The ‘Secret’ Behind the Good Performance of Tithonia diversifolia on P Availability as Compared to Other Green Manures

Abstract

Use of organic materials to improve soil nutrient and increase crop production is well documented. Organic resource quality influences the effect of these organic materials. Although characterization of these organic materials has been done for most parameters, a comprehensive characterization in terms of type and concentration of organic anions is still lacking. An incubation experiment was conducted to characterize Tithonia diversifolia, Lantana camara, Gliricidia sepium and farmyard manure (FYM) and relate the parameters to P availability. The experiment was in a completely randomized design, four treatments replicated four times. Tithonia produced the highest concentration of basic cations and oxalic acid while Gliricidia had the lowest. Farmyard manure and Lantana were intermediate. At 5 t ha–1 these organic materials significantly (p FYM>Lantana=Gliricidia. The influence of organic materials on P sorption was highly dependent on their pH, P, Ca and oxalic acid concentration. There was a significant (p < 0.05) negative correlation between P maximum and oxalic acid concentration of green manures (r = –0.97); this was attributed to the high Al complexation capacity of oxalic acid (log k Al = 6.1). Selection of organic materials, therefore, besides being based on other conventional quality parameters, should consider the concentration of oxalic acid. It was concluded that the better performance of Tithonia on P availability through reduction of P sorption is due to its higher oxalic acid. The agronomic implication of these results is that proper handling of Tithonia is required to avoid loss of oxalic acid during its application.