Main content area

Cropland age from grassland conversion to cropland affects nitrous oxide emissions

Jiao, Yan, JianHua, Hou, JiangHong, Zhao, WenZhu, Yang
Acta agriculturæ Scandinavica 2015 v.65 no.6 pp. 566-574
ammonium nitrogen, cropland, ecosystems, ecotones, emissions, grasslands, growing season, land use, nitrous oxide, soil water content, China
The effects of soil properties and cropland age on atmospheric nitrous oxide (N ₂O) emissions following the conversion of grassland to cropland in temperate grassland ecosystems are uncertain. In this study, N ₂O emissions were compared among grassland and cropland soils in the agro-pastoral ecotone of Inner Mongolia over three growing seasons. Four adjacent sites with different land-use histories were selected, including grassland and croplands cultivated for 5, 10, and 50 years after conversion. N ₂O flux measurements were obtained using a closed-chamber method and were performed continuously during vegetation periods. After the conversion of grassland to cropland, N ₂O emission initially decreased and thereafter increased in the study sites. The cumulative N ₂O emissions of the cropland soils 5 and 10 years in age were 10–50% less than those of the grassland, and the N ₂O emissions from the cropland soil 50 years in age were 10–30% greater than the grassland. When the seasonal emissions were correlated against single soil parameter, the key soil parameter that affected N ₂O emissions over the entire growing season was the soil moisture content. When the interactions among soil parameters were considered, the amount of N ₂O emissions could be quantitatively described by a linear combination of two soil variables, the soil ammonium nitrogen (NH ₄⁺-N) and moisture concentrations. This study demonstrates how the time of land use conversion from grassland to cropland can positively or negatively affect N ₂O emission.