无机氮与蔬菜废弃物耦合对土壤氮矿化的影响

为探明有机废弃物添加量与不同无机氮水平耦合对土壤氮矿化的影响,设计了3个甘蓝废弃叶添加量[B1:200 g.kg 1(土),B2:400 g.kg 1(土),B3:550 g.kg 1(土)]和4个无机氮水平[N0:0 mg.kg 1(土),N1:25mg.kg 1(土),N2:50 mg.kg 1(土),N3:100 mg.kg 1(土)]交互的控制培养试验(25℃,65%的田间持水量)。试验结果显示:各氮处理下土壤净累积氮矿化量是空白对照的4～5倍,N1水平下土壤净累积氮矿化量显著高于其他氮水平。各甘蓝废弃叶添加量处理下土壤净累积氮矿化量是空白对照的3～5倍,且B2添加量下土壤净累积氮矿化量显著高于B1和B3。统计分析表明,氮处理和甘蓝废弃叶添加量之间的交互效应不显著(P=0.275),甘蓝废弃叶的添加是影响氮矿化的主要因素(Eta2=0.16),而供氮水平为次要因素(Eta2=0.07)。B1添加量下,培养前期(0～20 d)土壤净累积矿化量逐渐升高,后期保持稳定水平;但B2和B3添加量下,培养前期(30 d)土壤呈现矿化、固持、再矿化现象,后期土壤净累积矿化量逐渐升高。氮矿化速率结果说明,甘蓝废弃叶添加后氮素矿化主要发生在培养前30 d。对培养期间土壤净累积氮矿化量随时间变化做一级动力方程模拟,拟合效果良好(R2=0.62～0.89)。     

祁连山东段青海云杉林区土壤氮矿化与土壤因子的相关性

以祁连山东段青海云杉(Picea crassifolia)林分布带土壤为研究对象,采用顶盖埋管的野外取样法和室内分析法,对海拔梯度上土壤铵态氮(NH+4-N)、硝态氮(NO-3-N)净矿化速率、氮净矿化量和净矿化速率进行测定分析,旨在探讨土壤净氮矿化量与气温降水和土壤理化性质的相关关系,以期建立环境变量与土壤氮矿化量和矿化速率模型,进而提高祁连山青海云杉林生产力及水源涵养能力。其结果表明:(1)土壤硝态氮、铵态氮净矿化速率、土壤净氮矿化量和矿化速率随海拔的升高差异性均极显著;土壤氮净矿化量和矿化速率随海拔梯度的升高呈"W"形变化,与硝态氮净矿化速率随海拔升高的变化规律一致,与铵态氮净矿化速率变化规律相反;在海拔2 800m处,硝态氮净矿化速率、土壤净氮矿化量和矿化速率均达到最大值,为0.372,160.3,0.44 mg/(kg·d),铵态氮净矿化速率出现最低值0.067 mg/(kg·d);在海拔2 900m处出现最低值,为0.155,94.7,0.26mg/(kg·d),在海拔3 100m处,铵态氮的净矿化速率出现最大值0.13mg/(kg·d);(2)回归分析表明,土壤净氮矿化量与年均气温呈极显著负相关(P0.01),R2=0.717 3;与年降水量呈极显著正相关(P0.01),R2=0.383 5;得出气候变化对土壤净氮矿化量的影响程度为:年均气温年降水量;(3)回归分析表明,土壤氮净矿化量与土壤全氮、有机质、含水量、pH值呈极显著正相关(P0.01),其R2依次为0.910 1,0.906 0,0.842 8,0.797 9;与土壤容重呈极显著负相关(P0.01),其R2为0.222 4;由R2值大小可知土壤养分对土壤净氮矿化量的影响程度为:土壤全氮土壤有机质土壤含水量土壤pH土壤容重。     

长期施肥条件下水稻土有机氮组分及矿化特性研究

为探明长期定位试验条件下不同施肥处理和地下水位对水稻土有机氮组分及其矿化特性的影响,采用Keeney和Bremer酸解法对土壤有机氮进行分组研究,并利用改进后的Warning淹水培养-间歇淋洗法研究水稻土有机氮矿化特性。结果表明,不同处理土壤酸解氮占全氮的61.2%～64.4%,其中酸解未知氮,氨基酸态氮,氨态氮和氨基糖态氮分别占全氮26.9%～34.0%,13.0%～18.0%,12.6%～14.3%和2.3%～4.7%。恒温淹水培养106d后,以酸解未知氮降幅最大,且酸解未知氮与土壤氮矿化势之间有显著的正相关关系(r=0.865*),表明酸解未知氮是土壤可矿化态氮的主要贡献者。有机肥处理土壤矿化氮累积量及氮矿化势显著高于化肥处理,表明长期施用有机肥是提高土壤供氮潜力的有效手段。此外,低水位土壤矿化氮累积量及氮矿化势略高于高水位土壤。     

土壤水分和氮添加对3种质地紫色土氮矿化及土壤pH的影响

为正确认识土壤水分、质地和外源氮添加对紫色土氮矿化作用和土壤pH的影响,以西南地区典型的紫色土为研究对象,通过90d的室内恒温(25℃)好气培养,研究了3种质地(粘土、粉粘壤土和砂土)紫色土在不同含水量(55%,65%和75%田间持水量)和尿素氮添加水平(0mg/kg土和250mg/kg土.)条件下,土壤氮矿化作用和pH的变化。结果表明:前30d的累积矿化氮量可占培养期间(90d)的78.48%~91.55%,且各处理的土壤累积矿化氮量和净矿化速率均随着培养时间的延长而快速增加;第30~90d,土壤累积矿化氮量增长缓慢,净矿化速率迅速下降并趋于稳定。土壤累积矿化氮量和净矿化速率在各培养阶段均随土壤水分含量的增加而逐渐增大,其中75%WHC(75%田间持水量)和75%WHC+U(75%田间持水量+尿素)处理的矿化作用最强。土壤质地从一定程度上对土壤的矿化产生影响,但其影响并不显著。外源氮添加能促进土壤氮矿化,其净氮矿化量和净矿化速率在各培养阶段均极显著(p0.01)高于未加氮处理,分别为未施氮处理的1.68~4.56倍,0.60~6.47倍。外源氮添加使土壤pH显著下降,55%WHC+U、65%WHC+U和75%WHC+U处理分别下降了0.57,0.66,0.72个pH单位,土壤有酸化趋势。土壤pH值与土壤氮素净矿化速率呈极显著线性相关,净矿化速率对pH变化贡献巨大。总之,土壤含水量增加和外源氮添加均促进了土壤氮矿化,增加了土壤矿质氮含量,同时外源氮添加也加速了土壤pH下降,土壤有酸化趋势。     

无机改良剂对皖南植烟红壤氮矿化的影响

以皖南植烟旱地红壤为研究对象,通过模拟试验分析了无机改良剂(T20、G20、硅藻土)对土壤氮矿化及硝化作用的影响。试验采用室内恒温间歇淋洗好气培养法(Stanford法),研究无机改良剂添加量处理(1%,2%,5%和10%)对皖南植烟红壤氮矿化的影响。结果表明,3种改良剂均可提高土壤淋洗液pH,pH增加幅度与改良剂添加量显著相关,T20、G20与硅藻土的土壤淋洗液pH增加幅度最大可提高0.30,0.50,0.43个单位;利用一级动力学方程N_t=N_0(1-e~(-kt))拟合土壤氮矿化过程,不同处理的相关系数R~2为0.970 9~0.998 0,相关性均达到极显著水平;39个供试土壤样品的有机氮矿化势N0为14.86~177.1mg/kg,平均50.53mg/kg。不同处理的N0均与改良剂添加量显著正相关,对照N0为14.86mg/kg,添加10%硅藻土、T20与G20处理的N0分别为104.1,177.1,26.01 mg/kg,是对照处理的7,11.9,1.75倍。39个土壤样品的供氮指数N0×k为0.66~6.39mg/(kg·d),平均为2.19mg/(kg·d);添加1%,2%的硅藻土处理及添加1%,5%,10%的G20处理的综合指数N0×k均显著高于对照处理。不同处理的土壤硝化累积量随时间变化符合Logistic的"S"形生长曲线,其决定系数R2为0.953 3~0.996 2,达到极显著水平。硅藻土、G20与T20处理的最大氮矿化促进率分别可达27.46%,94.76%,0.63%,而最大硝化促进率分别可达82.83%,136.4%,40.44%;氮矿化促进作用与无机改良剂添加量呈显著正相关。通过对3种改良剂的氮矿化与硝化作用比较,G20较硅藻土与T20在促进氮矿化与硝化方面具有比较优势。可见,合理增加无机改良剂,可以促进土壤有机氮的矿化以及硝化作用的进行,增强皖南旱地植烟土壤氮素的有效利用。     

特制有机肥提高贵州黄壤氮矿化和硝化率的研究

植烟土壤中的氮素形态比例是优质烟叶生产的关键,合理施用有机肥可以调节土壤中不同形态氮素矿化水平。以贵州植烟黄壤为研究对象,采用Stanford长期好气间歇淋洗培养法,研究并模拟了不同特制有机肥施用量(0(CK),750 kg·hm~(–2)(1F),1 500 kg·hm~(–2)(2F),2 250 kg·hm~(–2)(3F))下的土壤氮素矿化过程。结果表明,供试贵州黄壤培养5 d后硝化率低于10%,后期硝态氮释放比例严重偏低,土壤在烟草旺长期能供给的硝态氮总量为66.89 mg·kg~(–1),不能满足烟草全生育期内的需氮情况。特制有机肥施用后土壤速效氮矿化速率均呈"前快后慢"趋势,前期矿化量高,后期矿质氮素释放减少并逐渐稳定,符合烟草生长对氮的吸收规律。特制有机肥施用显著提高了土壤速效氮矿化量,速效氮矿化量最多增长420.1%,硝态氮最多增长276.6%。添加特制有机肥显著提高了植烟黄壤硝化率,硝化率增幅范围为8.1%～50.4%。3F处理特制有机肥施用量条件下,土壤硝化率变化范围为43.69%～51.22%,最符合烟草对不同形态氮素的吸收比例,有助于提高烟株产质量。综上所述,每公顷施用2 250 kg特制有机肥最适宜贵州黄壤烟草种植。     

长期施肥对水稻土碳氮矿化与团聚体稳定性的影响

水稻土有机碳、氮矿化过程对水稻土质量和作物养分吸收具有重要的作用,但是它们对施肥措施的响应及其与土壤结构之间的关系尚不清楚。本研究基于红壤性水稻土长期施肥定位试验,分析了不施肥(CK)、施用常量化肥(NPK)、2倍化肥(NPK2)和常量化肥配施有机肥(NPKOM)等处理下水稻土碳氮矿化特征,并研究了其与土壤团聚体稳定性的关系。结果表明NPKOM处理显著提高了土壤有机碳和全氮含量(P0.05),而单施化肥处理(NPK2和NPK)则同CK处理没有显著差异。土壤有机碳矿化速率、累积矿化量和矿化率均为NPKOMNPK2NPKCK处理,其中NPKOM处理显著高于其他处理(P0.05),而后3个处理间没有显著差异。土壤氮矿化速率、累积矿化量和矿化率同土壤碳矿化的规律一致,NPKOM、NPK2和NPK处理累积矿化氮量较CK处理分别提高110.0%、29.4%和8.8%,矿化率分别提高110.8%、25.6%和13.0%。单施化肥处理(NPK和NPK2)的平均质量直径(MWD)分别降低了17.1%和15.5%,而NPKOM处理则增加了19.4%。相关分析表明,土壤碳氮矿化主要取决于土壤有机碳氮含量,而与土壤团聚体水稳定性无直接关系。在今后研究中,应重点分析土壤孔隙结构与有机碳氮周转的关系。     

长期不同比例有机肥-化肥配施下红壤性水稻土氮素矿化特征

土壤有机氮的矿化是土壤氮素肥力的重要指标之一,也是影响作物产量至关重要的因素。以33年长期定位试验为依托,对红壤性双季稻田土壤氮累积、矿化动力学特征等进行系统研究。定位试验始于1984年,选取其中5个施肥处理:不施肥(CK),施氮磷钾肥(NPK),施50%化肥+50%有机肥(50F+50M),施30%化肥+70%有机肥(30F+70M),施70%化肥+30%有机肥(70F+30M),于2017年早稻种植前采集耕层(0～20 cm)土壤样品,采用淹水密闭间歇淋洗法,对土壤氮矿化量和速率进行测定,并采用一级动力学方程拟合土壤氮矿化势(N_0)、矿化速率常数(k)等。结果表明,长期施肥显著提高土壤有机碳、全氮、碱解氮含量,以有机无机肥配施提升效果最为显著,且随有机肥投入量增加而递增,30F+70M处理较NPK处理显著提高铵态氮、硝态氮及总矿质氮含量,分别提高了47.0%、64.6%和49.7%。连续施肥33年后,施肥显著提高了土壤净矿化速率和土壤矿化氮释放量,排序为30F+70M50F+50M70F+30MNPKCK,配施有机肥较施化肥处理显著提高了土壤矿化氮累积释放量和土壤氮素矿化率,分别是化肥处理的2.70和1.41倍。长期施肥均显著提高了土壤氮素矿化势(N_0),提高幅度为65.9%～196.0%,配施30%有机肥(70F+30M)较施化肥处理(NPK)可显著增加水稻土氮素矿化势,降低氮矿化速率常数。土壤有机质、全氮、碱解氮及铵态氮含量显著影响N_0、N_0/N、累积矿化量及矿化率,土壤氮矿化速率常数(k)与C/N呈现极显著负相关。长期化学氮肥与低比例有机肥配施,使水稻土供氮缓慢而持久,在水稻的生长发育过程中能够不断地补充氮素。     

闽江河口互花米草入侵过程对短叶茳芏湿地土壤氮矿化的影响

对闽江河口湿地互花米草入侵对土壤氮矿化影响进行时空变化研究,选择闽江口鳝鱼滩湿地互花米草入侵斑块中央(A)、互花米草入侵斑块边缘(B)及未被入侵的短叶茳芏沼泽群落(C)为研究对象,探讨互花米草入侵过程对土壤氮矿化的影响,并对其进行原因分析。结果表明:互花米草入侵闽江河口短叶茳芏湿地后,从时空两个方面均改变了原有湿地土壤氮的矿化水平,总体上互花米草入侵在一定程度上增强了土壤的矿化作用。从季节上来看,春夏秋冬4个季节互花米草入侵斑块中央(A)矿化速率变化范围分别为(-2.50~6.25),(-5.0~8.5),(-0.35~0.9),(-0.37~0.22)mg/(kg·d);互花米草入侵斑块边缘(B)分别为(-3.37~6.25),(-7.5~5.5),(-0.15~0.55),(-0.25~0.21)mg/(kg·d);未被入侵的短叶茳芏沼泽群落(C)分别为(-5.8~3.6),(-5.7~5.4),(-0.12~0.55),(-0.13~0.09)mg/(kg·d)。互花米草入侵对土壤氮矿化速率的影响随着季节变化表现出显著的规律,即入侵过程中3种不同土壤类型均表现为夏季春季秋季冬季;相同季节3种样地同层土壤氮矿化速率总体表现为ABC。从土壤分层来看,在培养时期内各土层土壤氮矿化速率总体呈现出随着培养时间的增加而降低的趋势;在同一培养时期内,不同土层土壤矿化速率总体呈现出随土层深度的增加而降低的现象。这主要是由于互花米草入侵对闽江口湿地土壤温度、湿度、微生物活动、植物的生长周期以及生长特性等因子随时空变化的改变有关。     

施氮量和土壤含水量对黑麦草还田红壤氮素矿化的影响

目标 氮素矿化是决定土壤供氮能力的重要生态过程,养分添加和水分在调节土壤的氮转化方面起着重要的作用。探讨施氮和土壤水分对黑麦草还田过程中土壤氮素矿化的影响有利于进一步优化红壤旱地作物生产的水肥管理。 【方法】 通过室内培养试验,研究了施氮量 (0、60、120 mg/kg) 和土壤含水量 (15%、30%、45%) 对红壤旱地黑麦草还田过程中土壤净硝化量、氨化量和氮矿化量的影响。 【结果】 土壤含水量15%时,施氮有利于提高黑麦草还田初期土壤净硝化量,施氮量120 mg/kg抑制了黑麦草还田后期土壤硝化作用。在30%土壤含水量时,施氮量120 mg/kg明显抑制了黑麦草还田后期土壤硝化作用。土壤含水量45%抑制了黑麦草还田初期不同施氮水平下土壤净硝化量,但增加了黑麦草还田91 d时土壤净硝化量,且施氮量60 mg/kg下的净硝化量显著高于120 mg/kg水平下的。土壤净氨化量在整个黑麦草还田过程中均为正值,且呈现多次升高-降低的往复动态变化。土壤净氨化量在三种土壤含水量下均表现为施氮条件下的显著高于不施氮处理。土壤含水量的增加有利于提高施氮量120 mg/kg下黑麦草还田初期土壤的氨化作用,但降低了黑麦草还田后期土壤净氨化量。相比不施氮,三个含水量条件下的施氮处理在黑麦草还田过程中的大部分阶段都显著增加了土壤净氮矿化量,土壤含水量30%条件下土壤净氮矿化量的变化最大。相比土壤含水量15%,30%含水量促进了黑麦草还田中期 (13～57 d) 土壤净氮矿化量的增加,45%含水量抑制了黑麦草还田后期 (73～91 d) 土壤净氮矿化量。 【结论】 红壤区旱地黑麦草还田时应合理施入化学氮肥 (60 mg/kg),在黑麦草还田初期保持较高的土壤含水量 (45%) 能够抑制土壤的氮矿化作用,还田中后期适当降低土壤含水量 (30%)有利于增加土壤氮素的矿化。      

残落物混合分解对杨树-农作物复合系统土壤碳氮矿化的影响

采用室内培养的方法研究杨-麦、杨-花生等不同复合经营模式下,杨树叶与农作物秸秆混合后对土壤碳、氮矿化及土壤微生物量的影响。结果表明:(1)单一模式中,花生叶处理的有机碳矿化累积量最大,花生茎秆、杨树叶处理次之,小麦秸秆处理最低。混合处理有机碳矿化累积量依次为杨树叶-花生叶>杨树叶-花生茎秆>杨树叶-小麦秸秆,且培养结束时,混合物表现出明显的促进作用;(2)土壤微生物量碳、氮与各残落物氮含量、C/N比存在显著的相关性;(3)杨树叶、小麦秸秆及其混合物处理的土壤矿质态氮含量均低于对照,而添加花生叶、花生茎秆以及它们与杨树叶的混合物使矿质态氮含量高于对照。试验说明杨-麦、杨-花生复合模式均能有效提高土壤微生物的生物量,调节碳的动态及氮的供应,而选择种植含氮量高的农作物更有利于促进残落物分解和养分归还,这对深入研究林-农复合系统的模式筛选、结构优化及可持续经营具有一定的现实意义。     

Nitrogen Mineralization in Mississippi River Deltaic Plain Freshwater Floating Marshes

ABSTRACT

The mineralization of soil organic nitrogen in two floating marshes types in Louisiana, USA with different vegetation and mat thickness (and biomass) was measured by incubating peat soil in situ in polyethylene bottles at depths of 10 and 25 cm. The size of the extractable inorganic N (NH₄⁺ – N) pool was related to mat thickness and soil bulk density. The N mineralization rates were twice as great at the thick mat site (1.5 mg N/kg soil/day) compared to the thin mat floating marsh (0.71 mg N/kg soil/day). The amount mineralized on a volume basis to 30 cm depth were 22 mg N/m²/day for the thick mat marsh and 6 mg N/m²/day for the thin mat marsh. The nitrogen mineralization rates observed in this study reflect plant biomass differences between the thick mat and thin mat marshes, with the former exhibiting approximately 7-fold greater biomass. These low overall mineralization rates suggest that nitrogen entering these freshwater floating marshes from Mississippi River water percolating through the root zone, would result in increased plant productivity-increasing marsh stability and also providing a natural mechanism contributing to the processing and removal of dissolved inorganic nitrogen in river water entering these wetlands.     

外源有机碳对黑土有机碳及颗粒有机碳的影响

为了阐释外源有机碳在土壤有机碳运转中的作用机制,以黑土为供试材料,进行了5年的室外培养试验,并结合室内全土及颗粒组分单独矿化培养试验,研究了不同外源有机碳对黑土有机碳(SOC)、颗粒有机碳(POC)含量及其矿化特征的影响。试验包括单施化肥、牛粪配施化肥、鸡粪配施化肥、秸秆配施化肥和树叶配施化肥5个处理。结果表明:(1)单施化肥黑土SOC的损失主要来源于POC的损失,外源有机碳有利于SOC和POC的累积,与对照相比,禽畜粪便处理的SOC和POC平均增加幅度分别为16.6%和27.8%,植物残体处理的SOC和POC平均增加幅度分别为27.0%和46.4%;(2)一级动力学方程能较好地描述SOC和POC的矿化动态(R~20.9),且POC比SOC易矿化,POC的60d累积矿化量是SOC的3倍以上;(3)禽畜粪便处理和植物残体处理的POC平均矿化率分别为31.5%和29.8%,禽畜粪便处理的POC更易矿化;(4)外源有机碳有效降低了黑土有机碳的矿化,尤其是牛粪,其SOC矿化率为1.9%,比对照低了3.4%,其POC矿化率为24.8%,比对照低17.4%;(5)外源有机碳在黑土中的碳累积能力表现为树叶秸秆牛粪鸡粪。     

辽河平原地区长期施肥水稻土氮素矿化及其模拟的研究

采用长期淹水密闭——间歇淋洗培养方法和分析手段,研究了辽河平原地区连续16年长期不同施肥(不施氮肥、氮肥、氮肥+有机肥、氮肥+有机肥+放萍)水稻土氮素的矿化过程。结果表明长期不同施肥水稻土氮矿化量为N15.61～103.57mgkg-1,为全N的1.25%～5.66%;氮肥+有机肥处理土壤氮矿化量最高,占全氮比率最大,而氮肥处理土壤氮矿化量最低,占全氮的比率最小;氮矿化量与全氮、有机质、C/N之间呈显著相关关系(P<0.05)。选择有效积温式(EATM);一级反应式(One-pool模型);带常数项的一级反应式(Special模型),对实验数据进行拟合。非线性拟合结果表明Special模型明显优于One-pool模型和有效积温式(EATM)。分析表明Special模型能更为准确地描述长期不同施肥措施下水稻土有机氮素的矿化。     

Drivers of soil respiration and nitrogen mineralization change after litter management at a subtropical Chinese sweetgum tree plantation

Leaf litter decomposition transfers elements from litter to soils that are essential for regulating nutrient cycles in plantation ecosystems, especially carbon and nitrogen. However, soil carbon and nitrogen dynamics in response to tree litter management remains insufficiently researched. We conducted a one-year field experiment at a fast-growing sweetgum tree plantation to evaluate the effects of leaf litter management on soil available nutrients, respiration rate and nitrogen mineralization rate. Three leaf litter treatments were applied, which were: (1) natural input (control); (2) double input and (3) non-input. It was found that the double input treatment increased soil inorganic nitrogen and microbial biomass nitrogen, but had little effect on microbial biomass carbon, dissolved organic carbon or dissolved organic nitrogen compared with natural input. The non-input treatment caused dissolved organic carbon to decrease compared with natural input. The respiration rate increased in the double input treatment, with a positive priming effect observed. Soil net ammonification, nitrification and mineralization rates also increased in the double input treatment in specific seasons. Meanwhile, positive linear relationships between respiration rate and all nitrogen transformation rates were observed for all treatments. Soil temperature was found to be an important prediction factor for predicting the respiration rate and mineralization as seasonal variations, but not for litter-induced fluctuations. Soil water content and mineral nitrogen were the primary drivers of litter-induced change to the respiration rate, whereas mineral nitrogen and microbial biomass were primary drivers of mineralization change. These results suggest that changes in soil nitrogen mineralization rate are strongly associated with the soil respiratory process, resulting in a potentially strong plant–soil feedback mechanism.     

玉米秸秆不同构件混合分解的非加和效应及其对土壤有机碳矿化的影响

[目的]研究玉米秸秆不同构件混合分解的非加和效应及其对黄绵土土壤有机碳矿化的影响,为秸秆还田背景下坡地土壤CO2排放提供理论支撑。[方法]采用室内模拟试验,试验设置无玉米秸秆土壤对照(CK)及4种玉米秸秆添加处理:茎+土壤(CKS)、叶+土壤(CKL)、鞘+土壤(CKLS)、混合玉米秸秆+土壤(CKM)。[结果]培养结束土壤有机碳矿化累积排放量实测值显著高于预测值,且促进作用主要是由培养初期快速分解阶段(1~28d)导致的。培养结束后混合玉米秸秆剩余质量预测值明显高于实测值,且元素含量发生明显改变,其中全氮含量预测值明显低于实测值,C/N预测值明显高于实测值。培养结束后CKS处理土壤微生物碳含量明显高于其他几种处理,其他几种处理差异不显著;添加玉米秸秆处理土壤微生物量氮明显降低,相应的土壤微生物量C/N增大,CKS,CKL和CKM处理与CK处理差异达到显著水平。土壤可溶性有机碳(DOC)含量CKLS和CKM处理明显高于其他3种处理,CKS与CKL处理与对照差异不显著。[结论]玉米秸秆不同构件按比例混合对玉米秸秆分解产生协同促进作用,混合分解过程促进氮累积。     

Nitrogen release from a 15N‐labeled compost in a sorghum growth experiment

In the near future, composted bio‐solids are expected to play a major role in agriculture. In order to evaluate their contribution to plant growth and nutrition, a mixed sorghum–poultry manure compost was prepared using ¹⁵N‐labeled materials. Four treatments were compared in a pot trial: fertilized with compost vs. unfertilized, both of them combined with (cultivated) and without (bare) plants of fibre sorghum (Sorghum bicolor [L.] Moench.). Soil mineral nitrogen (N‐min), plant growth, and N uptake were monitored over a whole growing season (167 d after fertilizer treatment; DAT). Apparent soil mineralization (ASM) and apparent recovery fraction of nitrogen by the plant (ARF) were assessed, as well as the ¹⁵N recovery fraction by the plant (¹⁵NRF). Compost enhanced sorghum biomass at mid growth (+ 200% of dry weight compared to the unfertilized). However, the difference between the control and the fertilized plants progressively decreased towards the end of the season (+ 70%). Fertilized and unfertilized plants followed different growth patterns over time, although of the same sigmoid type. Conversely, N concentration in plant tissues followed a common dilution curve, indicating that fertilized sorghum efficiently used the supplied N, avoiding luxury consumption. Apparent soil mineralization approximately reached 45% of compost total N in pots without plants. Apparent recovery fraction attained 100% at about two third of the growing season (DAT 111), then declined to about 50% because of root and leaf decline. Compared to it, ¹⁵NRF only reached ≈ 20% at mid growth (DAT 83), then declined to 12%. Despite the large difference in absolute values, ARF and ¹⁵NRF exhibited a significant correlation, indicating a common trend in time. In contrast to ¹⁵NRF, the amount of nutrient derived from fertilizer (Ndff) taken up by the plant decreased over the growth season, proving that compost contributed more to plant nutrition in the early (Ndff ≈ 50%) than in the late growing season (Ndff ≈ 25%). The large difference between ARF and ¹⁵NRF suggests that sorghum exerted a strong nutrient demand on the soil and on the fertilizer. Both ¹⁵NRF and ARF are considered valuable traits: the former better describes fertilizer behavior and actual supply of N, while the latter outlines the overall effect of fertilizer application on crop nutrition.     

Effects of fertilizer application and fire regime on soil microbial biomass carbon and nitrogen,and nitrogen mineralization in an Australian subalpine eucalypt forest

The effects of a range of fertilizer applications and of repeated low-intensity prescribed fires on microbial biomass C and N, and in situ N mineralization were studied in an acid soil under subalpine Eucalyptus pauciflora forest near Canberra, Australia. Fertilizer treatments (N, P, N+P, line + P, sucrose + P), and P in particular, tended to lower biomass N. The fertilizer effects were greatest in spring and smaller in summer and late actumn. Low-intensity prescribed fire lowered biomass N at a soil depth of 0–5 cm with the effect being greater in the most frequently burnt soils. No interactions between fire treatments, season, and depth were significant. Only the lime + P and N+P treatments significantly affected soil microbial biomass C contents. The N+P treatment increased biomass C only at 0–2.5 cm in depth, but the soil depth of entire 0–10 cm had much higher (>doubled) biomass C values in the line + P treatment. Frequent (two or three times a year) burning reduced microbial boomass C, but the reverse was true in soils under forest burn at intervals of 7 years. Soil N mineralization was increased by the addition of N and P (alone or in combination), line + P, and sucrose + P to the soil. The same was true for the ratio of N mineralization to biomass N. Soil N mineralization was retarded by repeated fire treatments, especially the more frequent fire treatment where rates were only about half those measured in unburnt soils. There was no relationship between microbial biomass N (kg N ha^-1) and the field rates of soil N mineralization (kg N ha^-1 month^-1). The results suggest that although soil microbial biomass N represents a distinct pool of N, it is not a useful measure of N turnover.     

Soil nutrient supply and biomass production in a mixed forest on a skeleton‐rich soil and an adjacent beech forest

In the natural forest communities of Central Europe, beech (Fagus sylvatica L.) predominates in the tree layer over a wide range of soil conditions. An exception with respect to the dominance of beech are skeleton‐rich soils such as screes where up to 10 broad‐leaved trees co‐exist. In such a Tilia‐Fagus‐Fraxinus‐Acer‐Ulmus forest and an adjacent mono‐specific beech forest we compared (1) soil nutrient pools and net nitrogen mineralization rates, (2) leaf nutrient levels, and (3) leaf litter production and stem increment rates in order to evaluate the relationship between soil conditions and tree species composition. In the mixed forest only a small quantity of fine earth was present (35 g l^—1) which was distributed in patches between basalt stones; whereas a significantly higher (P < 0.05) soil quantity (182 g l^—1) was found in the beech forest. In the soil patches of the mixed forest C and N concentrations and also concentrations of exchangeable nutrients (K, Ca, Mg) were significantly higher than in the beech forest. Net N mineralization rates on soil dry weight basis in the mixed forest exceeded those in the beech forest by a factor of 2.6. Due to differences in fine earth and stone contents, the volume related soil K pool and the N mineralization rate were lower in the mixed forest (52 kg N ha^—1 yr^—1, 0—10 cm depth) than in the beech forest (105 kg N ha^—1 yr^—1). The leaf N and K concentrations of the beech trees did not differ significantly between the stands, which suggests that plant nutrition was not impaired. In the mixed forest leaf litter fall (11 %) and the increment rate of stem basal area (52 %) were lower than in the beech forest. Thus, compared with the adjacent beech forest, the mixed forest stand was characterized by a low volume of patchy distributed nutrient‐rich soil, a lower volume related K pool and N mineralization rate, and low rates of stem increment. Together with other factors such as water availability these patterns may contribute to an explanation of the diverse tree species composition on Central European screes.