不同种植年限果园土壤有机氮组分变化特征

为了揭示不同种植年限(0、2、10、20和30 a)果园土壤有机氮组分变化规律,本文采用Bremner有机氮分级方法研究种植年限对果园土壤有机氮组分的影响。结果表明:耕作30年范围内果园土壤全氮含量随种植年限的延长而显著增加,增加的氮量在酸解未知态氮、非酸解性氮、氨态氮、氨基酸氮和氨基糖氮中的分配比例分别为38.9%、25.7%、20.5%、9.9%和4.9%;随着种植年限的延长,土壤有机氮组分中非酸性氮比例呈上升趋势,氨态氮和酸解未知态氮比例呈下降趋势,各有机氮组分比例的大小顺序也随之发生变化;非酸解性氮比例的提高降低了土壤有机氮矿化速率,影响土壤无机氮供应能力。     

连续施用炭基肥及生物炭对棕壤有机氮组分的影响

为了揭示连续施用炭基肥及生物炭条件下棕壤有机氮组分的变化情况,本文基于田间定位试验,研究了连续定位施用炭基肥及生物炭对棕壤有机氮组分的影响。试验共设置5个处理:不施肥、低量生物炭、高量生物炭、氮磷钾配施、炭基肥。于2014年花生收获后每个小区按"S"型设置3个采样点,采集0~20、20~40 cm的土壤样本,利用Branmer有机氮分组方法对土壤有机氮组分进行测定与分析。结果表明:经过连续4年的不同施肥处理,不同处理土壤全氮含量均有所提升;炭基肥处理土壤全氮含量显著高于原始土和CK处理,增幅分别达到69.8%、4.8%;不同施肥处理中有机氮各组分的含量顺序为酸解铵态氮氨基酸态氮非酸解氮酸解未知态氮氨基糖态氮;施用炭基肥显著增加了土壤酸解有机氮中酸解铵态氮、氨基酸态氮的含量,与原始土相比增加了65.9%、128.0%;随着生物炭用量的增加,酸解铵态氮含量处于增加趋势,但增加幅度远低于等碳投入的炭基肥处理;对于未知态氮、非酸解有机氮总量无论施用生物炭、氮磷钾化肥或炭基肥均提高了其含量,但各处理间差异不显著;连续施用炭基肥或生物炭显著提高了土壤酸解有机氮中酸解铵态氮和氨基酸态氮的含量,促进了氮素的活化,有利于花生中低产田氮素的吸收和运转。     

水氮调控对设施土壤供氮潜力的影响

利用连续3年不同灌水下限(25、35和45 kPa)和施氮量(75、300和525 kg N·hm~(-2))的膜下滴灌设施番茄田间试验,探讨水氮调控对设施土壤供氮潜力的影响。结果表明:灌水下限和施氮量对土壤有机碳和全氮储量的影响显著,而水氮交互作用对二者影响均不显著;灌水下限、施氮及其交互作用对休耕期0～30 cm设施土壤有机氮组分、微生物量氮和固定态铵储量的影响显著;不同水氮调控下,设施番茄休耕期0～30 cm土壤酸解氮组分储量及占酸解总氮比例的大小顺序依次为酸解氨基酸氮酸解铵态氮酸解未知氮酸解氨基糖氮;酸解氨基酸氮是设施土壤中最主要的有机氮形态;酸解氨基酸氮与酸解铵态氮、酸解氨基糖氮、酸解总氮、非酸解氮、有机碳和全氮均呈显著相关;土壤固定态铵与酸解氨基酸氮呈显著正相关;土壤微生物量氮与酸解铵态氮、酸解氨基糖氮呈显著正相关,与酸解氨基酸氮呈显著负相关。土壤酸解氨基酸氮、土壤微生物量氮和固定态铵在一定程度上可作为设施土壤供氮潜力的反映指标,科学合理的水氮措施对提升设施土壤供氮潜力具有重要意义。     

尕海湿地退化演替过程中土壤有机氮组分的变化特征

为探究尕海湿地退化演替过程中土壤有机氮各组分变化规律,采用野外采样与室内分析相结合的方法,研究尕海湿地未退化(UD)、轻度退化(LD)、中度退化(MD)和重度退化(HD)4个退化演替阶段的土壤总氮(TN)和有机氮组分[未知态氮(HUN)、酸解氨态氮(AMN)、酸解氨基酸态氮(AAN)以及氨基糖态氮(ASN)]含量及其分布特征。结果表明: 当尕海湿地退化演替到LD时,0～10 cm层土壤TN、HUN、AMN和AAN含量分别降低17.3%、19.4%、8.6%和-5.6%,MD时分别降低28.0%、19.4%和17.1%和0,HD时分别降低35.8%、28.8%、28.6%和55.6%;10～20 cm层,LD时上述氮素含量分别降低4.0%、10.3%、2.9%和9.1%;MD时分别降低21.0%、18.3%、-2.9%和-9.1%;HD时分别降低9.9%、38.9%、21.2%和51.4%;而20～40 cm无显著变化;4个退化阶段各酸解氮组分占TN比例大小顺序为HUN(25.9%～32.5%)> AMN(6.7%～11.1%)> AAN(4.8%～11.1%)> ASN(1.2%～4.4%)。冗余分析显示,土壤含水量是土壤有机氮组分变化的主要驱动因子。尕海湿地退化显著降低了0～10 cm层土壤TN及酸解氮各组分含量,减弱了土壤氮“汇”功能,AAN和ASN对湿地退化最为敏感。     

黄土高原典型区域土壤腐殖酸组分剖面分布特征

黄土高原作为典型的气候敏感带和生态环境脆弱区,诸多因素影响着这个区域的土壤有机碳及其组分的分布特征。本文以黄土高原典型区域土壤剖面 0—200 cm土样为对象,分析了土壤腐殖酸、胡敏酸（HA）和富里酸（FA）含量随地理位置及土层深度的分布特征,并进一步探讨了土壤腐殖酸、HA和FA与全氮含量及土壤颗粒组成的关系。结果表明,黄土高原主要类型土壤腐殖酸、HA和FA含量均较低,且存在明显地理位置和土层分异性：从南到北同层次土壤腐殖酸、HA和FA含量均显著降低,同一区域随土层深度增加各组分含量均表现为在 0—40 cm土层明显下降, 40—120 cm土层稍有下降,120 cm土层以下基本稳定;土壤腐殖酸占有机碳比例变化范围为26.6%—54.7%,相对较小,且在整个剖面变化幅度不大,从南向北土壤腐殖酸占有机碳比例有增加趋势;土垫旱耕人为土在 0—40 cm、 40—120 cm和 120—200 cm土层中HA占腐殖酸比例分别为39.8%、49.0%和53.5%,HA/FA分别为0.66、0.96和1.15,黄土正常新成土在以上土层中HA占腐殖酸比例分别为26.3%、33.9%和42.3%,HA/FA分别为0.36、0.51和0.73,干润砂质新成土在以上土层中HA占腐殖酸比例分别为13.4%、37.1%和45.2%,HA/FA分别为0.16、0.59和0.82,说明黄土高原南北主要类型土壤腐殖酸品质总体较差,均属富里酸型土壤,且从南到北腐殖酸品质逐渐下降;土壤腐殖酸、HA和FA均与全氮含量呈极显著线性相关（P<0.01）,土壤有机碳、腐殖酸及HA含量与粘粒及砂粒百分含量亦呈高度线性相关（P<0.01）。     

黑河流域中游芦苇湿地土壤碳垂直分布特征

黑河流域是中国的第二大内陆河流域, 在该流域中游分布的湿地面积有170411.2 hm2, 其中水陆交错带芦苇湿地面积30000 hm2。以黑河流域中游芦苇湿地为例, 探讨了其土壤剖面中碳的垂直变化规律。结果表明, 土壤剖面0-20 cm 土层的容重较小, 容重均值为 0.365 g·cm3, 在 20-50 cm 容重均值急剧升高; 50 cm 以下, 容重均值均在1.29 g·cm3 以上, 容重随土壤深度增加呈“S”型增长; 土壤有机碳主要集中在土壤表层0-40 cm 处, 40 cm 以下不同土层有机碳含量之间无显著性差异(p<0.01), 土壤有机碳随土层深度的增加呈指数下降趋势; 土壤有机碳含量和土壤容重之间存在显著的相关性。     

土壤有机氮组分的年际变化及其对秸秆还田的响应

阐明土壤有机氮组分的年际变化特征及其对秸秆还田的响应对合理调控土壤有机氮库和土壤可持续利用具有重要意义。在沈阳农田生态系统国家野外科学观测研究站进行田间微区试验(土壤类型为潮棕壤),设置单施氮肥(200 kg N·hm^-2,下同)、50%秸秆还田配施氮肥和100%秸秆还田配施氮肥3个处理,采用Bremner酸水解法对试验第1、3、6、9年的土壤有机氮组分进行分级。结果表明: 氨基酸态氮含量随着耕作年限的增加逐渐提升,提升幅度为39.8%;酸解未知态氮含量提升幅度为10.8%,且在第3年时最高;土壤总氮和其他有机氮组分含量随耕作年限变化不大。相对容易矿化的酸解总氮占土壤总氮的比例随耕作年限的增加逐渐增加,比较稳定的未酸解态氮占土壤总氮的比例随耕作年限的增加逐渐下降,说明随着耕作年限的增加土壤氮素有效性提高,土壤供氮能力增强。与单施氮肥相比,加入秸秆提高了土壤总氮和各酸解态氮含量,秸秆还田量越多,提升效果越明显。秸秆还田对酸解态氮组分的影响主要发生在试验第6、9年,增加的土壤总氮主要为氨基酸态氮和酸解未知态氮,从而提高了土壤中酸解态氮占土壤总氮的比例。秸秆还田能够提升土壤氮库容,提高土壤保氮供氮能力。     

内蒙古典型草原马粪分解过程中氮素组分的变化

2008年6月至2009年9月,在野外条件下,采用堆置于地表和埋入地下2种处理方式,研究了内蒙古典型草原马粪分解过程中氮素组分的变化特征.结果表明： 2种处理残留马粪中,氨态氮、氨基酸态氮和氨基糖态氮在分解前期(0~90 d)维持较高浓度,后期(330~450 d)浓度显著降低;酸解未知氮和非酸解未知氮浓度随分解呈升高趋势,分解后期升高幅度更为明显.鲜马粪中,铵态氮是无机氮的主要存在形态,随分解呈逐渐降低趋势;鲜马粪中的硝态氮浓度较低,其在残留马粪中的淋溶损失较低,随分解逐渐累积.马粪埋入地下,对铵态氮以气态氨的挥发过程有显著影响,对其他氮素组分的影响不明显.马粪分解前期,氮素矿化的主要有机氮源为氨态氮、氨基酸态氮和氨基糖态氮,后期主要为酸解未知氮和非酸解未知氮.铵态氮的生物有效性主要体现在马粪分解前期,硝态氮则体现在分解后期.     

内蒙古典型草原马粪分解过程中氮素组分的变化

2008年6月至2009年9月,在野外条件下,采用堆置于地表和埋入地下2种处理方式,研究了内蒙古典型草原马粪分解过程中氮素组分的变化特征.结果表明:2种处理残留马粪中,氨态氮、氨基酸态氮和氨基糖态氮在分解前期(0～90 d)维持较高浓度,后期(330～ 450d)浓度显著降低;酸解未知氮和非酸解未知氮浓度随分解呈升高趋势,分解后期升高幅度更为明显.鲜马粪中,铵态氮是无机氮的主要存在形态,随分解呈逐渐降低趋势;鲜马粪中的硝态氮浓度较低,其在残留马粪中的淋溶损失较低,随分解逐渐累积.马粪埋入地下,对铵态氮以气态氨的挥发过程有显著影响,对其他氮素组分的影响不明显.马粪分解前期,氮素矿化的主要有机氮源为氨态氮、氨基酸态氮和氨基糖态氮,后期主要为酸解未知氮和非酸解未知氮.铵态氮的生物有效性主要体现在马粪分解前期,硝态氮则体现在分解后期.     

长三角典型水稻土有机碳组分构成及其主控因子

准确把握水稻土有机碳组分构成特征及其主控因子,对定量化评价土壤有机碳质量和未来演变趋势具有重要意义。通过室内土壤呼吸培养实验结合有机碳三库一级动力学方程,模拟得到长三角地区典型水稻土剖面(0—100 cm)各土层有机碳组分含量及其分布特征;并利用主成分分析获取主控因子,建立有机碳组分回归预测模型。结果表明:水稻土活性碳、慢性碳和惰性碳含量随剖面深度增加而降低,上层土壤(0—40 cm)有机碳组分含量下降速度明显快于下层土壤(40—100 cm);水稻土活性碳构成比例不超过5.3%,惰性碳构成比例大于活性碳与慢性碳比例之和,达到60%以上,水稻土有机碳总量变异主要取决于慢性碳和惰性碳组分变异。因此,水稻土固碳重点在于慢性和惰性组分。同时,研究还发现水稻土类型和剖面深度主要在表层对有机碳组分含量和比例构成产生显著影响,土壤有机碳量、全氮和pH是影响水稻土有机碳组分含量分异的主控因子,利用主控因子可较好预测水稻土有机碳组分含量。     

半湿润农田生态系统长期施肥对土壤团聚体中有机氮组分的影响

通过对黄土高原半湿润农田生态系统25年的田间肥料定位试验,研究了长期不同施肥模式对土壤有机氮组分及其在各级团聚体中分布的影响.结果表明:长期施肥对水解氨态氮、水解未知氮在土壤各级团聚体中分布的影响最大,对氨基酸态氮的分布有一定影响,而对氨基糖态氮分布的影响较小.长期施用化肥和有机肥能有效地影响水解氨态氮和水解未知氮与团聚体的结合作用,而氨基糖态氮在土壤氮循环转化过程中具有较强的稳定性.长期施肥条件下土壤水解全氮与有机碳、全氮以及团聚体分形维数均呈极显著正相关,其r分别为0.942,0.981,0.910(P<0.001),说明土壤有机氮组分对土壤团聚体的形成和性质具有显著影响.相关分析表明,土壤全氮或有机质对1～2mm和0.25～1mm土壤团聚体中各有机氮组分的影响较大.     

Relationship Between Root Biomass and Soil Organic Matter Pools in the Shortgrass Steppe of Eastern Colorado

We examined the distribution of soil organic carbon (SOC) fractions and roots with depth to improve our understanding of belowground carbon dynamics in the shortgrass steppe of northern Colorado. Weaver and others (1935) found that the surface 15 cm of soil contained over 70% of the total roots found in a tallgrass prairie soil profile, while only accounting for 40% of the profile soil organic matter. We asked whether the relationship between roots and SOC that Weaver and others (1935) found in the tallgrass prairie was also found in the shortgrass steppe. Weaver and others (1935) suggested that the dissimilarity between belowground biomass and SOC with depth is the result of variability in decomposition rates. In an effort to determine whether patterns of SOC are the result of short-term plant input patterns or decomposition, we measured the ¹⁴C content of potentially mineralizable C and particulate organic matter (POM) C ten years after pulse labeling shortgrass steppe vegetation. We also estimated the mass specific decomposition rate constant (kPOM) for POM C through a shortgrass steppe soil profile. We found that the distribution of roots and SOM in the shortgrass steppe were similar to those observed in tallgrass prairie (Weaver and others 1935), with a higher proportion of total root biomass in the surface soils than total soil organic matter. Fifty-seven percent of root biomass was found in the surface 15-cm, while this same soil layer contained 23 percent of profile soil organic C. We measured the highest accumulation of ¹⁴C at the soil surface (12.0 ng ¹⁴C·m^-2·cm^-1 depth), with the least accumulation from 75-100 cm (0.724 ng ¹⁴C·m^-2·cm^-1 depth). The highest values of potentially mineralizable C were at the soil surface, with no significant differences in total mineralizable C among the 10-100 cm soil depths. The contribution of POM C to total C reached a profile minimum at the 15-20 cm depth increment, with profile maxima in the surface 5 cm and from 75-100 cm. We estimated that the proportion of particulate organic matter lost annually (kPOM) reached a profile maximum of 0.097 yr^-1 within the 10-15 cm depth increment. The 75-100 cm depth increment had the lowest kPOM value at 0.058 yr^-1. Thus, within the same physical fraction of SOC, decomposition rates vary with depth by nearly twofold. This pattern of high decomposition rates from 10-15 cm with lower decomposition rates at the soil surface and deeper in the soil profile may be the result of higher water availability in sub-surface soils in the shortgrass steppe.     

Movement and chemical distribution of isotopic nitrogen down the soil profile

Summary The downward movement and accumulation of added fertilizerin situ was studied for fine-textured, loess-terrace derived soils of Rimski Sanchevi, Navisad, Yugoslavia. Three N-treated, fallowed plots from a nitrate movement experiment were selected for this study. Soil samples were obtained upto 200 cm depth at 20 cm interval and the isotope ratio analyses were done for different forms of residual N.Fertilizer moved down the profile upto 140 cm depths and the accumulated residual N in the profile was about 55 percent of total added¹⁵N. The maximum accumulation of added fertilizer was at 0–20 cm depth (98 kg/ha) followed by 60–80 cm (32 kg/ha) depth. The fertilizer¹⁵N converted to alkali-stable (amino acid) and alkali-labile (amino sugar)-N forms were about 17 and 12 percent respectively. Only 0.41 percent of added fertilizer was converted to fixed NH₄–N. It is hoped that these findings will help the proper management of nitrogen fertilization to reduce the risk of ground water pollution.     

Changes in the soil organic N fractions of a tropical Alfisol fertilized with 15N-urea and cropped to maize or pasture

Qualitative and quantitative changes in soil and fertilizer-derived organic N fractions were assessed during a cropping season in an intertropical Alfisol, under maize and pasture, fertilized with¹⁵ N-urea. Before the sowing, after fertilizing and after the harvest, the organic N of top soil samples was fractionated by a two-step acid hydrolysis under reflux (H1 = 1 M HCl for 3 h; H2 = 3 M HCl for 3 h). The total hydrolysable N (HN) from H1 decreased significantly during the cropping season in both maize and pasture soils. Contrastingly, the content of HN from H2 and that of non-hydrolysable N did not vary significantly during the cropping season. The easily hydrolysable fractions, especially amino acid N, amino sugar N and amide N, were the most active N pools and the major source of N potentially available for plants. The urea-derived N that remained in the soil was mainly in organic forms at both 7 and 108 d after fertilizing (70–82% and 93–98%, respectively), higher figures being found in pasture than in maize soil. The total amount of urea-derived HN decreased significantly during the crop period in both maize and pasture soils. This decrease was largely due to the decline in HN from H1. The amount of non-hydrolysable urea-derived N was significantly higher in pasture than in maize soil and it decreases in the former and increases in the latter, during the cropping season. During the crop period, the decrease of urea-derived organic N was 4.6 to 9.1 times higher than that of native organic N. Shortly after fertilizing, the proportion of urea-derived N in the easily hydrolysable (H1) organic fractions was higher than that of soil N, whereas the reverse was true for the slowly hydrolysable (H2) or insoluble fractions. These differences were less marked, but still significant, at the end of cropping. The easily hydrolysable organic N fractions were more sensitive than total N to the impact of land use intensification and are, therefore, a more useful index for early detection of soil biological degradation.     

Impact of land use change on soil aggregate dynamics in the dry tropics

A 2‐year study was conducted to elucidate land use change (LUC) impact on the distribution of aggregate size fractions and associated carbon (C) concentration involving natural forest (NF), degraded forest (DF), cropland (CL), and biofuel plantation (JP, Jatropha plantation) in the dry tropical region of India across the soil profile (0–10, 10–20, and 20–30 cm). Across the seasons and the land uses, the proportion of macro‐ and microaggregates was maximum at upper and minimum at lower layer whereas mesoaggregates increase with depth. The trend of macro‐ and microaggregate fractions through the soil profile was NF > JP > DF > CL whereas that of mesoaggregates was CL > DF < JP > NF. Dry mean weight diameter was highest at upper layer and decreased down the depth in all the land uses and followed the trend NF > JP > DF > CL. Aggregate associated organic carbon (OC) concentration in all the fractions decreased from NF to DF, CL, or JP indicates that macroaggregate associated OC concentration was more susceptible to loss than that of meso‐ and microaggregate associated OC concentration. LUC induced decline in macroaggregate associated OC stock and increase in meso‐ and microaggregate associated OC stock; indicated redistribution of OC stock among aggregate fractions. It may be concluded that JP in dry tropics can be an efficient strategy for rehabilitation of degraded land as it improves aggregate structure and stability in the whole profile and aggregate associated OC stock in upper layer of soil.     

不同土地利用类型下土壤活性有机碳库的变化

分析了中国科学院沈阳生态试验站不同土地利用类型长期定位试验土壤0～40cm活性有机碳含量,结果表明:0～20cm土层内荒地土壤有机碳、易氧化碳、微生物生物量碳、溶解性有机碳和轻组有机碳含量高于割草地和裸地,而割草地颗粒有机碳含量略高于荒地;在20～40cm土层,割草地土壤有机碳、易氧化碳和颗粒有机碳含量较高,而荒地微生物量碳、溶解性有机碳和轻组有机碳含量较高。不同土地利用类型土壤活性有机碳含量均随着土层加深而递减。土壤微生物量碳、溶解性有机碳和轻组有机碳的分配比例为荒地>割草地>裸地,易氧化碳和颗粒有机碳的分配比例为割草地>荒地>裸地。土壤活性有机碳的分配比例随土层加深而下降,但溶解性有机碳的分配比例变化趋势相反。     

Organic N and particulate organic matter fractions in organic and conventional farming systems with a history of manure application

Indicators of soil fertility are needed for the effective management of organic farming systems. Sustainable management hinges upon our gaining an improved understanding of C and N dynamics. The influence of cropping systems and amendments applied in the Lakeland Wisconsin Integrated Cropping Systems Trial on total hydrolyzable organic N (THN) fractions and particulate organic matter (POM) was investigated after a decade in a conventional cash grain system (Conv) of continuous maize amended with inorganic fertilizer, an organic cash-grain system (Org-CG) that relied on legume N, and an organic animal-based system (Org-AN) that included alfalfa and manure additions. Maize yields had consistently ranked Org-CG < Conv < Org-AN. The THN and amino acid-N (AA-N) contents were ranked Org-AN > Org-CG > Conv. Amino sugar-N (AS-N) contents, which reflect microbially derived N, did not differ among systems and concentrations were quite high (346.5 mg AS-N/kg soil in the 0–50 cm depth). This, and soil variability were attributed to the sites’ history of manure application. The amount (1.3 g POM-C/kg soil) and proportion (≈7.5% of total SOC) of POM-C were quite low and did not differ among systems. Failure to accumulate SOC or POM in these soils, even under organic management, is attributed to rapid C decay and/or limited root growth. An N rate study was added the fall before samples were taken and N addition did increase yield in the Conv and Org-CG systems despite evidence of soil N surplus. This suggests that either amino N is unavailable to plants or that root N acquisition is limited by other constraints. Low POM-C contents accompanied by high AS-N and AA-N levels reveal an imbalance in these soils which are likely to be C limited. Based on this, we conclude excess N has prevented use of organic practices from enhancing soil quality at this site.     

川西卧龙岷江冷杉林土壤有机碳组分与氮素关系随海拔梯度的变化特征

土壤碳氮沿海拔梯度变化及其耦合关系是山地生态系统碳氮循环研究的重要内容。为分析不同土层土壤有机碳,土壤全氮及有机碳活性组分在海拔梯度上的分布规律及相互之间的耦合关系,选取亚高山物种岷江冷杉(Abies faxoniana)原始林为研究对象,以卧龙邓生野牛沟岷江冷杉原始林2920—3700 m的样地调查数据为基础,分析不同土层土壤碳氮及活性组分沿海拔的变化规律,总结土壤有机碳稳定性沿海拔主要规律,从土壤有机碳活性组分和碳氮关系的角度揭示其对土壤有机碳沿海拔变化的影响。结果表明:1)腐殖质层土壤有机碳(SOC)随海拔升高逐渐增加,与温度显著负相关,轻组有机碳(LFOC)及颗粒态有机碳(POC)随海拔上升均表现先增加后降低的趋势,土壤全氮(TN)随海拔变化不显著,但林线处LOFC、POC和TN均显著增加;0—10 cm土壤有机碳及全氮则表现为双峰特征,峰值分别在3089 m和3260 m处,与年均温度无显著关系。2)LFOC及POC在腐殖质层和0—10 cm土层中所占比例较大,是表征土壤有机碳含量沿海拔变化规律的主要活性组分,腐殖质层LFOC/SOC和POC/SOC随海拔上升逐渐增高,0—10 cm层则逐渐降低,暗示腐殖质层有机碳稳定性沿海拔逐渐降低,0—10 cm有机碳稳定性逐渐升高。3)SOC与TN显著正相关,SOC是影响TN的主要因子,但腐殖质层TN与有机碳活性组分无显著相关关系。4)土壤C/N和微生物量C/N在3177 m大于25:1,是引起土壤有机碳含量显著降低的主要因素。     

不同土地利用类型下氮、磷在土壤剖面中的分布特征

在北京市东南郊大兴区采取了44处0～20cm,20～40cm,40～60cm,60～80cm,80～100cm5个不同深度的土壤剖面样品。按土地利用类型,采样点可分为农田、菜地、果园、林地、草地。土壤剖面中,由表层向深层,pH值升高,有机质、速效磷、全磷、硝态氮、全氮降低,且在20～40cm处有较大变化。表层土壤受土地利用影响,不同土地利用类型的土壤性质差别较大,尤以菜地土壤,pH为8.01低于其他类型土壤的平均值8.27,有机质、速效磷、全磷、硝态氮、全氮都高于其他类型的土壤,分别是其他类型土壤的110%～198%,355%～1629%,162%～224%,724%～1540%,130%～248%,速效磷和硝态氮远高于其他土壤。深层土壤性质差异不大,各项土壤性质差异随深度而变小,但菜地80～100cm处,硝态氮含量为18.8mgkg-1,是同深度其他类型土壤的175%～389%。土壤中硝态氮的积累情况,菜地>农田、果园、林地>草地。磷的积累与氮不同,速效磷在0～20cm大量积累,不同类型的土壤,速效磷积累差异显著,在40～60cm处,菜地速效磷含量是其他利用类型土壤的161%～602%;在80～100cm处,不同利用类型的土壤中速效磷无显著性差异。这一情况表明,菜地的过量施用氮、磷肥导致了土壤中的磷和氮大量积累,并以速效磷、硝态氮的形态向下淋溶并在深层土壤中积累。硝态氮在80～100cm的积累仍相当严重,有继续向下淋溶的可能,速效磷的淋溶在80～100cm处已较为微弱,其淋溶过程主要在0～60cm处。对速效磷和硝态氮的累积进行多元线性回归分析,发现速效磷与全磷含量有着良好的线性相关性,而与有机质和全氮含量关系不大。硝态氮则受土壤中pH、有机质和全氮3因素的共同影响。