Comparative Effect of Siam Weed (Chromoleana odorata) and Mexican Sun Flower Weed (Tithonia diversifolia) On Soil Chemical Composition.

Investigation into the potentias of Tithonia diversifolia and Chromoleana odorata to improve soil fertility was carried out in the laboratory between  January and September, 2008 at the Department of Crop Soil and Pest Management of the Federal University of Technology, Akure . Nigeria. Soil samples collected at 0 -5, 5 -10 and 10 – 15cm soli depths under Tithonia, chromoleana and mixed cropping fallow were subjected to textural and chemical analysis. Results show that soils under Tithonia and Chromoleana fallow had higher values of Nitrogen (N), Phosphorous (P), Potassium (K), exchangeable calcium (Ca), exchangeable magnesium (Mg)  and organic matter (OM) compared to soil under mixed cropping.  At 0 – 10cm soil depth, it was observed that chromoleana fallow had the highest soil nitrogen (N) and organic matter whereas Tithonia fallow soil, had highest values of soil P and K.  Tithonia and chromoleana were able to improve soil fertility.