不同能源作物对土壤剖面盐分离子迁移的影响

为了筛选耐盐能源作物、挖掘利用盐渍土资源、促进农业可持续发展。以甘肃白银市东大沟盐渍化土壤作为研究对象,在大田试验条件采用对比研究的方法探讨种植四翅滨藜(Atriplex canescens)、油菜籽(Brassica napus)、甜高粱(Sorghum bicolor(L.)Moench)、荻(Triarrherca sacchariflora)、柳枝稷(Panicum virgatum)5种不同能源作物对土壤剖面盐分及其离子(HCO3-、Cl-、SO42-、K+、Na+、Ca2+、Mg2+)迁移的影响。结果表明:在盐渍化土壤,种植柳枝稷、四翅滨藜能明显减少土壤剖面0—100cm土层盐分、Cl-、Na+、Ca2+、Mg2+的含量,脱盐的同时会导致HCO3-在土壤剖面0—100cm土层累积。种植油菜可以抑制0—50cm土层盐分的累积。种植荻可以抑制50—100cm土层盐分、0—100cm土层HCO3-、60—100cm土层SO42-的累积。种植柳枝稷可明显减少土壤剖面0—100cm土层K+的含量。研究发现四翅滨藜、柳枝稷两处理的电导率均与其他处理之间达显著水平(P0.05),荻与其他处理之间水溶性Na+含量均达显著水平(P0.05),柳枝稷与其他处理之间HCO3-含量均达极显著水平(P0.01)。     

固体磷肥和液体磷肥对石灰性土壤不同形态无机磷及磷肥肥效影响的研究

土壤磷固定是影响石灰性磷肥肥效的主要原因。本文在田间滴灌条件下采用连续浸提的方法对液体磷肥和固体颗粒磷肥及其不同施用方法对石灰性土壤各形态无机磷含量动态变化的影响进行了研究,并比较了不同处理下加工番茄磷素营养效应。结果表明:各施肥处理0—20 cm土层Ca2-P和Ca8-P含量随施肥时间明显下降,而Ca10-P含量则显著上升,表明磷肥在石灰性土壤中不断向Ca10-P转化并被固定。液体磷肥追肥处理0—20 cm土层Ca2-P含量在各时期均显著高于其他施肥处理(P＜0.05),且液体磷肥追肥可以明显保持土壤0—20 cm土层较高的Ca8-P含量。与其他施肥处理相比,液体磷肥追施可减少石灰性土壤对磷的固定,增加0—20 cm土层Ca2-P和Ca8-P含量(P＜0.05),显著提高土壤磷的有效性。液体磷肥追施处理可显著提高加工番茄叶片含磷量和经济产量(91725 kg/hm2)。与传统过磷酸钙颗粒磷肥作基肥处理（CK1）相比,液体肥料全做追肥可使加工番茄经济产量提高26.7%,并明显提高了磷肥利用率。在滴灌条件下石灰性土壤上液体磷肥分次追施比传统的固体颗粒磷肥基施具有明显的优势,是一种非常具有应用前景的施肥方式。     

施肥对割草场土壤养分和化学计量学的影响

长期连年刈割导致草地生态系统物质循环被打破,养分的输入与输出失去平衡,造成土壤贫瘠。以呼伦贝尔羊草草甸草原天然割草地为研究对象,研究不同施肥处理对羊草割草地土壤养分和化学计量学的变化规律,探求施肥对退化羊草割草地改良效果的最优方案,为退化草地的恢复和改良提供理论指导。研究结果表明,随着施肥年份的增加,土壤全碳、全钾含量逐年递减,土壤速效氮和有效磷逐年递增。高浓度施肥处理有利于增加0～10 cm土层土壤全氮和20～30 cm土层土壤全钾含量(P<0.05),而低浓度化肥处理下0～10 cm土层土壤全碳和全磷含量、10～20 cm土层土壤全碳、20～30 cm土层土壤全氮和全磷含量最高;中浓度施肥和高浓度施肥处理显著增加0～10 cm土层土壤有效磷含量,而低浓度施肥处理对10～20和20～30 cm土层土壤有效磷含量有显著增加作用(P<0.05);随着施肥年份的增加,不同土层土壤C∶N逐年显著降低,2017年不同土层土壤C∶N最低,其中高浓度施肥处理下土壤C∶N显著低于对照处理(P<0.05);土壤C∶P逐年显著降低,其中2016年0～10 cm土层土壤C∶P显著低于其他年份(P<0.05);土壤N∶P年份变化相对平稳,施肥后期0～10和20～30 cm土层土壤N∶P显著低于第一年(P<0.05)。施肥以补充土壤中限制性元素含量而影响土壤和植物的化学计量学特征,并且确定植被的最适化学计量比值和判定其限制元素类型。高浓度施肥处理(N 10.5 g·m-2+P 5.1 g·m-2)有利于降低土壤C∶N,同时氮素仍是限制本地区植物生长的一个主要因素。     

耕作方式对黄绵土无机磷形态的影响

以设置在陇中黄土高原并已经进行了5年的田间定位试验为基础,采用蒋-顾石灰性土壤无机磷分级法,研究了不同耕作方式对黄绵土无机磷形态的影响。结果表明,供试土壤中78.6%的磷以无机磷形式存在,且以Ca-P占绝大多数。无机磷各形态含量排列顺序为:Ca10-P Ca8-P O-PAl-P Fe-PCa2-P。与传统耕作不覆盖(T)相比,免耕秸秆覆盖(NTS)、免耕不覆盖(NT)、传统耕作结合秸秆还田(TS)均可降低土壤中的Ca8-P、O-P和0—5 cm土层中的Ca10-P含量,其中NTS最为明显;NTS处理可提高土壤中的Al-P、Fe-P含量。不同处理中,Ca2-P、Ca8-P、Al-P、Fe-P均以0—5 cm土层中含量最高,且随着土层的增加呈下降趋势;但是Ca10-P 以5—10 cm土层含量最高;各处理O-P在土壤剖面中的变化没有显著差异。     

耕作方式对麦–玉轮作农田固碳、保水性能及产量的影响

【目的】 农田固碳保水性能是影响作物产量的关键因素,研究耕作方式对耕层 (0—20 cm) 土壤碳、水含量和产量的影响,为选择适宜该地区的最佳耕作措施提供参考。 【方法】 保护性耕作长期定位试验始于2002年,种植制度为冬小麦–夏玉米一年两熟,两季秸秆全量粉碎 (3～5 cm) 还田,试验设传统翻耕、深松、旋耕和免耕4种耕作方式。对2015—2016年作物生长各时期土壤有机碳含量、土壤含水量、碳水储量、产量和等价产量等进行了测定。 【结果】 不同处理麦–玉轮作农田0—20 cm土层有机碳含量有所不同。耕作措施对土壤有机碳含量有显著 (P < 0.05) 影响,表现为深松和免耕能显著增加0—10 cm土层有机碳含量,且以深松效果最为显著 ( P < 0.05)。与传统翻耕相比,免耕和旋耕降低了10—20 cm土层土壤有机碳含量;深松比传统翻耕显著 ( P < 0.05) 增加了小麦季土壤有机碳含量,玉米季没有显著性差异 ( P < 0.05)。0—10 cm土层,玉米季旋耕和免耕处理的土壤含水量高于深松和传统翻耕;在10—20 cm土层小麦季免耕处理土壤含水量高于其他三种耕作方式。产量结果表明,深松能有效增加作物的有效穗数、穗粒数和千粒重,进而增加籽粒产量和周年等价产量;免耕显著 ( P < 0.05) 降低了亚表层 (10—20 cm) 有机碳含量,降低穗粒数和千粒重,不利于作物增产。两年小麦玉米单作产量和周年等价产量均表现为深松 > 传统翻耕 > 旋耕 > 免耕。 【结论】 深松能有效促进耕层土壤有机碳积累和保水性能提高,增加作物的有效穗数、穗粒数和千粒重,从而增加产量;免耕显著 (P < 0.05) 提高了表土层 (0—10 cm) 碳储量,有助于增强耕层土壤的保水性能。      

基于CT扫描技术研究有机无机肥长期配施对土壤物理特征的影响

  【目的】  研究长期有机无机肥配施对土壤孔隙特征、土壤水分参数等土壤剖面物理特征的影响，深入认识有机无机肥配合施用效果的机理。  【方法】  试验基于渭北旱塬12年苹果园长期定位试验，设不施肥 (CK)、单施化肥 (NPK) 和有机无机肥配施 (MNPK) 3个处理，采用CT扫描法定量分析了0—40 cm土壤样品中大孔隙 (>1000 μm) 的数量，计算了大孔隙度及大孔隙在土壤剖面中的分布特征, 同时采用常规方法测定了0—10、10—20和20—40 cm土壤样品的土壤容重、田间持水量及饱和导水率等。  【结果】  1) 相比NPK处理，有机无机肥配施对0—20 cm土层土壤大孔隙度有提高的趋势，在20—40 cm土层，有机无机肥配施相比单施化肥土壤大孔隙度提高了91.7% (P < 0.05)；MNPK处理土壤大孔隙数量在3个土层均为最大，在0—10和20—40 cm土层，分别较NPK处理提高了38.4%和54.8% (P < 0.05)。NPK处理大孔隙数量在0—10和10—20 cm分别显著高于CK。2) 与不施肥相比，单施化肥除10—20 cm土层土壤的饱和导水率、田间持水量有明显升高外，其它土层没有明显变化，而有机无机肥配施0—10、20—40 cm土层土壤的饱和导水率、田间持水量较不施肥均有明显提升；有机无机肥配施相比不施肥、单施化肥在不同土层的土壤容重均为最小，而20—40 cm土层单施化肥的土壤容重较不施肥提高了2.8% (P > 0.05)。3) 相关分析表明，土壤大孔隙数量、大孔隙度与田间持水量、土壤饱和导水率呈极显著正相关 (P < 0.01)，与土壤容重呈极显著负相关 (P < 0.01)，而与土壤机械组成无显著相关性。  【结论】  相比单施化肥，长期有机无机肥配施改善了苹果园0—40 cm土层土壤的大孔隙状况和土壤的持水、导水性能，在20—40 cm土层效果更明显，有机无机肥配施可改善渭北旱塬苹果园土壤物理性质。     

不同耕作模式对小麦—玉米轮作下潮土养分和作物产量的影响

通过分析裂区设计下的6个处理,即小麦季深耕和旋耕2个主处理×玉米季免耕播种、行间深松和行内深松3个副处理:(1)旋耕+免耕播种(RT—NT);(2)旋耕+行间深松(RT—SBR);(3)旋耕+行内深松(RT—SIR);(4)深耕+免耕播种(DT—NT);(5)深耕+行间深松(DT—SBR);(6)深耕+行内深松(DT—SIR),对土壤养分含量和作物产量影响,筛选适宜于小麦—玉米轮作体系的耕作模式。结果表明,各处理土壤养分含量在小麦、玉米两季中均随土层深度增加而降低。小麦季,旋耕处理0—10cm土层土壤全氮、碱解氮、有效磷含量、硝态氮含量显著高于深耕处理;但深耕增加当季30—40cm土层土壤有机质、全氮、碱解氮、有效磷、硝态氮、铵态氮含量。玉米季,DT—NT处理0—30cm土层有机质含量较RT—NT处理增加40.1%～64.3%。RT—SBR、RT—SIR处理显著提升土壤0—30cm全氮含量,其中RT—SBR处理0—10cm土层全氮含量最高,为1.4g/kg。RT—SIR处理显著增加0—20cm土壤碱解氮含量,较RT—NT显著增加15.0%～25.3%。在0—40cm土层,DT—SBR处理的有效磷含量最高,而RT—SBR处理的速效钾含量最高。DT—SIR处理显著提升20—50cm土层硝态氮和铵态氮含量,其中硝态氮含量为8.5～30.4mg/kg,铵态氮含量为2.6～8.9mg/kg。与小麦季相比,玉米季提升10—20cm土层有机质含量、0—50cm土层的碱解氮、有效磷、速效钾含量以及40—50cm土层的硝态氮、铵态氮含量。DT—SBR和DT—SIR处理穗长、百粒重、收获指数和产量显著高于其他处理,且二者产量较RT—NT处理显著增加6.4%～10.8%。玉米季DT—SIR处理的肥料偏利用率和经济效益最高。综上所述,深耕+行内深松处理有利于增加土壤养分含量,且增产效果较好,在本研究中最优。     

东北三省典型春玉米种植区土壤剖面碳库变化特征

【目的】 农田土壤碳储量及变化影响着农田肥力、生产力以及地力的可持续性。本文研究了东北三省典型春玉米种植区在0—90 cm土层土壤碳库的变化特征,分析了东北三省典型春玉米种植区农民习惯施肥措施下土壤的碳贮存情况。 【方法】 于2012年春玉米全生育期定点跟踪了黑龙江、吉林和辽宁省各17户,总计51户农民习惯施肥处理,测定了0—30、30—60、60—90 cm土层中全碳 (TC)、有机碳 (SOC)、无机碳 (IC)、颗粒有机碳 (POC)、微生物生物量碳 (SMBC) 以及可溶性有机碳 (DOC)含量。 【结果】 黑龙江、吉林、辽宁省典型春玉米种植区0—90 cm土层全碳储量分别为159.8、128.5、108.1 t/hm2,有机碳储量分别为141.7、120.5、90.2 t/hm2,无机碳储量分别为18.2、8.0、17.9 t/hm2。三个省份间0—90 cm土层SOC储量差异均达显著性水平 (P < 0.05),黑龙江的储量显著高于吉林的,吉林的储量又显著高于辽宁的。关于0—30 cm土壤TC、SOC储量,黑龙江、吉林、辽宁三省间差异均达显著水平 ( P < 0.05),在30—60 cm、60—90 cm土层,黑龙江的TC、SOC储量显著高于吉林和辽宁的 ( P < 0.05),吉林和辽宁间差异不显著;土壤剖面TC、SOC储量表现为 0—30 cm > 30—60 cm > 60—90 cm深。在土壤活性碳库方面,0—30 cm土层中,随着纬度的降低,黑龙江、吉林、辽宁省内POC、POC/SOC、SMBC/SOC、DOC/SOC呈增加趋势,而SMBC则呈降低趋势,三省间POC/SOC、SMBC、DOC/SOC平均含量差异均达显著性水平 ( P < 0.05),黑龙江POC平均含量显著低于吉林、辽宁的 ( P < 0.05),吉林的DOC平均含量显著高于黑龙江、辽宁的 ( P < 0.05);30—60 cm土层,黑龙江、吉林、辽宁省内POC、POC/SOC、DOC/SOC随着纬度的升高而降低,且三省间POC/SOC平均值差异达显著性水平,黑龙江POC、DOC/SOC显著低于吉林、辽宁的 ( P < 0.05),但SMBC含量黑龙江显著高于吉林、辽宁的 ( P < 0.05);在60—90 cm土层,黑龙江土壤的POC、POC/SOC、DOC/SOC、SMBC/SOC含量平均值显著低于吉林、辽宁的 ( P < 0.05),吉林的SMBC显著高于辽宁的 ( P < 0.05)。随着土壤剖面深度的增加,各省土壤TC、SOC、IC及活性碳库呈降低趋势,而土壤IC/TC呈增加趋势。 【结论】 在东北三省典型春玉米种植区,0—90 cm土层以黑龙江的有机碳贮存最大,三省由于气温、土壤母质和施肥的影响,土壤活性碳库变化规律并不完全一致,随着土层深度增加土壤无机碳对全碳贡献增加,因此,下一步研究需重视无机碳库和剖面碳库在碳贮存中的作用。      

火烧对大兴安岭樟子松天然林土壤有机碳组分的影响

以大兴安岭轻度火烧迹地为研究对象,通过对比研究,探讨火烧对樟子松天然林土壤有机碳组分的影响。结果表明:轻度火烧改变了樟子松天然林土壤有机碳的组成和含量。轻度火烧使樟子松天然林0—5cm土层土壤有机碳、易氧化碳和颗粒有机碳含量分别下降了8.52g/kg,1.36g/kg和5.85g/kg;5—10cm土层分别下降了4.78g/kg,0.19g/kg和2.98g/kg,与对照样地差异达到显著水平(P0.05)。轻度火烧使樟子松天然林表层土壤黑碳含量显著增加,0—5cm土层黑碳含量较对照样地增加了9.95g/kg,与对照样地差异达到显著水平(P0.05)。火烧迹地0—5cm和5—10cm土层BC/SOC分别增加了25.4%和6.12%,ROC/SOC分别减小了1.49%和0.65%,与对照样地差异达到显著水平(P0.05)。轻度火烧对樟子松天然林土壤POC/SOC影响不大。回归分析表明,火烧迹地和对照样地土壤有机碳各组分与有机碳之间都呈极显著的线性关系(P0.01)。     

亚热带2种针叶林土壤碳氮磷储量及化学计量比对混交的响应

针叶林混交阔叶树是改善土壤肥力、增强林地养分循环的重要措施,而混交效应受到针叶树种自身特性的影响,马尾松(Pinus massoniana)和湿地松(P.elliottii)是亚热带地区广泛种植的针叶树种,但目前2种针叶林对阔叶树混交的响应特征还不清楚。选取马尾松、湿地松纯林以及木荷(Schima superba)补植后形成的马尾松—木荷和湿地松—木荷混交林为研究对象,采集剖面土壤样品,测定土壤容重、有机碳(OC)、全氮(TN)和全磷(TP)含量,计算碳氮磷储量及化学计量特征,比较不同森林类型间的异同。混交阔叶树显著增加了马尾松林0—60cm各土层OC含量,而湿地松纯林与其混交林间OC含量无显著差异。同时,混交增加了2种针叶林土壤TN含量。马尾松林混交后0—60cm土层碳储量显著增加95.8%,而混交阔叶树对湿地松林土壤碳储量无显著影响。混交阔叶树后马尾松和湿地松林0—60cm土壤总氮储量分别增加了15.8%和28.4%,但混交对土壤磷储量无显著影响。混交显著增加了马尾松林0—40cm各土层C/N,而降低了湿地松林0—10cm土层C/N。混交阔叶树后马尾松林0—20cm土层C/P和0—10cm土层N/P显著增加,而混交仅增加湿地林0—10cm土层N/P。混交阔叶树增加了针叶林土壤氮储量,但对磷储量无显著影响,同时混交改变了土壤碳氮磷生态化学计量特征。与湿地松林相比,马尾松林土壤养分含量、储量及其化学计量特征对混交的响应更敏感。     

中亚热带四种森林土壤团聚体及其有机碳分布特征

选择中亚热带地区4种典型森林类型:杉木林、湿地松林、毛竹林和次生林4种森林土壤为研究对象,研究了森林类型对土壤不同发生层水稳性团聚体及其有机碳分布特征的影响。结果表明:不同森林类型对>5 mm和2~5 mm土壤团聚体含量影响显著(p<0.05),表现为次生林>杉木林>毛竹林>湿地松林,而在其他粒径无显著差异。0~30 cm土层内团聚体R0.25和MWD次生林显著高于其他人工林,杉木林次之,湿地松林和毛竹林最低,其他土层无显著差异。各森林类型同土层不同粒径团聚体中有机碳含量随粒径大小变化,团聚体粒径越小,有机碳含量越高。0~10 cm土层同粒径土壤团聚体有机碳含量从大到小依次是次生林、杉木林、湿地松林和毛竹林,而在其他土层各森林类型之间差异不显著。     

石羊河流域干旱荒漠区人工梭梭林对土壤碳库的影响

采用野外调查与室内分析相结合的方法,研究石羊河流域民勤干旱沙区种植人工梭梭林4,13,36年后的土壤有机碳(Soil organic carbon,SOC)、无机碳(Soil inorganic carbon,SIC)、全氮(Total nitrogen,TN)和总碳(soil total carbon,TC)含量及储量变化特征。结果表明:流动沙地种植梭梭后,0-50cm层灌丛下和行间SOC和TN含量总体随造林年限增加而增加,5-50cm层灌丛下SIC含量在13年梭梭林地最高。36,13年林地0-50cm层灌丛下SOC和TN储量均高于行间,而13年灌丛下SIC储量低于行间,4年灌丛下5-50cm层SOC、TN和SIC储量均低于行间。0-50cm层土壤有机碳、无机碳、全氮储量增幅分别为102.44%,24.66%,54.55%,36年林地SOC和TN储量随土层加深先降低后增加,但4,13年和流动沙地SOC、SIC和TN储量均随土层加深而增加。土壤有机碳占总碳比例随造林年限增加而增加。相关分析结果表明,土壤颗粒组成、造林年限、土层深度等与土壤有机碳和全氮储量显著相关(P0.01)。民勤干旱沙区造林提高了土壤碳库截存量,并且随林龄增长而增长。     

湿地松林土壤生化特性和酶活性对模拟硫沉降的响应

以亚热带湿地松人工林为研究对象,通过3种水平(对照CK:pH 6.5;低硫LS:pH 4.5;高硫HS:pH 2.5)的模拟硫沉降控制试验,分析土壤生化特性及酶活性对硫添加的响应。结果表明:(1)硫输入促进了土壤酸化,0—5 cm土层土壤pH在HS处理下显著降低,5—10 cm土层土壤pH在LS和HS处理下显著降低(P0.05);(2)硫输入对土壤有机碳库存在一定影响,土壤总有机碳(TOC)对硫输入无显著响应,但土层间的差异性显著增加(P0.05),土壤可溶性有机碳(DOC)受影响有限,5—10 cm土层微生物量碳(MBC)LS显著降低(P0.05);(3)硫输入对土壤有效氮库影响存在差异,土壤可溶性有机氮(DON)、铵态氮(NH_4~+—N)尚未表现出显著变化,土壤硝态氮(NO_3~-—N)、土壤微生物量氮(MBN)均在HS处理下显著降低,且硫输入加剧土层间的差异性(P0.05);(4)硫输入抑制了酶活性,土壤脲酶活性在HS处理下显著降低(P0.05),土壤蔗糖酶活性无显著变化,但硫输入均弱化了土层间酶活性的差异性。综合分析所有处理下的土壤生化性质和酶活性等指标发现,对硫添加响应敏感的是土壤pH和酶,土层是另外一个主要影响因子,硫添加和土层的交互作用则影响有限。采用Pearson分析得出,硫输入改变了土壤生化特性、酶活性等指标间的相关性程度。可见,酸雨对土壤酸化的影响是一个逐渐累积的过程,外源性硫添加对土壤碳氮及酶活性的影响存在一定差异,这可为硫沉降环境胁迫下森林管理提供科学依据。     

Soil biological changes for a natural forest and two plantations in subtropical China

Conversion of natural forests into pure plantation forests is a common management practice in subtropical China. To evaluate the effects of forest conversion on soil fertility, microbe numbers and enzyme activities in topsoils (0-10 cm) were quantified in two 33-year-old monoculture plantations of Castanopsis kawakamii Hayata (CK) and Cunninghamia lanceolata Lamb. (Chinese fir) (CF), and compared to a neighboring relict natural C. kawakamii forest (NF), in Sanming, Fujian. Five soil samples were collected once each in January, April, July, September and November in 2000 in each forest for laboratory analysis. Over the sampling year, there were significant differences for bacteria, fungi and actinomycetes between forests and between seasons (P < 0.05). The largest bacteria and fungi populations were in NF, while CF contained the greatest number of actinomycetes. There were also significant differences (P < 0.05) with microbial respiration for forests and seasons. Additionally, compared with NF, urease and acid phosphatase were significantly lower (P < 0.05) in CK and CF. Also, the correlations of soil hydrolysable N and available P to soil microbial and enzymatic activities were highly significant (P < 0.01). Thus, to alter the traditional Chinese fir monoculture so as to mimic the natural forest conditions, managing mixed stands of Chinese fir and broadleaf trees or conducting crop rotation of conifers and broadleaf trees as well as minimizing forest disturbances like clear-cutting, slash burning and soil preparing, could be utilized.     

中亚热带杉木林和常绿阔叶林土壤C、N库及其火烧后的变化

Soil organic carbon (C) and total nitrogen (N) pools of a Chinese fir (Cunninghamia lanceolate, (Lamb.) Hook.) (CF) forest, and an evergreen broadleaf (EB) forest located in mid-subtropical, southeastern China, were compared before clearcutting, with the effect of slash burning on organic C and total N in the top 10 cm of soil before and after burning also being evaluated. Prior to clearcutting CF forest had significantly lower (P < 0.05) organic C and total N in the soil (0-100 cm) compared to EB forest with approximately 60% of the C and N at the two forest sites stored at the 0 to 40 cm soil. In post-burn samples of the 0-10 cm depth at 5 days, 1 year, and 5 years for CF and EB forests, significantly lower levels (P < 0.05) of organic C and total N than those in the pre-burn samples were observed. Compared to the pre-burn levels, at post-burn year 5, surface soil organic C storage was only 85% in CF forest and 72% in EB forest, while total N storage was 77% for CF forest and 73% for EB forest. Slash burning caused marked long-term changes in surface soil C and N in the two forest types.     

土地利用变化对中国西南热带湿润地区土壤磷动态的影响

Land use changes can greatly influence soil phosphorus (P) dynamics, especially when converting native forests to agricultural land. Soils in Xishuangbanna, which is one of southwest China’s tropical areas that maintain fragments of primary forests, were studied to a) evaluate the effect of two common land use changes, conversion of forests to agricultural land or rubber tree plantation, on the dynamics of available P and total P in bulk soils as well as total P in particle size fractions; b) assess the relationship between soil P dynamics and soil organic carbon (SOC); and c) elucidate the relationship between soil P content and soil properties such as pH and texture. Clearing secondary forests with subsequent shifting cultivation and establishment of rubber tree plantation caused significant decreases (P < 0.05) in available P in 0--20 cm soil depths, whereas for total P there was a significant decrease (P < 0.05) when converting to shifting cultivation, rubber tree plantation, or fallow fields at both 0--20 and 20--40 cm depths. Abandonment of fields used for shifting cultivation led to significant increases (P < 0.05) in available P at 20--40 cm depth. In addition, there was a significant positive relationship between soil organic carbon and soil P content. Compared to secondary forests, the ratio of organic carbon to total P in surface soils (0--20 cm) of shifting cultivation and rubber tree plantation was significantly lower (P < 0.05).     

Soil carbon turnover and sequestration in native subtropical tree plantations

Approximately 30% of global soil organic carbon (SOC) is stored in subtropical and tropical ecosystems but it is being rapidly lost due to continuous deforestation. Tree plantations are advocated as a C sink, however, little is known about rates of C turnover and sequestration into soil organic matter under subtropical and tropical tree plantations. We studied changes in SOC in a chronosequence of hoop pine (Araucaria cunninghamii) plantations established on former rainforest sites in seasonally dry subtropical Australia. SOC, δ¹³C, and light fraction organic C (LF C<1.6 g cm⁻³) were determined in plantations, secondary rainforest and pasture. We calculated loss of rainforest SOC after clearing for pasture using an isotope mixing model, and used the decay rate of rainforest-derived C to predict input of hoop pine-derived C into the soil. Total SOC stocks to 100 cm depth were significantly (P<0.01) higher under rainforest (241 t ha⁻¹) and pasture (254 t ha⁻¹) compared to hoop pine (176-211 t ha⁻¹). We calculated that SOC derived from hoop pine inputs ranged from 32% (25 year plantation) to 61% (63 year plantation) of total SOC in the 0-30 cm soil layer, but below 30 cm all C originated from rainforest. These results were compared to simulations made by the Century soil organic matter model. The Century model simulations showed that lower C stocks under hoop pine plantations were due to reduced C inputs to the slow turnover C pool, such that this pool only recovers to within 45% of the original rainforest C pool after 63 years. This may indicate differences in soil C stabilization mechanisms under hoop pine plantations compared with rainforest and pasture. These results demonstrate that subtropical hoop pine plantations do not rapidly sequester SOC into long-term storage pools, and that alternative plantation systems may need to be investigated to achieve greater soil C sequestration.     

Nitrogen mineralization in relation to site history and soil properties for a range of Australian forest soils

Rates of N mineralization were measured in 27 forest soils encompassing a wide range of forest types and management treatments in south-east Australia. Undisturbed soil columns were incubated at 20°C for 68 days at near field-capacity water content, and N mineralization was measured in 5-cm depth increments to 30 cm. The soils represented three primary profile forms: gradational, uniform and duplex. They were sampled beneath mature native Eucalyptus sp. forest and from plantations of Pinus radiata of varying age (<1 to 37 years). Several sites had been fertilized, irrigated, or intercropped with lupins. The soils ranged greatly in total soil N concentrations, C:N ratios, total P, and sand, silt, and clay contents. Net N mineralization for individual soil profiles (0–30 cm depth) varied from 2.0 to 66.6 kg ha^-1 over 68 days, with soils from individual depths mineralizing from <0 (immobilization) to 19.3 kg ha^-1 per 5 cm soil depth. Only 0.1–3.1% of the total N present at 0–30 cm in depth was mineralized during the incubation, and both the amount and the percentage of total N mineralized decreased with increasing soil depth. N fertilization, addition of slash residues, or intercropping with lupins in the years prior to sampling increased N mineralization. Several years of irrigation of a sandy soil reduced levels of total N and C, and lowered rates of N mineralization. Considuring all soil depths, the simple linear correlations between soil parameters (C, N, P, C:N, C:P, N:P, coarse sand, fine sand, silt, clay) and N mineralization rates were generally low (r<0.53), but these improved for total N (r=0.82) and organic C (r=0.79) when the soils were grouped into primary profile forms. Prediction of field N-mineralization rates was complicated by the poor correlations between soil properties and N mineralization, and temporal changes in the pools of labile organic-N substrates in the field.     

黄土丘陵区人工刺槐林恢复过程中土壤氮素与微生物活性的变化

为了探讨不同生长年限的人工刺槐(Robinnia pseudoacacia)林对土壤中氮素组成与微生物活性的影响及机理,本文采用"时空互代"法进行野外选点调查和采样,对典型黄土丘陵区陕西省安塞纸坊沟小流域不同林龄(10 a、15 a、30 a、38 a)人工刺槐林和撂荒地3个土层(0~10 cm、10~30 cm和30~60 cm)中的全氮、铵态氮、硝态氮、有机氮、微生物生物量碳和磷、基础呼吸及基本理化性质进行了研究。结果表明:人工刺槐林地土壤微生物生物量碳、磷含量和微生物熵都显著高于撂荒地(P<0.05)。随着人工刺槐林生长年限的增加,各层土壤铵态氮、硝态氮和有机氮含量均逐渐增加,其中有机氮的增加最显著;土壤微生物生物量碳、磷含量显著增加;微生物熵显著增大而呼吸熵显著减小;土壤有机碳、速效磷含量总体上显著增加(P<0.05);容重和碳氮比则呈下降趋势。随着土层深度的增加,氮素、有机碳、速效磷和微生物生物量碳、磷含量显著减小(P<0.05);容重和pH显著增加。土壤微生物生物量碳、磷和呼吸熵均与有机氮、全氮、硝态氮显著正相关(P<0.05)。分析发现,刺槐的生长促使土壤中微生物可利用碳增加,提高了碳的利用率,使土壤微生物量碳、磷含量增加;微生物活性的提高反过来促进了土壤氮素含量的提高,土壤中有机氮含量显著增加。与10 a生刺槐林相比,30 a生林地土壤表层的全氮含量明显增加,氮素肥力由7级(0.40 g.kg 1)上升为5级(0.87 g.kg 1)水平。