Abstract
Soil aggregate is extremely important for soil health and sustainable land management. Overgrazing has caused serious degeneration of grassland in the past decades and how to restore the degraded soil through grazing management is urgently needed. In this research, we investigated effects of long-term grazing exclusion and short-term rotational grazing with different grazing intensities on aggregate stability in the upper 10 cm of soil at two grazing sites in Xilinhot, Inner Mongolia. Treatments included long-term (34 years) exclusion, moderate-term (21 years) exclusion, and continuous grazing at adjacent reference plots. In addition, effects of rotational grazing under different grazing intensity [i.e., no grazing (0 days/month), light grazing (3 days/month), moderate grazing (6 days/month) and high grazing (12 days/month)] were investigated after 5 years. Stability of aggregate fractions were determined using wet sieving. Our results showed that the stable aggregates fraction were significantly increased under grazing exclusion for both fine (0.25–1 mm) and coarse (1–2 mm) size fractions. At the rotational grazing site, stability of fine aggregates was significantly enhanced under grazing compared with no grazing, while there was little influence on stability of coarse aggregates. Our results showed that grazing exclusion significantly increased soil aggregate stability and the peak appeared in moderate-term exclusion, meanwhile, rotational grazing had little influence on aggregate stability. We suggest that rotational grazing rather than long-term grazing exclusion is a better way for soil aggregate stability and soil health, and current grazing prohibition policies may need to be adjusted.
Highlights
The steppe in arid and semi-arid of northern China is among the largest remaining natural grassland in the world (Kawamura et al, 2005)
It is worth to note that, livestock exclusion is commonly found to be positive to soil aggregate stability in Inner Mongolia (Su et al, 2005; Steffens et al, 2008; Kölbl et al, 2011), our results suggest that coarse aggregate stability shows a non–linear response to the length of exclusion period (Figure 3E)
Our results showed that rotational grazing significantly increased the fine aggregate stability but had little influence on stability of coarse aggregates with the exception of a significant reduction under light grazing (Figure 4E)
Summary
The steppe in arid and semi-arid of northern China is among the largest remaining natural grassland in the world (Kawamura et al, 2005). Overgrazing has caused serious grassland soil deterioration in the past decades (Tong et al, 2004). Researchers have shown that grazing exclusion is effective to restore the degraded grassland soil (Mekuria et al, 2007; Cheng et al, 2011). Several policies (e.g., Prohibiting Grazing Policy and Returning Grazing Lands to Grasslands) were implemented to restore the degraded grassland in northern China. Long-term absence of grazing may inhibit important ecosystem functions. The positive effects of controlled livestock grazing and prohibiting grazing on grassland ecosystems are widely reported, its potential negative effects on soil quality is rarely mentioned in Inner Mongolia
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