The characterization of soil profile distribution for nitrate leached in the paddy soil

Experiment was conducted for five successiveyears under large undisturbed monolith lysime-ters(2m×2m in square,l m in depth).Thesoil was silty clay loam texture and had a con-tent of total N 1.55 g/kg.The soil was flood-ed with penetration rate controlled at approxi-mate 3 mm per day in duration of double-riceseason and laid fallow and natural in winterand spring.Results showed that nitrate was the mainform of nitrogen in percolates.The change of

Organic carbon stratification and size distribution of three typical paddy soils from Taihu Lake region,China

Developing realistic soil carbon （C） sequestration strategies for China＇s sustainable agriculture relies on accurate estimates of the amount, retention and turnover rates of C stored in paddy soils. Available C estimates to date are predominantly for the tilled and flood-irrigated surface topsoil （ca. 30 cm）. Such estimates cannot be used to extrapolate to soil depths of 100 cm since soil organic carbon （SOC） generally shows a sharp decrease with depth. In this research, composite soil samples were collected at several depths to 100 cm from three representative paddy soils in the Taihu Lake region, China. Soil organic carbon distribution in the profiles and in aggregate-size fractions was determined. Results showed that while SOC decreased exponentially with depth to 100 cm, a substantial proportion of the total SOC （30%-40%） is stored below the 30 cm depth. In the carbon-enriched paddy topsoils, SOC was found to accumulate preferentially in the 2-0.25 and 0.25-0.02 mm aggregate size fractions. δ^13C analysis of the coarse micro-aggregate fraction showed that the high degree of C stratification in the paddy topsoil was in agreement with the occurrence of lighter δ^1313C in the upper 30 cm depth. These results suggest that SOC stratification within profiles varies with different pedogenetical types of paddy soils with regards to clay and iron oxyhydrates distributions. Sand-sized fractions of aggregates in paddy soil systems may play a very important role in carbon sequestration and turnover, dissimilar to other studied agricultural systems.

Beta-Glucosidase Activity in Paddy Soils of the Taihu Lake Region, China

The profile distribution of β-gulcosidase activity in twelve typical paddy soil profiles with high productivity in the Taihu Lake region of China were investigated. Activities of β-gulcosidase in the plow layers were in the range of 52.68- 137.02μg PNP g^-1 soil h^-1 with a mean of 89.22μg PNP g^-1 soil h^-1. However, most plow layers ranged from 70 to 110 μg PNP g^-1 soil h^-1. The profile distribution of β-gulcosidase activity in the 12 soil profiles decreased rapidly with soil depth, with activity at the 60 cm depth only about 10% of that in the surface layers （0-15 cm or 0-20 cm）. In these soil profiles, β-gulcosidase activity was significantly positively correlated with soll organic carbon and arylsulphatase activity. Meanwhile, a significantly negative correlation was shown between β-gulcosidase activity and soil pH.

Effects of elevated atmospheric CO_2 concentration and temperature on the soil profile methane distribution and diffusion in rice–wheat rotation system

The aim of this experiment was to determine the impacts of climate change on soil profile concentrations and diffusion effluxes of methane in a rice-wheat annual rotation ecosystem in Southeastern China. We initiated a field experiment with four treatments：ambient conditions（CKs）, CO2 concentration elevated to - 500 μmol/mol（FACE）,temperature elevated by ca. 2°C（T） and combined elevation of CO2 concentration and temperature（FACE ＋ T）. A multilevel sampling probe was designed to collect the soil gas at four different depths, namely, 7 cm, 15 cm, 30 cm and 50 cm. Methane concentrations were higher during the rice season and decreased with depth, while lower during the wheat season and increased with depth. Compared to CK, mean methane concentration was increased by 42%, 57% and 71% under the FACE, FACE ＋ T and T treatments, respectively, at the 7 cm depth during the rice season（p 〈 0.05）. Mean methane diffusion effluxes to the 7 cm depth were positive in the rice season and negative in the wheat season, resulting in the paddy field being a source and weak sink, respectively. Moreover, mean methane diffusion effluxes in the rice season were 0.94, 1.19 and 1.42 mg C/（m^2·hr） in the FACE,FACE ＋ T and T treatments, respectively, being clearly higher than that in the CK. The results indicated that elevated atmospheric CO2 concentration and temperature could significantly increase soil profile methane concentrations and their effluxes from a rice-wheat field annual rotation ecosystem（p 〈 0.05）.

Combining Ridge with No-Tillage in Lowland Rice-Based Cropping System: Long-Term Effect on Soil and Rice Yield

A tillage method of combining ridge with no-tillage (RNT) was employed in lowland rice-based cropping system to study the long-term effects of RNT on soil profile pattern, soil water stable aggregate distribution, nutrients stratification and yields of rice and post-rice crops. After flooded paddy field (FPF) was practiced with RNT for a long time, soil profile changed from G to A-P-G, and horizon G was shifted to a deeper position in the profile. Also the proportion of macroaggregate (> 2 mm) increased, whereas the proportion of silt and clay (< 0.053 mm) decreased under RNT, indicating a better soil structure that will prevent erosion. RNT helped to control leaching and significantly improved total N, P, K and organic matter in soil. The highest crop yields were found under RNT system every year, and total crop yields were higher under conventional paddy-upland rotation tillage (CR) than under FPF, except in 2003 and 2006 when serious drought occurred. RNT was proven to be a better tillage method for lowland rice-based cropping system.

Water-efficient sensing method for soil profiling in the paddy field

The comprehensive and reliable perception of moisture in a soil profile is essential to irrigation.To establish an efficient method for sensing soil moisture,field trials were conducted to analyze the spatial and temporal variations of moisture in a paddy soil profile by using coefficients of variation.The results showed that soil layers at shallow depths undergo more extensive changes in the coefficients of variation.Moisture perception is most sensitive within a depth range of 0-60 cm in the vertical soil profile of a paddy field.By using the clustering algorithm of Euclidean distance,the paddy soil profile was divided into three categories based on soil depth.The first category includes depths ranging from 10-20 cm,the second is from 30-40 cm,and the third is from 50-100 cm.Path analysis indicated that the most sensitive depths for moisture sensing in a paddy soil profile were 20 cm,30 cm,and 50 cm,whereas the most sensitive depths for moisture sensing by time stability analysis were 20 cm,40 cm,and 60 cm.Based on the multiple regression of sensitive depths,the results of quantitative inversion indicated that the time stability analysis results were 0.962 when the(y,y)Coryy of path analysis was 0.980,and the time stability analysis was 0.61 when the root mean square error(RMSE)of path analysis was 0.40.The relative error range between the measured and predicted values of path analysis was less than that of time stability analysis.These findings suggest that it is feasible to effectively sense the moisture of the entire vertical soil profile based on the sensitive depth.The present study has also determined that path analysis is superior to time stability analysis.

太湖水稻土中的芳基硫酸酯酶活性

选取了 1 2个太湖地区的水稻土表土及其剖面 ,分析芳基硫酸酯酶活性变化。耕作层芳基硫酸酯酶活性平均为PNP 1 60 μgg- 1h- 1。大多数土壤其酶活性在PNP 1 0 0～ 2 0 0 μgg- 1h- 1之间。最低值和最高值分别为PNP 75 ,31 5 μgg- 1h- 1。犁底层土壤芳基硫酸酯酶活性明显低于耕作层 ,60 %的土壤其酶活性低于PNP 5 0 μgg- 1h- 1。犁底层酶活性与耕作层酶活性之间没有相关性。土壤芳基硫酸酯酶活性与土壤有机碳有显著正相关 (R2 =0 .5 33) ;与土壤pH关系较为复杂 ,在pH小于 5 .2时 ,随pH升高 ,酶活性增加 ,大于 5 .2时 ,酶活性则明显下降。除个别土壤外 ,大多数土壤芳基硫酸酯酶活性沿剖面下降 ,在大于 60cm的土层中基本上没有芳基硫酸酯酶存在。不同土壤芳基硫酸酯酶活性的剖面分布有所不同。根据酶活性变化下降趋势 ,其剖面分布基本上可以归结为四个类型。

污染水稻田中土壤含砷量的空间变异特征

利用地统计学方法研究在长期淹水和频繁干湿交替影响下污染水稻田中砷的小尺度空间分布特征。采用变异函数定量描述含砷量分布特征 ,用克立格插值法对表层土壤未测点的含砷量进行最优估计 ,并绘制含砷量等值线分布图。结果表明 ,来自表面污染源的砷进入农田土壤后主要积累在耕层 0～ 2 0cm中 ,对 4 0～ 80cm土壤影响不大。耕层土壤含砷量半方差值呈有规律持续增加趋势 ,可用直线方程很好地拟合。表层土壤含砷量存在很好的空间结构性 ,高砷区出现在进水口附近 ,并以其为中心呈斑块状向周围扩散 。

成都平原区水稻土成土剖面Cd形态分布特征及影响因素研究

成土过程中不同形态镉（Cd）迁移转化的影响因素研究对于了解Cd的地球化学行为具有非常重要的意义。以四川省成都平原区农田生态系统水稻土剖面中不同形态CA分布特征为例，探讨成土过程中不同形态Cd的迁移转化影响因素及其生态危害性。结果表明：总量Cd、离子交换态Cd和碳酸盐Cd均表现出表层富集，深层含量稳定的特征；岷江流域和沱江流域水稻土Cd含量的背景值分别为0．147，0．215mg·kg^-1。外源输入耕层土壤中Cd主要为活动态，其增加量占Cd总量增加量的60．71％～90．52％，向下垂向迁移能力非常弱。成土过程随着土壤中Cd总量增加，稳定态Cd含量显著增加，而活动态Cd含量明显降低。土壤的pH值主要对碳酸盐态Cd含量有影响，pH值越大，其含量越高；随着土壤成熟度增高，粉粒和粘粒含量增加的同时，残渣态Cd含量显著降低，而有机结合态Cd含量显著增高。耕层土壤中Cd的生物有效性系数高达0．59～O．65，已经严重地影响到农作物安全。

6000年以来水稻土剖面中多环芳烃的分布特征及来源初探

研究了多环芳烃（PAHs）在含6000a（马家浜文化时期）古水稻土的土壤剖面中的分布特征，并对其可能来源进行了分析。结果显示，各层土壤中PAHs的总量在25．9—202．9μgkg^-1之间，并主要富集在表层土壤，其中含量较高的化合物及其大小顺序为Nap〉Phe〉Fla〉Pyr，4环以上的PAHs占总量的51.8％。表层以下各层土壤中PAHs含量大幅降低，检出种类也有所减少，并主要以2、3环化合物为主，古水稻土中4环以上的芳烃也占有一定的比例，达37％。聚类分析和主成分分析表明，Chr、BkF、BaA、IcP、BbF、Pyr、BaP、DaA和Fla等化合物主要是人为产生，Flu和Phe由生物合成，而Nap、BgP和Ant则可能来源于人为产生和生物合成的共同作用。

陕西三种类型土壤剖面硝酸盐累积、分布与土壤质地的关系

研究了陕北黄绵土,关中(土娄)土与陕南水稻土土壤剖面中硝酸盐的分布与累积,分析了硝酸盐淋移与土壤剖面粘粒含量的关系.结果表明,黄绵土由于粘粒含量少,土壤疏松,氮肥施入土壤后硝化作用速度快,氮素多以硝态氮存在于土壤中,遇到过量的灌溉或降水,容易引起硝酸盐淋失.在米脂的川道地,施肥2个月后,硝酸盐峰值在50 cm 左右,4个多月后,峰值下移至100 cm 左右,6个月后,该峰值下降到130 cm 左右,一年内,硝酸盐的峰值已经消失,分布在130至 350 cm 之间.因此,在黄绵土地区可以灌溉的川道地,氮素损失的主要途径是硝酸盐淋失.关中(土娄)土,粘粒含量相对较高,硝化作用速度快,但由于在80-120 cm有一粘化层,阻碍了水分与硝酸盐的向下淋移,使得大部分硝酸盐累积在0-100 cm 土层,其累积量占到0-400 cm总累积量的64% ～ 74%,而200-400 cm仅占到7% ～ 13%.而且淋移到100 cm 以下的硝酸盐,也通过反硝化损失了.陕南水稻土,由于深层土壤水饱和,硝酸盐难以向下淋移,氮素主要累积在土壤表层.由于下层土壤长期处于厌气条件,即使淋移到下层的硝酸盐也通过反硝化作用而损失掉了.

太湖地区典型水稻土FDA水解酶活性的剖面分布特征

本文主要对太湖地区12个典型水稻土剖面的荧光素二乙酸酯（FDA）水解酶活性及其它相关酶活性进行了分析。耕作层的FDA水解酶活性最高，随土层加深活性明显下降，其中部分土壤在犁底层已经很难检测到其活性。部分样点的酶活性在剖面中呈明显的梯度下降趋势。高产水稻土壤表层FDA水解酶活性差异较大，在50～100μg／（g·h）范围内，多数为60～80μg／（g·h）。土壤酶活性最高与最低间的差异达到近一倍左右。同时FDA水解酶活性与β-葡糖苷酶、脲酶、脱氢酶、酸性磷酸酶和芳基硫酸酯酶活性之间有极显著正相关关系（P〈0．01），与碱性磷酸酶呈显著相关（P〈0．05）；与土壤养分指标如全氮、全磷、速效氮、有机碳之间有极显著相关性，与土壤pH呈显著负相关（P〈0．01）关系。

苏南某些水稻土中Cu Pb Hg As的剖面分布及其影响因素

采用田间深度间隔采样法,分析了苏南6个处于不同环境影响下的水稻土剖面中Cu、Pb、As和Hg全量深度分布。结果表明,4种元素在土壤剖面中的移动能力均较差;在工业环境下田块的土壤中的Hg、Cu、Pb的表层富集和垂直分异较为明显,而在非工业环境下,重金属纵向分异不明显;个别田块存在较严重的As污染,耕层As达56.93 mg.kg-1,超出国家土壤环境质量二级标准;重金属元素在稻田土壤中表层富集系数大于果园利用下的旱地土壤。工业化进程中污染物的输入是影响供试土壤中重金属元素含量的主导因素,土壤的基本性质也在一定程度上影响了重金属的纵向迁移。重金属剖面分布特征可以在一定程度上反映水稻土的重金属污染积累程度。

长期施肥对红壤稻田氮储量的影响

稻田背景氮高是我国氮肥利用率低的主要原因之一,减少氮肥施用量对提高氮肥的农学利用率和缓解环境压力具有重要的意义。研究采用长期定位试验(19902006年)土壤全氮、稻谷产量等数据,分析施肥模式对稻田耕层土壤氮储量、氮肥农学利用率的影响,探讨在降低常规施用氮量的33.3%而不明显减产措施的可行性。结果表明:长期有机物质循环利用能显著提高耕层土壤全氮含量,氮储量与试验前相比平均提高了18.8%,仅施用化肥对土壤全氮含量没有显著影响,减量施肥处理(JS)对耕层土壤氮的积累效应一直优于仅施化肥的处理(NP、NPK)。17a的JS处理并没有降低稻谷产量,与常量NPK储量相比年际产量相对误差仅为3.2%,而输入N的农学利用率提高了12%。在半量稻草还田的条件下减少氮肥的施用量到180kg·hm-2是可行的,红壤稻田产量可维持在10t·hm-2左右。

史前水稻土剖面中多环芳烃(PAHs)的分布特征

采用现场采样及室内测试方法,研究了罗家角遗址(7000aBP)和跨湖桥遗址(8000aBP)两个含有史前古水稻土的土壤剖面中的多环芳烃(PAHs)分布特征。结果显示:罗家角遗址剖面中表层水稻土PAHs含量最高,其次是古水稻土层,各层中含量均较高的化合物为萘(Nap)和菲(Phe);而跨湖桥遗址剖面中,表层的荒地土壤含量最低,PAHs最高含量出现在底部的古水稻土层,各层含量较高的化合物为菲(Phe)和芴(Flu)。相关分析表明,PAHs与土壤有机碳含量显著相关(r2=0.868),与粘粒含量之间也有良好的相关性(r2=0.585),这表明土壤的理化性质会影响PAHs在土壤中的分布,但在耕作土壤中,现代人类生产活动的扰动可能会削弱这种影响。

南宁市郊不同类型土壤腐殖质垂直分布特征研究

[目的]分析南宁市郊不同类型土壤腐殖质垂直分布特征，以揭示土壤有机碳、腐殖质碳的分布特征及其与土壤含水量、pH的相关性。【方法】采用野外采样和室内分析相结合的方法，对南宁市郊菜园土、水稻土两类土壤剖面0-80cm有机碳含量及腐殖质组分进行相关分析。【结果】土壤腐殖质碳含量随土层深度增加呈递减趋势，菜园土有机碳含量由表层16．16g／kg递减为5．32g／kg，水稻土由表层最大值12．37g／kg递减到4．19g／kg；但菜园土有机碳含量总体上大于水稻土。两类土壤的胡敏酸、富里酸总碳量随土层深度增加呈下降趋势，菜园土中胡敏酸与富里酸比值总体上大于水稻土；两种类型土壤腐殖质全碳量均与富里酸呈极显著的正相关，与胡敏酸、胡敏素均呈正相关，与pH、含水量、HA／FA的值则呈负相关。【结论】南宁市郊两种不同类型土壤中有机碳含量均随土层深度递减，腐殖质全碳量与胡敏酸、富里酸、胡敏素呈正相关，与pH、土壤含水量、HA／FA呈负相关；菜园土腐殖化程度较高。

水稻土和潮土中铁锰氧化物形态与稀土元素地球化学特征之间的关系研究

稀土元素在土壤中的含量和分馏特征对它们在环境中的分布、迁移、转化、归宿以及生态效应都有重要的影响。铁锰氧化物矿物的表面作用已被认为是表生环境中元素活化迁移和污染的重要机制之一。本研究以亚热带北端的长江三角洲地区和亚热带南端的珠江三角洲地区的典型水稻土和潮土剖面为例,探讨了铁锰体系对土壤稀土元素含量和地球化学分馏的影响。研究结果表明:铁锰氧化物中以晶质态氧化铁与土壤稀土元素的结合作用为主,并且对潮土的作用要比水稻土更为显著。游离态氧化铁对水稻土Ce富集和Eu亏缺均有积极贡献;锰氧化物可能会通过对二价Eu的氧化而减少其在土壤中的亏缺程度。水稻土和潮土中稀土元素在剖面中的分馏程度也受到铁锰氧化物含量的影响,低含量的铁锰氧化物会使不同发生层之间稀土元素的分馏差异增大。Eu在铁游离度高的南亚热带水稻土中会通过还原并随Sr元素一起淋失。

南方典型红壤区旱地与水田土壤酸度的剖面差异性

为探明红壤区不同耕地利用类型下土壤酸度的剖面变化特征及其主要影响因素,选取江西省余江县和湖南省祁阳县的典型水田、旱地两种耕地利用类型下、第四纪红色黏土母质发育的红壤,分5层(0~20、20~40、40~60、60~80和80~100 cm)测定土壤pH、交换性铝、交换态盐基阳离子及有机质含量等指标,分析剖面酸度特征及其相互关系。结果表明:土壤pH均随土层深度的增加呈增加趋势,不同耕地利用类型下以水田剖面p H较高,范围为5.80~6.43,旱地剖面p H较低,范围为4.68~5.41。土壤交换性铝含量以水田含量较低,范围为0.16~1.56 cmol/kg,旱地的含量较高,范围为4.22~7.02 cmol/kg,水田的交换性铝含量随土层深度的增加呈降低趋势,旱地则呈现相反的变化趋势。0~20 cm土层的交换性铝与有机质含量呈显著负相关,40~100 cm土层的交换性铝与交换态盐基阳离子含量呈显著负相关。耕地利用类型是影响土壤酸度的主要因素之一,旱地土壤酸度强于水田。增加耕层土壤有机质含量可能是减缓酸化、降低交换性铝含量的策略之一。

皖南山区潜育性水稻土剖面性状及无机改良剂改良效果

诊断分析代表性田块土壤剖面性状，在此基础上采取田间定位试验的方法研究石灰、白云石、沸石、凹凸棒和钙镁磷肥对潜育性水稻土改良效果。结果表明：皖南山区潜育性水稻土以表潜型为主，剖面构型为Ag-Pg-W1-W2-C型；无机改良剂均能降低还原性物质含量，石灰对还原性物质的消减效应最明显，其次为钙镁磷肥和白云石，沸石、凹凸棒效果不明显；白云石、沸石、钙镁磷肥、凹凸棒均能提高土壤微生物数量，白云石、沸石效果较好，石灰效果较差；无机改良剂均能提高水稻产量，增产1.4％～12．1％，钙镁磷肥增产效果显著。从本试验结果看，钙镁磷肥是皖南山区潜育性水稻土较好的土壤改良剂。

湖南省几种母质类型水稻土土壤肥力特征

水稻土是亚热带红壤丘陵区最重要的粮食生产基地,有机质和土壤氮、磷、钾含量等常作为水稻土肥力水平的重要评价指标,可有效的表征土壤的基本肥力状况和供肥强度。选取长沙市郊5种母质类型的水稻土,按土壤发生层的分层取样,研究土壤有机质及氮、磷、钾等养分肥力指标在土壤剖面中的分布特点,探讨亚热带不同母质类型水稻土的供肥特性。结果表明,不同母质类型水稻土剖面各层次有机质含量之间存在显著性差异（P〈0.05）,耕作层（A）、渗育层（P）显著高于母质层（C）。土壤全氮、碱解氮、速效磷、有效钾含量随土壤深度的增加而减少。不同稻田土壤层次间供肥强度各不相同,碱解氮供应强度介于5.55~7.26之间,有效磷介于1.04~6.31之间,速效钾介于0.45~2.41之间,麻沙泥田的W2层、黄泥田Ⅱ的C层、红黄泥的We层供氮强度明显高于其他层次,河沙泥田、黄泥田Ⅰ则是随深度增加强度减弱。供钾强度和供磷强度在稻田土壤剖面中变化趋势相似,A层相对较强,P层和W层较弱。不同母质稻田土壤整体供肥强度差异明显,黄泥田Ⅱ和红黄泥田供肥强度较高,其次分别是黄泥田Ⅰ、河沙泥田、麻沙泥田。土壤有机质与土壤氮磷的表聚系数存在显著相关,综合供肥强度及表聚性系数,黄泥田Ⅱ的土壤肥力相对较高,红黄泥田、黄泥田Ⅰ的土壤肥力水平次之,河沙泥田和麻沙泥田最低,这与利用第二次全国土壤普查地力分级标准得到的结果一致。