Research on the Factors Affecting Nitrification Inhibition of Dicyandiamide(DCD) in Latosol

[Objective] This research aimed at studying the effects of application amount of DCD and physics and chemistry characteristics of soil such as temperature,moisture content,organic matter content and pH on the inhibition of nitrification when applying nitrification inhibitor DCD in latosol.[Method] The experiment was carried out under aerobic incubated conditions.[Result] A significant delay period of nitrification was observed when the application amount of DCD was 10 mg/kg soil,and the inhibition can at least last for 56 d.When the cultural temperature had increased from 10 to 30 ℃,the duration of nitrification inhibition was shortened from 90 to 30 d.The nitrification inhibition of DCD was reduced with the increasing soil moisture content,organic matter content and soil pH,while the duration of nitrification inhibition was prolonged with the decreasing soil moisture content,organic matter content and soil pH.[Conclusion] Nitrification inhibition of DCD can be improved by increasing the application amount or reducing soil temperature,moisture content,organic matter content and pH.

The Content of Pb Element and Environmental Quality Assessment in Latosol of Hainan Island

[Objective] To research the content of Pb element in latosol of Hainan island and to assess its environmental quality.[Method] Samples were selected for lab analysis.27 samples from different landforms of Hainan Island were selected（the same place was sampled for three times） to analyze the content of Pb in latosol of Hainan Island,study the spatial distribution feature of this element in latosol from different places and evaluate the content of Pb element in latosol of Hainan Island by geo-accumulation index.[Result] The content of Pb generally stays at high level in latosol of Hainan Island;however,the mean content of Pb in east Hainan is lower than the mean value of west Hainan;vertically,the mean content of Pb shows descending order from hills,mountainous area to plain;the pollution assessment result showed that latosol of Hainan Island was hardly polluted by Pb element and only its content in the latosol from middle,south area stays at high level.[Conclusion] The research provided scientific reference for constructing a national tropical modern agricultural base in Hainan as well as controlling Pb pollution.

Distribution Characteristic and Potential Ecological Risk Assessment of Heavy Metals in Latosol in the Western Area of Hainan Island

[Objective] The paper was to carry out ecological geochemical survey and ecological risk assessment on the heavy metals in latosol in western area of Hainan Island.[Method] The contents of six heavy metals including Cr,Cu,Zn,As,Cd and Pb in latosol in western area of Hainan Island were analyzed.Single-factor index method and Hakanson ecological risk index method were used to evaluate the integrated pollution effect of heavy metals in latosol.[Result] The average contents of Cr,Cu,Zn,As,Cd and Pb in latosol in western area of Hainan Island were 65.57,35.16,93.56,8.50,0.24 and 79.29 mg/kg,respectively.The major pollution factor of heavy metal was Pb.The sequence of influence factors of various heavy metals was PbCu = ZnCrAsCd.The potential ecological risk coefficient of various heavy metals was PbCdCuAsCrZn.The average value of potential ecological risk index（RI）was 45.14,belonging to low ecological risk range.[Conclusion] The heavy metal pollution in latosol in western area of Hainan Island belongs to slight pollution.

Application Effect of Water-absorbent Slow Release Nitrogen Fertilizer in Latosol

[Objective] A new-type water-absorbent slow release nitrogen fertilizer（WASRNF） was produced through polymerization reaction. Its physicochemical property and application effect in latosol were studied. Feasibility of using WASRNF to improve the serious problems of latosol in rubber planting area in Hainan Island including vulnerable nutrient, free-running fertilizer and water was studied. [Result] The results showed that raw materials of WASRNF, urea and water-retention material formed co-polymer through hydrogen-bond interaction that the WASRNF contained many hydrophilic groups. The p H value of WASRNF is near neutral and its water absorbent rate in tap water could reach 167.17 g·g-1. The water absorbent rates in latosol leach liquors with water/soil ratios of 1：5, 1：10 and 1：20 were 104.66, 122.93 and 145.38 g·g^-1, respectively. The maximum water holding ratio of latosol increased by 23.72%, 30.89% and 39.68% when 0.5%, 1% and 2% WASRNFs were added to latosol, and water evaporation rate of latosol decreased efficiently. Compared with common urea, WASRNF could slow down the leaching rate of nitrogen and the initial leaching amount was only 22.17% of the total amount. [Conclusion]The results indicated that WASRNF in latosol had strong water absorption and water-retention abilities in addition to the good slow release effect, and could efficiently decrease nutrient loss, increase utilization ratio of water and fertilizer and promote interaction between water and fertilizer.

Capacities of Clay Fraction of a Latosol to Retain Cations and Anions as Inferred from the Wien Effect in Soil Suspensions

Suspensions of a latosol with a clay concentration of 30 g kg^(-1) wereprepared from electrodialyzed clay fractions, less than 2 μm in diameter, five nitrate solutionswith a concentration of 1 X 10^(04)/z mol L^(-1), where z is the valence, and five sodium saltsolutions with a concentration of 3.3 X 10^(-5)/2 mol L^(-1). The direct current (DC) electricalconductivities (ECs) of the colloidal suspensions were measured at a constant temperature of 25 ℃,using a newly established method of measuring the Wien effect in soil suspensions at field strengthsranging from 13.5 to 150 kV cm^(-1), to determine their electrical conductivity-field strengthrelationships and to infer the order of the bonding strength (retaining force) between soilparticles and various ions. The measurements with the latosol suspensions in NaNO_3, KNO_3,Ca(NO_3)_2, Mg(NO_3)_2 and Zn(NO_3)_2 solutions resulted in increments of the suspension ECs, ΔECs,of 7.9, 5.0, 7.1, 7.0 and 5.8 μS cm^(-1), respectively, when the applied field strength increasedfrom 14.5 to 142 kV cm^(-1). As for the suspensions in NaNO_3, NaCl, Na_2SO_4, Na_3PO_4 andNa_3AsO_4 solutions, the ΔECs were 6.2, 5.3, 4.1, 4.0 and 3.7μS cm^(-1), respectively, when theapplied field strength increased from 13.5 to 90 kV cm^(-1). Thus, it can be deduced that theretaining forces of the clay fraction of the latosol for the cations were in the descending orderK^+ > Zn^(2+) > Mg^(2+) ≥ Ca^(2+) > Na^+, and for the anions in the descending order H_2AsO_4^- >H_2PO_4^-≥ SO_4^(2-) > Cl^- > NO_3~ -.

Influence of Neutral Salts and pH on Exchangeable Acidity of Red Soil and Latosol Colloids

In the present work, the exchangeable acidity of a red soilcolloid and a latosol colloid at different pH during reacting withfour neutral salts was measured. The results show that theexchangeable acidity increased with increasing amounts of the neutralsalts added, and the relation between them was almost linear. Whenthe amount of the neutral salt added was lower than a certain value,the slop of the line was high, and the slop turned low when theamount exceeded that value, so there was a turning point in eachline. The addition amounts of the neutral salts for the turningpoints were affected by the cation species of the neutral salts, butpH had less effect on them. After the turning points occurred, theexchangeable acidity of the red soil colloid still graduallyincreased with the addition amounts of the neutral salts, but that ofthe latosol colloid did not increase any more.

Different Fertilization Modes of Sugarcane in Latosolic Red Soil of Guangxi

[Objectives] This study aimed to compare the effects of water-fertilizer integrated drip irrigation modes and traditional fertilization mode on growth,yield,production costs and economic benefit of sugarcane in latosolic red soil of Guangxi. [Methods]A field test was conducted. [Results] The agronomic traits and comprehensive economic benefit of sugarcane under the water-fertilizer integrated drip irrigation modes were superior to those under the traditional fertilization mode. Among them,the comprehensive economic benefit of sugarcane with special granular fertilizer as the base fertilizer and water-fertilizer integrated drip irrigation as topdressing were the highest,increased by 15 813 kg/ha,an increase of 15. 8%. Considering the cost input,the comprehensive economic benefit increased by 5 676 yuan/ha. [Conclusions]Taking the production cost,economic benefit and input-output ratio into account,it is recommended to promote the application of water-fertilizer integrated drip irrigation mode in bases with water and fertilizer equipment conditions.

砖红壤中铬的溶出和外源三价铬的氧化转化

砖红壤铬(Cr)的背景值和锰氧化物的含量均较高,当土壤中Cr溶出或者受到Cr(Ⅲ)污染,可能被氧化生成毒性较高的Cr(Ⅵ),从而对周围环境造成威胁。为考察砖红壤中Cr的环境风险,以云南、海南和广东采集的部分砖红壤为对象,研究土壤中Cr的溶出和外源Cr(Ⅲ)的氧化。连二亚硫酸钠-柠檬酸钠-重碳酸钠法提取和电子探针扫描分析的结果表明,砖红壤中的Cr主要与铁氧化物和硅酸盐矿物结合,呈非活性状态。盐酸和柠檬酸的酸化和络合作用促进了Cr的溶出,但即使1 mol·L^(-1)的盐酸也仅使海南3和广东9砖红壤中3.68%和3.54%的Cr溶出。向砖红壤中添加Cr(Ⅲ)并培养42d,发现少量添加的Cr(Ⅲ)氧化为Cr(Ⅵ),但不同土壤中Cr(Ⅵ)的生成量与亚锰的净产生量不一致,说明土壤中Cr(Ⅲ)氧化生成的Cr(Ⅵ)可能会被土壤有机质重新还原为Cr(Ⅲ)。去除土壤有机质后,一次平衡实验中观察到外源添加的Cr(Ⅲ)氧化为Cr(Ⅵ),氧化量与土壤易还原锰的含量一致。随着溶液pH的增加,Cr(Ⅲ)的氧化量呈先上升后降低的趋势,在pH4.5时Cr(Ⅲ)氧化量达最大值,但Cr(Ⅲ)的氧化转化量在Cr(Ⅲ)添加量中的占比很小,外源Cr(Ⅲ)在土壤中氧化转化的风险也很低。虽然砖红壤的背景Cr和易还原锰的含量较高,但自然条件下Cr的溶解和Cr(Ⅲ)的氧化反应很难发生,Cr(Ⅲ)不易转化为Cr(Ⅵ),因此无需过度担忧砖红壤中Cr的环境风险。

珠三角赤红壤常年菜地土壤肥力质量评价

赤红壤是广东省地带性土壤,研究位于该地带性土壤的菜地肥力变化特征,以客观评价耕作施肥管理的科学性,助力耕地质量保护与提升。在广东省珠三角地区广州市、江门市、肇庆市、惠州市惠阳区选取了89个蔬菜常年种植菜地,测定了耕层(0~20 cm)土壤理化指标,利用第二次全国土壤普查养分分级标准和内梅罗综合指数法分析评价土壤肥力状况。珠三角赤红壤常年菜地土壤质地以壤土、砂质壤土、粉壤土为主,分别占比46.1%、23.6%和19.1%;pH 5.83,呈微酸性;有机质含量23.83 g·kg-1,为中等水平;阳离子交换量8.67 cmol(+)·kg-1,为中等偏下水平;全氮(N)、全磷(P)、全钾(K)含量分别为1.19、1.47、12.53 g·kg-1,其中全氮和全磷含量均属中等水平,全钾含量为中等偏下水平;有效态养分中碱解氮、有效磷、速效钾含量分别为135.24、120.24、222.48 mg·kg-1,属于丰富(碱解氮和速效钾)和极丰富水平(有效磷)。内梅罗综合指数法评价结果显示,珠三角赤红壤常年菜地土壤综合肥力指数为1.69,属良好等级。相比第二次全国土壤普查广东省赤红壤普查结果,土壤全钾含量不同程度降低,pH值、有机质、全氮、碱解氮含量均不同程度提高,增幅分别为16.6%、23.5%、38.4%和62.5%;阳离子交换量、全磷、有效磷和速效钾含量大幅增加,增幅分别达1.29、6.00、65.80和3.07倍,其中土壤有效磷累积较为普遍。全氮和全磷的年均累积量分别为8.46、32.31 mg·kg-1,碱解氮、有效磷和速效钾年均累积量分别为1.20、3.04、4.30 mg·kg-1。总体上,经过近40年耕种,珠三角赤红壤常年菜地肥力水平不同程度改善,土壤pH由酸性改善为微酸性,阳离子交换性能、有机质、全氮含量提升1个等级,碱解氮和有效钾含量提升2个等级,全磷和有效磷含量分别提升3和5个等级。各肥力指标总体上由原来的极度缺乏至中等偏下状态改善为目前的中等偏下至极丰富水平,总体肥力状况良好。在实施蔬菜有机无机肥配施技术基础上,合理施用氮、钾肥,降低磷肥投入量,可以进一步提升珠三角赤红壤区菜地地力水平,维持土壤资源的可持续利用。

长期施肥对赤红壤旱地有机质含量影响及其灰色预测研究

【目的】阐明长期不同施肥处理对赤红壤旱地土壤有机质(SOM)含量的影响,为区域土壤培肥和高产稳产提供最佳养分管理依据。【方法】根据闽东南旱地花生-甘薯轮作制赤红壤连续16年化肥定位试验和14年化肥配施有机肥定位试验的历年SOM含量监测结果,探讨长期施肥下SOM含量动态变化,构建SOM灰色预测模型。【结果】与不施肥相比,施肥均能提高土壤SOM含量;化肥推荐施肥模式的SOM含量为(19.83±0.77)g·kg^(-1),显著高于其他化肥处理;化肥配施有机肥可进一步提高SOM含量,尤其是配施农家腐熟猪粪的SOM达到(22.53±1.69) g·kg^(-1),年递增速率是化肥推荐施肥的2.8倍。SOM灰色预测模型显示,不同施肥模式的拟合误差在1.226%~3.307%。不施肥模式的SOM含量变化趋势仍然处于下降状态;化肥推荐施肥模式的SOM趋势值为(20.220±0.002)g·kg^(-1),在该试验点中排序第一;化肥配施有机肥均提高了SOM长期趋势值,尤其是配施农家腐熟猪粪的SOM趋势值达到(23.777±0.017)g·kg^(-1),排序位居第一,显著高于该试验点的化肥推荐施肥模式。【结论】从SOM含量和未来含量趋势综合评价,化肥推荐施肥有利于提高赤红壤旱地SOM含量,在推荐施肥基础上配施有机肥尤其是配施农家腐熟猪粪的效果更佳。

化肥有机肥配施改善花生–甘薯轮作土壤钾平衡和供钾能力的机理

【目的】通过分析土壤钾素表观平衡、钾含量和库容、钾素吸附位点及钾素释放过程,全面探讨长期施用化肥和化肥配施有机肥对赤红壤旱地花生–甘薯轮作体系土壤供钾能力的影响。【方法】位于福建省莆田市的花生–甘薯轮作长期施肥定位试验始于2007年,设置5个处理:不施肥(CK)、化肥对照(NPK)、化肥配施商品有机肥(NPK+CM)、化肥配施猪粪(NPK+PM)、化肥配施秸秆(NPK+RS)。2022年(定位试验第15年)甘薯收获后,调查甘薯生物量和产量,采集植株样品分析植株钾含量;采集0—20 cm土壤样品,分析土壤全钾含量及各形态钾含量,采用连续浸提法分析土壤黏土矿物吸附点位钾含量,采用有机酸和四苯硼钠模拟试验分析钾素释放过程。【结果】花生–甘薯轮作体系长期施肥试验中,4个施肥处理土壤钾素表观平衡均为盈余。NPK+PM和NPK+RS处理的土壤非交换性钾、交换性钾、水溶性钾含量提升效果最佳,非交换性钾含量较CK分别提高260和188 mg/kg,交换性钾含量分别提高72.3和75.0 mg/kg,水溶性钾含量分别提高45.0和71.7 mg/kg。与CK相比,NPK和NPK+CM对黏土矿物层间(i位点)、楔形边缘(e位点)和矿物表面(p位点)这3个位点的钾含量均没有显著影响,而NPK+PM和NPK+RS处理p位点钾含量分别提高了25和36 mg/kg,e位点钾含量分别提高58和66 mg/kg;NPK+PM处理的i位点钾含量提高了132 mg/kg;NPK和NPK+CM处理对p位点、i位点和e位点钾的占比没有显著影响,NPK+PM处理显著提高e位点钾的占比,NPK+RS处理显著提高p位点和e位点钾的占比,显著降低i位点钾的占比。无论是以有机酸还是以四苯硼钠为浸提剂,NPK以及NPK+CM处理钾的释放速率和释放量与CK均无显著差异。以有机酸为浸提剂,NPK+PM处理快速释放期释放量、总钾释放量及释放速率均最高,且显著高于N P K+RS处理。以四苯硼钠为浸提剂,NPK+PM与NPK+RS处理快速释放期释放量、总钾释放量及释放速率无显著差异。【结论】化肥配施猪粪或秸秆能提高土壤非交换性钾、交换性钾和水溶性钾含量。单施化肥不会改变黏土矿物吸附位点钾所占的比例,化肥配施猪粪处理主要增加了吸附于黏土矿物层间(i位点)的钾,化肥配施秸秆处理增加的钾主要分布在楔形边缘(e位点)和矿物表面(p位点)。长期单施化肥不能提高土壤钾的生物有效性,缺钾条件下化肥配施猪粪土壤钾的生物有效性最高,钾充足条件下化肥配施猪粪与配施秸秆的土壤钾的生物有效性没有明显差异,但均高于化肥单施。

海南农田不同质地砖红壤及其细菌群落与番茄青枯病发生的关联分析

青枯病对农田土壤环境的影响深远。为探究海南砖红壤质地和细菌群落与番茄青枯病发生的关系,为农业防治青枯病提供参考依据,以海南农田砖红壤为对象,番茄为茄科模式作物,采用大田试验,分别在3种不同质地砖红壤试验田设置了6个处理组(砂土对照、砂土+接种青枯菌、壤土对照、壤土+接种青枯菌、黏土对照与黏土+接种青枯菌),采用伤根接种法,通过定期采集发病植株和土壤样品,统计植株发病率、测定土壤理化性质和微生物多样性。结果表明:(1)接种青枯菌后番茄植株均出现青枯病症状,壤土、砂土、黏土发病率分别为:52.3%、77.9%、95.1%,病情指数分别为:20.3、52.1、83.2;(2)患病植株中壤土pH值远低于砂土和黏土;砂土和壤土pH值与发病率显著负相关(P<0.05),土壤有机质、有效磷含量均与发病率呈负相关;(3)发病植株所在土壤细菌α多样性指标比健康植株所在土壤更低,砂土芽孢杆菌属(Bacillus)相对丰度高于壤土和黏土,黏土中雷尔氏菌属(Ralstonia)、德沃斯氏菌属(Devosia)、中慢生根瘤菌属(Mesorhizobium)、慢生根瘤菌属(Bradyrhizobium)、硝化螺菌属(Nitrospira)、unclassified_Gemmatimonadaceae属与Haliangium属相对丰度比砂土和壤土高;壤土中与土壤养分有关的苔藓杆菌属(Bryobacter)、地杆菌属(Terrabacter)相对丰度均高于砂土和黏土。综上说明海南农田不同质地砖红壤番茄青枯病发病率不同,且土壤pH值是影响发病率的关键因素,番茄青枯病的发生会导致土壤有机质和有效磷的流失,同时会降低土壤细菌多样性。

有机质对广西酸性富硒土中Se(Ⅳ)吸附解吸特性的影响

为探究有机质在酸性富硒土吸附Se(Ⅳ)过程中的作用,以广西典型富硒区的赤红壤为材料,研究了酸性富硒土去除有机质后,土壤硒的赋存形态、土壤对Se(Ⅳ)的吸附解吸特征及吸附前后土壤基团的变化。结果表明:①去除有机质后,土壤中有机结合态硒大幅度减少,铁锰结合态硒成为土壤硒的主要赋存形态。②吸附试验表明,土壤对Se(Ⅳ)吸附过程以多分子层的不均质表面吸附为主,吸附过程受控于化学反应与化学吸附;去除有机质后,土壤对Se(Ⅳ)吸附量和吸附强度均显著下降。③解吸试验表明,吸附以难解吸的专性吸附为主;去除有机质后,解吸量与解吸率下降,固液分配系数Kd值下降。④傅里叶变换红外光谱表明,土壤吸附Se(Ⅳ)与静电引力、络合反应和配位体交换有关;去除有机质减少了有机官能团的数量,导致吸附量减少。综上,有机质的存在,提升了酸性富硒土对Se(Ⅳ)的吸附容量和吸附强度,是造成酸性富硒土硒有效性较低的重要因素。

pH值对X70管线钢在北部湾钦州砖红壤模拟溶液中腐蚀行为的影响

为探究X70管线钢在不同pH值下的腐蚀规律及机理,采用动电位极化曲线和电化学交流阻抗谱测试技术、质量法、X射线衍射技术研究了在恒温条件下不同pH值X70管线钢在北部湾钦州砖红壤模拟溶液中的电化学腐蚀行为。结果表明:随着pH值的降低,X70管线钢的容抗弧阻值不断减小,随之极化电阻减小,且自腐蚀电位负移,自腐蚀电流密度增加,X70管线钢溶解速率变大,腐蚀性增强。极化过程中,阳极X70管线钢活化溶解,阴极反应存在吸氧腐蚀和析氢腐蚀。溶液酸性越强,H^(+)会促进腐蚀产物FeO(OH)和Fe_(2)O_(3)向FeO(OH)的转变,并且H^(+)在反应过程中会生成氢气,造成腐蚀产物的疏松,对管线钢基体保护性变弱,腐蚀加剧。

高吸水性树脂在赤红壤及砖红壤上的保水保肥效果研究

在旱地赤红壤和砖红壤上分别以小白菜和辣椒为供试作物,进行盆栽试验和大田试验,以研究高吸水性树脂及其肥料制品对土壤水肥的保持作用。结果表明:PAA能显著降低氮素淋失量,将更多的肥料养分保留在土壤中,同时又能减少土壤水分的无效消耗,从而提高水肥的利用率,最终提高作物产量。在PAA各种处理中,以0.02%、pH6.5的PAA稀凝胶与自来水交替灌溉对水肥保持效果最好,试验条件下,可使N素淋失量减少72.0%,水分利用率提高14.65%,作物产量增加33.20%。以高吸水性树脂和单质肥料为原料的掺混型节水专用肥与等养分的复合肥比较,辣椒果长、肩径宽、果肉厚、单果重明显增加,产量增加5.16%;节水449m3/hm2,相当于45mm降水,节水率27.7%。

生物炭对花岗岩砖红壤团聚体稳定性及其总碳分布特征的影响

通过不同浓度生物炭处理进行海南花岗岩砖红壤的小区试验,研究生物炭对花岗岩砖红壤水稳性团聚体以及土壤总碳的影响。结果表明:18个月后,与对照相比,0.5%或1.0%生物炭处理的水稳性团聚体几何平均直径(GMD)分别提高15.64%和10.80%;大于5mm水稳性团聚体含量分别增加98.75%和88.37%。1.0%生物炭处理下的3～5mm,2～3 mm和0.5～1 mm粒级水稳性团聚体总碳含量比对照分别增加32.24%,39.31%和306.36%;1.0%生物炭处理下>5mm粒级的水稳性团聚体的总碳分配比例比对照增加90.44%。综合分析认为,生物炭对改善花岗岩砖红壤团聚结构、增加土壤总碳含量有积极意义。

尿素在砖红壤中的淋失特征Ⅱ——NO_3^-—N的淋失

通过室内大型土柱模拟试验研究了不同尿素施用量与砖红壤中NO3--N的淋失关系。结果表明,各处理渗漏液中20cm处NO-3-N浓度变化趋势相似;60cm处渗漏液中各处理NO-3-N最高浓度值均显著高于对应的20cm处;120cm处渗漏液中各处理NO-3-N浓度在39d前无显著变化,之后迅速上升并且随着施肥量的增加而增大,其最高浓度值与施肥量的关系可用方程y=0.5257x+138.2来表示。从120cm处NO-3-N累计淋失量来看,其累计淋失量与施肥量的关系可以用下式来表示:y=0.478x+204.26;最后对各处理NO3--N累计淋失量Yt(gN)与时间t(d)的关系进行拟合。

草酸活化磷矿粉对砖红壤中外源铅的钝化效果

磷矿粉被广泛用于固定污染土壤中的重金属,然而施用草酸活化磷矿粉后对土壤中铅形态的研究非常有限。该文采用Tessier连续提取法分析砖红壤中施加未活化和经草酸活化的磷矿粉后,砖红壤中外源铅形态的变化。结果表明:随着磷矿粉施加量的增加,各处理中交换态铅质量分数比对照(64.1mg/kg)显著下降,未活化磷矿粉处理(PR)的交换态铅质量分数为0.1mg/kg,而草酸活化磷矿粉处理(APR)中未检出;醋酸盐提取态铅质量分数除草酸活化磷矿粉2000mg/kg处理为24.5mg/kg(APR3)减少外,其他处理均高于对照(27.2mg/kg),在未活化磷矿粉500mg/kg(PR2)处理时达到最大值41.8mg/kg;铁锰氧化物结合态除未活化磷矿粉50mg/kg(PR1)处理为69.5mg/kg低于对照(74.2mg/kg)外,其余均高于对照,在APR3处理时达最大值117.2mg/kg;有机物结合态铅质量分数除PR1处理为20.7mg/kg,其余均高于对照处理(21.8mg/kg),在APR3处理时达到最大值46.5mg/kg;PR处理残渣态铅与对照相比(44.2mg/kg)显著增加至60.6mg/kg,对APR处理其变化范围为42.7～43.5mg/kg,各处理稍低于对照,但差异不显著(p<0.05)。显然,磷矿粉的施加可有效降低砖红壤中交换态铅质量分数,增加稳定态铅质量分数,且草酸活化磷矿粉的效果更佳。同时,草酸活化后磷矿粉的释磷能力增加,除草酸活化磷矿粉最高施磷量处理外(5000mg/kg),施入磷矿粉和草酸活化磷矿粉后释放的磷对环境构成风险可能性极小。X-射线衍射光谱(X-ray diffraction,XRD)和扫描电镜(scaning electron microscope,SEM)结果分析也表明草酸活化磷矿粉的释磷能力增加,更有利于固定土壤中的铅。该研究可为草酸活化磷矿粉固定土壤中的铅提供参考依据。

海南岛西部地区砖红壤中微量元素含量及其分布特征

对海南岛西部地区发育典型的5个砖红壤剖面微量元素的组成特征进行研究发现,5个剖面微量元素的含量变化趋势具有一定的相似性,其中Cu、Pb、Zn、As平均含量大多高于中国南方砖红壤的平均值,而Ni、Mo、Cd、Sn、Sb等微量元素则刚好相反。各剖面微量元素含量的纵向变化规律显示,土壤中微量元素含量及其垂直变化从根本上取决于土壤母质的特征。受区内自然条件影响,区内土壤微量元素的垂向迁移能力相对较弱,而人类的工业活动、农业活动也可导致少量As、Cd、Pb等有害外源微量元素进入土壤并趋向于在土壤的浅层富集。

不同改良剂对镉污染土壤中小白菜吸收镉的影响

采用盆栽试验,研究了施用石灰、钙镁磷肥、泥炭、碱渣4种土壤改良剂对外加镉污染的赤红壤上小白菜产量、镉吸收量、土壤有效态镉及pH的影响。结果表明:外加1mg·kg-1和5mg·kg-1镉对小白菜生物量无显著影响,且1mg·kg-1镉对小白菜生长有一定的促进作用;施用改良剂对镉污染土壤上小白菜无显著增产效果。施用4种改良剂均能降低小白菜地上部镉含量,作用效果为石灰≈泥炭>碱渣>钙镁磷肥。不同改良剂对小白菜根部镉含量影响不同,泥炭和石灰在所有镉浓度下、钙镁磷肥在0和1mg·kg-1镉浓度下可显著降低根部镉含量,而碱渣无明显作用,种植两茬规律一致。土壤有效态镉含量与pH呈显著负相关;施用石灰、碱渣、钙镁磷肥使土壤pH显著升高,有效态镉含量显著降低,从而降低小白菜对镉的吸收;泥炭可显著提高土壤pH,虽降低土壤有效态镉作用效果不显著,但显著降低小白菜体内镉含量,这可能与土壤中形成难以被植物吸收的镉有机结合物有关。两茬蔬菜种植结果显示,施用后期改良剂对镉污染的抑制效果也较明显。