ABSTRACT

A study was conducted in three land use systems (Theobroma cacao, Gmelina arborea and secondary forest) in Urnuahia North of Abia State of Nigeria to assess the plant composition and determine the contribution of the land use to the soil physicochemical properties. Plant species enumeration and identification were done using a 20m x SOm transect in each of the land use. Three profile pits per land use type were dug and used to study the soil physicochernical properties. Results of the soil analysis were statistically analyzed using Analysis of variance (ANOVA) test at p< 0.05 to determine how the values for the soil physicochemical properties differed from one another across the land use types. Least significance difference (LSD) at p< 0.05 was applied to separate difference between treatment means. Result of the study showed that plant density per ha was highest in the secondary forest (1440 plants ha') followed by the T cacao (700 plants ha') and the least was G. arborea (600 plants ha'). Plant species which were observed to be dominant in terms of density in the three land use types were as follows; Chromolaena odorata, Acanthus inontanus, Euphorbia heterophylla, Ficus exasperata, Hannoa klauneana, Ipomea involucrata, Laipotea ovalifolia, Lannea nigritana, C'nestis ferrugina, Icacina involucrata, Fanicuin maximum, Pennisetuni pz.lrpureum , Spondias mombin and Combretum zenkeri. The texture of the soils was predominantly sandy loam particularly in the surface layers. The soil pH generally declined (i.e. becoming more acidic) from the topsoil to > 80cm (horizon 5) in all the land uses. The pH for G. arborea, T. cacao and secondary forest were 5.54, 5.21 and 5.98 respectively at the surface layer (0 - 20cm). T.cacao had the highest organic level in all the layers 'investigated compared to other land use followed by G. arhorea. The organic C for horizonl (0 -20cm) and horizon 5 (>80cm) were 28.3gkg' and 1.50gkg' for G. arborea; 30.7gkg and 8.3gkg 1for T cacoa and 26.8gkg' and 3.20gkg' for secondary forest respectively. Total N was higher in G. arborea followed by T cacao for all the horizons. The levels of Av. P, Ca, and Mg were higher in secondary forest followed by that of G. arborea plantation for all the horizons. T cacao plantation had significantly highest copper (Cu) distribution and the least iron (Fe) distribution. Aluminium (Al) was in trace amount in the three land use systems. Nutrient distribution seemed to be affected by management practices in each land use types. Some soil properties were significantly different in the three land use types while most soil properties in G. arborea and secondary forest were not statistically different (p~0.05) exchangeable Al. In the T. cacao plantation, Copper correlated positively and significantly with organic carbon and Calcium. Al also significantly, but negatively correlated with K and Na. In G. arborea, weak correlation relationships were obtained between Fe and N, Av. P and a negative correlation with Al. In secondary forest, iron correlated negatively with silt and cfay.