黄河上游灌区连作稻田N2O排放特征及影响因素

黄河上游灌区高产连作稻田氮肥的过量施用引起土壤氮素盈余,进而导致稻田N2O排放量增大.为了探明水稻连作模式下稻田N2O排放特征及影响因素,采用静态箱-气相色谱法,开展了为期2年的连作水稻田试验研究.试验共设置3个施氮处理,包括常规氮肥300kg.hm-2(N300)、优化氮肥240kg.hm-2(N240)和对照不施氮肥(N0),并在稻田连作的第2年,对N240处理灌溉节水30%.2年连作试验结果表明,水稻生长季稻田N2O排放主要发生在水稻施基肥后及水稻生长的中后期,在稻田灌水泡田后N2O排放速率达最大值.稻田高氮肥(300kg.hm-2)施用显著增加N2O的排放量,优化氮肥(240kg.hm-2)处理可有效降低土壤N2O排放量(p<0.01).水稻生长季稻田淹水状态时N2O排放量极低,稻田灌溉节水会相应增加土壤N2O排放量.土壤温度变化对稻田N2O的生成和排放会产生较大影响,但受稻田肥水管理等因素的影响,温度与N2O排放量相关性不显著.灌区稻田土壤N2O排放通量与田面水NO3--N含量变化及耕层0～40cm土壤NO3--N积累量变化有显著的相关性.稻田连作显著增加了耕层土壤剖面0～40cm土层NO3--N的积累量,耕层土壤NO3--N积累量的增加进而加大了土壤N2O排放的风险.在宁夏黄灌区稻田常规灌水和高氮肥(300kg.hm-2)水平下,2年连作稻田水稻生长季土壤N2O总排放量分别达55.98×104kg.a-1和51.48×104kg.a-1,在100a时间尺度上的全球增温潜势(GWPs)均值为16.02×107kg.hm-2(以CO2计),表明黄灌上游灌区高氮肥施用导致稻田N2O排放量增大,由此引起的增温潜势严重.

Characteristics and factors of the N2O emission from the continuous cropping paddyfield in irrigation area of the Yellow River

Some nitrogen oxides in the atmosphere are increasing year by year due to the overuse or misuse of fertilizers in the upstream of the Yellow River. Field experiments were carried out in a continuous cropping paddyfield in the Ningxia Hui Autonomous Region in northwestern China. The static chamber-gas chromatograph method was used to measure the N₂O emission from the paddyfield of the irrigation area in the Yellow River. Three field N treatments were conducted, including the conventional N application rate of 300 kg·hm^-2 (N300), the optimized N application rate of 240 kg·hm^-2 (N240) and no N fertilizer application plot (N0). The results showed that N₂O emissions mainly occurred after the application of basal fertilizer or at the mid-to-late stages of rice growth. More N₂O emissions were measured before rice planting and irrigation, and the N₂O emission rate reached its maximum at 2~3 d after irrigation during the rice growing stage. The key factors affecting N₂O emissions from the continuous rice-cropping field were N application rate, water-saving treatment, soil temperature and soil NO₃^--N content. Excessive application of N fertilizers in the irrigated paddyfield will significantly increase N₂O emissions. However, optimization of N application can reduce N₂O emissions from the paddy soil during the rice growing season (p<0.01). With the continuous yearly rice planting, the conventional high-level N fertilizer application significantly increased nitrate accumulation in 0~40 cm layer topsoil, and increased N₂O emissions from the paddy soil. Based on statistical data, with the conventional irrigation practice and high nitrogen fertilizer of 300kg·hm^-2, the total amount of N₂O emissions from the paddyfields reached at 55.98×10⁴ kg·a^-1 in 2009 and 51.48×10⁴ kg·a^-1 in 2010 during the whole rice growing season. In the scales of 100a, the global warming potential (GWPs) was 16.02×10⁷ kg·hm^-2 in the irrigation area of Yellow River. Compared with N300 treatment, the cumulative N₂O emissions in N240 treatments decreased by 11.16×10⁴ kg·a^-1. In the scales 100a, GWPs caused by N₂O emissions in the paddy field decreased 3.30×10⁷ kg CO₂·hm^-2, indicating GWPs of N₂O emissions from the paddy field was immense in the Yellow River irrigation area.