Land-use type, and land management and disturbance affect soil δ15N: a review.

Purpose: We compared the patterns of natural abundance of nitrogen (N) isotope ratio (δ¹⁵N) of total soil N among cropland, forest, and grassland soils, with special interests in the effects of farming system on cropland and grassland, and climate zone on forest soils, as well as the general effect of land-use change and site disturbance. Material and methods: We analyzed data on δ¹⁵N of terrestrial N sources (n = 532), cropland (n = 168), forest (n = 227 for organic and 428 for mineral soil layers), and grassland soils (n = 624). Results and discussion: Forest soils had the lowest δ¹⁵N (– 1.0 ± 0.2‰ and + 3.1 ± 0.2‰ for mineral and organic soil layers, respectively), reflecting the influence of the ¹⁵N-depleted source N and the more closed nature of the N cycle. Tropical forest soil had higher δ¹⁵N than other climate zones, reflecting the influence of the high N availability and loss in tropical forests. The low δ¹⁵N in subtropical forest soils likely reflected the influence of the high rate of deposition of ¹⁵N-depleted N. The δ¹⁵N of cropland (+ 5.0 ± 0.2‰) and grassland (+ 6.2 ± 0.1‰) soils was greater with manure than with synthetic fertilizer applications. Soil δ¹⁵N was also affected by land-use change and was often increased (followed by progressive decreases) by site disturbance. Conclusions: Land-use type and land management effects on soil δ¹⁵N reflect changes in both the N sources and loss, while land disturbance effects are primarily associated with the degree of N loss. We also conclude that subtropical forest soil δ¹⁵N is affected by the high rate of atmospheric N deposition. [ABSTRACT FROM AUTHOR]