Evaluating aggregate stability of soils under different plant species in Ziwuling Mountain area using three renowned methods

Abstract

Soil stability is a characteristic property and is frequently used as an indicator of soil quality. Considering the large variation among stability tests, existing studies usually employ more than one stability test in order to better understand soil behavior against various disruptive forces. The main purposes of this study were to evaluate the impact of aggregate disruptive mechanisms (slaking, clay swelling, mechanical breakdown, and cavitation) on soils developed under different plant species. We aimed as well to compare the results of three renowned soil stability methods: modified Yoder (Yod), Le Bissonnais (LB) and Ultrasonic agitation (UA) on surface (0–20 cm) and subsurface (20–40 cm) soils. Overall, soils of three plant communities developed under eight plant species were investigated. These include forestland (Quercus wutaishansea, Pinus tubulaeformis, Platycladus orientalis, and Robinia pseudoacacia), shrubland (Sophora viccifolia, Hippophae rhamnoides, and Rosa xanthina) and grassland (Stipa bungeana). The mean weight diameter (MWD) was used as a stability parameter for modified Yoder’s and Le Bissonnais’ methods. In contrast, specific dispersion energies (SE) at the initial (10%, w/w), middle (50%, w/w) and final (90%, w/w) stages of aggregate disruption were used as stability parameters by the UA method. The results of MWD (Yod) indicated that surface and subsurface soils were in the range of 1.23–2.86 mm, which accounted for medium (0.8–1.3 mm) to very stable (>2 mm) soils. Among the three LB tests (fast wetting (FW), slow wetting (SW), and wet stirring (WS)), the order of aggregate disruption was FW > WS > SW, suggesting that FW was the most destructive among the three tests with the lowest MWD value (0.45 mm, unstable soil). SW showed the highest MWD values (0.82–2.82 mm), and most of the soils were ranked in the stable (1.3–2 mm) to very stable (>2 mm) range. The MWD trend of WS was similar to FW test. Although the range of SE at three levels was different: SE10 (8.1–29.4 J g−1), SE50 (53.0–193.4 J g−1), and SE90 (176–642 J g−1), they all showed a similar association with soil characteristics and stability parameters of other tests. The strong positive correlation of soil organic carbon (SOC), total nitrogen (TN), fine root biomass (FRB), and clay contents, and the negative correlation of soil water content (SWC) with the five tests, indicated that these five factors were the major characteristics responsible for the resistance of the studied soils against different destructive mechanisms (p < 0.05–0.01). Overall, the results of all five tests indicated that soil under Quercus wutaishansea (QW) was the most stable, while that under Robinia pseudoacacia (RP) was the most unstable. Although all methods were based on different breakdown mechanisms, initial and final soil fractions and parameters, they were strongly positively correlated with each other. This indicated that all these tests were equally good at stability assessment, with some distinctions and limitations.