Effect of polyethylene sheet colour and in situ solarization durations on the phytosociological structures of the predominant weeds in humid environment of southern Nigeria.

High humidity favours the proliferation of a wide range of weed species. Studying the phytosociological attributes of weeds in a humid area provides insight into the dynamism and relative importance of each weed species peculiar to the area which is very important in understanding crop-weed interrelationships and highlights the bases for effective management stratages. An experiment was conducted in 2019 and 2020 cropping seasons at the Department of Crop Science Teaching and Research Farm, University of Calabar, to identify the predominant weeds in the farm area and assess their responses to polyethylene colour and soil solarization duration. The experiment was a factorial combination of two polyethylene colour (black and transparent) and five in situ soil solarization durations (0, 8, 12, 16 and 48 weeks), laid out in randomized complete block design (RCBD) with three replications. Data were collected on the phytosociological characteristics of the weeds on four weekly intervals up to the twentieth week. The predominant weeds identified in the experimental area were Eragrostis ciliaris L., Cynodoon dactylon L., Panicum maximum Jacq., Axonopus compressus Beav., Kyllinga bulbosa Beav. and Kyllinga erecta Schum., Gloriosa superba L., Ipomoea involuncrata P., Calapogonium mucunoides Desv., Aspillia bussei O. Hoff, Ageratum conyzoides L., Phyllantus amarus Schum., Caldum bicolor Vent., Triumfeta rhomboidea Jacq., Cleome rutidosperma DC., Euphorbia heterophylla L., Mitracarpos villosus DC., Oldenladia. herbacea L. The relative density of Caladum bicolor was higher across the treatment in both years, reaching up to 37.7 % in the plot solarized for 16 weeks using black polyethylene, followed by P. maximum with upto 18.40 % in 2019 and Gloriosa superba (20.50 %) in 2020. The highest Important Value Index was recorded by Caladum bicolor reaching up to 28.7 % in the plot solarized for 16 weeks using black polyethylene. The lowest species variation was recorded in the plots solarized for 16 to 48 weeks irrespective of the polyethylene colour. In situ solarization of up to sixteen weeks using black polyethylene effectively controlled majority of the weed species in both years and is recommended for effective weed suppression in cassava farms in humid environment.