Bringing a shift of soil pH from 4 to 8 is a stupendous task particularly under field conditions. Further, soil pH does not remain static as it is a dynamic property. Even if one succeeds in shifting soil pH to a desired level under laboratory test conditions, it does not remain constant and keeps on changing due to its dynamic nature as influenced by other factors. 

Firstly, you can determine soil pH buffering capacity, and then calculate the amount of CaCO3. This adjustment will change NH4+ to NH3 and may increase the loss of NH3 from soil.

Dear Xin,

You may use SMP (Shoemaker, McLean and Pratt) Buffer  method for determining Lime Requirement of acid soils (Shoemaker et al. 1961).

Application and Principle: The SMP buffer method for lime requirement determination is best suited for silt loam soils with a wide range of extractable Al. The SMP buffer is added to a soil-water slurry after measurement of soil pH. The SMP buffer has an initial pH of 7.5.  Bases in the buffer react with soil acidity to reduce the pH of the buffer from 7.5 to some measured soil-buffer pH.  The greater a decline in soil-buffer pH from an initial value of 7.5, the greater the lime requirement for neutralizing soil acidity. A calibration of soil-buffer pH to actual lime requirement to some target soil pH from incubating Ohio soils with varying amounts of CaCO3 provided a means of estimating lime requirement from soil-buffer pH (Shoemaker et al., 1961).

I suggest you to go through the following paper for detailed method: 

Shoemaker, H.E., E.O. McLean, and P.F. Pratt.  1961.  Buffer methods for determining lime requirement of soils with appreciable amounts of extractable aluminum.  Soil Sci. Soc. Am. Proc. 25:274-277.

Raising of soil pH by liming will influence other properties of the soil.

Bringing a shift of soil pH from 4 to 8 is a stupendous task particularly under field conditions. Further, soil pH does not remain static as it is a dynamic property. Even if one succeeds in shifting soil pH to a desired level under laboratory test conditions, it does not remain constant and keeps on changing due to its dynamic nature as influenced by other factors. 

I agree with Kunuthur Srinivasa Reddy.  The weathering of soil minerals and hydrolysis of Al in acid soils change soil pH. The rates of these reactions are normally slow. So soil pH will change with time after adjustment. This pH adjustment may be just used for short-term lab work. 

Yes , shifting soil pH from 4 to 8 would be next to impossible  either under laboratory or under  field condition for considerable time , more so under latter case.  Soil pH is stabilized over a period of time as a predominant function of soil mineralogy . I agree with Dr Reddy and Ren- Kou... .Neither such changes will retain the natural properties of soil..?

The appropriate soil pH for crop production depends on the crop  type grown and the soil type. Crops differ in their susceptibility to soil acidity. The pH of soils for best crop yields is considered to be between 6.5 and 7.5.  Levels of both Al and Mn tends to increase at pH levels less 5.5. So the aim of lime application is to reduce the levels of exchangeable Al and Mn to below toxic levels. Before lime application, it is necessary to determine the amount of exchangeable acidity using appropriate and the presence of sub-soil acidity.

The measurement of lime requirement can be defined as the part of the charges that depend on pH between the natural soil pH and the pH required for a given crop. When total soil acidity is more than about 15% of cation exchange capacity, problems of phytotoxicity can appear depending on: 1) acidity itself for certain plants and micro-organisms;  2) toxicity of aluminum and/or manganese by inhibition of root growth; and 3) induced deficiencies in major elements (e.g. Ca or Mg lixiviation) or in trace elements.

In the laboratory, lime requirement is expressed in milli-equivalents of CaCO3 per kg of soil and in agronomy in tons of CaCO3 per hectare. The lime requirement could then be estimated from T – S (T is total cation exchange capacity in buffered solution at pH 7, S is the sum of exchangeable cations. Mehlich (1939) indicated the lime requirement between the exchangeable acidity extracted by a not buffered saline solution and the total acidity neutralized by a buffer solution adjusted to pH 8.1. According to Duchaufour and Souchier (1980) an estimate of the exchangeable acidity per T – S with T measured at soil pH also enables calculation of the quantity of calcium needed for the correction of acidity. Lime requirements can also be evaluated by titration using techniques similar to those used for the measurement of exchange acidity.

As Dr. Dilip mentioned above,  SMP Buffer Method is a complex buffer method which is used with a pH close to neutral, that of carbonate–bicarbonate–CO2 equilibrium of the soil atmosphere at normal pressure. It enables neutralization of both bases and acids and avoids variations in pH in a soil system that itself possesses buffering power. Exchangeable acidity method is also the quickest method.

One should consider the following factors to determine the lime requirement: the desired change in pH, buffering capacity of the specific soil, type of liming material, and the fineness or texture of the liming material. For instance, the finer the liming material, the greater the neutralizing activity, but application of very fine lime may be difficult, especially under windy conditions.

Yes, increasing pH from 4 to 8 would require drastic shifting of electrical charges, to sustain it over a time is a issue to deal with. 

When adjusting soil pH in an acid condition and depleted soils liming to neutrality would be both uneconomical and unnecessary.

Generally the recommendation would be to lime until soil toxicity from Iron, Aluminum and Manganese was no longer an issue this would be about 5.7 pH. 

Conversely in adjusting downward the alkaline condition the acidifying to neutral is not either necessary or economical. For that condition the acidification goal should by 7.3 where micronutrient deficiencies should not be an issues. 

In a low CEC acidic soil over liming can be a problem it is a good idea to apply fine lime in 1 T/ha a year and to take pH soil readings to adjust your desired level gradually. After your goal is met than the maintaining of it can be assessing through continuing monitoring. 

Besides the use of lime the improvement of soil organic matter content works to buffer the soil reaction and optimize the crop performance. 

What is the aim of increasing a soil pH from 4 to 8? Most crops are well grown between pH 5.5 and 7.0.

A very good query from Dr. Getachew to Xin Shu, possibly an young researcher. The objective of experimentation or research should be farsighted and practical. It should not be purely academic for the sake of a degree or diploma whatever. The very desire to shift from pH 4 to 8 of a soil sounds amusing. Dear Xin Shu, please revise your objective of soil research.

Good point Dr Shirgure  and  Dr Reddy . We are discussing,  just for the sake of discussion , it seems .  The question should have some practical significance  in field as well. By such colossal shift in soil/solution pH , infact we destabilise the very electro-chemical behaviour of  the soil/solution..?

Dr Srivastava its a good point to consider. Dr Reddy I appreciate your concern.

Yes, I agree Dr. Anoop, rising a soil pH from 4 to 8, which is 100% using CaCO3 appears a bit unpractical. I think first someone needs to know the reason and extent of a pH of an extremely low pH soil like this can be improved to a practical and desirable level. The type and source of acidity should also be identified before the intervention.

Dear all,

Many thanks for your answers and help. I want to test if the the short-term changes of pH would changes soil microbial community structure. This is the lab based experiment, and no crop would be grown on the soil. I really appreciate your suggestions. I will rethink about its practical meaning.  Much appreciated. 

Best regards,

Xin

I draw your attention to the following steps:

A. Add a lime source to make the soil less acidic

B. Select your lime source depending on the needs of your plant

C. Apply the liming source 2 to 3 months before planting (usually in the fall or winter) so there is plenty of time for the pH to change.

D. Mix the lime thoroughly into the soil because most liming sources are not very water-soluble.