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 (delta N-15) 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 delta N-15 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 delta N-15 (- 1.0 +/- 0.2 parts per thousand and + 3.1 +/- 0.2 parts per thousand for mineral and organic soil layers, respectively), reflecting the influence of the(15)N-depleted source N and the more closed nature of the N cycle. Tropical forest soil had higher delta N-15 than other climate zones, reflecting the influence of the high N availability and loss in tropical forests. The low delta N-15 in subtropical forest soils likely reflected the influence of the high rate of deposition of(15)N-depleted N. The delta N-15 of cropland (+ 5.0 +/- 0.2 parts per thousand) and grassland (+ 6.2 +/- 0.1 parts per thousand) soils was greater with manure than with synthetic fertilizer applications. Soil delta N-15 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 delta N-15 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 delta N-15 is affected by the high rate of atmospheric N deposition.