The influence of water and nutrient management on oil palm yield trends on a large-scale plantation in Ghana

Oil palm (Eleais guineensisJacq.) production in West Africa is limited by poor soils and suboptimal climate. The potential to improve fruit bunch (FB) yields with appropriate water and nutrient management in Ghana is thus considerable. To assess the effects of water and nutrient management on oil palm yields, a 2 x 2 factorial randomized complete block design with irrigation and fertilizer was implemented for three years in the main oil palm production area of Western region, Ghana. Treatments included i) zero irrigation + zero fertilizer (control), ii) zero irrigation + fertilizer, iii) irrigation + zero fertilizer and iv) irrigation + fertilizer, all replicated four times. Fertilized treatments received annual nutrient application rates of 2.0 kg palm -1 nitrogen (N), 0.4 kg palm -1 phosphorus (P), 2.5 kg palm -1 potassium (K), 0.3 kg palm -1 magnesium (Mg) and 0.15 kg palm -1 boron (B). Irrigation (using sprinklers) was scheduled using tensiometers, and was given to meet the daily evaporation of oil palm (± 450 l palm -1 day -1 , or 6.5 mm day -1 ). Average attainable yields of 32.6 t ha -1 FB were achieved with irrigation and fertilizer, which was 4.7 t ha -1 greater than the control (27.9 t ha -1 ) and 4.1 t ha -1 greater than with irrigation alone (28.5 t ha -1 ). Fertilizer was therefore essential for a maximum response to irrigation. Whilst yield increases were mostly attributed to increases in bunch number, large variations in monthly yield persisted at all treatments despite the use of irrigation, with production peaks typically coninciding with the onset of the long rain season (March–July).Whilst a number of factors may contribute (e.g. vapour pressure deficit), the process(es) regulating yield cycles remain unclear and require further research.