A STATE-SPACE ANALYSIS OF SOIL ORGANIC CARBON IN CHINA'S LOESS PLATEAU

An accurate estimation of soil organic carbon (SOC) is important for the evaluation and management of carbon (C) flux in terrestrial ecosystems. However, there is little work on the spatial variability of SOC in deep soils and its driving factors. Thus, the objective of the study was to derive the primary factors dominating the spatial distribution of SOC in different soil layers with the use of the autoregressive state-space approach. The concentration of SOC was measured to the depth of 500 cm (n = 86) along a south-north transect of China's Loess Plateau. The mean SOC of the 500-cm soil profile generally decreased from south to north following the decreasing rainfall gradient. Based on the investigated factors, the state-space model was able to capture 90.3-99.9% of the spatial variability of SOC in the various soil layers. According to the coefficients in the optimal state-space model for each soil layer, climatic factors such as precipitation and temperature had a dominant control over the spatial distribution of SOC at shallow depths. However, both climatic and edaphic (e.g. soil texture) factors, and to a small extent land use, influenced the spatial behavior of SOC at the 40-200 cm soil depth. For soil layers below 200 cm, the importance of land use was revealed, and the spatial characteristics of SOC were together driven by land use, climatic and edaphic factors. This is critical for the management of soil C flux in deep soils and the C stock and cycle in terrestrial ecosystems. Table SI. Basic properties of soils and climate and elevation under three land uses along the south-north transect on the Loess Plateau (mean +/- standard deviation). Note that SWC is gravimetric soil water content. Copyright (C) 2016 John Wiley & Sons, Ltd.