Analyzing the Relation between Loss-on-Ignition and Other Methods of Soil Organic Carbon Determination in a Tropical Cloud Forest (Mexico)

The objective of this study was to analyze the relationship between soil organic carbon content, determined by dry combustion (%OC_LECO) and the Walkley–Black method (%OC_WB), and loss on ignition (LOI). Soil samples were collected from noncalcareous O and A1 horizons within a tropical cloud forest. Linear regression equations were developed to estimate organic carbon from LOI. The applicability of the predictive equations was evaluated by comparison of measured and predicted organic carbon data for independent soil samples. The results showed that the LOI method produced a better linear relationship with the %OC_LECO (R ² = 0.96, P < 0.001) than with the %OC_WB (R ² = 0.88, P <0.001) method. These results also showed that %OC_WB and %OC_LECO prediction equations underestimate and overestimate soil organic carbon by 0.74% and 0.56%, respectively. This study suggests that LOI may be a good estimator of soil organic carbon for noncalcareous O and A1 horizons in a tropical cloud forest.     

Comparison of Analytical Methods for Organic Matter in Composts and Organic Mulches

Abstract

The conventional dichromate (Walkley and Black), carbon analyzer, and weight loss‐on‐ignition (WLOI) methods are compared for determination of organic matter contents in composts and organic mulches. The objective of this study was to evaluate these three methods for their reliability in determining the organic matter contents of composts and organic mulches that also contain inorganic carbon. The carbon analyzer method overestimated organic matter contents for samples containing inorganic carbon (C) as carbonate or charcoal C. The removal of inorganic C improved the correlation coefficients (r) of results obtained by the carbon analyzer method and the Walkley and Black method (0.95 vs. 0.89). The WLOI method produced results more similar to those obtained with the Walkley and Black method than with a carbon analyzer. Oven drying samples for 16–24 h at 105°C as a basal temperature for WLOI improved results compared with a basal temperature at 70°C, which is commonly used. A heating temperature of 500°C for 12 h resulted in organic matter determinations by the WLOI method in the closest agreement with those obtained by the Walkley and Black method.     

Predicting Total Organic Carbon Content of Soils from Walkley and Black Analysis

Globally, there is problem of computing soil carbon stock because the Walkley–Black method gives only an approximation of soil organic carbon content. Until now, no universal relationship between Walkley–Black carbon (WBC) and total soil organic carbon (TOC) has been developed that could be applicable in all kinds of soil. In the present study, relationships between WBC and TOC were established from samples collected from central and northern India. TOC was measured by dry combustion technique and WBC was determined by wet digestion methods. A relationship between WBC and TOC was developed by taking into account silt + clay content (SICL) of soil and mean annual rainfall (MAR) of the region (adj. R² = 0.99, n = 100). The present study gives an easy approach to measure TOC by easily available data sets (WBC, SICL, and MAR). Using this relationship, computation of soil carbon stock that was done earlier with WBC values could be revisited and improved.     

Comparison of Total Nitrogen Methods Applied for Histosols and Soil Horizons with High Organic Matter Content

Abstract

This study was carried out to correlate total nitrogen analyzed by two different methods: Kjeldahl (wet oxidation) and Perkin‐Elmer 2.400 Series II–CHN Mode (dry oxidation or combustion) in Histosols and soil surface horizons with high organic matter content, sampled in different regions of Brazil. A positive correlation (r=0.95**) was verified between the methods, showing that Kjeldahl, because of its simplicity, can be used to routinely determine total nitrogen content in the evaluated soils.     

辽宁地区保护地土壤有机质含量及其影响因素的研究

在对辽宁省主要保护地蔬菜生产区生产状况进行实地调查的基础上,自蔬菜保护地和与之相邻的露地大田采集土壤样品,研究保护地土壤有机质含量变化特点,分析了改作保护地后种植年限、有机肥施用量等因素对保护地土壤有机质含量的影响。结果表明:(1)蔬菜保护地土壤有机质含量总体上已经显著高于露地大田土壤,且这一差异0~20 cm土层明显大于20~40 cm土层;(2)保护地土壤有机质含量表现出随着改作保护地后种植年限延长而增加的变化趋势;(3)在改作保护地后种植年限相近的条件下,保护地土壤有机质含量及其增量与有机肥施用量呈明显的正相关关系。(4)辽宁各地保护地土壤有机质含量差异明显,其中大连地区保护地土壤有机质含量较高,其他地区处于中-低水平,需要增加投入、提高土壤有机质含量以进一步培肥地力。     

Comparison of Chemical Methods of Assessing Potentially Available Organic Nitrogen from Organic Residues Applied to a Sandy Soil

Abstract

More than 90% of the nitrogen (N) in soils is bond as organic N compounds. The available N can be estimated on the mineral N released during time‐consuming incubations of soil. Several chemical methods have been developed as substitutes for incubations. On the other hand, there has been an increase in waste production. Residues could potentially offset the need for mineral fertilizers, being both an economic and environmental benefit. Thus, the development of a routine method for prediction of N supply both from soil organic matter (SOM) and the application of organic residues is of great interest. An incubation experiment was performed in a Cambic Arenosol to evaluate different chemical methods. Air‐dried soil was mixed with increasing amounts of composted solid municipal waste, secondary pulp‐mill sludge, hornmeal, poultry manure, the solid phase from pig slurry, and composted pig manure. Samples were incubated for 244 days under a controlled environment. Among the chemical extractants studied, hot 2 M potassium chloride (KCl) and hot 0.01 M calcium chloride (CaCl₂) showed promise in indicating values of N₀ (potentially available nitrogen), and these simple methods are suitable for use in routine laboratory conditions.     

Quantification of Organic Carbon in Soils: A Comparison of Methodologies and Assessment of the Carbon Content of Organic Matter

Abstract

Renewed interest in temporal soil organic carbon (SOC) stock changes has stressed the importance of reliable methods for quantitative assessment of organic compound (OC) content. Particularly with the establishment of modern dry‐combustion analyzers, which are replacing the traditional wet‐oxidation methods, the need for correct relationships between both is of crucial importance for comparison of past and current SOC data in long‐term SOC stock change studies. Dry combustion with a Variomax CNS‐analyzer was the standard to evaluate three other methods for Belgian agricultural soils. Excellent linear relationships were found with the Walkey and Black method and the Springer and Klee method, whereas a Shimadzu TOC‐analyzer slightly underestimated the OC content. Precision of the investigated methods was comparable and tended to be dependent on the sample size used for measurement. The OC oxidation efficiency of the most widely applied method of Walkey and Black for the soils in this study was very close to the generally accepted 75%. Mass loss on ignition at 800°C could be very well related to the soil OC content and the clay content. The traditional factor of 1.724 used to convert OC measurements to organic matter percentages is not valid for the investigated soils, which demonstrates that rather regional‐specific factors (in this study 1.911) should be determined and adopted.     

海伦市耕层土壤有机质含量空间预测方法研究

有机质含量是表征土壤肥力质量的重要属性,其空间分布模式对于施肥等耕作管理措施的推荐具有重要的指导意义。本文以我国黑土区黑龙江省海伦市为研究区域,在土壤采样点数量较有限的情况下,分别采用普通克里格、反距离权重、遥感反演和基于土壤学专业知识四种方法对耕层土壤有机质含量进行了空间预测。结果表明:四种方法表征的海伦耕地土壤有机质含量空间分布特征具有相似性,即由东北向西南方向递减。空间预测精度从高到低依次为反距离权重、普通克里格、基于土壤学专业知识和遥感反演法;而在有机质的局部变异细节表达方面,从高到低为遥感反演、基于土壤学专业知识、反距离权重和普通克里格法。四种方法中仅遥感反演法预测结果的极差范围较宽,普通克里格法则存在明显的平滑效应,而综合比较结果则表明,最合适的方法是基于土壤学专业知识的方法。     

风沙土不同有机组分对磷的吸附特征影响

采用平衡吸附法研究了风沙土不同有机组分对磷的吸附特征影响,可为有机组分吸附态磷携载量估算提供依据。结果表明：去除有机质后的风沙土对磷的吸附能力大大降低,其碳标化饱和吸附量（Гmo）c和吸附分配系数（ko）c分别只能达到重组的27.76%和8.45%,说明有机质是影响磷在风沙土上吸附特征的重要因素;磷在轻组有机组分上的吸附以分配作用为主（koc=51.02）;风沙土有机组分中的重组有机质对磷的吸附起主导作用（Гmoc=388.35mg.kg-1）,重组有机组分中的紧结态腐殖质（胡敏素）对磷的吸附起关键作用（Гmoc=1007.96mg.kg-1）,影响机制主要为稳、紧结态腐殖质是形成土壤疏松多孔团聚体结构的重要胶结物质。在其所形成的有机矿质复合体中除分配作用吸附外,还存在着孔隙填充方式的磷吸附;考查土壤对磷的吸附能力不但要考虑有机质的含量,更要考虑有机质的存在形态,它也是影响土壤对磷吸附特征的重要因素。以重组为基准,轻组有机组分以及重组有机组分中稳结态腐殖质和紧结态腐殖质携载的吸附态磷分别可按0.69倍以及1.37、2.75倍估算。     

黑河中游荒漠绿洲过渡带斑块植被区土壤水分与有机质空间变异特征

以黑河中游荒漠绿洲过渡带斑块植被区土壤为研究对象,对土壤含水量与土壤有机质含量空间变异特征及两者相关性进行研究,并对土壤含水量和土壤有机质含量的空间变异函数模型进行拟合。结果表明:(1)20~40 cm土层的土壤含水量空间变异性最为强烈,C_V=1.780;而40~60 cm土层的土壤有机质含量空间变异性最为强烈,C_V=0.561。(2)0~120 cm土层的土壤含水量空间变异函数理论模型均为指数模型;0~60 cm土层的土壤有机质含量空间变异函数理论模型为纯块金模型;而60~120 cm土层的土壤有机质含量空间变异函数理论模型为指数模型和球状模型。(3)土壤含水量和土壤有机质含量均随土层深度的增加而相应的增加,且二者之间呈显著对数相关关系,R~2=0.9597。     

耕作方式对黄绵土水稳定性团聚体形成的影响

研究了不同耕作方式对黄绵土水稳性团聚体形成的影响。结果表明,>0.25mm土壤水稳定性团聚体含量:免耕+秸秆覆盖(NTS)>免耕(NT)>传统耕作+秸秆还田(TS)>传统耕作(T),团聚体稳定率:免耕+秸秆覆盖(NTS)>免耕(NT)>传统耕作+秸秆还田(TS)>传统耕作(T)。水稳定性团聚体数量以及团聚体的水稳定性均与耕作方式有关。免耕+秸秆覆盖(NTS)、免耕(NT)和传统耕作+秸秆还田(TS)有利于土壤水稳定性团聚体的形成。分析结果同时说明,采用适当耕作方式的同时增加土壤有机质更有利于土壤团聚体的形成和稳定性的增加。