Long-term soil organic carbon and nitrogen dynamics in forage-based crop rotations in Northern Sweden (63–64°N)

Abstract

For carbon sequestration estimates it is necessary to evaluate effects of management practices on soil organic carbon (SOC) and nitrogen (SON) dynamics in a wide range of production systems and climatic zones. At higher latitudes with cold temperate climate, crop rotations dominated by forage are common and often highly productive—and the climate as well as the forage cropping systems favour large stocks of SOC and SON. The objective of this study was to estimate SOC and SON stock dynamics in the arable layer (0–25 cm) for different 6-year forage-based rotations using sampling data from three long-term field experiments in Northern Sweden. At the site with the lowest initial amount of SOC (8.2 kg C m −2), SOC stocks increased by 12 g C m −2 yr −1 over a 50-year period for the continuous forage rotation (‘A’), which received ca. 10 Mg ha −1 of cattle manure per year (wet mass). At the same site, SOC stocks were more or less at steady state in rotation ‘B’ with 4 years of forage and 2 years of annuals, receiving the same amount of manure. For rotation ‘C’ with 3 years of forage and receiving ca. 6.5 Mg ha −1 of manure, the SOC stocks decreased by 18 g C m −2 yr −1, while the SOC stocks for rotation ‘D’ with only annuals and no manure application decreased by 24 g C m −2 yr −1. At the other two sites, with higher initial SOC stocks (12.1 and 12.8 kg C m −2), the SOC stocks in all treatments decreased during a 30-year period, at a rate ranging from 11 to 95 g C m −2 yr −1. Similar trends were found for the change in SON stocks, although they were more variable. The topsoil SOC stocks were high compared to southern Sweden and regions of similar climate in northeast Canada, in particular for rotation A. These results indicate that the estimates of SOC and SON storage rate changes for a particular management system van vary widely within a small region of a given climatic zone.