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Thesis Chapters by Vincent Van Der Berg
A laboratory study was conducted to evaluate seven widely used methods to predict soil lime requi... more A laboratory study was conducted to evaluate seven widely used methods to predict soil lime requirement (LR) using 20 acidic South African top and sub-soils with a wide range of properties. The LR methods which were evaluated against a standard CaCO3 incubation LR procedure, included: the original Eksteen method with organic matter correction factor (OMCF) , commonly used in the Western Cape; two modifications of the Eksteen method, namely: (i) Eksteen-KCl method, involving the use of 1 M KCl exchangeable acidity instead of titratable acidity at pH 7, and (ii) Modified-Eksteen method, where a correction factor was applied to titratable acidity that was derived from soil data obtained in this study; the Cedara method, most commonly used in KwaZulu-Natal; the ARC-SGI method, developed primarily for Free State soils by the ARC- Small Grain Institute in Bethlehem; the Shoemaker-McLean-Pratt single buffer (SMP-SB) method most commonly used in the North East and North Central regions of the USA; the Adams and Evans single buffer (AE-SB) method most commonly used in the South East and Mid-Atlantic regions of the USA.
The original Eksteen method, although highly correlated with incubation LR, was found to be a relatively inaccurate predictor of LR. The Eksteen-KCl and Cedara methods were found to be highly correlated with incubation LR, yet consistently underestimated LR. The modified-Eksteen method was found to be highly correlated with incubation LR, and was a good predictor of LR. The ARC-SGI method was a considerably poorer predictor of LR, and tended to grossly overestimate LR. The SMP-SB method was found to be highly correlated with incubation LR, and was shown to be reasonably accurate to achieve a target pHKCl of 5.5. Recalibration of the SMP-SB soil-buffer pH with incubation LR resulted in considerable increases in accuracy. The AE-SB method was found to be highly correlated with incubation LR, yet tended to overestimate LR. Recalibration of the AE-SB soil-buffer pH with incubation LR resulted in a sufficient increase in accuracy.
A correlation study was conducted to investigate the relationship between soil properties and both incubation LR and LR methods. It was revealed that soil properties other than soil pH, which are useful indicators of LR are: soil C > variable charge > CECpH 7 > clay + silt. Soil C was found to be a significant contributor to LR due to its association with exchangeable Al and due to its high pH dependent acidity. Titratable acidity was found to be the soil property that most strongly related to soil LR. Variable charge was also shown to exhibit significant relationships with soil parameters that most strongly influence LR. For these reasons, a multiple regression equation was developed that utilised only titratable acidity and variable charge. The multiple regression equation was able to predict 96.76% of the variation observed for incubation LR, and was 97.86% accurate in predicting the LR for each specific soil to obtain a target pHKCl of 5.5. Regarding the relationship between soil properties and LR methods, it was revealed that the local methods, except the ARC-SGI method, were most strongly influenced by exchangeable acidity and Al, and had significant relationships with soil C. The American direct buffer methods were strongly correlated with essentially all of the soil properties studied. This is indicative of the ability of these methods to directly determine the amount of acidity that may originate from various sources in the soil, in order to make a sufficiently accurate LR. It is therefore recommended that the application of direct buffer methods be further developed for use on South African soils in order to further improve the accuracy of LR determination in South Africa. The existing method that was found to most accurately predict LR on a wide range of soils was the modified-Eksteen method.
Conference Presentations by Vincent Van Der Berg
This review aims to firstly describe and discuss the phenomenon of soil reaction. Secondly a sho... more This review aims to firstly describe and discuss the phenomenon of soil reaction. Secondly a short discussion follows on the effect of soil reaction on nutrient availability, as it is considered as one of the main chemical factors related to biological activity. Thirdly, a discussion follows on the effects of soil reaction on the occurrence of soil-borne pathogens within the soil environment. Lastly, a discussion is given on common lime requirement methods used in South Africa, pertaining to the manipulation of soil reaction in order to obtain a more suitable soil environment.
A laboratory study was conducted to evaluate seven widely used methods to predict soil lime requi... more A laboratory study was conducted to evaluate seven widely used methods to predict soil lime requirement (LR) using 20 acidic South African top and sub-soils with a wide range of properties. The LR methods which were evaluated against a standard CaCO3 incubation LR procedure, included: the original Eksteen method with organic matter correction factor (OMCF) , commonly used in the Western Cape; two modifications of the Eksteen method, namely: (i) Eksteen-KCl method, involving the use of 1 M KCl exchangeable acidity instead of titratable acidity at pH 7, and (ii) Modified-Eksteen method, where a correction factor was applied to titratable acidity that was derived from soil data obtained in this study; the Cedara method, most commonly used in KwaZulu-Natal; the ARC-SGI method, developed primarily for Free State soils by the ARC- Small Grain Institute in Bethlehem; the Shoemaker-McLean-Pratt single buffer (SMP-SB) method most commonly used in the North East and North Central regions of the USA; the Adams and Evans single buffer (AE-SB) method most commonly used in the South East and Mid-Atlantic regions of the USA.
The original Eksteen method, although highly correlated with incubation LR, was found to be a relatively inaccurate predictor of LR. The Eksteen-KCl and Cedara methods were found to be highly correlated with incubation LR, yet consistently underestimated LR. The modified-Eksteen method was found to be highly correlated with incubation LR, and was a good predictor of LR. The ARC-SGI method was a considerably poorer predictor of LR, and tended to grossly overestimate LR. The SMP-SB method was found to be highly correlated with incubation LR, and was shown to be reasonably accurate to achieve a target pHKCl of 5.5. Recalibration of the SMP-SB soil-buffer pH with incubation LR resulted in considerable increases in accuracy. The AE-SB method was found to be highly correlated with incubation LR, yet tended to overestimate LR. Recalibration of the AE-SB soil-buffer pH with incubation LR resulted in a sufficient increase in accuracy.
A correlation study was conducted to investigate the relationship between soil properties and both incubation LR and LR methods. It was revealed that soil properties other than soil pH, which are useful indicators of LR are: soil C > variable charge > CECpH 7 > clay + silt. Soil C was found to be a significant contributor to LR due to its association with exchangeable Al and due to its high pH dependent acidity. Titratable acidity was found to be the soil property that most strongly related to soil LR. Variable charge was also shown to exhibit significant relationships with soil parameters that most strongly influence LR. For these reasons, a multiple regression equation was developed that utilised only titratable acidity and variable charge. The multiple regression equation was able to predict 96.76% of the variation observed for incubation LR, and was 97.86% accurate in predicting the LR for each specific soil to obtain a target pHKCl of 5.5. Regarding the relationship between soil properties and LR methods, it was revealed that the local methods, except the ARC-SGI method, were most strongly influenced by exchangeable acidity and Al, and had significant relationships with soil C. The American direct buffer methods were strongly correlated with essentially all of the soil properties studied. This is indicative of the ability of these methods to directly determine the amount of acidity that may originate from various sources in the soil, in order to make a sufficiently accurate LR. It is therefore recommended that the application of direct buffer methods be further developed for use on South African soils in order to further improve the accuracy of LR determination in South Africa. The existing method that was found to most accurately predict LR on a wide range of soils was the modified-Eksteen method.
This review aims to firstly describe and discuss the phenomenon of soil reaction. Secondly a sho... more This review aims to firstly describe and discuss the phenomenon of soil reaction. Secondly a short discussion follows on the effect of soil reaction on nutrient availability, as it is considered as one of the main chemical factors related to biological activity. Thirdly, a discussion follows on the effects of soil reaction on the occurrence of soil-borne pathogens within the soil environment. Lastly, a discussion is given on common lime requirement methods used in South Africa, pertaining to the manipulation of soil reaction in order to obtain a more suitable soil environment.