Can the shrub Chromolaena odorata (Asteraceae) be considered as improving soil biology and plant nutrient availability?

Abstract

This paper attempts to provide a new perception of the weed Chromolaena odorata (Asteraceae) which is considered as a plague in agriculture or as a soil fertility indicator. The study was conducted in the forest-savanna transition zone of Cote d’Ivoire and aimed to compare soil biological activity and plant nutrient availability under three well-represented vegetation features, including C. odorata lands (ChrO), shrub savannas (ShrS), and grass savannas (GraS). Each of these vegetation features included five plot replicates (50 m × 50 m size) distributed in the landscape. Soil chemical parameters such as pH, organic matter, soluble phosphorus, exchangeable bases, and biological parameters such as abundance and diversity of earthworms, and soil enzymatic activities were investigated. Composite soil samples were collected and analyzed for chemical and microbial parameters while earthworms were sampled using the Tropical Soil Biology and Fertility 25 × 25 × 30 cm soil monolith method. A principal component analysis showed a clear demarcation between C. odorata plots and the savanna ones. Soluble P and exchangeable bases were significantly higher under ChrO than under both savannas. Earthworm density was twice higher under ChrO (433.3 ± 90.8 ind m−2) than under ShrS (173.9 ± 61.5 ind m−2) and GraS (176.0 ± 40.6 ind m−2) and this was accounted for by the abundance of detritivores and polyhumics. Acid and alkaline phosphatase activities under ChrO (2.9 ± 0.2 and 2.5 ± 0.3 μmol pNP g−1 soil h−1, respectively) were twice higher than under both savannas. Based on the fact that ChrO and ShrS were located on similar soil types and had the same topographic position, we concluded that the establishment of C. odorata in a savanna land and its subsequent high biomass and quality-litter production were mostly the reasons of the improvement in soil biology and plant nutrient availability. Between-savanna comparison showed that ShrS, with higher CEC and exchangeable bases, was somewhat more fertile than GraS, probably because of a better soil physical status. In view of the agronomic potentials of the shrub C. odorata, it may be taken as a basis for improved fallow in Africa.