CO₂ and N₂O emissions in the red soils of agro-forestry (grass) systems conversed from cropland in subtropical hilly region of China

Not much information exists on soil respiration and nitrous oxide emissions in soils under different terrestrial ecosystems in subtropical China. Field experiments were conducted in static chambers to investigate the effects of soil environmental conditions on CO₂ and N₂O fluxes from red soils under six different land use types. The investigated land use types included maize land, Amorpha fruticosa plantation, Vetiveria zizanioides plantation, A. fruticosa + maize and V. zizanioides + maize agro-forestry (grass) systems, and wasteland. Also variations in soil greenhouse gases, water, nitrogen, organic carbon, microbial biomass carbon and net nitrogen mineralization were determined. The results were as follows: 1) during maize growth season, CO₂ flux in wasteland was lower than that in A. fruticosa + maize agro-forestry system, sole maize, V. zizanioides + maize agro-grass system, A. fruticosa plantation and V. zizanioides plantation, in that order. However, no significant differences in CO₂ flux were noted among five land use types. 2) N₂O fluxes were 508 g·hm^-2·a^-1, 470 g·hm^-2·a^-1, 390 g·hm^-2·a^-1, 373 g·hm^-2·a^-1, 372 g·hm^-2·a^-1 and 285 g·hm^-2·a^-1 for A. fruticosa + maize agro-forestry system, A. fruticosa plantation, wasteland, V. zizanioides + maize agro-grass system, V. zizanioides plantation and sole maize, respectively. 3) No significant relationships existed between CO₂ fluxes and soil organic carbon, microbial biomass carbon or water content. Significant positive linear relationship was, however, observed between N₂O flux and soil mineralization. The study suggested that land conversion from cropland to agro-forestry potentially increased soil CO₂ and N₂O release. While land conversion from cropland to forestland and/or grassland potentially decreased soil CO₂ emission, it increased N₂O emission.