控制灌溉下秸秆还田对稻田土壤氮素组成的影响

Effects of Straw Returning on Nitrogen Composition in Paddy Soil under Controlled Irrigation

为探明控制灌溉模式下秸秆还田与不同施氮量对稻田表层土壤氮素组成的影响,以黑龙江省寒地黑土为研究对象,于2017—2018年进行了田间连续定位试验,试验秸秆还田量设置为有秸秆还田(还田量为6 t/hm^2)和无秸秆还田2个水平,全生育期施氮量设置N0(0 kg/hm^2)、N1(85 kg/hm^2)、N2(110 kg/hm^2)和N3(135 kg/hm^2)4个水平,共8个处理。基于氮稳定性同位素技术,分析了秸秆还田后,稻田土壤表层总可溶性氮组分分配比例,铵态氮(NH4^+-N)、硝态氮(NO3^--N)、可溶性有机氮(SON)、δ15 N含量变化以及与土壤表层总可溶性氮含量的相关性。2年结果表明:控制灌溉模式下,秸秆还田提高了土壤表层可溶性有机氮占总可溶性氮的比例、氮矿化量以及δ15 N含量。施加秸秆各施氮量处理土壤表层SON含量均低于无秸秆处理,其中N3处理土壤表层NH4^+-N与NO3^--N含量较无秸秆N3处理分别降低40.3%、38.7%。与无秸秆处理相比,秸秆还田不仅提高了土壤供氮能力,而且促进了土壤表层总可溶性氮以较稳定的可溶性有机氮形态存在,当施氮量仅为0 kg/hm^2时,土壤表层氮矿化量与无秸秆处理最高氮矿化量无显著性差异,且随着施氮量的增加,土壤表层氮矿化量显著高于无秸秆处理(P<0.05)。秸秆中δ15 N含量高,促使土壤表层富集δ15 N,施加秸秆N1、N2处理土壤表层δ15 N含量与无秸秆N2、N3处理无显著性差异,N3处理土壤表层δ15 N含量显著高于无秸秆处理(P<0.05),而且连续2年秸秆还田,导致土壤表层总可溶性氮与铵态氮(NH4^+-N)、硝态氮(NO3^--N)、可溶性有机氮(SON)以及δ15 N的相关性发生变化。研究结果可为东北地区推行秸秆还田的可行性提供科学依据,对保障东北地区农业水土资源可持续利用具有重要意义。

A continuous in situ field experiment from 2017 to 2018 in the cold and black soil region of Heilongjiang Province was carried out to explore the effect of straw returning and different N application rates in successive years on nitrogen composition in surface soil of paddy field under controlled irrigation mode.Two straw returning levels:6 t/hm^2 and 0 t/hm ^2,and four N application rates:N0(0 kg/hm^2),N1(85 kg/hm^2),N2(110 kg/hm^2)and N3(135 kg/hm^2)were set,a total of eight treatments.The changes of ammonium nitrogen(NH4^+ -N),nitrate nitrogen(NO3^- -N),soluble organic nitrogen(SON),δ15 N content and total soluble nitrogen distribution ratio in paddy soil surface after straw returning were analyzed based on nitrogen stable isotope technique.The results of 2-year experiment showed that under controlled irrigation condition,straw returning increased the ratio of SON to total soluble N,N mineralization and the content ofδ15 N in soil surface layer.The SON content in the surface soil layer of treatments with straw was lower than those without straw at different N application rates.Among all the treatments,the NH4^+ -N and NO3^- -N contents in the surface soil of N3 treatments were decreased by 40.3%and 38.7%compared with those treatments without straw at the same N application rate.Straw returning promoted the existence of total soluble nitrogen in the soil surface in a more stable form of SON.Straw returning improved soil nitrogen supply capacity compared with treatments without straw returning,there was no significant difference in N mineralization in the surface soil between N0 with straw and maximum N mineralization of the treatment without straw(P>0.05).With the increase of N application,the N mineralization in the surface layer of soil treated with straw returning was significantly higher than that without straw(P<0.05).The high content ofδ15 N in straw promoted the enrichment ofδ15 N in soil surface.There was no significant difference in the content of soil surfaceδ15 N between the treatments of N1 and N2 with straw and treatments of N2 and N3 without straw.The content of soil surfaceδ15 N of the treatment with straw was significantly higher than that without straw(P<0.05).Moreover,the correlation between total soluble nitrogen and NH4^+ -N,NO3^- -N,SON andδ15 N in the soil surface was changed after two years of straw returning.The results of this study can provide scientific basis for the feasibility of straw returning in Northeast China,which had important significance for ensuring the sustainable utilization of agricultural water and soil resources in Northeast China.