不同水旱轮作体系稻田土壤剖面N2O的分布特征

Distribution characteristics of soil profile nitrous oxide concentration in paddy fields with different rice-upland crop rotation systems

通过原位采集淹水和排水状态下土壤剖面4个层次的气体,研究氧化亚氮(N2O)在水旱轮作体系稻田土壤剖面中的动态分布特征.试验设置小麦-单季稻和油菜-双季稻两种轮作体系,包括施N和不施N两种施肥方式.结果表明:施用N肥极显著促进了土壤剖面N2O的产生(P<0.01),不同层次间N2O浓度相关性极显著(P<0.01),小麦、油菜生长期施N和无N处理下层30cm和50cm处N2O浓度均高于表层7cm和15cm处;早稻无N处理则为表层7cm和15cm处高于下层30cm和50cm处(P<0.05),其他水稻处理各层次间无显著差异.无N处理土壤N2O峰值出现在旱作向水稻的转变期,施N处理则出现在旱作第2次追肥后,季节转变期也有较高的N2O浓度.

To investigate the dynamic distribution patterns of nitrous oxide （N2O） in the soil profiles in paddy fields with different rice-upland crop rotation systems, a special soil gas collection device was adopted to monitor the dynamics of N2O at the soil depths 7, 15, 30, and 50 cm in the paddy fields under both flooding and drainage conditions. Two rotation systems were installed, i.e., wheat-single rice and oilseed rape-double rice, each with or without nitrogen （N） application. Comparing with the control, N application promoted the N2O production in the soil profiles significantly （P0.01）, and there existed significant correlations in the N2O concentration among the four soil depths during the whole observation period （P0.01）. In the growth seasons of winter wheat and oilseed rape under drainage condition and with or without N application, the N2O concentrations at the soil depths 30 cm and 50 cm were significantly higher than those at the soil depths 7 cm and 15 cm; whereas in the early rice growth season under flooding condition and without N application, the N2O concentrations at the soil depth 7 cm and 15 cm were significantly higher than those at the soil depths 30 cm and 50 cm （P0.05）. No significant differences were observed in the N2O concentrations at the test soil depths among the other rice cropping treatments. The soil N2O concentrations in the treatments without N application peaked in the transitional period from the upland crops cropping to rice planting, while those in the treatments with N application peaked right after the second topdressing N of upland crops. Relatively high soil N2O concentrations were observed at the transitional period from the upland crops cropping to rice planting.