复播大豆土壤微生物区系对麦-豆轮作体系周年施氮量的响应

Response of Soil Microbial Flora of Reseeding Soybean to Annual Nitrogen Application Rate Under Rotation of Wheat and Soybean

为了揭示周年施氮对复播大豆土壤微生物区系的后效及叠加效应,于2017—2019年采用裂区试验设计,在麦–豆周年轮作体系下,设置不同施氮组合(麦季施氮0、104、173、242 kg/hm^(2),分别标记为N0、N1、N2、N3;复播大豆施氮0、69、138 kg/hm^(2),分别标记为S0、S1、S2),探究豆茬土壤细菌、真菌和放线菌数量,土壤菌群结构和氮素生理群数量的变化规律。结果表明:前茬麦季施氮对复播大豆土壤微生物数量具有显著的后效;复播大豆不施氮条件下,麦季N2~N3施氮范围有利于增加豆茬土壤细菌、真菌、放线菌和氮素生理群数量。在冬小麦不施氮条件下,当季豆茬施氮较不施氮处理能显著增加土壤3大类微生物和氮素生理群数量,但豆茬施氮量较高反而显著降低氨化细菌和好气性自生固氮菌数量。麦季各施氮处理与豆茬S1处理组合下土壤3大类微生物数量,细菌与真菌比值(B/F)及放线菌与真菌比值(A/F),氨化细菌、固氮菌和硝化细菌数量基本均高于与S2处理组合,其中N1S1施氮组合下豆茬土壤放线菌数量、好气性自生固氮菌数量、B/F和A/F值达到最高,N2S1施氮组合下土壤细菌、真菌和氨化细菌数量基本达到顶峰,当季施氮或周年施氮量过高则增加了土壤反硝化细菌数量,显著降低B/F、A/F值,对土壤3大类群微生物及其他氮素生理群数量均产生不同程度的抑制作用。因此,前茬小麦和后茬大豆适量施氮是维持土壤优势菌群的重要措施,周年氮肥的优化施用要充分考虑前、后茬氮肥的叠加效应。在本研究条件下,麦季施氮104~173 kg/hm^(2)(N1~N2),大豆季增施氮肥69 kg/hm^(2)(S1)的周年施氮量组合有利于改善土壤微生物生存环境,良化土壤质量,对提高土壤肥力及维持农田生态环境具有重要的意义。

In order to reveal the after-effects and superimposed effects of annual nitrogen application rate on soil microbial flora of reseeding soybeans,a split-plot experiment was conducted in 2017—2019 under wheat soybean rotation,in which the annual nitrogen application included 0(N0),104(N1),173(N2)and 242(N3)kg/hm^(2) in wheat season,while 0(S0),69(S1),138(S2)kg/hm^(2) in reseeding soybean season,then the changes of the number of soil bacteria,fungi and actinomycetes,the structure of soil flora and the number of nitrogen physiological groups in soybean stubble were analyzed.The results show that nitrogen application in the wheat season has a significant after-effect on the number of soil microorganisms in reseeding soybean.Under the condition of no nitrogen application in reseeding soybean,the range of N2 to N3 nitrogen application in wheat season is beneficial to increase soil bacteria,fungi,actinomycetes and nitrogen physiological groups.Under the condition of no nitrogen application in wheat season,nitrogen application in soybean stubble significantly increases the number of three types of soil microorganisms and nitrogen physiological groups,but the higher nitrogen application in soybean stubble significantly reduces ammoniating bacteria and aerobic autogenous nitrogen-fixing bacteria.Nitrogen treatment in wheat season combined with S1 in soybean stubble increases the three types of soil microorganisms,B/F and A/F values,ammonifying bacteria,nitrogen-fixing bacteria and nitrifying bacteria compared with combined with S2,among of which,N1S1 is the highest in soil actinomycetes,aerobic autogenous nitrogen-fixing bacteria,B/F and A/F values,while N2S1 is near the highest in soil bacteria,fungi and ammonifying bacteria.Excessive annual nitrogen application increases soil denitrifying bacteria,significantly reduces B/F and A/F values,and inhibits three soil microorganisms and other nitrogen physiological groups to varying degrees.Therefore,proper amount of nitrogen application for wheat and subsequent soybeans is an important measure to maintain the dominant soil flora,the optimal application of annual nitrogen fertilizer should fully consider the superimposed effects of nitrogen fertilizer of the preceding and subsequent crops.Under the conditions of this study,the combination of 104-173 kg/hm^(2)(N1 to N2)nitrogen in wheat season and 69 kg/hm^(2)(S1)nitrogen fertilizer in soybean season is beneficial to soil microbial survival,soil fertility and quality,and ecological environment of farmland.