Questions about som

thank you for your help!

But i am still confused by the "acidity" of FA. if this is not equal with pH value. What does it imply? High acidity means more H+ in the soil?

One more other question about Ammonium fixation: is Ammonium fixation the same with isomorphic substitution ?

you're right. fulvic acid does have a low pH. an acid is just a compound or ion that contributes to H+ activity in the soil. isomorphic substitution occurs during the weathering of rocks and minerals, when primary minerals are altered or transformed into secondary minerals (ie. 2:1 phyllosilicate clays). remember the octahedral and tetrahedral sheets of montmorillonite for example. Mg can substitute for Al INSIDE the crystal structure, leading to a net negative PERMANENT charge on the colloid. ammonium fixation is when NH4 gets stuck BETWEEN two layers of vermiculite or illite (fine-grained mica) because it is just the right size. this also happens to K because of similar size, remember lyotropic series: Al3 > Ca2 > Mg2 > K=NH4 > Na. in this state the nutrient are non-exchangeable and only slowly available to plants, so it represents a decrease in available N. hope that helps.

Hi there, For the FA and HA, I am thinking that the FA is more acidic than HA since FA has more H+, and relatively it should has higher CEC. Since there will be more coo- that attract other cations such as fe3+ or al3+ and so on, FA "SOLUTION" (pure FA) will have higher CEC Refer back to lecture 17 slide 16, it says "CEC IS HIGH AT HIGH PH AND LOW AT LOW PH". Is it because coo- is organic anion that can lead to flocculation? (Since FA is so soluble that large amount of H+ being released with COO- leftover). Correct me if I am not thinking it in a right way. Thanks