La réduction de la croissance végétative à forte densité de semis comme stratégie d'adaptation variétale aux semis tardifs en culture cotonnière pluviale au Bénin

Reduced Vegetative Growth at High Planting Density as Varietal Adaptation Strategy for Late Sowing in Rainfed Cotton Cultivation in Benin. To study the effects of the factors sowing date and density on vegetative growth and yield of cotton in rainfed area, four trials were conducted at two sites in Benin in 2002 and 2003. A split-split plot design with three replications was performed to compare 10 different varieties, at three densities (42,000; 125,000; 167,000 plants.ha-1) and, two planting dates (June, July/August). Plant height, number of nodes per stem, branch length and field performance were evaluated. Planting date affected the morphology in limiting water conditions (shorter plants in late sowing). Delayed sowing reduced yields by 12% for early and compact variety Mar 88-214 against more than 30% for varieties with high vegetative development. At high densities, all genotypes were shorter with shorter branches. In delayed planting and high densities, Mar 88-214 and Guazuncho 2 produced at least 100 kg.ha-1 more than the vegetative varieties. Early and compact varieties sown at high densities are more suitable when the water conditions are limiting. Sowing density affects more clearly vegetative growth and yield of cotton than sowing date.