Evaluating Changes in Fertility Status of an Alfisol and Cassava (Manihot esculenta Crantz) Performance under Different Weed Species in a Cassava Field in Southwestern Nigeria

Abstract

Although, empirical evidence from many parts of the world indicates that, vegetation (plants) can ameliorate soil conditions on lands, once badly degraded, and hence, improving productive potential of such lands. However, in Southwestern Nigeria, there is hitherto, dearth of published scientific data and information on the relative effectiveness of weed species in ameliorating poor soil conditions, with resultant improved agricultural productivity of such soils. To this end, this study was designed to assess ameliorating effects of certain weed species on a severely degraded Alfisol and yield performance of cassava (Manihot esculenta Crantz). The study was carried out at the Teaching and Research Farm of the Ekiti State University, Ado ­­- Ekiti, Ekiti State, Nigeria, during 2011 and 2012 cropping seasons. The experiment was laid out in a randomized complete block design with three replicates. The different weed species included: Tithonia diversifolia (TD); Pueraria phaseoloides (PP); Chromolaena odorata (CO); Panicum maximum (PM); Aspilia Africana (AA); and weed – free (WF), which served as the control treatment. The results obtained indicated existence of significant (P = 0.05) differences among the weed species as regards their ameliorating effects on nutrient status of a degraded Alfisol, cassava root yield and yield components. At the end of 2011 cropping season, weed species significantly increased soil organic carbon (SOC) from 0.33 g kg^-1 for WF to 0.70, 0.62, 0.77, 0.40 and 0.55 g kg^-1 for TD, PP, CO, PM and AA, respectively. Similarly, at the end of 2012 cropping season, weed species significantly increased SOC from 0.22 g kg^-1 for WF to 0.74, 0.67, 0.83, 0.45 and 0.60 g kg^-1 for the respective TD, PP, CO, PM, and AA. At the end of 2011 cropping season, weed species significantly increased total N from 0.18 g kg^-1 for WF to 0.36, 0.49, 0.42, 0.25 and 0.31 g kg^-1 for TD, PP, CO, PM and AA, respectively. At the end of 2012 cropping season, weed species significantly increased total N from 0.13 g kg^-1 for WF to  0.40, 0.56, 0.48, 0.30 and 0.35 g kg^-1 for the respective TD, PP, CO, PM, and AA. Means of cassava root yield data across the two years of experimentation indicated that, weed species significantly reduced cassava root yield from 9.23 t ha^-1 for WF to 4.27, 7.31, 5.61, 4.57 and 5.37 t ha^-1 for  TD, PP, CO, PM and AA, respectively.

Keywords: Cassava, field, fertility, status, species, weed.