郝翔翔(1984—),男,博士,高级工程师,主要从事土壤有机质研究。E-mail:
土壤颜色作为土壤的一项重要物理指标,被广泛应用于土壤诊断、分类以及土壤性质判断。在矿物成分大致相同条件下,土壤有机质(SOM)是控制土壤变黑的重要因素。采用基于CIE
Soil color is an important soil property. It is frequently used by soil scientists for the identification and classification of soil. It is also used as an indicator of many soil properties. Soil organic matter(SOM)is the most important pigment, that colors the soil in black color.
In this study, a total of 30 mollisol samples were collected from the typical black soil region of northeast China. The SOM was physically separated into four fractions: light fraction, coarse particle fraction, fine particle fraction, and mineral‐associated fraction. Based on the CIE
Bulk soil blackness was strongly positively correlated with the SOM content. Similarly, significant relationships were observed between the blackness of physical fractions and the organic carbon content in corresponding fractions. This relationship was gradually strengthened with the increase in the stability of the fractions. As for the color of soil physical fractions, the blackness value of light and coarse particle fractions was greater than that of fine particle and mineral‐associated fractions. Also, correlation analysis showed that there was no significant relationship between the blackness of light or coarse particle fractions and the bulk soil blackness, and the contribution rate of the two fractions to bulk soil blackness was only 2.6%.
The the mineral‐associated fractions, as the main storage location of soil humus, contributed more than 81% to bulk soil blackness and plays a decisive role in coloring the soil black.
土壤颜色不仅是土壤分类的关键指标,也是判断土壤肥力和养分变化的重要依据[
黑土作为一种以黑色为主色调的土壤,其矿物组成中富含2︰1型硅酸盐黏土矿物,该类型矿物在颜色上呈现亮度较高的白色,但另一方面,黑土所富含的有机质,会对黏土矿物的白色产生掩蔽作用[
SOM组成复杂,不同组分对土壤颜色的影响也各异,例如,胡敏酸对土壤的着色能力强于富里酸[
综上,本研究假设:(1)有机质和矿质含量不同的物理组分,在颜色上可能存在着一定的差异;(2)含量和成分上的差异,会导致不同组分对土壤颜色的贡献不同。为验证以上假设,以典型黑土为研究对象,采用基于CIE
土壤样品采自于黑龙江省海伦市,该市位于中国典型黑土分布带的中部,成土的气候条件为温带大陆性季风气候,年均降水量500 ~ 600 mm,年均气温约1.5 ℃,年均≥ 10 ℃有效积温2 400 ~ 2 500 ℃;成土母质为第四纪黄土状物质;大地形为平原,海拔高度为200 ~ 240 m,10 000 m水平距离内起伏高差10 ~ 30 m不等,存在大量排水不畅的低洼地;自然土壤的植被为草原化草甸植被,土壤垦殖期大约120年,种植作物包括玉米(
采用物理分组方法[
黑度值采用便携式分光测色仪(NS-800,深圳市三恩驰科技有限公司)进行测量。该仪器以国际通用的CIE
采用以下公式计算不同有机质组分对土壤黑度的贡献率:
式中,
土壤及其物理组分的碳含量采用元素分析仪测定(EA3000,Euro Vector,Italy)进行测定,研究土壤不含碳酸盐,全碳含量即总有机碳含量。本文重点讨论土壤有机质与黑度的关系,因此将土壤总有机碳含量换算为了土壤有机质,但土壤有机碳与有机质的转换系数不适用于各物理组分,因此,物理组分以有机碳浓度表示。
运用SPSS V19.0和GraphPad Prism 8软件进行数据分析和绘图。采用Pearson相关系数来评估不同变量之间的线性关系,包括原土黑度值与SOM含量、土壤物理组分黑度值与组分有机碳浓度间的关系,以及组分黑度与原土黑度间的关系。采用Spearman相关分析来评估土壤黑度值与土壤含水量间的定量关系。
分析样品的土壤有机质(SOM)含量范围为30.81~76.29 g·kg–1,平均值为48.96 g·kg–1(
分析样品的土壤有机质含量和黑度的描述性统计(
The descriptive statistics of the SOM content and blackness of the 30 samples
土壤属性 |
最小值 |
最大值 |
平均值 |
标准差 |
变异度 |
注:黑度值为烘干样品所测。Note:Blackness is the value of an oven-dried sample. | |||||
土壤有机质 |
30.81 | 76.29 | 48.96 | 11.61 | 23.22 |
黑度 |
60.51 | 68.29 | 64.05 | 2.39 | 3.73 |
分析样品土壤有机质含量的频率分布直方图
Frequency distribution histogram of soil organic matter of samples
在5个不同土壤含水量条件下,土壤的黑度值与SOM含量均呈现极显著正相关关系(
不同含水量条件下土壤黑度与有机碳含量相关性
Relationship between bulk soil organic carbon and blackness under different soil water content
土壤含水量与土壤黑度间的相关性
Relationship between bulk soil water content and blackness
土壤4个物理组分中,LFOM、cPOM、fPOM和MAOM组分含量的平均值分别为3.50、14.23、114.6和837.7 g·kg–1(
土壤不同物理组分的含量
Content of soil physical fractions
从每个独立组分的黑度来看,LFOM、cPOM、fPOM和MAOM组分的黑度值分别为65.77、66.01、48.89和43.04(
土壤不同物理组分的黑度
Blackness of soil physical fractions
LFOM、cPOM、fPOM和MAOM四个土壤物理组分的黑度均与各自相应的有机碳浓度呈显著正相关(
土壤不同物理组分的黑度与其有机碳浓度的关系
Relationship between organic carbon content and blackness of soil physical fractions
原土黑度与不同物理组分黑度的相关性
Relationship between the blackness of bulk soil and blackness of soil physical fractions
MAOM组分对土壤黑度的贡献率最高,达到81.46%(
不同物理组分对原土黑度的贡献率
Contribution rate of soil physical fractions to bulk soil blackness
土壤颜色是土壤物质组成的集中体现,SOM、锰可使土壤变黑,石英、碳酸盐可使土壤变白[
黑土的黑度值与其有机质含量呈显著正相关关系(
水分含量也是影响土壤颜色一个重要因素,随着含水量的升高,土壤的黑度值逐渐增大(
土壤分组结果表明,黑土的MAOM组分含量最大,可达80%以上(
土壤颜色分析结果证实了本文的第一个假设,即有机质和矿质含量不同的物理组分,在颜色上存在差异,表现为LFOM/cPOM > fPOM > MAOM。一般认为,腐殖化程度越强,SOM中颜色较深的胡敏酸和胡敏素含量越高,其颜色也会越深,但本文对土壤组分的独立分析得到了看似相反的结论,这是由于不同组分间所含黏土矿物的差异造成的。有研究证实,黏土矿物中富含的SiO2可使土壤呈现白色,并具有较高的亮度值[
值得注意的是,4个土壤组分的黑度值均与组分有机碳浓度呈现显著正相关关系,且随着组分稳定程度的增加,相关性逐渐增强(
本研究认为,原土的黑度是各个物理组分混合后的结果,即各个组分的含量和组分本身的黑度共同决定了土壤的整体黑度,因此,采用加权法来计算不同组分的贡献率。组分的含量即为权数,不同组分的黑度值乘以相应的权数,然后加和得到总体数,再用某一组分黑度值与含量的乘积除以总体数,即为该组分对土壤黑度的贡献值。这一计算方法可能存在着一定的局限性,因为不同组分对土壤黑度的贡献可能不是简单的加和效应,但以现有的数据来看,我们认为该计算方法可有效评价不同组分对土壤黑度贡献。尽管LFOM和cPOM组分的黑度较高,但由于其占土壤的比例非常低,二者的黑度与原土的黑度无显著相关性(
本文重点讨论土壤不同物理组分对其黑度的贡献,从传统知识来看,土壤腐殖物质对黑度贡献巨大,这也是本研究中MAOM组分对土壤黑度贡献率最高的原因,因为MAOM组分中的有机质几乎全部以腐殖质形式存在。此外,腐殖质组分的黑度值往往表现为:胡敏素 > 胡敏酸 > 富里酸,即腐殖化程度越高,腐殖质的黑度值越大,因此,SOM的腐殖化程度也是影响土壤黑度的重要因素。今后的研究可以进一步从化学组分的角度,研究SOM的腐殖化程度与土壤黑度间的关系。
在5种不同含水量条件下,黑土的黑度均与SOM含量呈极显著正相关关系。土壤含水量越大,其对光的吸收越强,黑度值越高,但当土壤含水量达到36%以上时,其黑度值趋于稳定。土壤不同物理组分的黑度存在差异,LFOM和cPOM组分的黑度值大于fPOM和MAOM组分。虽然MAOM组分的黑度值最低,但其数量优势及其所富含的腐殖质,使MAOM组分在土壤的黑化过程中发挥着决定性作用。
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