Crystalline oxides and hydrous oxides of Fe (e.g, goethite and hematite) and Al (e.g., gibbsite and boehmite) are common in many tropical soils, where high temperatures and rainfall cause relatively rapid decomposition of plant debris and few organic acids remain to chelate and mobilize Fe and Al.
oxalate ... シュウ酸塩 chelate ... キレート化
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