Effects of plant productivity and species on soil carbon and nitrogen sequestration under seasonal grazing in a semi-arid grassland of North China

Seasonal grazing is a common alternative to the rest-rotation grazing management regime. Although that research has been extensive on the impacts of grazing on soil organic carbon (SOC) and nitrogen (N) sequestration, there is limited understanding of the regulatory mechanisms of plant productivity and species on SOC and N sequestration under seasonal grazing. To address this problem, the response of plant properties was quantified in five different seasonal grazing regimes (no grazing control, continuous grazing, early summer and late summer grazing, mid summer and early autumn grazing, late summer and mid autumn grazing) in a semi-arid grassland of North China between 2012 and 2018. The results indicated that early summer and late summer grazing had little damage to the plant communities but reduced the SOC and N sequestration in the 10-20 cm layer, while mid summer and early autumn grazing maintained a relatively high plant productivity but resulted in the losses of SOC and N sequestration in the 0-20 cm layer. The late summer and mid autumn grazing regime enhanced SOC and N sequestration in the 0-20 cm layer by producing higher yields of Stipa krylovii and root biomass. The improved biomass of S. krylovii and roots is an indicator of soil quality evolution in the context of grazing management. It is therefore proposed that the late summer and mid autumn grazing regime, including a two-month rest period, is likely to be a beneficial strategy to conserve both plant communities and soil nutrients for sustainable management of the studied grassland.