Soil texture analysis revisited: Removal of organic matter matters more than ever

Jensen, Johannes L.; Schjønning, Per; Watts, C. W.; Christensen, Bent T.; Munkholm, Lars J.

doi:10.1371/journal.pone.0178039

Cited by 57 publications

(42 citation statements)

References 26 publications

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“…Since all the Bouyoucos treatments evaluated in this study estimated the silt concentration as the difference between 100 percent and the percent sand and clay (Equation 3), any analytical errors would impact the estimation of the silt content when determining these two fractions. This nding is consistent with the observations of [22] who reported that the silt fraction was systematically overestimated when soil organic matter was not removed. The average silt content determined using the Bouyoucos methods was 6.89% (P = <0.001) lesser than that determined using the Pipette method.…”

Section: Comparison Of the Pipette Methods With Bouyoucos Treatmentssupporting

confidence: 93%

“…This necessitates the pre-treatment of the soil samples to remove organic matter before texture analysis. This observation is consistent with the ndings of [22], who reported underestimation of the clay content in samples where organic matter was not removed. The 4%Calgon treatment was negatively correlated with the Pipette method (r = -0.712; P-value = 0.021) at the 0.05 level which can be attributed to the low concentration of the dispersant that could have led to incomplete dispersion.…”

Section: Comparison Of the Pipette Methods With Bouyoucos Treatmentssupporting

confidence: 92%

“…This observation leads to the conclusion that, in the interest of accuracy, samples should be subjected to complete digestion by increasing days of digestion or increasing the concentration of hydrogen peroxide. This nding is consistent with the observations of [22] who reported that failure to remove organic matter underestimated the clay proportion.…”

Section: Removal Of Organic Mattersupporting

confidence: 93%

“…It also lucidly exposes the need to use 10% instead of 5% calgon proposed in the Bouyoucos procedure. The importance of removal of organic matter was also supported by [22].…”

Section: Resultsmentioning

confidence: 86%

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The Mwendwa Protocol: A modification of the Bouyoucos method of soil texture analysis

Mwendwa¹

2020

Preprint

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Background This study aimed to modify the Bouyoucos method of soil texture analysis by proposing the best sample treatment and analysis protocol that would give the most accurate results. The Bouyoucos method lacks sample pre-treatment whereby samples are dispersed for only 2 minutes after being soaked in 5% sodium hexametaphosphate (calgon) for 15 to 20 hours. In this study, the Pipette method was used as the standard method due to its increased precision and reproducibility. Different treatments modified from the Bouyoucos procedure were compared with the Pipette method aiming to identify the treatment whose soil texture proportions were closest to those obtained through the Pipette method. The treatments involved variation in the concentration of the digesting material during sample pre-treatment, concentration of the dispersing material, time of hydrometer readings, method of agitation before taking the first hydrometer reading and method of dispersing. Obtained data was analyzed statistically using Genstat and SPSS. Results Percent sand obtained through the Pipette method significantly correlated with that obtained through Shaking at the 0.01 level (r = 0.862; P-value = 0.001) and that obtained through Shaking + Stirring at the 0.05 level (r = 0.737; P-value = 0.015). The sand measurements made using the hydrometer variations overestimated the sand fraction in the soil samples. None of the Bouyoucos treatments estimated the percentage silt with sufficient accuracy. There was a positive correlation in the clay proportion between the Pipette method and Shaking + Stirring treatment (r = 0.644, P-value = 0.044) at the 0.01 level. There was a negative correlation between the clay proportion obtained using the Pipette method and no-digestion treatment (r = -0.234). The 4%Calgon treatment was negatively correlated with the Pipette method (r = -0.712; P-value = 0.021) at the 0.05 level. Treatments involving shaking and increased concentrations of hydrogen peroxide and calgon estimated the clay proportion with sufficient accuracy. Conclusions These observations are indicative of the need for soil pretreatment with hydrogen peroxide and also the use 10% calgon as the dispersing agent during soil texture analysis. A modification to the Bouyoucos method was proposed and dubbed The Mwendwa Protocol.

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Section: Comparison Of the Pipette Methods With Bouyoucos Treatmentssupporting

confidence: 93%

Section: Comparison Of the Pipette Methods With Bouyoucos Treatmentssupporting

confidence: 92%

Section: Removal Of Organic Mattersupporting

confidence: 93%

“…It also lucidly exposes the need to use 10% instead of 5% calgon proposed in the Bouyoucos procedure. The importance of removal of organic matter was also supported by [22].…”

Section: Resultsmentioning

confidence: 86%

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The Mwendwa Protocol: A modification of the Bouyoucos method of soil texture analysis

Mwendwa¹

2020

Preprint

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“…Soil texture and SOC data for the Highfield experiment at Rothamsted Research, UK (51°80′N, 00°36′W), were extracted from Jensen et al . (). This experiment is on a silt loam soil belonging to the Batcombe series; the parent material includes a silty (loess‐containing) deposit overlying and mixed with clay‐with‐flints (Avery & Catt, ).…”

Section: Methodsmentioning

confidence: 97%

Converting loss‐on‐ignition to organic carbon content in arable topsoil: pitfalls and proposed procedure

Jensen

Christensen

Schjønning

et al. 2018

European J Soil Science

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SummaryAssessments of changes in soil organic carbon (SOC) stocks depend heavily on reliable values of SOC content obtained by automated high‐temperature C analysers. However, historical as well as current research often relies on indirect SOC estimates such as loss‐on‐ignition (LOI). In this study, we revisit the conversion of LOI to SOC using soil from two long‐term agricultural field experiments and one arable field with different contents of SOC, clay and particles <20 μm (Fines20). Clay‐, silt‐ and sand‐sized fractions were isolated from the arable soil. Samples were analysed for texture, LOI (500°C for 4 hours) and SOC by dry combustion. For a topsoil with 2 g C and 30 g clay 100 g−1 soil, converting LOI to SOC by the conventional factor 0.58 overestimated the SOC stock by 45 Mg C ha−1. The error increased with increasing contents of clay and Fines20. Converting LOI to SOC by a regression model underestimated the SOC stock by 5 Mg C ha−1 at small clay and Fines20 contents and overestimated the SOC stock by 8 Mg C ha−1 at large contents. This was due to losses of structural water from clay minerals. The best model to convert LOI to SOC incorporated clay content. Evaluating this model against an independent dataset gave a root mean square error and mean error of 0.295 and 0.125 g C 100 g−1, respectively. To avoid misleading accounts of SOC stocks in agricultural soils, we recommend re‐analysis of archived soil samples for SOC using high‐temperature dry combustion methods. Where archived samples are not available, accounting for clay content improves conversion of LOI to SOC considerably. The use of the conventional conversion factor 0.58 is antiquated and provides misleading estimates of SOC stocks.Highlights Assessment of SOC contents is often based on less accurate methods such as LOI.Reliable accounts of changes in SOC stocks remain high on the agenda (4‰ initiative).Conversion of LOI to SOC is considerably improved by accounting for clay content.Converting LOI to SOC by the conventional factor 0.58 leads to grossly overestimated SOC stocks.

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Machine learning models for predicting soil particle size fractions from routine soil analyses in Quebec

Martinelli

Gasser

2022

Soil Science Soc of Amer J

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Soil texture and particle size distribution are important soil properties for understanding and interpreting the multiple processes and interactions in soil agrosystems. However, soil particle size analysis is rarely included in routine soil laboratory analyses due to cost but can be derived from other soil physico‐chemical properties and from more powerful regressions using machine learning techniques. The performance of multiple linear regression and four machine learning algorithms (MLAs)—K‐nearest neighbor (KNN), Random Forest, extra‐gradient boosting (XGBoost), and multilayer neural network (NeuralNetwork)—was compared to predict particle size fractions of clay, sand, and silt using routine analyses of soil pH, cation exchange capacity, Mehlich‐3 extracted elements, and density of dried sieved soil from 8,364 soil samples distributed across Quebec. Particle size fractions were predicted as compositional data using isometric log ratio transformation. The XGBoost model performed best, with RMSE values of 7, 10, and 12% and R2 values of .77, .57, and .73 for the prediction of clay, silt, and sand fractions, respectively. Feature importance classification varied from one model to another, but the best predictors remained the same regardless of the model used. Sieved soil density measured in the laboratory and Mehlich‐3 Mg, K, Fe, and Zn ranked as better predictors of particle size fractions. Predicting soil particle sizes using routine soil physico‐chemical properties and MLAs appears an option for incomplete legacy datasets and a promising economic alternative to current methods carried out in commercial laboratories.

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Soil texture analysis revisited: Removal of organic matter matters more than ever

Cited by 57 publications

References 26 publications

The Mwendwa Protocol: A modification of the Bouyoucos method of soil texture analysis

The Mwendwa Protocol: A modification of the Bouyoucos method of soil texture analysis

Converting loss‐on‐ignition to organic carbon content in arable topsoil: pitfalls and proposed procedure

Machine learning models for predicting soil particle size fractions from routine soil analyses in Quebec

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