Low-cost drip irrigation—A suitable technology for southern Africa?: An example with tomatoes using saline irrigation water

Abstract

Using saline water for irrigation increases water productivity by freeing up fresh water that can be allocated to domestic or other uses. Drip irrigation is widely regarded as the most promising irrigation system in combination with saline water. Simple drip irrigation kits that are affordable for smallholder farmers have successfully been implemented for irrigation of vegetable gardens in several countries in sub-Saharan Africa. The possibility of using low-cost drip irrigation with saline water to successfully irrigate a common garden crop, tomatoes, was tested in this study. Two low-cost drip irrigation systems with different emitter discharge rates (0.2 and 2.5 l h −1) were used to irrigate tomatoes ( Lycopersicon esculentum Mill. cv. “ Daniella”) with water of three different salinity levels (0, 3 and 6 dS m −1). In addition, plastic mulch to minimise soil evaporation was also compared to a “bare soil” or uncovered treatment. Two consecutive tomato crops (spring and autumn) were produced during two growing seasons, starting from September 2003 and ending in April 2004, at the Hatfield Experimental Farm in Pretoria, South Africa. An average yield of 75 Mg ha −1 was recorded for all treatments and seasons, which can be compared with the average marketable yield for South Africa of approximately 31.4 Mg ha −1. Even at the highest irrigation water salinity (6 dS m −1), a yield above the average marketable yield was achieved, indicating that low-cost drip irrigation works well in combination with saline water. Furthermore, the study showed that the choice of drip irrigation system with regard to discharge rate is of minor importance when irrigating with saline water. However, combining low-cost drip irrigation with plastic mulch increased the yield by on average 10 Mg ha −1 for all treatments. For the bare soil treatments, rainfall had an important role in the leaching of salts from the soils. Finally, the study showed that specific leaf area was higher at high irrigation water salinities, which is contrary to results from other studies. To be able to generalise the promising findings from this study, there is a need to mechanistically model the impact of different climates, soils and irrigation management practices, as well as the long-term sustainability of these systems.