Fallowing is considered an important management practice in maintaining soil productivity. In this study, soils fallowed to mexican sunflower (Tithonia diversifolia), siam weed (Chromolaena odorata), spear grass (Imperata cylindrica) and soil cropped to cassava for 3 years were chemically analyzed. Soil physical properties such as bulk density, total porosity, moisture content and temperature were also determined. The soils collected from the fallows were used to grow okra (Abelmoschus esculentus) in pot experiment using randomized complete block design with three replications. The results showed that soils fallowed to Tithonia and Chromolaena had significantly higher organic matter, N, P, K, Ca and Mg at 0-15 cm depth and higher organic matter, N, P and Ca at 15-30 cm depth compared with soils fallowed to spear grass and cropped to cassava. Soil fallowed to Tithonia had significantly higher organic matter, N and K than Chromolaena fallow. The growth and yield parameters like okra height, leaf area, stem circumference and fruit weight of okra were significantly higher in soil under Tithonia fallow than soils under Chromolaena, spear grass and cassava fallow. Relative to soil cropped to cassava, soils fallowed to Tithonia, Chromolaena and spear grass increased fruit weight of okra by 161, 122 and 22%, respectively. Soils under Tithonia and Chromolaena showed significant improvement in soil physical properties compared with soils under cassava and spear grass as indicated by lower bulk density and higher porosity. This can be attributed to the high fertility potentials of the Tithonia and Chromolaena weeds with sound potential for protecting the soil against erosion and leaching, proliferating surface soil with their roots, and attracting fungi, producing high biomass and building soil organic matter to adequate level that will meet nutritional needs of crops as well as improve the nutrient element status of nutrient depleted soils into which organic sources are used as fallow weeds.
