Soil N2O and CO2 Emissions from Red Soils Following Land Conversion in Subtropical China

Chinese forestlands and grasslands have undergone great changes in land use in recent decades for arresting soil erosion and degradation, but its impact on trace gas emissions has not well documented. The study was conducted in situ to assess the comprehensive effects of conversion cropland to forestlands, grasslands and agrofoestry systems on soil N₂O and CO₂ emissions under maize cultivation (June 2003-October 2003). In order to document the dynamics and importance of these emissions, soil carbon, nitrogen, nitrogen mineralization and microbial biomass C, soil potential for N₂O and CO₂ emissions and soil climatic data were measured. The total amount of soil N₂O emission through the growing season in summer maize field, which were slightly lower than the values of 390, 470, 512, 372 and 423 g N₂O-N ha^-1 in natural fallow, A.fruticosa, A.fruticosa+faba bean-maize, vetiver, vetiver+faba bean-maize plot, respectively. Equivalent values for CO₂ emissions were 3480, 1737, 2449, 5335, 2672 and 3309 kg CO₂-C ha^-1. The differences in N₂O and CO₂ emissions between different treatments resulted from the climatic conditions and some potential such as soil microbial biomass C, nitrogen mineralization and hedge species to a great extent. The results indicate that conversion from cropland to hedgerow agroforestry might potentially increase the release of soil CO₂ and N₂O; and conversion from cropland to forestland and/or grassland might potentially decrease the release of soil CO₂, whereas the opposite trend for the release of soil N₂O was observed. However, the responses to land conversion reported here need be verified in longer term experiments before they can be used to predict the effects of land conversion on the net soil N₂O and CO₂ balance.