A field experiment aiming at testing oil palm (Elaeis guineensis Jacq.) (Fam. Arecaceae) progenies that were shown (in Indonesia) to be more efficient in mineral uptake and use was set up in Nigeria in 2011. The trial consisted of a factorial split-plot design with two factors (mineral nutrition (MN) x genetic material: GM) replicated six times. Three levels (K0 = 0g, K1= 1500g, and K2= 3000g) of potassium chloride (KCl: 60% K2O) and three levels (Mg = 0g, Mg1= 750g, and Mg2= 1500g) of kieserite (MgSO4: 27% MgO) were tested, giving a total of nine fertilizer treatments applied to four oil palm progenies (C1, C2, C3 of Deli x La Mé origin and C4 of Deli x Yangambi origin). The latter progenies were selected based on contrasting leaflet potassium and magnesium concentrations after having received similar fertilizer amounts, hence compromising the development of standardized fertilizer recommendations for this crop. Regular measurements of growth, yield, biomass, mineral content, and photosynthetic activity were taken for seven years, from Y3 (2013) to Y9 (2019).
We found that with equal amounts of fertilizers applied, progeny C3 had better morphological traits (frond length, leaf area and projected canopy area) than the other progenies, suggesting that the most appropriate nutrient requirements should be assessed for each progeny, and fertilization regime should be adapted accordingly. On the other hand, the four oil palm progenies showed contrasting yield figures. Analysis of factors influencing yield showed that progenies C1 and C3 had their highest fresh fruit bunch (FFB) yields (13.62 and 16.54 t ha-1 year-1, respectively) at K2 (3.0 kg KCl palm-1 year-1), whereas progenies C2 and C4 showed their highest yields (14.62 and 12.39 t ha-1 year-1, respectively) at K1 (1.5 kg KCl palm-1 year-1). Our study also found specific optimum leaflet K and Mg concentrations for different progenies in a given environment, allowing the adoption of a science-based K and Mg fertilizer application rates adapted to the specific requirements of each type of oil palm planting material.
Progenies C2 and C3 which had the highest bunch yields displayed the highest and statistically similar K contents (3.81 kg K.palm-1 and 3.86 kg K.palm-1, respectively). The highest Mg content was observed in progeny C3 (0.54 kg Mg.palm-1). Progeny C3 is the more efficient planting material in terms of K and Mg uptake as well as in K use for crude palm oil (CPO) production (9.97 kg palm-1 year-1 of CPO/kg of K) with the lowest leaflet K concentrations, whereas progeny C4 which had the highest leaflet K concentration, uses more K than the other progenies for vegetative biomass synthesis (91.87 kg of DM/kg of K).
We further investigated the functional root traits of our oil palm progenies to identify the most relevant root traits involved in nutrient uptake as these could explain differences in oil palm progenies’ nutrient uptake efficiencies. The highest bunch and oil producing progeny (C3) which had the highest K and Mg contents, exhibited a higher specific root length (SRL) and a smaller mean diameter for fine roots. Monitoring root diameter and SRL values of oil palm seedlings could allow early and quick selection of progenies with more efficient mineral uptake potential for higher oil production.
To gain insight into mineral use mechanisms, we studied progenies’ photosynthesis response to increasing KCl applications. Photosynthetic efficiency significantly differed between progenies (p < 0.001). Higher bunch producing progenies (i.e. C2 and C3), reached highest photosynthetic activity, expressed as μmol m−2 s−1 at K2 whereas the lowest bunch producing progeny (i.e. C4) had highest photosynthetic activity at K0. Increasing KCl levels did not enhance C4 progeny photosynthetic activity. We can conclude that breeders may rely on photosynthetic efficiency in the selection of efficient K use oil palm progenies.
As a result, progeny C3 (DA 115 D AF x LM 5 T AF) oil palms had highest growth and yield, and was thus pointed out as an excellent planting material for the West African environment. Future oil palm plantations should be established with specific genotypes, whereby specific fertilizer has to be recommended to oil palm growers with regard to their environment.