Aggravation of nitrogen losses driven by agriculture and livestock farming development on the Qinghai-Tibet Plateau

Nitrogen (N) losses from crop-livestock production is a major threat to the environment and human health at regional, national and global scales. A comprehensive understanding of the sources, spatiotemporal distribution and drivers of N losses is of great significance for mitigating its negative impacts and promoting N sustainable management. Here, we used the county-scale N flow model to quantitatively analyze the N losses and their driving forces of crop-livestock production on the Qinghai-Tibet Plateau (QTP). Between 2000 and 2018, the total N losses increased for more than 79% of counties on the QTP. The hotspot areas accounted for over 80% of total N losses, expanding from the east and south to the north and west of the QTP. NH3 was the main source of atmospheric N losses (over 80%) while the direct discharge of manure was the main source of water N losses. Structural equation modeling (SEM) showed that chemical fertilizer caused the largest driving effect on atmo-spheric N losses, and the total output value of agriculture and forestry was the main driver of water N losses. Uneven distribution of crop production and livestock contributed to the aggravation of N losses. Over 70% of counties had grater manure N excretion than crops could take up, and large proportion of manure could not be returned to the field. More than 90% of the counties used grater amount of chemical fertilizer N than crops could take up, indicating that livestock manure has not yet fully replaced chemical fertilizer N. The results provide effective guidance and support for N utilization and management of livestock in agricultural and pastoral areas.

Automated summary

Nitrogen losses from crop-livestock production on the Qinghai-Tibet Plateau have increased significantly between 2000 and 2018, with hotspots of N losses expanding from the east and south to the north and west of the plateau. Ammonia and manure were identified as the main sources of atmospheric and water N losses respectively, while the use of chemical fertilizer and agricultural output value were found to be the main driving forces. Uneven distribution of crop production and livestock further contributed to the aggravation of N losses.