The effect of sulfur fertilization on rice yields and nitrogen use efficiency in a floodplain ecosystem of northern Ghana

River floodplains are potential land resources to extend rice cultivation areas, most of which are not currently used for farming in West Africa. The major constraints that limit expansion of crop production in floodplain areas include difficulties of water management and lack of access to tractor services for land preparation at the appropriate timing for planting. However, there have been no field experiments to demonstrate the potential of rice cultivation in the floodplain ecosystems in West Africa. The objective of this study was to determine rice productivity and the responses to various fertilizer applications on different topographical positions within floodplain ecosystems. Three years of field experiments were conducted in no-till and no-bund conditions in various topographical positions including flood-prone areas with no farming history near back-swamps and conventional farmlands in the middle to upper slopes along a transect away from the White Volta River. The effects of different combinations of S, P and K fertilizer were evaluated with a constant rate of 60 kg N ha−1 applied as urea or ammonium sulfate. Rainfall varied widely, with heavy rainfall during the initial growth stage in 2012, a long dry spell during the middle stage in 2013, and consistent rainfall in 2014. Both grain yields and responses to N application tended to increase at lower elevations and near the river, benefiting from the carbon- and clay-rich soils and moisture availability, except when a submergence stress suppressed grain yield in the lowest field in 2012. The yield response was amplified with S application. On average, application of S resulted in an increase of agronomic N use efficiency from 13.4 to 22.8 kg grain per kg N applied. The effect of N and S applications were particularly large in the unutilized lowlands that produced the highest average yields ranging from 3.21 to 4.00 t ha−1, compared to yields ranging between 0.38 and 1.40 t ha −1 achieved on conventional farmlands. Our results clearly showed empirical evidence of high productivity and high N use efficiency for rice particularly with S application in the currently unutilized floodplain areas under no-till and no-bund rainfed conditions. Although the risk of reduced yields due to complete submergence exists, cultivation of rice in productive floodplain areas offers good opportunities to increase rice production in West Africa.