Supplementary feeding yak with oat hay improves nitrogen cycling in an alpine meadow on the Qinghai-Tibet Plateau, China

CONTEXT: A large number of field trials assessing supplementary feeding have been conducted on the Qinghai Tibet Plateau but its influence on nitrogen (N) cycling particularly N addition to soil through litter or dung deposition and the effect on soil N levels remain poorly understood. OBJECTIVE: Here we investigated the effects of oat hay supplementation on forage biomass, N return from litter and dung to soil and soil N levels by comparing supplemented and non-supplemented systems. METHODS: The non-supplemented system of yak was based on typical native grazing practices and was established in 2010. Grazing in supplementary feeding system was identical but each yak received oat hay (0.5, 1.0 or 1.5 kg/day, dry matter basis) during the cold season. For each system, forage biomass, N return from litter and dung to soil, and soil N levels were measured from 2010 to 2014. RESULTS AND CONCLUSIONS: The results showed that supplementation systems increased 12.8% of forage biomass and enhanced N return from litter and dung to soil by 8.0% and 6.2%, respectively, compared with native grazing systems, but did not change soil N stock. Forage biomass (slope, 0.596 to 1.769) and return of N from litter to the soil (slope, 0.359 to 0.677) increased significantly as the trial progressed in supplementation systems. Increased forage biomass resulted in increased N uptake offsetting the supplement-induced soil N input resulting in minimal change in soil N. SIGNIFICANCE: The conceptual framework firstly quantized the effect size of supplementary regime on N cycling of grazing systems and soil N levels in alpine meadows. It can be used for an essential model and extended to other agroecosystem that show the influence of external disturbances on nutrient cycling.

Automated summary

Supplemental feeding with oat hay increased forage biomass by 12.8% and enhanced N return from litter and dung to soil by 8.0% and 6.2%, respectively, compared to non-supplemented systems. However, it did not have a significant effect on soil N stock. Forage biomass and N return from litter to soil increased significantly over time in the supplementation systems. The increased forage biomass led to increased N uptake, balancing out the supplement-induced soil N input and resulting in minimal changes in soil N levels.