between physiographic regions when averaged across soil moisture regime. The TC fraction of SOM changed more over time (P < 0.01) in the Ozark Highlands under aquic soil moisture conditions (1.3% yr−1) compared to the other three soil moisture regime/region combinations. This study demonstrates the value of direct measurements over time for assessing temporal changes in soil properties so that results can be used to guide expectations of the effects of physiographic region and soil moisture regime for future restoration activities to be as successful as possible.