Yield parameters of cassava (Manihot esculenta) as affected by method of addition of organic matter in two consecutive minor seasons of Sri Lanka

A study was carried out at the experimental farm, University of Peradeniya, Sri Lanka, to evaluate the influence of 2 organic materials [rice (Oryza sativa L.) straw and Gliricidia leaves, applied as a surface mulch or incorporated at planting on soil moisture, growth and yields of cassava [Manihot esculenta (L.) Crantz] planted in 2 dry seasons (2002 and 2003) and the rainfall-utilization efficiency by this crop. Application of straw or Gliricidia leaves as a mulch increased the soil-moisture contents and enhanced vegetative growth, yield components, yields, harvest indices of cassava and rainfall-use efficiency in both seasons compared to incorporation of organic matter. The mean yield increment owing to the straw mulch were 46% and 54% in the 2 seasons and 25% due to Gliricidia in both seasons respectively. Incorporation of straw and Gliricidia reduced yields by 14–16% and 8%, respectively, compared with surface application. The benefit of rice straw was greater owing to its ability to maintain greater soil-moisture content in the minor dry season.