I worked in three different acidic soils.

Field 1 (pH 4.23, Al3+=1.60 cmol(+)/kg, Bray1-P=14.2 mg P/kg)

Field 2 (pH 4.98, Al3+=1.13 cmol(+)/kg, Bray1-P=26.9 mg P/kg)

Field 3 (pH 5.15, Al3+=0.32 cmol(+)/kg, Bray1-P=7.7 mg P/kg)

I applied lime rate 0, 0.5 and 1.0 t/ha.

The response of Al was linear that increasing lime rates increased soil pH reduced Al in Field 1 and Field 2. Low pH had a higher exchangeable Al.

However, Field 3 is not behaving like other fields, that when the pH was low (3.7 to 4.5), the Al concentration was low as well. I spotted about 7 samples from 56 samples behaving like this from Field 3.

I assumed it was because of the organic C. The percentage of organic C in fields 1, 2, and 3 were 1.50%, 1.28%, and 2.46% respectively.

In spite of organic-C, what else contributes to the low concentration of Al in Field 3?

Is that P-available also involved, Al? But Field 3 had a low P-available compared to other Fields.

FYI, all fields had a low CEC (13 to 15 cmol (+)/kg)

Please your opinion.

thank you