Effects of yak and Tibetan sheep trampling on soil properties in the northeastern Qinghai-Tibetan Plateau

Grassland soil is affected by trampling, ingestion and excretion by herbivores, of which the effects of trampling are most pronounced and intense. However, the mechanism of livestock trampling on grassland soil remains uncertain. The objective was to ascertain the differential effects of trampling by yaks and Tibetan sheep on grassland at different grazing intensity. Therefore, we simulated yak and sheep trampling during two consecutive years of 2015 and 2016 at different intensities and investigated their effects on soil properties in a Tianzhu alpine meadow in Gansu Province, China. Our results revealed that soil bulk density under heavy trampling at 0-10 cm depth was significantly higher than that of untrampled treatment (CK), while saturated hydraulic conductivity, respiration rate, and number of microbial colonies (bacteria, fungi, and actinobacteria) significantly decreased. With increase in trampling intensity, the soil available nitrogen (AN) and available potassium (AK) increased at 0-20 cm depth, while total nitrogen (TN) and total phosphorus (TP) at 0-20 cm and available phosphorus (AP) at 0-10 cm decreased. Total potassium (TK) and organic matter did not differ significantly with trampling intensity. Yak trampling increased bulk density, AN, and AK, and decreased the soil respiration rate, saturated hydraulic conductivity, number of microbial colonies, TN, TP, and AP. Soil consolidation was alleviated after freeze-thaw cycling and the off-season grazing in the cold season. Our results demonstrated that heavy trampling by livestock compacted surface soil, reduced soil permeability, and weakened the living environment for microorganisms. Therefore, yak trampling had more severe effects on soil consolidation than that by Tibetan sheep in the alpine meadow of the Qinghai-Tibetan Plateau.