紫色土菜地生态系统土壤N_2O排放及其主要影响因素

N_2O emissions from vegetable farmland with purple soil and the main factors influencing these emissions

应用静态箱/气相色谱法对种菜历史超过20a的紫色土菜地进行了1a N2O排放的定位观测,分析了菜地N2O排放特征及施氮、土壤温度、土壤湿度和蔬菜参与对N2O排放的影响.结果表明,紫色土菜地生态系统在不施氮和施氮(N150kg/hm2)情况下N2O平均排放通量为(50.7±13.3)和(168.4±37.3)μg.m-.2h-1,N2O排放系数为1.86%.菜地生态系统N2O排放强度高于当地粮食作物农田,其主要原因在于菜地较高的养分水平和频繁的施肥、浇水等田间管理措施.从菜地N2O排放总量的季节分配来看,有64%的N2O排放量来自于土壤水热条件较好的夏秋季蔬菜生长期,冬春季蔬菜生长期N2O排放量较少,仅占34%.因此,土壤水热条件不同是造成菜地N2O排放量季节分配差异的重要原因.氮肥对增加N2O排放的效应因蔬菜生育期内单位时间施肥强度不同而异,蔬菜生育期越短,施氮对增加N2O排放的效应越明显.不施氮和常规施氮菜地N2O排放通量与地下5cm处土壤温度呈显著的正相关,但不种蔬菜的空地两者之间的关系不显著,并且常规施氮菜地土壤温度(T)对N2O排放通量(F)的影响可用指数方程F=11.465e0.032 T(R=0.26,P<0.01)表示.土壤湿度对菜地N2O排放的影响存在阈值效应,当土壤含水空隙率(WFPS)介于60%—75%时更易引发N2O高排放.因此,依据蔬菜生育期特点,结合土壤水分状况调节施肥量与施肥时间可能会减少菜地N2O排放.

Static chambers coupled with GC methods were used to perform in situ monitoring of N_2O emissions from vegetable fields during the period from October 2006, to October 2007. The monitoring was conducted in vegetable fields with purple soils with a history of vegetable planting for more than 20 years in the hill region of Middle Sichuan Basin, China. Characteristics of N_2O emissions from the vegetable ecosystem were analyzed, and the effects of the factors influencing these emissions, such as nitrogen （N） application, soil temperature, soil moisture and vegetable planting, are discussed. The results of the analysis showed that the mean emission fluxes of N_2O in CK （no N applied） and conventional fertilization treatment （ N application at rate of 150 kg N/hm2 ） were （ 50.7 _＋ 13.3 ） and （ 168.4_＋ 37.3 ） , respectively. The N_2O emission coefficient derived from N fertilizer application at 150 kg N_2Owas 1.86%. The N_2Oemission rate from the vegetable field observed in this study was higher than the emission rate from the grain farmland reported previously. The increase in N_2O emissions from the vegetable ecosystem was associated with enhanced soil nutrients, frequent fertilization and irrigation practices. The seasonal pattern of N_2O emissions showed that 34% of the annual flux of N_2O emissions occurred in the winter and spring and that 64% occurred in the summer and autumn due to more favorable soil moisture and temperatures in summer and autumn. The seasonal differences in N_2O emissions from vegetable fields were attributed to the variations in soil moisture and temperature due to vegetable planting. The application of N stimulated N_2O emissions in the vegetable field. There is a significant positive relationship between theN_2O emission flux and the soil temperature. An exponential equation （F= 11. 465e^0.032（R = 0.26, P〈0.01 ）） can be employed to quantify the relationship between soil temperature （T） and N20 emission flux （F） in a vegetable field treated by conventional fertilization. A threshold range of waterfilled pore space （WFPS） between 60%-75% has been observed for N_2Oemissions in this study. The N_2O emissions from vegetable farmland can be reduced by optimizing the N application rate and time while limiting irrigation frequencies according to vegetable growth and antecedent soil moisture conditions.