Rainwater harvesting for supplemental irrigation under tropical inland valley swamp conditions*

Abstract

AbstractAgricultural water management, if well implemented, could increase water supply and food security across the developing world. Simple earth dams or reservoirs are sufficient in this case for gravity‐driven irrigation to support agricultural production throughout the year. This is critical for regions with little energy and limited farm irrigation, but abundant precipitation. In Sierra Leone, energy especially as electricity is hardly available and farming is over 80% rainfed. This critical shortfall has limited crop cultivation to almost entirely the wet season in the country. Here, we developed an earthen micro‐dam and analysed its potential for rainwater harvesting and supplemental irrigation in the dry season in an inland valley swamp at Njala University. For the 2014–2017 dry season cropping period, average daily evaporation, seepage and irrigation from the 4.2 × 104 m3 dam were respectively 2.84, 0.51 and 7.76 mm. Thus, with 124 mm (79.5 m3) dam water irrigation and 409 mm precipitation in the dry season, grain yield increased by 67% (1430 kg ha¯¹) over that (2130 kg ha¯¹). This implies that the additional rice harvest in the dry season in excess of the rice harvest in the wet season was 67%. In other words, the harvest in the dry season was 3560 kg ha¯¹. The higher harvest in the dry season was attributed to the more favourable crop growth conditions (including solar radiation and supplemental irrigation) in the dry season than in the wet season. The additional harvest in the dry season could be significant in closing food security gaps, especially in tropical Africa where rainfall is plenty and energy availability limited.