Soil fertility thresholds driven by sand content indicate drylands degradation phases on the Tibetan Plateau

Abstract

Understanding the process of dryland degradation is crucial to combating desertification and maintaining land sustainability. To identify important indicators of dryland degradation, we conducted a field survey of 46 drylands spanning an aridity gradient across the Tibetan Plateau. Our random forest model suggested that soil sand content was the most important predictor of variation in soil fertility (carbon, nitrogen, and phosphorus). Most soil fertility showed a nonlinear and abrupt decline with increasing soil sand content, and displayed three sequential thresholds. First, soil organic carbon sharply decreased beyond a soil sand content threshold of 47%. Second, exceeding a subsequent threshold of 70%, the total nitrogen and light fraction carbon declined dramatically with increasing soil sand content. Finally, soil heavy fraction carbon, inorganic carbon, and total carbon were drastically reduced when the soil sand content exceeded 80%. The three soil fertility thresholds along the gradient of the soil sand content indicated a sequence of dryland degradation phases. Our findings provide an approach for detecting the severity of dryland degradation and suggest vulnerable areas of degradation on the Tibetan Plateau.

Fertile island effects across soil depths in drylands of the Tibetan Plateau

“…At every site, we established three quadrats measuring 10 m by 10 m. Within each quadrat, we collected four soil samples: one from the uppermost layer of soil (depth ranging from 0 to 30 cm) and one from the underlying layer of soil (depth ranging from 30 to 50 cm) in areas where vegetation was absent; and one each from the topsoil and subsoil beneath the overhead covering formed by the prevailing perennial plants, following the methodology outlined in Cai et al (2023). Consequently, a combined sum of 12 samples of soil were gathered at every location.…”

“…The soil samples underwent ltration using a 2 mm mesh before being transported to further measurement and analysis. To measure the impact of fertile islands, we measured six soil fertility variables related to carbon, nitrogen, and phosphorus, including total carbon, organic carbon, inorganic carbon, total nitrogen, organic nitrogen, total phosphorus (Cai et al, 2023). We measured total carbon, total nitrogen, and organic carbon utilizing an elemental analyzer manufactured by Elementar (Vario MACRO Cube model from Germany).…”