任凯璐(1997—),女,山东安丘人,硕士研究生,研究方向:土壤胶体与界面化学。E-mail:
土壤胶体的凝聚与土壤团聚体的形成密切相关。施肥改变土壤溶液环境,对土壤团聚体形成、土壤结构和土壤物质组成产生影响。探索长期不同施肥影响土壤胶体微观性质和相互作用进而影响土壤宏观现象的关联十分必要。依托35年棕壤长期定位施肥监测试验站,选取不施肥处理(CK)、施用氮肥(N)、施用有机肥(M)、氮肥与有机肥配合施用(N+M)四种处理的棕壤为研究对象,采用动态光散射技术监测不同施肥处理的棕壤胶体凝聚动力学过程,通过对比分析棕壤有机质含量、表面化学性质和棕壤矿物组成等探究不同施肥处理对棕壤胶体凝聚过程的影响。研究发现:四种长期不同施肥处理的棕壤胶体凝聚特征均表现为在低电解质浓度条件下发生慢速凝聚(RLCA)与高电解质浓度条件下的快速凝聚(DLCA);不同施肥处理胶体在相同电解质体系中的临界聚沉浓度的大小顺序均为M > N+M > CK > N。有机肥的长期施用增加了棕壤有机质含量,从而提高了胶体颗粒表面电场强度,加大了胶体颗粒间的静电斥力,加之有机质组分的空间位阻效应使得胶体的凝聚现象减弱;另一方面,长期不同施肥处理并未改变棕壤黏土矿物组成类型,但对其相对含量产生影响:其中,有机肥的长期施入使2︰1型伊利石的相对含量增加,1︰1型高岭石的相对含量减少,长期施用氮肥使伊利石相对含量减少而高岭石相对含量增加。综上,长期不同施肥处理会改变棕壤胶体的基本理化性质和矿物组成比例关系,进而影响棕壤胶体的凝聚动力学过程。
The aggregation of soil colloids is closely related to the formation of soil aggregates. Fertilization can change the environment of soil solution, and affect the formation of soil aggregates, soil structure and soil mineral composition. It is necessary to explore the relationship between the long-term effects of different fertilization on the microscopic properties and interactions of soil colloids and thus the macroscopic phenomena of soils.
Based on a 35-year long-term fertilization monitoring experiment in the experimental station of brown earth, soils treated with no fertilization(CK), nitrogen fertilizer(N), organic fertilizer(M) and the combination of nitrogen fertilizer and organic fertilizer(N+M) were selected as the research objects in this study. Dynamic light scattering technology was used to monitor the dynamic aggregation process of soil colloids with different fertilization treatments. The effects of fertilization treatments on colloid aggregation were comparatively analyzed through the organic matter content, soil mineral composition and surface chemical properties.
The soil colloids of the four treatments showed the characteristics of slow aggregation(RLCA) at low electrolyte concentration and fast aggregation(DLCA) at high electrolyte concentration. The order of critical coagulation concentration of four different fertilization treatments was M > N+M > CK > N. Also the long-term application of organic fertilizer increased soil organic matter, thereby increasing the electric field strength near the surface of colloidal particles and the electrostatic repulsion between colloidal particles. Furthermore, the steric hindrance effects of humus weakened the phenomenon of colloid aggregation; On the other hand, long-term fertilization did not change the soil clay mineral composition type, but had an impact on its relative content. The application of organic fertilizer increased the relative content of 2︰1 type illite and decreased the relative content of 1︰1 type kaolinite. The application of nitrogen fertilizer reduced the relative content of illite and increased the relative content of kaolinite.
Different fertilization treatments for a long time changed the basic physicochemical properties and mineral composition ratio of brown earth colloids, which in turn affected the aggregation kinetics of brown earth colloids.
良好的土壤结构使土壤具有良好的保肥保水性,是土壤具有肥力的基础。土壤胶体十分微小且性质活跃,是土壤团聚体的基本组成单元,土壤胶体多以有机无机复合胶体的形态存在,研究普遍认为土壤中的微团聚体是由有机无机复合体逐步胶结形成的[
土壤胶体颗粒的凝聚被认为是在体系中不断地“接近-接触-黏结”的过程,当胶体颗粒间的有效碰撞概率为1,胶体颗粒一经碰撞就会发生不可逆的凝聚,此方式称为扩散控制簇团凝聚(Diffusion limited cluster aggregation,DLCA);当胶体颗粒间有效碰撞概率小于1,此时的凝聚称为反应控制簇团凝聚机制(Reaction limited cluster aggregation,RLCA)[
施肥作为一种重要的农业管理措施,主要通过改变土壤溶液环境和物质组成两个方面影响土壤胶体的凝聚和分散,从而影响土壤结构。其一,施肥改变土壤溶液环境。肥料的施用使土壤溶液中离子种类和含量发生改变,从而影响胶体的凝聚行为。现有的研究也发现长期施用化肥会导致土壤pH下降[
土壤胶体的相互作用影响着土壤中众多微观与宏观过程,微观角度上根据团聚体分级构建学说,土壤团聚体的形成与土壤胶体密切相关[
供试土壤为棕壤,取自沈阳农业大学棕壤长期定位实验基地(41°49′ N,123°49′ E),该地区海拔75 m,属暖温带大陆性季风气候,年均温8.0 ℃,年平均降水量705 mm。该长期定位实验始于1987年,连作作物为玉米。选取不施肥处理(CK)、氮肥处理(N:尿素N 270 kg·hm–2)、有机肥处理(M:猪厩肥N 270 kg·hm–2)、氮肥+有机肥处理(N+M:尿素N 135 kg·hm–2+猪厩肥N 135 kg·hm–2)四种不同施肥处理的0~20 cm耕层土壤作为供试材料,采样时间为2021年10月,在每个施肥处理的小区中采用五点法取样。
土壤样品风干后去除杂质、过筛处理,测定土壤含水量、pH、有机质含量等基本性质[
利用静水沉降虹吸法[
本研究中矿物组成测定采用X射线衍射法,将不同施肥处理的棕壤全土和胶体粉末使用玛瑙研钵研磨,过300目筛,采用DCB(连二亚硫酸钠-柠檬酸钠-重碳酸钠)法进行脱铁处理,脱铁后超纯水饱和处理三次,用超纯水制成自然定向片,用于衍射分析。XRD衍射仪器选用Bruker D8 X衍射仪,Cu靶辐射,管压36 kV,管流20 mA,扫描角度范围(2
X射线衍射测定不同施肥处理棕壤及其胶体矿物组成和含量,需对所得的衍射谱图进行分峰拟合,根据布拉格方程(2
土壤胶体颗粒凝聚过程运用动态光散射仪(BI-200SM,Brookhaven,美国)监测胶体凝聚过程中粒径增长随时间的变化,数字相关器为BI-9000AT。凝聚实验中,将不同初始颗粒密度的土壤胶体悬液稀释适宜的倍数至光散射样品池中,保证测定时颗粒密度约为0.030 g·L–1。待测胶体悬液的配制遵循先加入土壤胶体,再加入超纯水,最后加入电解质的顺序。根据预实验,以KCl为电解质诱导土壤胶体凝聚时,不同处理电解质浓度梯度范围设为10、15、20、30、40、50、80、100、200、300 mmol·L–1。以CaCl2为电解质诱导土壤胶体凝聚时,不同处理电解质浓度范围梯度设为0.3、0.5、0.7、1.0、1.5、2.0、2.5、3.0、3.5、4.0 mmol·L–1。每份待测样品的监测时间设置为30 min,监测时机器参数按照功率200 mV、狭缝100 nm、波长532 nm设置。
根据凝聚体粒径随时间的增长计算平均凝聚速率,具体计算公式如下[
式中,
棕壤及棕壤胶体矿物组成谱图绘制及数据分析采用Origin软件,其余数据分析及图表绘制均采用Excel软件。
从
不同施肥处理棕壤基本理化性质
Basic physical and chemical properties of brown earth under different fertilization treatments
处理 |
pH | 有机质 |
Zeta电位 |
注:CK:不施肥处理;N:施用氮肥处理;M:施用有机肥处理;N+M:氮肥与有机肥配合施用处理。Note:CK:no fertilization;N:nitrogen fertilizer;M:organic fertilizer;N+M:the combination of nitrogen fertilizer and organic fertilizer. | |||
CK | 6.12±0.01 | 15.44±0.74 | –29.82±0.24 |
N | 4.33±0.00 | 20.85±0.70 | –27.28±0.16 |
M | 6.11±0.02 | 38.60±0.40 | –34.70±0.34 |
N+M | 6.06±0.03 | 28.88±0.54 | –32.91±0.29 |
由
不同施肥处理棕壤胶体粒径分布
Colloidal particle size distribution of brown earth under different fertilization treatments
四种处理风干棕壤的XRD图谱
XRD patterns of air-dried brown earth under four fertilization treatments
四种处理棕壤胶体的XRD图谱
XRD patterns of brown earth colloid under four fertilization treatments
本研究所使用棕壤胶体粒径小于200 nm,对比棕壤全土和胶体的XRD谱图可以发现,不同处理棕壤胶体的XRD谱图相较于全土的XRD谱图的峰更加低矮且圆滑,各施肥处理棕壤胶体中矿物结晶度较各全土差。这是由于结晶度差的晶体颗粒过于细小,晶体中存在多种缺陷,导致其衍射能力减弱,衍射峰变宽;而结晶程度好的晶体颗粒一般颗粒较大,衍射强度大且衍射峰尖锐[
不同施肥处理的棕壤全土和胶体矿物组成类型相似,但不同类型矿物的相对含量有所不同(
不同施肥处理棕壤及其胶体的主要矿物相对含量
Relative contents of main minerals of brown earth and colloid under different fertilization treatments
样品 |
处理 |
高岭石 |
石英 |
伊利石 |
长石 |
注:CK:不施肥处理;N:施用氮肥处理;M:施用有机肥处理;N+M:氮肥与有机肥配合施用处理。Note:CK:no fertilization;N:nitrogen fertilizer;M:organic fertilizer;N+M:the combination of nitrogen fertilizer and organic fertilizer. | |||||
棕壤全土 |
CK | 3.42 | 11.20 | 65.26 | 20.12 |
N | 4.18 | 9.79 | 64.04 | 21.99 | |
M | 3.19 | 9.82 | 71.26 | 15.73 | |
N+M | 5.51 | 12.11 | 67.95 | 14.43 | |
棕壤胶体 |
CK | 19.99 | 0 | 80.01 | 0 |
N | 43.57 | 0 | 56.43 | 0 | |
M | 3.75 | 0 | 96.25 | 0 | |
N+M | 7.25 | 0 | 92.75 | 0 |
从
KCl浓度为30 mmol·L–1(a)和200 mmol·L–1(b)时不同施肥处理棕壤胶体凝聚过程中有效粒径变化
Growth of brown earth colloidal agglomeration effective diameter with time under different fertilization treatments when KCl concentration was 30 mmol·L–1(a)and 200 mmol·L–1(b)
CaCl2浓度为0.7 mmol·L–1(a)和3 mmol·L–1(b)时不同施肥处理棕壤胶体凝聚过程中有效粒径变化
Growth of brown earth colloidal agglomeration effective diameter with time under different fertilization treatments when CaCl2 concentration was 0.7 mmol·L–1(a)and 3 mmol·L–1(b)
在较高的电解质浓度下(200 mmol·L–1KCl和3 mmol·L–1CaCl2),四种处理棕壤胶体的凝聚过程较为相似,均呈现幂函数增长的趋势,KCl体系中,各处理第30 min的有效粒径分别为CK:1 453 nm、N:1 471 nm、M:1 315 nm、N+M:1 455 nm,CaCl2条件下各处理的有效粒径分别为CK:1 271 nm、N:1 311 nm、M:1 172 nm、N+M:1 237 nm。由此可见,当电解质浓度增大后M处理与其他处理最终有效粒径的差值缩小。通过对比可以看出,高电解质浓度下各处理棕壤胶体有效粒径增长速度更快,低电解质浓度下棕壤胶体有效粒径增长较慢,两种电解质体系中棕壤胶体有效粒径的增长趋势相似。电解质浓度越高,对双电层的压缩力越强,凝聚速率越高,且电解质浓度越高,不同施肥处理的棕壤胶体凝聚体粒径差异越小。
从上述结果中可知,不同施肥处理会影响棕壤胶体的稳定性,与不施肥相比施用有机肥可以显著提高棕壤胶体的分散稳定性,而单一施用氮肥和氮肥与有机肥配合施用对棕壤胶体分散稳定性的影响相对较小。
四种施肥处理下的棕壤胶体在KCl体系中的总体平均凝聚速率和临界聚沉浓度
Average aggregation rates of brown earth colloid and critical coagulation concentration of KCl in four kinds of colloid under four kinds of fertilization treatments
四种施肥处理下的棕壤胶体在CaCl2体系中的总体平均凝聚速率和临界聚沉浓度
Average aggregation rates of brown earth colloid and critical coagulation concentration of CaCl2 in four kinds of colloid under four kinds of fertilization treatments
Kretzschmar等[
长期不同施肥处理影响棕壤基本理化性质,施用有机肥的棕壤pH、有机质含量和Zeta电位绝对值高于其他处理;长期不同施肥处理对棕壤黏土矿物组成类型无影响,对不同黏土矿物的相对含量有明显影响,施用有机肥处理的棕壤黏土矿物中伊利石的相对含量最高;长期不同施肥处理对棕壤胶体凝聚动力学过程具有显著影响,相同条件下施用有机肥处理的棕壤胶体更难凝聚具有更强的分散稳定性,施用氮肥处理的棕壤胶体分散稳定性较弱。综上,长期施肥通过影响棕壤pH、有机质含量、表面电荷、矿物组成等理化性质来间接影响微观角度胶体颗粒的相互作用,进而影响宏观角度棕壤团聚体的形成。在一定情况下,施用有机肥可以提高土壤胶体的分散稳定性,有利于促进土壤形成较为疏松良好的结构,还可以改善土壤理化性状。但施肥处理对土壤矿物风化的影响过程和机制仍需进一步探索研究。
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