硝化抑制剂类型和剂量对不同类型土壤硝化抑制作用机理的研究

氮肥配施硝化抑制剂是提高氮肥利用率、减少活性氮损失和降低环境代价风险的有效措施。为探讨不同硝化抑制剂类型和剂量对不同类型土壤硝化作用的机理,采用室内土壤培养试验,对3种硝化抑制剂[双氰胺（DCD）、3,4-二甲基吡唑磷酸盐（DMPP）和2-氯-6-（三氯甲基）吡啶（NP）]设置不同剂量,研究其对我国不同区域典型土壤（红壤、水稻土、潮土）硝化过程无机氮含量、土壤pH值及土壤表观硝化率变化特征的影响。结果表明,与单施硫酸铵处理相比,3种硝化抑制剂均能抑制水稻土和潮土中铵态氮向硝态氮的转化,且对潮土铵态氮向硝态氮转化抑制效果优于水稻土,而对红壤硝化作用的抑制效果均不明显,3种土壤pH值差异是影响硝化抑制剂作用效果的主因。此外,DCD和NP随着用量的增加,对水稻土和潮土的硝化抑制效果越明显,而DMPP对2种土壤硝化抑制作用无明显的剂量效应。在水稻土中,NP的抑制效果强于DMPP和DCD;在潮土中,DCD的抑制效果优于NP和DMPP,这可能是由于不同硝化抑制剂类型硝化抑制机理性的差异以及其自身特性的差异导致的。综上,针对特定土壤类型筛选适宜的硝化抑制剂类型和用量对农业优化氮肥管理、提高氮肥利用率...     

外源氮在中、低肥力红壤中的转化与去向研究

采用盆栽15N示踪技术,研究了外源化肥氮和有机氮在中、低肥力红壤中的转化过程及其在土壤团聚体中的分配特征。结果表明:无论是低肥力还是中等肥力红壤上,化肥与有机肥配施都能显著增加土壤硝态氮、微生物生物量碳、氮及酶活性,且显著提高氮肥在土壤中的残留率,减少氮肥损失。相同施氮条件下,小麦生育期内中等肥力红壤上微生物生物量碳、氮及硝态氮含量分别相当于低肥力土壤的1.8、1.3和2.0倍。中等肥力红壤上尿素的施入对小麦生育期土壤硝态氮无影响,而低肥力红壤上施用尿素使土壤硝态氮含量提高了5.7倍。施肥可以显著提高低肥力红壤上小麦的地上部吸氮量,相当于不施肥的2.1~3.3倍,但对于中等肥力红壤,不同施氮条件对小麦的地上部吸氮量无明显影响。施入有机肥可以显著增加土壤各粒级团聚体中外源氮的残留量,是单施化肥的2.1~5.0倍。与单施化肥氮相比,有机氮或与有机肥配施的化肥氮优先进入到大团聚体中,而外源氮在微团聚体和粉粘粒中的残留与分配并无明显差异。本研究说明有机肥或化肥与有机肥配施能有效降低氮肥的损失,提高氮肥在土壤中的保存,特别是对于中等肥力的土壤,有机肥的配合施用对于后季作物的生长具有重要意义。     

不同生物硝化抑制剂对红壤性水稻土N2O排放的影响及其机制

为揭示不同生物硝化抑制剂(BNIs)对红壤性水稻土N₂O排放的影响差异及作用机制,通过21 d的土柱淹水培养试验,比较了三种BNIs 1,9-癸二醇(1,9-D)、亚麻酸(LN)和3-(4-羟基苯基)丙酸甲酯(MHPP)与化学合成硝化抑制剂双氰胺(DCD)对土壤N₂O排放及相关硝化、反硝化功能基因的影响。结果表明:不同BNIs(1,9-D、LN、MHPP)可以显著平均降低土壤N₂O日排放峰值40.1%;1,9-D和MHPP可分别抑制N₂O排放总量44.5%和43.9%,而DCD和LN对N₂O排放总量没有显著影响。1,9-D和MHPP对AOA(氨氧化古菌)、AOB(氨氧化细菌)硝化菌和nirS、nirK型反硝化菌的调控均有所不同,1,9-D可以同时抑制AOA、AOB和nirS微生物的生长;MHPP仅可以抑制AOA的生长;其中,AOA-amoA和nirS基因丰度与土壤N₂O的排放呈显著正相关关系。同时,1,9-D和MHPP均增加了nosZ基因丰度及其与AOA-...     

采用15N同位素稀释法研究不同层次土壤氮素总转化速率

采用15N同位素稀释方法,开展短期(7天)室内培养实验,估算了一水稻土0~20、20~60和60~90 cm土层土壤主要N素转化过程的总转化速率,结果表明,标记N溶液加入后2 h内各土层土壤的总矿化、硝化、固定速率显著高于其他时间段(p<0.01)。2 h后,矿化速率在小范围内起伏。0~20 cm土层土壤N素的硝化速率随培养时间延长而降低,另外两层土壤则基本保持稳定,硝化速率的变化与硝化作用底物NH4+-N浓度的变化呈显著正相关。值得注意的是,外源无机N溶液加入后2 h内,大量NH4+-N和NO3--N被固定,并认为N素的非生物固定起主导作用。2 h后,出现了N素在固定与再矿化间反复转换的现象。实验结果表明,与净转化速率相比总转化速率能更好地描述单个N素转化过程,但由于外源N加入对N素转化的影响、再矿化作用以及忽略了N素转化过程中的气体损失、DNRA(硝态氮异化还原为铵)过程等,本研究结果与真实值间存在一定差异。     

不同利用方式红壤反硝化势和气态产物排放特征

采用厌氧培养-乙炔抑制法测定了4种不同利用方式红壤的反硝化势和气态产物N₂O和N₂的排放速率。结果表明，不同利用方式红壤反硝化势和N₂O和N₂的排放速率差异明显，土壤反硝化势强弱顺序依次为：竹林>茶园>林地>旱地。反硝化势与土壤有机碳(P<0.05)、厌氧培养期间土壤CO₂累积排放量(P<0.01)、nirS基因丰度( P<0.05)和nirK基因丰度(P<0.05) 呈显著正相关关系。逐步回归分析结果表明，CO₂累积排放量表征的易矿化碳是造成不同利用方式红壤反硝化势差异的主要原因，可以解释反硝化势变化的66%(P<0.01)。不同利用方式红壤N₂O和N₂排放速率差异明显，旱地红壤N₂O和N₂排放速率均最低，表明土壤pH的提升并没有增加旱地红壤的反硝化损失风险和N₂O排放速率。土壤易矿化有机碳含量也是影响不同利用方式红壤N₂O和N₂排放速率的主要因素。反硝化功能基因nirS、nirK和nosZ的丰度均与CO₂累积排放量呈显著正相关关系，进一步支持了土壤易矿化有机碳含量是影响不同利用方式红壤反硝化势和气态产物排放的主要因子。土壤pH是影响不同利用方式红壤反硝化气态产物N₂/N₂O的主要因素，但是pH影响红壤N₂/N₂O的微生物机制仍需要进一步研究。     

Effects of decreasing water potential on gross ammonification and nitrification in an acid coniferous forest soil

Changes in the soil water regime, predicted as a consequence of global climate change, might influence the N cycle in temperate forest soils. We investigated the effect of decreasing soil water potentials on gross ammonification and nitrification in different soil horizons of a Norway spruce forest and tested the hypotheses that i) gross rates are more sensitive to desiccation in the Oa and EA horizon as compared to the uppermost Oi/Oe horizon and ii) that gross nitrification is more sensitive than gross ammonification. Soil samples were adjusted by air drying to water potentials from about field capacity to around −1.0 MPa, a range that is often observed under field conditions at our site. Gross rates were measured using the ¹⁵N pool dilution technique. To ensure that the addition of solute label to dry soils and the local rewetting does not affect the results by re-mineralization or preferential consumption of ¹⁵N, we compared different extraction and incubation times.T₀ times ranging from 10 to 300 min and incubation times of 48 h and 72 h did not influence the rates of gross ammonification and nitrification. Even small changes of water potential decreased gross ammonification and nitrification in the O horizon. In the EA horizon, gross nitrification was below detection limit and the response of the generally low rates of gross ammonification to decreasing water potentials was minor. In the Oi/Oe horizon gross ammonification and nitrification decreased from 37.5 to 18.3 mg N kg⁻¹ soil d⁻¹ and from 15.4 to 5.6 mg N kg⁻¹ soil d⁻¹ when the water potential decreased from field capacity to −0.8 MPa. In the Oa horizon gross ammonification decreased from 7.4 to 4.0 mg N kg⁻¹ soil d⁻¹ when the water potential reached −0.6 MPa. At such water potential nitrification almost ceased, while in the Oi/Oe horizon nitrification continued at a rather high level. Hence, only in the Oa horizon nitrification was more sensitive to desiccation than ammonification. Extended drought periods that might result from climate change will cause a reduction in gross N turnover rates in forest soils even at moderate levels of soil desiccation.     

两种水稻土氮初级矿化和硝化速率及其与氮肥利用率的关系

摘　要 　高氮肥施用量和低氮肥利用率是我国水稻生产可持续性发展面临的问题之一。氮肥损失途径与肥料进入土壤后的转化过程息息相关。了解水稻土中氮素转化过程并进行定量描述有助于提高人们对稻田氮素损失途径的认识水平。为此,本研究开展了连续2年的大田实验,测定了稻麦轮作条件下江苏淮安碱性水稻土（潮黄土,pH=8.3）和宜兴中性水稻土（黄泥土,pH=6.2）作物氮肥利用效率;同时采用15N同位素稀释方法,开展室内好氧培养实验,估算了两种土壤中的氮素初级矿化和硝化速率,以此解释田间试验中氮肥利用率差异的原因。田间试验结果表明,在获得相似的水稻或小麦产量的情况下,淮安潮黄土氮肥需用量高于宜兴中性水稻土,而氮肥利用率却低于宜兴黄泥土。15N室内培养实验结果表明,供试潮黄土氮素初级矿化和硝化速率均较黄泥土高,其较高的pH可能是主要原因。 潮黄土中相对较高的初级矿化和硝化速率可能会导致更多的NO3--N 在土壤中短暂累积,不能被作物及时吸收利用的NO3--N 便可通过各种途径损失掉。这可能是造成两种稻田土壤田间氮肥利用率差异的原因之一。     

Maize straw is more effective than maize straw biochar at improving soil N availability and gross N transformation rate

Soil nitrogen (N) transformation is vital in determining farmland N availability. Although many studies have investigated the effect of biochar on N retention and loss via leaching and gaseous emissions, few have determined the dynamics of gross N transformation during crop growth in long-term biochar-amended soils and compared the effect of the biochar with that of its feedstock. In this study, we conducted a five-time field measurement of soil gross N turnover rates via ¹⁵N isotope pool dilution during maize growth in 2021. Three treatments were employed, including no amendment, biochar and straw applied annually at rates of 2.63 and 7.50 t ha⁻¹, respectively, since 2013. The results showed that biochar did not change the rate of gross N mineralisation when compared with no amendment, but straw increased it by 139% in August, resulting in significantly higher cumulative gross N mineralisation than biochar and no amendment (701 vs 489 and 499 mg kg⁻¹ in 200 d). The inconsistent influence was attributed to the fact that inherent biochar-N was recalcitrant and could not be mineralized like the straw. The gross nitrification rate was decreased by 72.9% and 77.4% by biochar and straw application, respectively, in June relative to no amendment, but then it increased from July to August in the straw treatment as a result of the elevated gross N mineralisation rate. The decreased nitrification in the biochar treatment was an outcome of the synergetic effect of a low ammonium pool (−59.4%) and a high gross ammonium immobilisation rate (+263%), which was likely due to excessive fertilizer N loss and abiotic adsorption to biochar. Meanwhile, biochar amendment inhibited bacterial 16S and fungal ITS genes, as well as ureC and bacterial and archaea-amoA gene copies. In conclusion, straw is more effective than biochar at improving soil N transformation and availability in the long term.     

Comparison of NH4 pool dilution techniques to measure gross N fluxes in a coarse textured soil

We compared gross N fluxes by ¹⁵N pool dilution in a coarse-textured agricultural soil when ¹⁵N was applied to the soil NH₄⁺ pool by either: (i) mixing a ¹⁵NH₄NO₃ solution into disturbed soil or (ii) injection of ¹⁵NH₃ gas into intact soil cores. The two techniques produced similar results for gross N mineralization rates indicating that NH₄⁺ production in soil was not altered by soil disturbance, method of application (gas vs. solution), or amount of N applied. This was not the case for immobilization rates, which were twofold higher when ¹⁵N label was applied to the soil NH₄⁺ pool with the mixing technique compared to the injection technique. This was attributed to the fact that more NH₄⁺ was applied with the mixing technique. Estimates of gross nitrification were accompanied by large error terms meaning differences between ¹⁵N labeling methods could not be accurately assessed for this process rate.     

Cold storage and laboratory incubation of intact soil cores do not reflect in-situ nitrogen cycling rates of tropical forest soils

Measurements of N transformation rates in tropical forest soils are commonly conducted in the laboratory from disturbed or intact soil cores. On four sites with Andisol soils under old-growth forests of Panama and Ecuador, we compared N transformation rates measured from laboratory incubation (at soil temperatures of the sites) of intact soil cores after a period of cold storage (at 5 °C) with measurements conducted in situ. Laboratory measurements from stored soil cores showed lower gross N mineralization and NH₄⁺ consumption rates and higher gross nitrification and NO₃⁻ immobilization rates than the in-situ measurements. We conclude that cold storage and laboratory incubation change the soils to such an extent that N cycling rates do not reflect field conditions. The only reliable way to measure N transformation rates of tropical forest soils is in-situ incubation and mineral N extraction in the field.     

三种硝化抑制剂在石灰性土壤中的应用效果比较

在人工气候室内采用25℃黑暗培养法研究双氰胺(DCD)、3,4-二甲基吡唑磷酸(DMPP)及2-氯-6-三氯甲基吡啶(Nitrapyrin)在石灰性土壤中的硝化抑制效果。结果表明:施用DCD、DMPP、Nitrapyrin的土壤NH4+-N含量较单施硫酸铵的土壤(对照)分别提高228.45~244.85 mg/kg(砂土)、209.75~254.79 mg/kg(黏土),NO3--N含量较对照分别降低93.85%~94.99%(砂土)、91.82%~95.38%(黏土)。表观硝化率随培养进程增加缓慢,培养期间只增加了1.28%~2.09%(砂土)、2.72%~8.40%(黏土),而对照增加了86.00%(砂土)、80.89%(黏土)。3种硝化抑制剂均显著抑制了石灰性土壤中硫酸铵水解铵硝化作用的进行,并且在砂土中的硝化抑制率高于黏土,硝化抑制效果最好的为DMPP处理,0.54%Nitrapyrin处理次之但用量最小,0.27%Nitrapyrin和10.8%DCD处理抑制效果相对较弱。     

夜间增温对免耕农田土壤氮矿化与硝化速率的影响

研究了农田土壤氮矿化速率和硝化速率对长期夜间增温和免耕的响应特征。试验设置4种处理:常温+翻耕(CK)、夜间增温+翻耕(W)、常温+免耕(NT)、夜间增温+免耕(WNT)。与对照相比,W处理下土壤中碱解氮和铵态氮明显增加,其中1~2月增幅分别为26%~28%和82%~133%,且土壤氮矿化速率和硝化速率均显著高于CK处理。NT处理下,土壤碱解氮和铵态氮的季节均值分别提高了15%和41%;土壤氮总矿化速率显著高于CK和W处理,硝化速率则显著低于CK和W处理。WNT处理下的土壤氮矿化速率显著高于NT处理,而硝化速率则显著低于CK和W处理,可见,在夜间增温条件下,采取免耕措施将有利于土壤有机氮的矿化过程,降低了土壤硝化速率,从而减小了土壤氮素损失的风险。     

红壤稻田不同生育期土壤氨氧化微生物群落结构

以福建省红壤稻田土壤为对象,通过提取土壤总DNA,利用特异引物进行PCR(聚合酶链反应)扩增和DGGE(变性梯度凝胶电泳)并结合DNA克隆测序,研究了水稻生长过程中稻田土壤氨氧化细菌和氨氧化古菌群落结构的变化。结果显示:稻田土壤具有丰富的氨氧化细菌和氨氧化古菌资源。水稻生长过程中土壤氨氧化细菌群落组成较为稳定,只表现出水稻生长前期(苗期、分蘖期)和中后期(孕穗期、成熟期)间存在一定差异。而土壤氨氧化古菌群落组成变化较大,在水稻生长的苗期、分蘖期、孕穗期和成熟期4个时期间均存在一定差异。在水稻生长过程中,土壤氨氧化细菌群落多样性指数无显著性变化,但氨氧化古菌群落多样性指数随水稻生长明显提高,孕穗期后才达到平稳。水稻生长前期土壤硝化势也具有显著上升趋势,孕穗期时达到最高,而后有所下降。土壤硝化势与氨氧化古菌群落多样性指数具有显著正相关性,与氨氧化细菌没有相关性。研究表明,氨氧化古菌对红壤稻田土壤硝化作用的影响程度较大,证实了氨氧化微生物尤其是氨氧化古菌在稻田土壤微生物组成及其生态系统功能中的重要性。