It is known that semi-arid soils are poor in organic matter, however I analyzed the MO several times by the method of Anne (1945) or by calcination, the contents can reach the 4% in the plots planted by Prickly pear (For example) or in the boundaries of salt lakes (Sebkhas) where it reaches up to 8%.
The results appear abnormal, but the analyzes are repeated several times.
In all classifications, soil with 4% is considered to be rich in MO. This is not the case in semi-arid soils where the process of humification is almost non-existent.
Thank you.
The value of organic matter in semi-arid soils are:
1. It improves physical conditions of the soil such as soil structure, porosity, water holding capacity.
2. It acts as reservoir for plant nutrients and prevents leaching of elements, which are vital for plant growth.
3. Formation of clay-humus complexes through the interaction of humic substances and clay increases the buffering and exchange capacity of soil.
4. It can form stable complexes with some metals and thus influence their availability to plants and microorganisms.
5. It acts as a source of N, P, S and micro-nutrients, which are vital for plant growth and are made available through the process of mineralisation.
6. Bio-degradation of pesticides, herbicides and fungicides through interaction of organic matter is an important phenomenon in relation to human and animal health.
M. Tarafdar,
Please help me to undestand this result.
In order to estimate the rate OM in the soil, I opted for the calcination method during 16h, at 375 °C. The values obtained are very high for a salt medium under arid climate.
Do you have an explanation? Where is the problem? Temperature or time of calcination?
Thank you.
I think both temperature as well as calcination time period is the problem. You can better use rapid titration method by Walkley and Black (1934). In this method known amount of soil is oxidized with a mixture of potassium dichromate and concentrated sulfuric acid, utilizing the heat of dilution of sulfuric acid. Unused potassium dicromate is back titrated with ferrous sulfate or ferrus ammonium sulfate. Soil organic matter content is calculated by multiplying the SOC content with 1.724 ( soil organic matter content on an average 58% carbon, so that 100/58 = 1.724, which is van Bemmelen Factor).. The organic matter can also extracted from soil using reagents like 0.5N NaOH and 0.1M Na4P2O7.
Perhaps organic matter matters in all the agro-climatic conditions, in terms of soil biology, nutrient dynamics, soil water dynamics etc.
It is particularly more important in semi arid dry and semi arid wet, arid eco systems was for multi-functions of soil organic matter.
Generally soil organic carbon determined by Walkley and Black (1934) method for arid and semi-arid soils are
According to FAO, the only thing common to all the semi-arid regions is low rainfall. To conserve the falling rains, organic matter plays a crucial role and hence it matters in semiarid sols for profitable farming.
According to M. Dilip Kumar Pal, the values obtained are the result of SOC+ SIC.
I chose the calcination method with 375 °C.during 16 hours, because at this temperature, we can ovoid the decomposition of the CaCO3 and, consequently, the overestimation of the MO content.
Read attached file, please.
I suggest estimation of organic carbon in a few samples by both Walkley and Black method and ignition and calcination at 375oC method to know whether you get comparable values by both methods.Other wise you may have to opt for Walkley and Black method as suggested by Dr.Tarafdar.
Interesting discussion . Since the soil is subjected to calcination , there is every possibility , soil SIC would a part of carbon , what we are erroneously calling soil SOC . I agree with Dr Pal sir
I found this publication. Determination of soil OM by using two methods: Walkly-Black and calcination.
Ms Souad,the paper attached by you is interesting.The ignition method estimated organic carbon almost double to that estimated by wet oxidation method (fig10).Even if one multiplies with Correction factor in the range of 1.2 to 1.3,the values obtained by wet oxidation will not be comparable with ignition method. I may not agree with the conclusion of the authors.The effect of CaCO3 is also not clearly isolated. This paper findings need discussion.
M. Annangi,I am very confused. There is certainly an overestimation of OM in all cases of calcination with different times and temperatures. In the publication of Bendor et al. (1989), in conclusion, they recommend 400 °C. for 8 h. At this temperature, decomposition of Ca C03 could occur.
As I understand it is a difficult proposition to use ignition method for estimating organic carbon in calcareous soils with high CaCO3.Probably we have to see for some improved wet digestion method ( Walkley and Black method with external heating etc.).I suggest you to analyse good number of samples by both methods and try Correlation between them.Also work out regression analysis to see the magnitude of difference or over estimation by ignition method.
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