집약 농업 유역에서 토지이용 방식과 시비 관리에 따른 토양의 화학양론과 동위원소비 = Land-Use Types and Fertilization Management Affect Stoichiometric and Isotopic Ratios of Soils in an Intensive Agricultural Watershed

다국어 초록 (Multilingual Abstract)

Farmers’ fertilization management, particularly application of livestock manure and compost which are typically enriched with heavy isotopes of carbon (C) and nitrogen (N) as well as copper (Cu) and zinc (Zn), may change these chemical variables in agricultural soils. This study was conducted to investigate variations in the concentrations of C, N, Cu and Zn, and stable C (δ¹³C) and N (δ¹⁵N) isotope ratios of paddy, upland, and orchard soils that received different rate of manure and compost. Forest (pine and oak) soils were additionally included as background soils. The elemental and isotopic compositions of agricultural inputs (including synthetic fertilizer, rice straw, and livestock feed, manure, and compost) and forest litter layer were also analyzed. There was no systematic variation in soil C and N concentrations among different land-use types. However, the δ¹³C, δ¹⁵N, and the concentrations of Cu and Zn of agricultural soils were higher than those of forest soils, reflecting repeated manure and compost applications in agricultural soils. Among agricultural soils, orchard soils which received higher rates of manure and compost had higher δ¹³C (-24.2‰), δ15N (+10.6‰), and the concentrations of Cu (16.3 mg kg^-1) and Zn (61.7 mg kg^-1), compared to paddy (-28.0‰, +4. 9‰, 10.3 mg kg^-1, and 41.9 mg kg^-1 for δ¹³C, δ¹⁵N, and Cu and Zn concentrations, respectively) and upland soils (-25.4‰, +9.6‰, 11.8 mg kg^-1, and 41.7 mg kg^-1, respectively). Such differences in the isotopic and metal compositions among agricultural soils were also found for soil solutions extracted with K₂SO₄. Our study suggests that farmers’ fertilization management such as repeated application of livestock manure and compost may change δ¹³C, δ¹⁵N, and Cu and Zn concentrations of agricultural soils. However, the potential effects of other compounding factors that co-vary with land-use type such as parent materials and topography need to be further evaluated.