African Journal of Biotechnology Vol. 6 (4), pp. 364-368, 19 February 2007   

ISSN 1684–5315 © 2007 Academic Journals        

Full Length Research Paper

Neutralization of soil acidity by animal manures: mechanism of reaction

A. O. Ano¹ and C. I. Ubochi²

¹Soil Science Laboratories, National Root Crops Research Institute, Umudike, PMB 7006, Umuahia, Abia State, Nigeria.

²Department of Pure and Industrial Chemistry, Imo State University, Owerri, Imo State, Nigeria.

*Corresponding authors E-mail: tonyanoh@yahoo.com.

Accepted 23 January, 2007

The mechanism of reaction leading to neutralization of soil acidity by animal manures was studied in the laboratory. Five animal manures; rabbit manure (RBM), swine manure (SWM), goat manure (GTM), poultry manure (POM), and cow manure (COM) were respectively added at rates equivalent to 10, 20, 30, and 40 t ha^-1 to an Ultisol having soil-water pH of 4.6 and KCl extractable acidity of 3.00 cmol kg^-1. The amended soils were incubated at 70% water holding capacity for 3 weeks. Animal manures significantly increased the soil pH from 4.6 to values above 5.6 and also reduced exchangeable acidity from 3.00 cmol kg^-1 to values below 0.35 cmol kg^-1. The mechanism that best explained the neutralization reaction was found to be microbial decarboxylation of calcium-organic matter complex leading to the release and subsequent hydrolysis of calcium ions. The hydroxyl ions released in the hydrolytic reaction then reacts with both the exchangeable hydrogen and aluminum ions to form water and insoluble aluminum hydroxide (Al(OH)₃) respectively.

Key words: neutralization, soil, acidity, animal, manures.