Spatial variations in soil and plant nitrogen levels caused by ammonia deposition near a cattle feedlot
2018
Shen, Jianlin | Chen, Deli | Bai, Mei | Sun, Jianlei | Lam, Shu Kee | Mosier, Arvin | Liu, Xinliang | Li, Yong
Cattle feedlots are significant ammonia (NH₃) emission sources, and cause high NH₃ deposition. This study was conducted to investigate the responses of soil mineral nitrogen (N), percent cover of plant species, leaf N content, and leaf δ¹⁵N to NH₃ deposition around a 17,500-head cattle feedlot in Victoria, Australia. Soil samples were collected in May 2015 at 100-m intervals along eight downwind transects, and plant samples were collected in June 2015 from five sites at 50- to 300-m intervals along a grassland transect within 1 km downwind of the feedlot. NH₃ deposition was also monitored at five sites within 1 km downwind of the feedlot. The estimated NH₃-N deposition rates ranged from 2.9 kg N ha⁻¹ yr⁻¹ at 1 km from the feedlot to 203 kg N ha⁻¹ yr⁻¹ at 100 m from the feedlot. The soil mineral N content was high (22–98 mg kg⁻¹, mainly nitrate), significantly decreased with increasing distance from the feedlot, and significantly increased with increasing NH₃-N deposition. With increasing NH₃-N deposition, the percent cover of the herb species Cymbonotus lawsonianus increased significantly, but that of the grass species Microlaena stipoides decreased significantly. The leaf total N contents of the grass and herb species were high (>4%), and were linearly, positively correlated with the NH₃-N deposition rate. Leaf δ¹⁵N values were linearly, negatively correlated with the N deposition rate. These results indicate that the leaf N contents and δ¹⁵N values of C. lawsonianus and M. stipoides may be bioindicators of N deposition.
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