Topographic influences on soil properties and aboveground biomass in lucerne-rich vegetation in a semi-arid environment

Abstract

Lucerne (Medicago sativa L.) is widely planted on the semi-arid Loess Plateau in China to control soil erosion, yet the extent to which topography affects the productivity of lucerne still remains poorly understood. This study aimed to evaluate how topographic position influences soil properties and aboveground biomass in lucerne-rich vegetation. A total of 112 quadrats were established in 28 fields covered with 11-year-old lucerne vegetation. In each quadrat, the slope, slope position, slope aspect, altitude, soil properties (soil moisture content, organic carbon, total nitrogen [N] and phosphorus [P], available P and inorganic N), and aboveground biomass were measured. Redundancy and multiple regression analyses were performed to determine the relationships among topographic factors, soil properties and aboveground biomass. A modest proportion of variation in soil variables was explained by topographic variables. The altitude, slope and slope position, rather than the slope aspect, were the key factors that influencing soil variables. Soil organic carbon, total N, inorganic N, the ratio of organic carbon to available P (C/P), and the ratio of total N to available P were positively correlated with altitude, whereas available P was negatively correlated with altitude. The soil moisture content was primarily affected by the slope and slope position. The topographic factors did not directly affect the total and lucerne aboveground biomass. The total and lucerne aboveground biomass were positively correlated to soil moisture content, inorganic N and C/P. Therefore, the aboveground biomass of lucerne-rich vegetation could be indirectly regulated by the slope and slope position through the effect on the soil moisture content and by altitude through the effect on soil inorganic N and C/P. This work highlighted the importance of soil properties such as soil moisture and P dynamics in the revegetation process of lucerne in this semi-arid region. As soil properties can be directly governed by topography, considering topography could enhance the quality of vegetation restoration in the large hilly region of the Loess Plateau.