Rainwater harvesting for smallholder farmers in Northern Ghana

Abstract

In this study, suitable rainwater harvesting techniques are investigated for smallholder farmers in northern Ghana, in order to reduce the impact of dry spells during the growing season. Dry spells and water shortage during the growing season have a negative impact on food production in northern Ghana, where 95% of the farms are rainfed. A potential solution for rainwater harvesting for smallholder farmers is adding organic materials to the soil. Here, we conduct a local field experiment comparing two plots in a maize field, one treated plot with added sheep excrement and one untreated plot as control plot. Results show twice as large grain yield for the treated plot, while observed soil moisture levels are not significantly different between the two plots. The behaviour of water in the maize field is analysed with a water balance model, which reproduces the overall dynamics of soil water storage, but overestimates peaks in response to precipitation events. The model confirms that soil water levels remain well above the wilting point in both plots during the growing season. The measured soil moisture is also used to calibrate an AquaCrop model, which is an FAO crop model giving yield outputs. The crop output of the AquaCrop model shows no difference between a field with and without manure, indicating again that soil moisture in this case is not the determining factor for yield differences found in the field experiments. A possible explanation for the difference in yield is the release of nutrients from the manure throughout the season, which were not yet captured in the soil sampling. Besides that, no dry spells occurred during the growing season, so the effects on a real dry soil could not be measured. A multi-criteria analysis is used to assess the suitability of rainwater harvesting solutions that are suitable for smallholder farmers in northern Ghana. It is found that multiple in-situ and micro-scale rainwater harvesting technologies are suitable, like deep tillage, adding manure and conservation agriculture. It should be noted that having the required knowledge to apply these rainwater harvesting technologies successfully is essential.