培养温度和土壤类型对土壤硝化特性的影响

采用室内恒温好气培养方法,研究了温度(15℃、20℃、25℃和30℃)和土壤类型(黑土、潮土和红壤)对土壤硝化率的影响。氮素加入比率为N 200 mg kg-1土壤。结果表明:在15～30℃培养范围内,随着培养温度的升高,硝化率呈升高趋势;硝态氮累积量和培养积温(培养温度×培养天数,温度以0℃为基准)之间的关系可用单参数指数模型表示。在相同培养温度条件下,供试土壤硝化率从大到小的顺序为:高有机质含量潮土>低有机质含量潮土>高有机质含量黑土>低有机质含量黑土>低有机质含量红壤>高有机质含量红壤。硝化率(25℃恒温培养)与土壤全磷含量、全钾含量、黏粒含量及pH呈极显著相关;土壤pH和全磷含量解释了硝化率差异的98.1%。土壤pH是影响其硝化率的主要因素,并抑制土壤有机质含量及温度对硝化率的影响。     

黑土、潮土和红壤可溶性有机质的光谱特征及结构差异

为探究不同类型土壤可溶性有机质(DOM)含量和结构的差异性,选取黑土、潮土和红壤3种土壤的表层土壤(0~20 cm)为研究对象,提取其中的DOM,应用紫外–可见光谱、荧光光谱等技术,分析土壤中DOM的数量和光谱特征。结果显示:3种不同类型土壤中可溶性有机碳(DOC)含量及其与土壤有机碳(SOC)的比值(SOC/DOC)大小为:红壤>黑土>潮土(P<0.05);A254值大小为黑土>潮土>红壤,但SUVA254值大小为:潮土>黑土>红壤(P<0.05),表明潮土DOM的芳香化程度最高,但芳香性结构物质含量低于黑土DOM,红壤DOM的芳香性结构物质含量和芳香性构化程度均低于黑土和潮土DOM;荧光发射光谱腐殖化指数(HIXem)和荧光效率(Feff)值大小为:红壤>黑土>潮土(P<0.05),说明红壤DOM的腐殖化程度和π电子共轭基团含量比潮土和黑土DOM高;荧光指数(FI)大小为:红壤>潮土>黑土(P<0.05),表明红壤DOM比潮土和黑土DOM含有更多的微生物源组分;荧光同步光谱显示,黑土和潮土DOM以类蛋白质基团为主,红壤DOM以木质素类基团为主;在土壤有机质含量、黏粒含量和黏土矿物种类不同的情况下,土壤对DOM的吸附能力不同,使土壤DOM的提取比例也存在显著差异。     

长期施肥对我国典型土壤活性有机质及碳库管理指数的影响

对我国重点农区的6种典型土壤红壤、灰漠土、垆土、潮土、褐土、黑土长期耕作施肥后的活性有机质及碳库管理指数(CMI)进行了研究,探讨施肥对不同土壤活性有机质和CMI的影响。土壤活性有机质用KMnO4氧化法测定,采用3种浓度KMnO4(33、1673、33.mmol/L)将土壤活性有机质分为高活性有机质、中活性有机质和活性有机质3部分。结果表明,只耕作不施肥(CK)10年后土壤活性有机质含量降低,CMI下降11.1～63.6,其中垆土、褐土下降幅度最大、黑土最小。施用化肥也使土壤活性有机质下降,其中单施氮(N)的潮土活性有机质下降最大,达31.3%;化肥配合施用(NPK)的红壤活性有机质下降最大,其余土壤相对较小。施肥使土壤活性有机质和总有机质含量增加,高于初始土壤和CK。施用有机肥或有机肥配施化肥,土壤活性有机质含量和CMI均显著增加,CMI以红壤上升最大,达91.4,潮土最小,仅为4.6。土壤活性有机质的数量及CMI变幅大于土壤总有机质的变化幅度,以CMI变化为大,说明CMI是评价施肥耕作对土壤质量影响的最好指标。土壤活性有机质分组结果表明,红壤活性有机质组成以高活性有机质为主;垆土、灰漠土活性有机质以高活性和中活性两部分为主;潮土以中活性有机质为主。施肥对红壤、灰漠土活性有机质组分影响明显,对垆土、潮土影响相对较小。     

旱地土壤的供氮潜力

对潮土、黄褐土、黄棕壤和红壤旱地的供氮潜力进行研究的结果表明,矿化势(No)变化于60340mgkg-1之间,矿化速率常数(K)0.00556-0,01280d-1,矿化势(No)、矿化速率常数(K)和矿化量(Nt)与土壤供氮量均呈显著相关,说明No、Nt和K是土壤供氮潜力的重要参数。这些参数与土壤全氮、有机质、有机氮、易分解有机质、C/N等土壤组成性质密切相关。测定表明,供试土壤粘土矿物多以2:1型为主,土壤固定态铵多在100mgkg-1以上,有部分可重新释放出来,是研究土壤供氮潜力时不容忽视的因素。     

安徽省几种主要土壤有机碳含量及其组分研究

研究了安徽省4种主要类型土壤(砂姜黑土、潮土、水稻土和红壤)有机碳(SOC)、可溶性有机碳(DOC)和微生物量碳(MBC)的含量剖面分布及其相互关系.结果表明,4种土壤SOC,DOC和MBC含量存在明显差异,但其剖面分布规律基本一致,表层含量较高.随着土壤层次加深而依次递减;表层土壤SOC含量顺序为:水稻土>砂姜黑土>潮土>红壤,DOC含量顺序为:砂姜黑土>潮土>水稻土>红壤,MBC含量顺序为:潮土>砂姜黑土>红壤>水稻土.DOC和MBC分别只占SOC的4.92%～18.97%和1.86%～5.68%.土壤SOC,DOC与MBC之间存在着密切的关系,3者之间的相关性均分别达到了10%,5%或1%的显著或极显著水平.     

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。     

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)。     

苏打盐碱化稻田土壤氮素矿化和硝化特征及其影响因子

  【目的】  为探明土壤盐碱化对氮素转化的影响,研究了不同盐碱化条件下氮素的矿化和硝化特征以及这些特征与土壤盐分、养分含量的关系,为盐碱化土壤养分的科学管理提供理论依据和数据支撑。  【方法】  随机采集了30个不同盐碱化程度的稻田土壤 (0—20 cm)样品,根据盐碱化程度将采集的土壤样品划分为轻度(含盐量0.1%～0.3%,碱化度5%～15%)、中度(含盐量0.3%～0.5%,碱化度15%～30%)和重度(含盐量0.5%～0.7%,碱化度30%～45%)盐碱土3类,每个类别中依据最小归类样品数选取盐碱化程度接近的3个土样作为3次重复,进行氮素矿化和硝化室内培养试验(25℃,24 h光照)。于培养的第0、3、6、9、15、21天取样测定土壤铵态氮、硝态氮含量及脲酶和碱性蛋白酶活性。通过相关性分析研究土壤各指标与氮素矿化、硝化过程间的相关关系,采用逐步回归分析筛选影响氮素矿化和硝化过程的主要因子。  【结果】  随着土壤盐碱化程度的加剧,氮素矿化和硝化作用显著下降(P<0.05)。与轻度盐碱土相比,中度和重度盐碱土的氮素最大净矿化速率分别低12.7%和29.8%,累积矿化氮量分别低15.7%和25.2%,最大净硝化速率分别低15.4%和23.1%,累积硝化氮量分别低15.4%和23.1%,最大脲酶活性分别低16.0%和34.8%,最大碱性蛋白酶活性分别低6.0%和15.6%。逐步回归分析表明,土壤电导率(EC)、pH、CO₃2–、Na+、全氮和有机质是影响土壤氮素矿化作用的主要因子,EC、pH、CO₃2–、Na+和有机质是影响土壤氮素硝化作用的主要因子。  【结论】  随着土壤盐碱化程度的增加,土壤氮素净矿化速率、净硝化速率、累积矿化氮量、累积硝化氮量、脲酶和碱性蛋白酶活性不断下降,土壤盐碱化显著抑制了氮素的矿化和硝化作用。     

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。      

长期有机培肥模式下黑土碳与氮变化及氮素矿化特征

土壤氮的矿化是土壤氮素肥力的重要指标,是影响作物产量至关重要的因素。本研究依托黑土长期定位试验,通过取样分析研究了32 a不同培肥模式下黑土碳、 氮及主要活性组分的变化,采用淹水培养法研究了不同施肥模式下黑土氮素的矿化特征。结果表明,施肥显著提高黑土可溶性碳（DOC）、 氮（DON）的含量及其比例。在氮、 磷、 钾化肥的基础上配施有机肥,显著降低了土壤微生物量氮（SMBN）占土壤总氮的比例,提高了土壤微生物量的C/N比值（SMBC/SMBN）,促进了土壤氮的生物固持。施肥32 a后,单施常量和高量有机肥处理的土壤氮的矿化量（Nt）显著提高,分别相当于不施肥的8.2倍和10.2倍,而单施氮或氮磷钾化肥对黑土氮素矿化量无明显影响。施用有机肥显著提高了土壤氮素的矿化率（Nt/TN）,但有机肥配施化肥（氮或氮磷钾）的处理与单施有机肥相比,黑土氮的矿化率显著降低,降低幅度分别为23.5%~32.1% 和14.1%~17.8%。土壤氮素矿化量与土壤有机质、 全氮储量、 活性碳、 氮组分均呈极显著线性相关,但氮素的矿化率随着有机质和全氮含量的提高而提高至0.4% 后基本稳定。表明尽管土壤氮的矿化与有机质的含量直接相关,但土壤有机质的品质同样决定着土壤氮素的矿化能力。施有机氮是提高土壤供氮能力的重要途径。     

Kinetic Parameters of Gross N Mineralization of Peat Soils as Related to the Composition of Soil Organic Matter

Peat land has been considered as an alternative type of land for agricultural development especially in the tropics. In the present study, the N-supplying capacity, one of the most important soil properties in terms of crop production, of peat soils was examined. Ten peat soil samples were collected from Indonesia, Malaysia, and Japan. Gross N mineralization in the soil samples was estimated using a zero-order model, and kinetic parameters of mineralization were determined using a simple type model. Soil organic matter composition was investigated using ¹³C CPMAS NMR. Mineralization potential ( N ₀), apparent activation energy ( E _a), and mineralization rate constant ( k ) ranged between 571–2,445 mg kg⁻¹, 281–8,181 J mol⁻¹, and 0.009–0.020 d⁻¹, respectively. Although none of the parameters showed a significant correlation with the soil C/N ratio, a negative correlation was observed between the k value and the ratio of the proportion of alkyl C in total C to that of O -alkyl C estimated by ¹³C CPMAS NMR. The latter suggested that the k values were higher in the peat soils relatively rich in readily decomposable organic matter including carbohydrates.     

Predictors of gross N mineralization and immobilization during decomposition of stabilized organic matter in agricultural soil

Long-term additions of different types of organic amendments affect the amount of soil organic matter. Less is known about how this in turn affects carbon (C) and nitrogen (N) mineralization from the pool of stabilized soil organic matter, or the extent to which gross N immobilization influences the net amount of N mineralized. Soils, differing in the quantity and quality of organic matter inputs they had received since 1956, were sampled approximately 6 or 18 months after the most recent applications of organic amendments. Two laboratory experiments were carried out to: (i) evaluate if, and how, the organic amendments had affected C mineralization, gross and net N mineralization; (ii) examine the relation between gross N immobilized and free-light fraction of organic matter; and (iii) assess predictors for gross N mineralization and immobilization rates in soils. The amount of soil organic C and N were major determinants of C and gross N mineralization, but not of net N mineralization. Carbon mineralization was related to gross N mineralization, but the ratio between the two was not constant. Gross N immobilization was related to the amount of free-light fraction material in the soil with 90% variation explained. For most common organic amendments applied in autumn, our results support the use of total soil organic N and C mineralization as predictors of gross N mineralization from stabilized soil organic matter. In addition, we propose that the amount of free-light fraction material present in the soil in spring is adequate as a predictor of the immobilization potential of the soil, without a need to consider the C-to-N ratio of this material.     

C and N turnover in structurally intact soils of different texture

The turnover of native and applied C and N in undisturbed soil samples of different texture but similar mineralogical composition, origin and cropping history was evaluated at −10 kPa water potential. Cores of structurally intact soil with 108, 224 and 337 g clay kg⁻¹ were horizontially sliced and ¹⁵N-labelled sheep faeces was placed between the two halves of the intact core. The cores together with unamended treatments were incubated in the dark at 20 °C and the evolution of CO₂-C determined continuously for 177 d. Inorganic and microbial biomass N and ¹⁵N were determined periodically. Net nitrification was less in soil amended with faeces compared with unamended soil. When adjusted for the NO₃-N present in soil before faeces was applied, net nitrification became negative indicating that NO₃-N had been immobilized or denitrified. The soil most rich in clay nitrified least N and ¹⁵N. The amounts of N retained in the microbial biomass in unamended soils increased with clay content. A maximum of 13% of the faeces ¹⁵N was recovered in the microbial biomass in the amended soils. CO₂-C evolution increased with clay content in amended and unamended soils. CO₂-C evolution from the most sandy soil was reduced due to a low content of potentially mineralizable native soil C whereas the rate constant of C mineralization rate peaked in this soil. When the pool of potentially mineralizable native soil C was assumed proportional to volumetric water content, the three soils contained similar proportions of potentially mineralizable native soil C but the rate constant of C mineralization remained highest in the soil with least clay. Thus although a similar availability of water in the three soils was ensured by their identical matric potential, the actual volume of water seemed to determine the proportion of total C that was potentially mineralizable. The proportion of mineralizable C in the faeces was similar in the three soils (70% of total C), again with a higher rate constant of C mineralization in the soil with least clay. It is hypothesized that the pool of potentially mineralizable C and C rate constants fluctuate with the soil water content.     

西藏高原自然生态系统转化为农田后提高了土壤的净矿化和净硝化

A comparative study was conducted to determine the NH4^＋ and NO3^- concentrations in soil profiles and to examine the net nitrogen （N） mineralization and nitrification in adjacent forest, grassland, and cropland soils on the Tibetan Plateau. Cropland soil showed significantly higher inorganic N concentrations in soil profiles compared with forest and grassland soils. NO3^- -N accounted for 70%-90^ of inorganic N in cropland soil, while NH4^＋ -N was the main form of inorganic N in forest and grassland soils. The average net N mineralization rate at 0 20 cm depth was approximately twice in cropland soil （1.48 mg kg^-1 d^-1） as high as in forest （0.83 mg kg^-1 d^-1） or grassland soil （0.72 mg kg^-1 d^-1）. Cropland showed strong net nitrification, with the net rate almost equal to the total net N mineralization. Urea addition stimulated soil respiration, particularly in forest soil. Most urea-N, however, remained as NH4^＋ in forest and grassland soils, while NO3^- was the main form of inorganic N to increase in cropland soil. Higher rates of net nitrification in cropland soils suggest that land use change on the Tibetan Plateau may lead to high N losses through nitrate leaching.     

Changes in soil organic matter and net nitrogen mineralization in heathland soils,after removal,addition or replacement of litter from Erica tetralix or Molinia caerulea

Summary The effects of different litter input rates and of different types of litter on soil organic matter accumulation and net N mineralization were investigated in plant communities dominated by Erica tetralix L. or Molinia caerulea (L.) Moench. Plots in which the litter on the soil had repeatedly been removed were compared with plots in the same plant community in which litter had been added to the soil. In another treatment, litter was removed and replaced by litter from the other plant community. Net N mineralization was measured in situ after 5 years. Less soil organic matter and soil N was found in plots in which litter had been removed, compared with control plots, or plots to which litter had been added, but these differences were significant for the Erica sp. soils only. Plots in which litter had been replaced and control plots did not differ significantly in the amount of soil organic matter. However, in both plant communities, the differences agreed with the faster decomposition rate of Molinia sp. litter compared with Erica sp. litter. The gravimetric soil moisture content was correlated positively with the amount of soil organic matter, both in the Erica sp. soils and the Molinia sp. soils. Net N mineralization rates (g N m^-2) differed significantly between treatments for Erica sp. soils but no for Molinia sp. soils. For Erica sp. soils, net N mineralization rates increased with increasing amounts of soil organic matter and soil N. Replacing the litter with Molinia sp. litter (which differs in chemical composition) had no clear additional effect on the net N mineralization rate.     

Impact of land-use types on soil nitrogen net mineralization in the sandstorm and water source area of Beijing,China

Changes of land-use type (LUT) can affect soil nutrient pools and cycling processes that relate long-term sustainability of ecosystem, and can also affect atmospheric CO₂ concentrations and global warming through soil respiration. We conducted a comparative study to determine NH₄⁺ and NO₃⁻ concentrations in soil profiles (0–200 cm) and examined the net nitrogen (N) mineralization and net nitrification in soil surface (0–20 cm) of adjacent naturally regenerated secondary forests (NSF), man-made forests (MMF), grasslands and cropland soils from the windy arid and semi-arid Hebei plateau, the sandstorm and water source area of Beijing, China. Cropland and grassland soils showed significantly higher inorganic N concentrations than forest soils. NO₃⁻-N accounted for 50–90% of inorganic N in cropland and grassland soils, while NH₄⁺-N was the main form of inorganic N in NSF and MMF soils. Average net N-mineralization rates (mg kg⁻¹ d⁻¹) were much higher in native ecosystems (1.51 for NSF soils and 1.24 for grassland soils) than in human disturbed LUT (0.15 for cropland soils and 0.85 for MMF soils). Net ammonification was low in all the LUT while net nitrification was the major process of net N mineralization. For more insight in urea transformation, the increase in NH₄⁺ and, NO₃⁻ concentrations as well as C mineralization after urea addition was analyzed on whole soils. Urea application stimulated the net soil C mineralization and urea transformation pattern was consistent with net soil N mineralization, except that the rate was slightly slower. Land-use conversion from NSF to MMF, or from grassland to cropland decreased soil net N mineralization, but increased net nitrification after 40 years or 70 years, respectively. The observed higher rates of net nitrification suggested that land-use conversions in the Hebei plateau might lead to N losses in the form of nitrate.     

Soil particulate organic matter effects on nitrogen availability after afforestation with Eucalyptus globulus

We examined the hypothesis that changes in the quality and/or quantity of soil particulate organic matter (POM) after afforestation of pasture land with Eucalyptus globulus Labill. plantations caused increased nitrogen (N) immobilization and a decline in N availability. The quantity of POM was measured on soils from 10 paired pasture/plantation sites in south-western Australia. Net mineralization of C and N were measured over a 14-day incubation of POM, whole soil, and a mix of POM (33%) and whole soil (67%) at 25 °C and optimal moisture content (matric potential of 25 kPa). There was no significant difference in total organic C between pasture and plantation. However, the POM fraction C was higher in plantation soils (75%) than under pasture (62%), reflecting the coarser nature of organic inputs under plantation. Total soil N concentration was 20% lower under plantation compared to pasture, and the proportion in the POM was higher (74% compared to 57% for pasture soil). The C:N ratios in POM under both pasture and plantation, and in the whole soil under plantation were around 19, but C:N ratios of whole soil under pasture was 17. Average C mineralization was 13% lower in plantation relative to that in pasture soil. The isolated POM fraction had 18% higher C mineralization rate than that in whole soil. The change in net N mineralization with afforestation was marked, with 50% lower net N mineralization in plantation than pasture whole soils. Net N mineralization in the isolated POM fraction was also about 50% of that in the whole soil for both pasture and plantation soils. Although, the pasture and plantation POM had similar C:N ratios, the net N mineralization was 2-fold greater in pasture POM than in plantation POM, suggesting that biochemical characteristics other than the C:N ratio had the main influence on net N mineralization rates. The POM fraction did not significantly immobilize N from the whole soil when placed in a mixture of POM and whole soil, suggesting that N immobilization was not the main mechanism for POM to influence N availability in these soils.     

Nitrogen Mineralization in Soils Related to Initial Extractable Organic Nitrogen: Effect of Temperature and Time

An important source of nitrogen (N) for crops is mineralization of soil organic matter during the growing season. Awareness is growing that dissolved organic nitrogen (DON) plays an important role in mineralization and plant uptake. We studied the influence of temperature and time on extractable organic nitrogen (EON) levels, which is a measure of DON, and their relationship with N mineralization. Aerobic incubation experiments were conducted in the laboratory for five soils at different temperatures (4 20, and 30 °C) and different time intervals with optimal water content (60% of its water-holding capacity). Net N mineralization ranged between 14 and 155 mg kg^–1 within 84 days and was correlated with the initial amount of EON. Net N mineralization among the soils, time, and incubation temperatures was linearly related to the square root of time multiplied by temperature, with mineralization rate k being independent of time and temperature. Because initial EON values were also related to these kvalues, we were able to describe the net N mineralization at different temperatures based on an analysis of initial EON. Preliminary validation with results from pot experiments in the literature suggests that the approach is promising, although the proposed model needs to be calibrated with more soils.     

温度和湿度对高寒湿地土壤碳矿化和氮矿化的影响

Relationships between carbon (C) production and nitrogen (N) mineralization were investigated in two alpine wetland soils of the Tibetan Plateau using laboratory incubation under different temperatures (5, 15, 25, and 35 ℃) and water saturation (noninundation and inundation). A significant positive relationship was found between CO2 production and N mineralization under increasing temperatures from 5 to 35 ℃ with the same water saturation condition in the marsh soil (r2 ＞ 0.49, P ＜ 0.0001) and the peat soil (r2 ＞ 0.38, P ＜ 0.002), and a negative relationship with water saturation increasing at the same temperature, especially 25 and 35 ℃, in the marsh soil (r2 ＞ 0.70, P ＜ 0.009) and the peat soil (r2 ＞ 0.61, P ＜ 0.013). In conclusion, temperatures and water saturation could regulate the relationship between CO2 production and net N mineralization in the Tibetan alpine marsh and peat soils.