, Volume 2, Issue 4, pp 345-357

Carbon and nitrogen turnover in adjacent grassland and cropland ecosystems

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The effects of cultivation and soil texture on net and gross N mineralization, CO2 evolution and C and N turnover were investigated using paired grassland and cropped sites on soils of three textures. Gross N mineralization and immobilization were measured using15N-isotope dilution. Grassland soils had high CO2 evolution and gross N mineralization rates, and low net N mineralization rates. Cropland soils had low CO2 evolution rates but had high net and gross N mineralization rates. Grassland soils thus had high immobilization rates and cropland soils had low immobilization rates. Cultivation increased N turnover but reduced C turnover. The data suggest that the microflora in grassland soils are N limited, while those of cropland soils are limited by C availability. Increasing clay content reduced N turnover. C turnover was less clearly related to texture. Differences in the immobilization potential of substrates help explain why agricultural soils have higher N losses than do grassland soils.