FeSO4 dissolution in water produces more H+ hence the solution is acidic (

Thanks to Professor Selvarajah for the answer very much

Dear Wei Tang, You are right to assert ferrous sulfate can negatively affect the acid buffering capacity. You also ask what could address this in terms of optimizing acid buffering capacity. To optimize acid buffering it is hard to beat the role of humic material. This ability to maximize the acid buffering capacity is particularly maximized at pH 6 which is ideal for most crop production. Humic matter can be increased by strategic employment of humic acids or materials such as composts manures and seaweed products such as soluble and granular kelp products. Hope you find this information useful for your interests.

Dear Paul Reed Hepperly

Thanks a lot for your answers. l learn a lot about humic acids in the soil. I really want to ask you: How does the solution of FeSO4 have a negative impact on the soil ABC? Would you like to recommend some articles or papers to me to help me for understanding the reaction of FeSO4 in the suspension of the soil?

Thanks for your kindness

Soil buffering or resistance to pH fluctuations is different at different pH. Optimized buffering is generally a function of a near neutral pH and is optimized by organic matter clay or silt. Since iron sulfate acidifies the soil it also compromises the buffering. When both organic matter clay silt and pH are optimized the buffering capacity is also optimized. Under the described conditions of buffering the Cation and Anion Exchange capacities are also optimized. The large number of sites for anion and cation exchange related to organic matter in particular serve as way to stabilize the pH from large solution pH changes from small additions of either acidic or alkaline materials. Minerals in solution seem to lessen the ability to buffer possibly related to fewer exchange sites. No matter how you figure the acid soil condition saturated with high soluble iron levels would be highly detrimental to the plants and the soil condition. In such acid conditions a situation of multiple toxicities and deficiencies result the reduction of acid toxicity iron, aluminum and manganese can proliferate and the optimization of key minerals such as P is all involved in the narrow window for plant optimization at a near neutral soil condition and the presence of sufficient organic matter and fine materials to stabilize the optimized plant nutrition while avoiding toxicity issues. This situation is something of a Goldilocks situation not too much not to little but just right.

In order to understand how soil buffer capacity works, you need to learn about permanent charges (caused by soil minerals) and variable charges (caused by organic matter) and how the above charges respond to acidic (e.g. elemental-S, FeSO4) or alkaline (lime) soil conditioners. A typical laboratory work to assess soil buffer capacity could explain the above phenomenon ( Article Soil pH buffering capacity: A descriptive function and its a...

Organic matter does play a significant role in controlling buffer capacity of soils hence it is important to learn the basics of organic matter and soil pH (

http://landresources.montana.edu/nm/documents/NM8.pdf).

I have worked on soil buffer capacity in the context of assessing the effect of urea hydrolysis in soil (which is a reverse process to adding FeSO4, since it causes soil pH to rise substantially), however, could not find any specific experimental work involving FeSO4 reaction with soil with wide ranging concentrations.

I am not sure within which context you are working on FeSO4. Are you assessing FeSO4 as a soil conditioner?