Growth, Yield and WUE of Drip and Sprinkler Irrigated Okra Grown On Sandy Soil Under Semi-Arid Conditions in Southeast Ghana.

Vegetable production systems at the Keta sand spit, Southeast Ghana, are typically managed with excessive amounts of irrigation water and fertilizers on sandy soils with low inherent water and nutrient retention capacities. The shallow groundwater which is the primary irrigation water resource is prone to salinization from the Keta lagoon, the Atlantic Ocean and brackish water underneath (Kortatsi and Agyeku, 1999). To ensure the sustainability of vegetable production at the Keta spit, introduction of water saving irrigation systems and improved irrigation management schemes are important. Thus, the main aim of our study was to explore the water sa ving potential of drip irrigation in order to save the shallow groundwater from over exploitation.

A two season study (minor dry season, 2011 and major dry season, 2012) were carried out to determine the okra crop response to the following treatments: 1. sprinkler irrigation with spread manure; 2. sprinkler irrigation with placed manure; 3. drip irrigation with placed manure and 4. drip irrigation with fertigation. Fertigation was done only two times (two weeks after emergence and immediately after flowering) during the first experiment while weekly fertigation (8 times from two weeks after emergence) was done during the second experiment. The treatment effects on growth, yield, biomass, water use efficiency of the economical fresh pod yield (WUEy), and on the total above ground biomass (WUEtbm) were studied. The results showed that the okra crop did not respond well when fertigation was done only twice; however, the second experiment in the major dry season, the 2012 season, showed a marked improvement in the fertigated treatment compared to the others when fertigation was done weekly. In the second experiment despite the application of the same amount of nitrogen (89 kg N/ha), there were significant differences (P≤0.05) between yield obtained with sprinkler spread manure (11.2 t ha-1), sprinkler placed manure (13.7 t ha-1), and drip fertigated (17.5 t ha-1); however, the yield difference between sprinkler placed manure (13.7 t ha-1) and drip placed manure (13.9 t ha-1) was insignificant (P≤0.05) and  WUEy and WUEtbm in the drip fertigated treatment was significantly (P≤0.05) higher  than in other treatments. Seasonal crop water use (ETc) for drip irrigation was 236 mm compared to 339 mm for sprinkler in the 2011 season. In the 2012 season, ETc for the drip irrigated okra crop was 269 mm compared to 379 mm for sprinkler. By adopting drip irrigation to okra, the seasonal crop water use could be reduced close to 30 %. From the results it is concluded that on rough textured sandy soil drip irrigation with frequent weekly fertigation resulted in significant water savings and yield increase compared with sprinkler irrigation.