Abundance of Rhamphicarpa fistulosa in rainfed lowland rice fields in the Savannah region of Togo: Moderate influence of physico-chemical characteristics of soils

Rainfed lowland rice fields in northern Togo are increasingly infested by the facultative hemiparasitic weed Rhamphicarpa fistulosa that is widely reported throughout sub-Saharan Africa to be one of the most damaging weeds in rice fields. In this geographical area, some studies have shown that soil characteristics may influence the presence and/or the level of infestation of some parasitic weeds, but none have been conducted on R. fistulosa. Based on surveys conducted in northern Togo over two years in 66 lowland rice fields, we characterised the level of infestation of R. fistulosa as well as physico-chemical characteristics of soils. We highlighted that fields with medium-to-high levels of infestation of R. fistulosa (more than 5 plants per m²) were mainly characterised by a coarser soil texture, a higher potassium content and a higher pH, while fields without R. fistulosa were characterised by a lower proportion of silt content. In contrast, the level of infestation of R. fistulosa appeared only marginally influenced by soil organic carbon and nitrogen in our study. Considering these results, options to modify the main physico-chemical characteristics of soils that influence the level of infestation of R. fistulosa are likely difficult to implement. In order to continue rice production in these lowland fields, we suggest several measures to better manage R. fistulosa seedbank and development.