控释肥施用对土壤N_2O排放的影响——以华北平原冬小麦/夏玉米轮作系统为例

Effect of controlled-release fertilization on nitrous oxide emission: a case study of a wheat-maize rotation system in the North China Plain

控释肥作为一种能够提高肥料利用率、保障作物产量和节约劳动力的新型肥料已经在作物生产中得到广泛应用,而控释肥对土壤N_2O排放影响结果的差异使其成为当前科学评估控释肥施用环境效应的焦点问题之一。因此,旨在探讨不同种类控释肥及氮素水平施用对华北平原冬小麦/夏玉米轮作系统土壤N_2O排放的影响,为科学评价控释肥施用的环境效应及其推广应用提供科学依据。本研究监测采用静态暗箱—气相色谱法对不同控释肥施用下土壤N_2O排放、环境因素以及产量进行了周年监测,探讨了不同处理(对照处理(CK)、控释肥处理1(CRF1)、优化控释肥处理1(80%CRF1)、优化控释肥处理2(80%CRF2)和控释肥处理3(CRF3+尿素))下土壤N_2O排放特征及土壤温湿度对其的影响。结果表明:控释肥施用下冬小麦/夏玉米轮作系统中土壤N_2O排放峰高值主要出现在基肥施用并伴随灌溉(或降雨)后,一般持续时间约为7—10 d,小麦返青期灌溉以及玉米后期降雨会引起微弱的N_2O排放峰。不同处理土壤N_2O排放通量变化范围为^(-2)35.61—2625.01μg N_2O m^(-2)h^(-1),平均排放通量为23.88—51.39μg N_2O m^(-2)h^(-1),与CRFI相比,80%CRF1和80%CRF2处理能够减小施肥期的N_2O排放峰值,但不改变轮作周期土壤N_2O排放季节变化规律。CK处理和CRF3+尿素处理土壤N_2O排放通量与5 cm深度土壤温度之间表现出显著的正相关性(r^2=0.38,P<0.01;r^2=0.30,P<0.05);CRF1处理和80%CRF1处理在冬小麦生长季及整个轮作周期内与土壤孔隙含水率(WFPS)表现为显著的正相关关系(冬小麦生长季分别为r^2=0.50,P<0.01;r^2=0.39,P<0.05;整个轮作周期分别为r^2=0.39,P<0.05;r^2=0.43,P<0.05)。80%CRF2处理N_2O年排放总量最高,为(2.89±0.24)kg N/hm^2。相同控释肥种类条件下,80%CRF1处理比CRF1处理减少了14.23%,但并未达到显著水平;相同施氮量水平下,CRF1处理与(CRF3+尿素)处理之间N_2O年排放总量差异不显著,而80%CRF1处理比80%CRF2处理N_2O年排放总量减少16.16%,并达到显著水平(P<0.05)。本研究不同处理之间N_2O直接排放系数在0.29%—0.42%之间,均明显低于IPCC 1.0%的默认值。各控释肥处理产量与当地农民常规施肥量条件下产量没有显著性差异。因此在华北地区冬小麦/夏玉米轮作系统中应用控释肥技术可以在保证产量的前提下有效减少土壤N_2O排放,并且仍存在一定的减排空间。

Nitrous oxide （N2O） plays an important role in global wanning. N2O is long-lived and cause harm to the stratospheric ozone. The concentration of N2O has increased from 270 ppbv during the preindustrial period to 319 ppbv in 2005. The greenhouse effect of N2O is 296 to 310-fold higher than that of carbon dioxide, although its contribution is only 5% （2.6 Tg） of the total annual man-made greenhouse gas emissions in 2010. Use of fertilizer is a major factor in the increase in N2O levels in agricultural systems. The wheat-maize rotation system is one of the most popular cultivating systems in the North China Plain. In recent years, a new method of fertilization （controlled-release fertilization ） has been introduced in this region to reduce N fertilizer losses and to save labor inputs ; this has mainly been used in crop lands, such as paddy fields, wheat and maize growing systems, but also in vegetable fields, such as tomato fields. The reported results mostly focus on crop growing and nitrogen leaching, but rarely on the N2O emissions characteristics related to controlled- release fertilizers in wheat-maize rotation systems, and even more rarely on exact quantities of various controlled-release fertilizers being applied in the North China Plain. This study was conducted from October 2013 to October 2014, with the major focus on the effects of application of controlled-release fertilizers on nitrous oxide and crop yields. The N2O emission driving factors, such as the soil temperature, soil moisture, and the content of soil NO3^--N, were also analyzed together with N2O fluxes. Five treatments were included in this study： control treatment （CK）, controlled-release fertilization treatment 1 （CRF1）, optimized controlled-release fertilization treatment 1 （80% CRF1 ）, optimized controlled-release fertilization treatment 2 （80% CRF2）, and controlled-release fertilization treatment 3 （CRF3 ＋Urea）. The results show that the high N2O peaks usually following the basal fertilization can be attributed to irrigation or precipitation, litigation during the period of wheat seeding establishment, and precipitation during the later period of maize cultivation may also result in weak N2O peaks. The N2O fluxes changed from -235.61 μg N2O m-2 h-1 to 2625.01 μg N20 m-2 h-1, and daily mean N2O fluxes ranged from 23.88 μg N20 m-2 h-1 to 51.39 μg N20 m-2 h-1. N2O fluxes were positively correlated to soil temperature at a depth of 5 cm for CK and CRF3＋Urea; the correlation coefficient （r2） was 0.38 and 0.30, respectively. N20 fluxes were positively correlated to soil water filled pore space （WFPS） during wheat and whole rotation system for CRF1 and 80% CRF1 （for wheat： r2= 0.50, P〈0.01; r2= 0.39, P〈0.05; for whole system： r2= 0.39, P〈0.05; r2= 0.43, P〈0.05）. For the same fertilizer type, compared to CRF1 treatment, 80%CRF1 reduced the annual N2O emission by 14.23%. For the same fertilizer rate, there was no significant difference between CRF1 and CRF3＋Urea, but 80%CRF1 significantly reduced the annual N2O emission by 16.16% compared to 80%CRF2 （P〈0.05）. There was no significant difference in crop yields between these treatments and the treatments practiced by farmers. In conclusion, controlled-release fertilizer management could reduce N2O emission from the wheat-maize rotation system while maintaining cropping yields.