Effect of aerial oxidation pretreatment on composition and effectiveness of a Nigerian lignite sample as soil organic matter amendment

A Nigerian lignite sample was analyzed for its nutrient element and organic components. The effect of two oxidation procedures, namely, oven-oxidation and wet-oxidation on the composition and extractability of organic fraction with 0.1 M sodium hydroxide (NaOH), was also studied. A pot experiment was conducted to investigate effect of the oxidized lignite samples on the growth of Gmelina arborea seedlings. The lignite sample is very acidic in reaction with a pH of 2.0, and has low quantity of macro- and micronutrient elements with a carbon (C):nitrogen (N) ratio of 103. It, however, has over 90% organic matter with more than 78% extractable humic substances. All these components were either increased, decreased, or unaffected by the oxidation pretreatments. Compared to the control, both the unoxidized and differently oxidized lignite samples, generally depressed growth of 12-week-old Gmelina arborea seedlings in the Alfisols while their addition to the Oxisols enhanced the growth of the seedlings. Wet-oxidized lignite stimulated growth of the seedlings more than either unoxidized or oven-oxidized sample while the latter performed the poorest of the three.