秸秆还田对关中地区麦玉轮作田N_(2)O排放的短期效应

Short-term effects of straw return on N_(2)O emissions from wheat and maize rotation fields in Guanzhong area

【目的】分析环境因子和土壤N_(2)O排放对短期秸秆还田的响应,以更准确地评价化肥施用下短期秸秆还田的增减排效益。【方法】于2020—2021年在关中地区开展了小麦–玉米轮作田间试验。采取双因素裂区设计,主处理为秸秆还田(W1)与不还田(W0),副处理为不施肥(W1、W0)、施氮肥(W1N、W0N)和施氮磷肥(W1NP、W0NP)。测定了土壤含水量、温度、NO_(3)^(-)-N、NH_(4)^(+)-N、速效磷含量及N_(2)O排放通量,调查了作物产量,并探讨了土壤N_(2)O排放与环境因子之间的关系。【结果】相比W0,W1处理土壤含水量提高了1.1%~16.2%;W1N处理的土壤NO_(3)^(-)-N含量峰值较W0N高17.6%~30.5%。4个施肥处理的土壤NO_(3)^(-)-N和NH_(4)^(+)-N含量随生育时期推进先迅速上升,然后缓慢下降,施氮肥处理的土壤NO_(3)^(-)-N峰值比施氮磷肥处理高17.0%~20.8%。W1NP与W0NP处理土壤的速效磷含量随生育期推进先上升后缓慢下降,平均速效磷含量显著高于处理W0、W1、W0N和W1N(P<0.05)。冬小麦季和夏玉米季分别在施肥后第6和第12天土壤N_(2)O排放通量达到峰值。W1N、W1NP的土壤N_(2)O排放峰值分别比W0N、W0NP高5.0%和38.5%,全年累计排放量分别比W0N、W0NP高291.13和379.99 g/hm^(2)(P<0.05);W1N处理的土壤N_(2)O全年累计排放量比W1NP处理高298.14 g/hm^(2),W0N处理的土壤N_(2)O全年累计排放量比W0NP高386.99 g/hm^(2),施氮磷肥处理的排放峰值比施氮肥处理低2.43%~54.67%。相关性分析发现,N_(2)O排放通量与土壤温度、含水量、NO_(3)^(-)-N、NH_(4)^(+)-N、速效磷含量呈极显著正相关(P<0.01)。各处理N_(2)O排放强度表现为:相同秸秆还田条件下,施氮肥>施氮磷肥>不施肥处理;相同施肥条件下,秸秆还田>不还田处理。【结论】不论是否秸秆还田,氮磷肥配施均提高了土壤速效磷含量,降低了NO_(3)^(-)-N峰值,因而降低了N_(2)O年累积排放量。秸秆还田后短期内虽然也提高了土壤速效磷含量,但其较高的土壤含水量和NO_(3)^(-)-N含量导致更高的N_(2)O排放通量和农田N_(2)O累计排放量。因此,评价秸秆还田在农业可持续发展中的生态与生产效益时,也应考虑其还田后短期存在的不利影响。

【Objectives】The responses of environmental factors and soil N_(2)O emissions to short-term straw return were analyzed for more accurate evaluation of the benefits of short-term straw return in terms of N_(2)O emissions under fertilization.【Methods】A field trial was conducted in Guanzhong area,Shaanxi Province,from 2020 to 2021.The cropping system was winter wheat and summer maize rotation.A two-factor split-zone design was adopted,with the main factor of straw return(W1)and no return(W0),and the sub-factor of fertilization,composing 6 treatments,as:no fertilizer(W1,W0),nitrogen fertilizer(W1N,W0N)and nitrogen and phosphorus fertilizer(W1NP,W0NP).Soil water content,temperature,NO3−-N,NH4+-N,and available P content,N_(2)O emission fluxes were measured,crop yields were investigated,and the relationships between soil N_(2)O emissions and environmental factors were explored.【Results】The soil water content in W1 treatment was 1.1%-16.3% higher than in W0,and the peak soil NO_(3)^(-)-N content in W1N treatment was 17.6%-30.5% higher than in W0N.The soil NO_(3)^(-)-N and NH_(4)^(+)-N contents of two N and two NP treatments first increased rapidly and then decreased slowly as the growth period progressed,and the peak soil NO_(3)^(-)-N of N treatments was 17.0%-20.8% higher than that of NP treatment.The soil available P content in NP treatments increased rapidly and then decreased slowly as the growth period progressed,and significantly higher than those in no fertilizer and N treatments on average.The soil N_(2)O emission fluxes arrived peaks at 6 days and 12 days after fertilization in winter wheat and summer maize seasons,respectively.Compared with W0N and W0NP,W1N and W1NP increased the peak soil N_(2)O emissions by 5.0%and 38.5%,and the annually cumulative N_(2)O emissions by 291.13 g/hm^(2) and 379.99 g/hm^(2),respectively(P<0.05).The cumulative annual soil N_(2)O emission in treatment W1N was 298.14 g/hm^(2) higher than in W1NP(P<0.05).W1NP decreased 2.43%and 298.14 g/hm^(2) of the peak and cumulative annual N_(2)O emission,compare to W1N,while W0NP decreased 54.67% and 386.99 g/hm^(2) of peak and cumulative annual N_(2)O emission,compared to W0N.Correlation analysis revealed that N_(2)O emission fluxes were positively correlated with soil temperature and water content in maze season,and NO_(3)^(-)-N,NH_(4)^(+)-N,and available P contents in both maize and wheat seasons(P<0.01).Under the same straw return condition,the N_(2)O emission intensity showed descent order of N fertilization,NP application,and no fertilization.Under the same fertilization,the N_(2)O emission intensity with straw return was higher than without straw return【Conclusions】Whether straw was returned to the field or not,the combined N and P application was more effective in reducing cumulative N_(2)O emissions than N fertilizer alone,as the increased soil available P content and lower soil NO_(3)^(-)-N peak content.Although straw returning to the field also increased the soil available phosphorus content in the short term,its higher soil moisture content and NO_(3)^(-)-N content led to higher N_(2)O emission flux and cumulative N_(2)O emissions from farmland.This short term adverse ecological impact should be considered in the evaluation of straw return.