Land use types with different fertilization management affected isotope ratios of bulk and water-extractable C and N of soils in an intensive agricultural area.

Purpose: This study was conducted to investigate variations in the stable isotope ratios of carbon (δ¹³C) and nitrogen (δ¹⁵N) of agricultural soils under different land uses (i.e., paddy, upland, and orchard) that subjected to different fertilization management (i.e., ¹⁵ N-depleted synthetic fertilizer and ¹³C- and ¹⁵ N-enriched livestock manure and compost application). Materials and methods: Soil samples were collected from paddy, upland, and orchard fields in an intensive agricultural area, and forest (pine and oak) soils were additionally included as background soils. The C and N concentrations and isotope ratios of both bulk and water-extractable soil fractions were analyzed. Results and discussion: The δ¹³C and δ¹⁵N of agricultural soils were higher than those of forest soils, reflecting repeated manure and compost applications (for both δ¹³C and δ¹⁵N) and higher N loss (for δ¹⁵N) in agricultural soils. Among agricultural soils, orchard (− 24.2‰ for δ¹³C and + 10.6‰ for δ¹⁵N) and upland (− 25.4‰ and + 9.6‰, respectively) soils which received higher rates of manure and compost were more enriched with ¹³C and ¹⁵N compared with paddy (− 28.0‰ and + 4.9‰, respectively). Such differences in the isotopic compositions among agricultural soils were also found for water-extractable soil fractions. Conclusions: Our study suggests that δ¹³C and δ¹⁵N of agricultural soils are affected by land use types with different fertilization management, particularly application of ¹³C- and ¹⁵ N-enriched livestock manure and compost. The δ¹³C and δ¹⁵N could be used as chemical indicators to evaluate the effects of the application of manure and compost on soil C and N dynamics. [ABSTRACT FROM AUTHOR]