Forms and Pedogenic distribution of extractable manganess in some soils of south‐western Nigeria

Abstract

The contents of various forms of manganese in 10 profiles from S. W. Nigeria was determined by selective extraction methods: dithionite (total), oxalate (amorphous), hydroquinone (easily reducible) and pyrophosphate (origanic).

All forms were generally highest in the surface horizon and decreased down the profile. Amorphous Mn is the dominant form, being between 80 ‐ 100% of the total Mn. This indicates that a high proportion of the total soil Hn is potentially available to plant.

The active Mn ratio remains fairly constant through most of the profiles suggesting that a dynamic equilibrum exists between the crystalline and the amorphous forms. X‐ray diffraction analysis of the manganese concretions picked out from the soils revealed birnessite as the prevalent crystalline form, and the formula derived for birnessite by chemical and thermogravimetric analyses is: (Mn_6.37 Co_0.16 Na_1.52 Ni_0.03 Ca_0.02 K_0.06 Cu_0.01 Mg_0.07) 0₁₄.4H₂0.

Key words:

• Dithionite‐Mn
• oxalate‐Mn
• easily reducible‐Mn
• Pyrophosphate‐Mn
• profile distribution
• birnessite
• tropical soils