Variation of soil infiltrability across a 79-year chronosequence of naturally restored grassland on the Loess Plateau, China

Soil infiltrability plays a critical role in controlling soil erosion and enhancing water storage in arid and semi-arid areas. Presently, knowledge is lacking regarding the dynamic mechanism and characteristics of soil infiltration during long-term natural vegetation restoration. This study evaluated how soil infiltrability changes along a 79-year chronosequence of natural restoration from cropland to permanently restored grassland. A slope cropland (control) and five grasslands of successive age-classes (6-, 16-, 36-, 56-, and 79-year natural restoration treatments) were selected to establish a chronosequence on China’s Loess Plateau. Soil infiltrability was measured under simulated rainfall conditions at three intensities (20, 40, and 60 mm/h) using a run off–on–out method. The steady-state infiltration rate (SIR) of the control treatment decreased with increasing intensity of rainfall while those of the natural restoration treatments showed a contrary tendency. With the extension of restoration period, the SIR was gradually increased while the runoff was decreased and the time-to-runoff and time-to-SIR were prolonged. The SIR had a significant negative exponential relationship with the restoration period under different rainfall conditions (P < 0.01). Soil infiltrability showed rapid increases within 16 year of natural restoration and slight changes thereafter. Soil parameters including SIR and the contents of macroaggregates (>0.25 mm) and organic matter were significantly correlated with each other (P < 0.01). Long-term natural restoration of grassland, especially for 16-year, significantly enhanced soil infiltrability and reduced soil erosion through organic matter accumulation and the resulting improvement of structural properties. This study provides reference data for describing hydrological parameters on the Loess Plateau.