Introduction
Oil palm (Elaeis guineensis Jacq.) is the world’s most productive oil-bearing crop, producing nearly 74 million Mg of oil in 2019, which account for 35% of the total world edible oil production (USDA, 2020). It is the highest-yielding oil crop among all oleaginous, reaching 9.5 Mg oil ha˗1 yr˗1 under optimum conditions (Rajanaidu and Kushairi, Reference Rajanaidu and Kushairi2006; Rajanaidu et al., Reference Rajanaidu, Kushairi, Din, Isa, Maizura and Noh2005). Palm oil is also the most consumed oil worldwide (Kushairi et al., Reference Kushairi, Meilina, Balu, Elina, Mohd, Izuddin, Razmah, Vijaya, Shamala and Ghulam2019; USDA, 2020). Oil palms require large amounts of nutrients to maintain their high-standing biomass and productivity (Dubos et al., Reference Dubos, Hernán, Jesùs, Lòpez and Ollivier2010). The minerals required by oil palm are specifically directed towards major sinks for mineral assimilation such as the development and growth of aerial organs, as well as the expression of yield-related traits in each progeny (Legros et al., Reference Legros, Mialet-serra, Caliman, Siregar, Clement-Vidal, Widiastuti, Jourdan and Dingkuhn2006).
Once these minerals are absorbed by the roots, the palm allocates them to the tissues of its various organs (Tinker and Smilde, Reference Tinker and Smilde1963) so that they contribute to the physiological and metabolic reactions associated with synthesis, transport, and storage of assimilates needed for growth, development, reproduction, and oil yield (Legros et al., Reference Legros, Mialet-serra, Caliman, Siregar, Clement-Vidal, Widiastuti, Jourdan and Dingkuhn2006; Lamade et al., Reference Lamade, Ollivier, Rozier-Abouab and Gérardeaux2014; Mirande-Ney et al., Reference Mirande-Ney, Tcherkez, Gilard, Ghashghaie and Lamade2019).
Mineral nutrition studies should go beyond simple evaluations of leaflet mineral concentrations and mineral uptake capacity by crops should also be taken into consideration as well as their distribution among tree organs (Aholoukpè et al., Reference Aholoukpè, Dubos, Flori, Deleporte, Amadji, Chotte and Blavet2013 and Prabowo et al., Reference Prabowo, Foster, Nelson, Sitepu and Nelson2012). Estimating the amount of minerals stored in oil palm tree organs is essential to assess the mineral uptake capacity of oil palm progenies (Aholoukpè, Reference Aholoukpè2013 and Ollivier et al. Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). However, these studies did not consider all oil palm organs or the effects of varying fertiliser application rates. In such scenarios, the root system is often neglected. In fact, roots are the most essential organs for plants to access water and minerals needed for plant growth and development (Nodichao et al., Reference Nodichao, Chopart, Roupsard, Vauclin, Ake and Jourdan2011; Nelson et al., Reference Nelson, Banabas, Scotter and Webb2006; Dassou et al., Reference Dassou, Nodichao, Aholoukpè, Cakpo and Jourdan2021). Compared to other palm organs, root minerals are rarely documented even with underground biomass representing about 19% of the total oil palm biomass (Rees and Tinker Reference Rees and Tinker1963). As yield variation was observed with oil palm progenies showing optimum leaflet K and Mg concentration (Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a,Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Dammeb,Reference Dassou, Bonneau, Aholoukpè, Vanhove, Ollivier, Impens, Flori, Durand-Gasselin, Mensah, Sinsin and Van Dammec), it is important to better understand the mineral distribution and storage among organs.
This paper aims to assess the potassium (K) and magnesium (Mg) amounts stored in the reproductive and vegetative biomass of oil palm progenies, by assessing the distribution pattern of these minerals among oil palm organs, that is, roots through which minerals are absorbed and bunches that export minerals from the field during harvest, especially when empty fruit bunches (EFBs) are not recycled. Such assessment would allow us to know if the mineral contents in the different oil palm organs are specific according to progenies, or if leaflet mineral concentration correlates with mineral concentration in other organs and whether the unequal distribution of minerals within the oil palm organs is linked to the mineral dilution phenomenon.
Materials and methods
Experimental site
The study was carried out at Ologbo (Edo state, 6.03652°N and 5.55609°E at an elevation of 20 m a.s.l.), near Benin City in Nigeria, between 2011 and 2018. The average annual rainfall in the study area between 1996 and 2018 was 2,069 mm (Bonneau and Impens, Reference Bonneau and Impens2022). Rainfall distribution is monomodal, with a rainy season from April to October, and a dry season from November to March (Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a,Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Dammeb). Due to the regular rainfall observed in the study area (Bonneau et al. Reference Bonneau, Vandessel, Buabeng and Erhahuyi2014), it is highly unlikely that oil palms suffer from drought unless an exceptionally dry period occurs. Between 1996 and 2018, average annual air temperatures ranged from 25.0 °C to 27.8 °C, and average daily irradiance was 13.78 MJ m˗2 d˗1. According to FAO nomenclature, the experimental land consisted of a vast sedimentary formation with a flat landscape and ferralsol soil type (Bonneau et al., Reference Bonneau, Impens and Buabeng2017; Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). The soils are deep without coarse elements, very sandy on the surface, with a gradual increase in clay content with depth. Soil fertility and organic matter content were low (Table 1).
Table 1. Physico-chemical soil characteristics at the onset of the Nigerian trials
Nitrogen (N); carbon (C); soil organic matter (MOS); phosphorus (P); aluminium (Al); sodium (Na); calcium (Ca); magnesium (Mg); base ion (cation) sum (S); cation exchange capacity (CEC); saturation rate (TS); pHco: pH cobalt (soil acidity assessed using the cobaltihexamine method)
Plant material and fertiliser management
Four different Tenera oil palms (Elaeis guineensis Jacq.) progenies (C1, C2 and C3 from Deli x La Mé origin, and C4 from Deli x Yangambi origin) tested in Indonesia (Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017) were chosen for this study. These four progenies showed optimal leaflet potassium (K) and magnesium (Mg) concentrations and yields in Nigeria (Table 2) after being fertilised equally (Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a). Oil palm trees of these origins were evaluated 7.5 year after planting (YAP).
Table 2. Genetic characteristics, varieties, origins of the parents of oil palm progenies, leaflet nutrient concentrations, and yield characteristics of the tested progenies (PIC, 2011)
D x L: Deli x La Mé; D x Y: Deli x Yangambi. The last letter after the PO number (e.g., PO 2630 D or PO 2766 P or LM 10 T) indicates the main varietal group: P = Pisifera, D = Dura, and T = Tenera; progenies C1, C2, C3, and C4 are all Tenera crosses (between a Dura and a Pisifera variety); data in the Dura and Pisifera columns show the genetic material from which female inflorescences and male inflorescences (pollen) were used to obtain the progenies. AF refers to self-pollinated trees (e.g., LM 10 T AF = LM 10 T x LM 10 T); FFB: fresh fruit bunch; CPOmill : crude palm oil in the mill; bunch number, FFB and CPO yields are average data from 5 to 8 years after planting (YAP).
a, b, c, and d indicate the differences in parameters among progenies revealed by the Tukey test.
In the experiment, palms received a basal and uniform fertilisation dressing in the first year after planting to start the trial conditions as homogeneously as possible. In the second year, urea (1 kg palm˗1) and triple superphosphate (500 g palm˗1) were applied to all palms. From the second year onwards, a gradient of K and Mg fertiliser amounts was applied during 7 years in the main fertiliser plots. The fertiliser application schemes are presented in Table 3.
Table 3. Fertiliser application scheme (g of fertiliser per palm) in Nigeria
Experimental design
The experiment was set up in 2011 on 33 ha with oil palms spaced 9 m apart in a staggered, equilateral triangle design, resulting in a planting density of 143 palms ha˗1 (Dassou et al. Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a). It consisted of a factorial trial design with three levels of each nutrient: 0, 1.5, 3.0 kg palm˗1 year˗1 of potassium chloride (KCl: 60% K2O), K0, K1, and K2, respectively; and 0, 0.75, 1.5 kg palm˗1 year˗1 of kieserite (MgSO4: 27% MgO), Mg0, Mg1, and Mg2, respectively. The nine (3 x 3) main factors were considered as a random effect and were split into four subplots, each corresponding to a Tenera oil palm progeny, yielding a total of 36 subplots per replicate. The experimental design contained six replicates, giving a total of 216 subplots. To compare progenies in terms of K and Mg uptake capacity, we focused on the following five fertiliser combinations (K0Mg1, K1Mg1, K2Mg1, K1Mg0, and K1Mg2) for budgetary reasons and to save labour time in sample collection and conditioning. The experimental design maintains statistical validity with these five combinations of fertilisers as the response curves for a fertiliser must have approximately the same shape whatever the level of the other fertiliser and to be approximately parallel to each other. Combinations K0Mg1, K1Mg1, and K2Mg1 enable the drawing of the K response curve with the average level of magnesium (Mg1), while combinations K1Mg0, K1Mg1, and K1Mg2 allow the drawing of the Mg response curve with the average level of potassium (K1).
Above-ground vegetative biomass
Measurements were performed on oil palm leaves and their sub-organs (leaflets, rachises, petioles, and petiole bases), and stems forming the vegetative biomass, and bunches (female inflorescences which produce the fruits) and their sub-organs (peduncles, spikelets, kernels, shells, and mesocarp) forming the reproductive biomass. Male inflorescences were not measured because at full maturity (prior to the end of pollen dissemination), they already begin to lose some spikelets. A non-destructive method was used to assess plant organ biomass (Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). Spear (leaf sub-organ) biomass which represents about 3.6% of the total oil palm biomass (Corley et al., Reference Corley, Hardon and Tan1971) was not assessed, because the latter can only be done through destructive methods, which might increase phytosanitary risks to the palms. Also, parthenocarpic fruit (unfertilised, immature white fruits without oil) biomass was not assessed because it was negligible and did not contribute to oil synthesis.
Leaf of rank 17 is the reference leaf used by scientists to assess biomass (Aholoukpè et al., Reference Aholoukpè, Dubos, Flori, Deleporte, Amadji, Chotte and Blavet2013; Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017), palm growth related to leaf length or area, and leaf mineral concentrations (Dubos et al., Reference Dubos, Baron, Bonneau, Dassou, Flori, Impens, Ollivier and Pardon2019; Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a,Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Dammeb,Reference Dassou, Bonneau, Aholoukpè, Vanhove, Ollivier, Impens, Flori, Durand-Gasselin, Mensah, Sinsin and Van Dammec). To obtain oil palm total leaf biomass or the biomass of the sub-organs (i.e., leaflets, rachis, petioles, and petiole bases), the biomass of leaf #17 was multiplied by the average number of fronds annually emitted by each palm of each progeny (Dassou et al., Reference Dassou, Bonneau, Aholoukpè, Vanhove, Ollivier, Impens, Flori, Durand-Gasselin, Mensah, Sinsin and Van Damme2022c) between 4 and 7 years after planting. We used the average number of fronds annually emitted by progenies because the number of emitted fronds varies according to the season and weather (Dassou et al., Reference Dassou, Bonneau, Aholoukpè, Vanhove, Ollivier, Impens, Flori, Durand-Gasselin, Mensah, Sinsin and Van Damme2022c). Pruning may also affect the number of fronds on the palm, depending on the pruning rule (e.g., only one frond remaining under the last bottom frond carrying the bunch). Therefore, some progenies may have produced more fronds than others or fewer fronds due to pruning if they are in the male reproductive cycle, which is shorter than the female reproductive cycle. Biomass of leaf #17 was obtained by summing the biomass of its sub-organs. Leaves #17 of each progeny were cut down, as close as possible to the trunk. It is known that oil palm fronds from rank 13 onwards are adult and have statistically similar weights (Aholoukpè et al., Reference Aholoukpè, Dubos, Flori, Deleporte, Amadji, Chotte and Blavet2013). Petioles and rachis were separated to assess the biomass and mineral contents of each component. The number of pruned leaves and functional leaves on the first spire were counted. The sum of these two parameters was multiplied by 8 (as the oil palm canopy is always composed of 8 spires) to assess the total number of petiole bases produced by each oil palm. The petiole base is the last part of the frond that is attached to the oil palm trunk. Following Henson et al. (Reference Henson, Betitis, Tomda and Chase2012), the petiole base on the first spire at a height of 1.1 m from the ground was then delicately removed from the trunk without injuring the tree. The latter petiole base should be representative of all petiole bases attached to the palm trunk. Total fresh weight of each sub-organ (leaflets, rachises, petioles, and petiole bases) was recorded, and the samples were oven-dried at 80°C (for 72 hours) until a stable weight was obtained to determine their dry biomass (CIGE, 2013).
Following Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017), segments of leaflet (a sample of 10 cm from the middle part of leaflets and 10% of the total leaflets on one side of the frond was considered), rachis (15 cm), and both petiole and petiole base (5 cm, from the lower, more humid part) were taken from the frond of rank 17 and oven-dried at 80°C (for 72 hours) until their constant weight. Sub-organ dry matter (DM) was calculated as:
$${\rm{DM}}\;{\rm{s}}.{\rm{o}}. = {{Fresh\;weight\;of\;S.O.\;\;\;\;\;\;X\;\;\;\;\;Dry\;weight\;of\;S.O.\;\;sample} \over {Fresh\;weight\;S.O.\;\;sample}}\;\;$$
where s.o. is sub-organ (whole leaflet, rachis, petiole, and petiole base) and s.o. sample is sample of the sub-organ which should be dried in the oven.
Oil palm trunk biomass was assessed following Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017) and Aholoukpè et al. (Reference Aholoukpè, Amadji, Blavet, Chotte, Deleporte, Dubos, Flori and Jourdan2016), using allometric equations:
$${\rm{Stem}}\;{\rm{biomass}}\; = \;{\rm{Stem}}\;{\rm{volumetric}}\;{\rm{density}}\;{\rm{x}}\;{\rm{oil}}\;{\rm{palm}}\;{\rm{stem}}\;{\rm{volume}}$$
$${\rm{SVD}} = {{ressler\;stem\;sample\;dry\;weight\;\;\left( g \right)} \over {Pressler\;auger\;cylinder\;internal\;volume}}\;\;$$
where SVD is the stem volumetric density (g cm˗3 or kg L˗1), Pressler stem sample dry weight is given in g, and Pressler auger cylinder internal volume is 74.09 cm3. A Pressler auger is a ‘Forestier’ auger used to drill a core in the wood (plant’s stipe) to sample a part of it for analysis purpose or to assess the wood density.
Oil palm trunk samples were taken with the Pressler auger after the petiole base removal. Due to the low height of the oil palm trees used, samples were collected at a height of 1.10 m from the ground (which is generally around the frond of rank 33) to avoid injury to the meristematic tissue of the palm (palm heart). For accuracy, trunk sampling procedure was the same for all progenies. Four Pressler core samples were drilled in the trunk of each useful palm of each subplot to obtain sufficient DM for mineral concentration analysis.
Above-ground reproductive biomass
Progenies yield and leaflet mineral concentration data were assessed previously (Dassou et al. Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a,Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Dammeb) and presented in Table 2. During 11 consecutive months (June 2018 to April 2019), a total of 600 bunches were analysed at the rate of 10 bunches per progeny subplot and thus 40 per fertiliser plot (main plot) across five treatments (K1Mg0, K1Mg1, K1Mg2, K0Mg1, and K2Mg1), with three replicates. The bunch sub-organs used for biomass assessment were peduncle, spikelet, kernel, shell, and mesocarp, following Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). Total fresh weight of each of sub-organ was recorded and a sub-sample of each was oven-dried at 80°C (for 72 hours) until constant weight to assess total DM weight. Peduncle and spikelets samples were made with 75% of spikelets fresh weight and 25% of peduncle fresh weight following Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). Following the CIRAD bunch analysis protocol (IRHO-CIRAD-IGK 9, 1996), 30 fruits were collected from the total amount of normal fruits in each bunch and were used to assess the oil extraction rate (OER). The latter parameter was used to assess the crude palm oil (CPO) produced by each progeny. The nuts of these 30 fruits were air-dried for a week to allow the kernels to detach from the shell. After cracking the nuts, the 30 kernels and their shells were separately oven-dried at 80°C for 72 hours. OER (Protocol IRHO-CIRAD-IGK 9, 1996) was obtained using two sets of 5 g of mesocarp pulp per bunch, extracted with hexane in a Soxhlet apparatus. After oil extraction, the residue represents the mesocarp’s fibre fraction. The latter fibre obtained from the 10 g of mesocarp pulp were oven-dried at 80°C for 72 hours.
Below-ground biomass
Oil palm root sampling and root processing were performed, and total root biomass (TRB) was assessed following Dassou et al. (Reference Dassou, Nodichao, Aholoukpè, Cakpo and Jourdan2021). Root collection was conducted in the ‘footpaths area’ – which has a homogenous soil type according to Aholoukpè et al. (Reference Aholoukpè, Amadji, Blavet, Chotte, Deleporte, Dubos, Flori and Jourdan2016), using the simplified Voronoi sampling method (Dassou et al., Reference Dassou, Nodichao, Aholoukpè, Cakpo and Jourdan2021). One palm tree having comparable growth size as its six immediate neighbours was selected in each subplot. Root sampling was performed following three soil horizons (H1: 0–20 cm, H2: 20–50 cm, and H3: 50–100 cm) and four zones, following Dassou et al. (Reference Dassou, Nodichao, Aholoukpè, Cakpo and Jourdan2021). After sampling, roots were categorised per root type (R1: primary root, R2: secondary roots, and RF: fine roots), washed, and weighed. A sample of each was oven-dried at 80°C (for 48 hours) until weight stabilisation to assess their total DM. Dead roots were discarded. Following the Voronoi sampling method, TRB per tree (kg palm˗1) was estimated. TRB was subsequently multiplied by 0.143 to obtain the root biomass in Mg ha˗1 (Dassou et al., Reference Dassou, Nodichao, Aholoukpè, Cakpo and Jourdan2021).
Subplot composite samples and mineral contents
From the nine useful palms of each subplot, a composite sample was obtained for each leaf sub-organ (i.e., leaflets, rachis, petiole, and petiole base), bunch sub-organs (i.e., peduncle + spikelet, kernel, shell, and mesocarp’s fibre), trunk, and roots. For each palm, equal amounts of biomass were used to compose the subplot samples: around 3 g of leaf # 17 sub-organs (leaflets, rachis, petiole, and petiole base); and 3 g of bunch sub-organs (peduncle + spikelets, kernel, shell, and mesocarp’s fibre) collected from 10 bunches per subplot.
Trunk biomass samples were obtained from Pressler auger core drills in the oil palm trunk. Each core sample was approximately 1 g dry weight (Aholoukpè et al., Reference Aholoukpè, Dubos, Flori, Deleporte, Amadji, Chotte and Blavet2013). Four cores were drilled per palm, yielding 4 g of trunk biomass. For the single palm used per subplot for root sampling, 1 g of each root type (R1, R2, and RF) was collected across all zones and horizons, yielding a total of 36 g of root sample. Sample were sent to the CIRAD plant tissue analysis laboratory (CIRAD, US 49, France), where K and Mg concentrations were assessed using inductive coupled plasma-optical emission spectrometry (ICP-OES Agilent 720-ES) after double calcination extraction (Pinta, 1973). In total, 60 samples (4 progenies × 5 fertiliser treatments × 3 replicates) were collected for each of the 10 organs/sub-organs (leaflet, rachis, petiole, petiole base, trunk, root, peduncle + spikelets, kernel, shell, and mesocarp’s fibre), yielding a total of 600 samples analysed.
Statistical analyses
A mixed model was used for analysis of variance (ANOVA). Fertiliser treatments were considered as a random effect. The experimental design allowed comparison of oil palm biomass as well as their respective mineral concentrations and quantities among the progenies and fertiliser treatments. K and Mg uptake were compared among progenies to select the one that absorbed the highest amount of minerals from the soil. The Tukey multiple comparison test was performed to compare mean values. The software XLSAT (Addinsoft, 2019, Version 2018-7, www.xlstat.com) and R, version R-3.6.0 of windows, 32/64 bit, were used.
Results
Oil palm vegetative biomass
Oil palm biomass (including root biomass) among the progenies was significantly different at 7.5 YAP (p = 0.02). Progeny C3 produced the highest biomass (268 kg DM palm˗1), whereas progeny C2 had the lowest value (239 kg DM palm˗1). Progenies C1 and C4 had intermediate biomass values (i.e., 244 and 261 kg DM palm˗1, respectively), as shown in Figure 1a. Above-ground biomass accounted for 86%, 85%, 87%, and 85% of the total biomass for progenies C1, C2, C3, and C4, respectively. Among the sub-organs compared (i.e., leaflets (p = 0.0001), rachis (p = 0.000), and trunk (p = 0.005)), biomass was significantly different among the progenies. Progenies C3 (32.1 kg DM palm˗1) and C4 (31.5 kg DM palm˗1) showed higher and similar leaflet biomass (14% of total aerial biomass in both progenies) compared to progenies C1 (25.4 kg DM palm˗1) and C2 (25.9 kg DM palm˗1) leaflet biomass (12% and 13% of total aerial biomass, respectively) (Figure 1a). Progenies C3 (36.7 kg DM palm-1) and C4 (34.3 kg DM palm-1) also had significantly higher rachis biomass (16% of total aerial biomass for both progenies) compared to progenies C1 (29.2 kg DM palm-1) and C2 (29.5 kg DM palm-1), which constituted 14% and 15% of their total aerial biomass, respectively. Progeny C4 had the highest trunk biomass (72.5 kg DM palm-1), representing 33% of its total aerial biomass, while progeny C2 showed the lowest trunk biomass (57.5 kg DM palm-1), accounting for 28% of its total aerial biomass. Progenies C1 (65.9 kg DM palm-1) and C3 (66.7 kg DM palm-1) had intermediate trunk biomass values (31% and 29% of total aerial biomass, respectively) (Figure 1a). No significant differences were observed among the progenies in the biomass of petiole, petiole base, and roots. On average, petiole base biomass was estimated at 61.7 kg DM palm˗1 (29% of total aerial biomass), while petiole biomass amounted to 27.6 kg DM palm˗1 (13% of total aerial biomass) and root biomass was 36.6 kg DM palm˗1 (14% of total oil palm biomass) (Figure 1a).
Figure 1. Oil palm vegetative biomass (a), K amounts (b), and Mg amounts (c) according to progenies at 7.5 years after planting (YAP). Leaflet (black bars), petiole (grey bars), rachis (dotted bar), petiole base (cross hatch bars), trunk (slanting brick bars), and root (vertical hatch bars). Upper-case letters indicate differences among progenies and lower-case letters differences among sub-organs (leaflets, petioles, rachis, petiole base, trunk, and roots) for each progeny as revealed by the Tukey test. The error bars stand for standard deviation. Progenies (C1, C2, C3, and C4) were classified in two categories for each mineral (K and Mg). Category (+): leaflet mineral concentration (lmc) > almc and category (−): lmc < almc; where almc is the average leaflet mineral concentration of all progenies (Dassou et al., Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Damme2022b).
K and Mg distribution among vegetative organs of oil palm plants
At the whole-palm level (including roots), the amounts of K and Mg differed significantly among progenies across all fertiliser treatments. Progenies C2 and C3 exhibited the highest K amounts, with statistically similar values of 3.25 and 3.23 kg palm-1, respectively. In contrast, progenies C1 and C4 showed comparable but lower K amounts, varying between 2.82 and 2.84 kg palm-1 (Figure 1b).
In the above-ground portion of the palm, K uptake reached 93% in progenies C1 and C3, 94% in progeny C2, and 90% in progeny C4. Of this amount of K uptake, the trunk accounted for the largest K stocks, comprising 47% (1.39 kg palm-1) in C1, 45% (1.68 kg palm-1) in C2, 54% (1.37 kg palm-1) in C3, and 56% (1.12 kg palm-1) in C4. The trunk absorbed more K than any other organ (Figure 1b). In the rachis, progeny C3 contained the highest K amount (601 g palm-1), while progenies C1, C2, and C4 had statistically similar amounts. Progeny C3 also showed the highest K amount in the petiole (283 g palm-1), whereas progeny C1 had the lowest (206 g palm-1) and progenies C2 and C4 had intermediate levels. In terms of leaflet K levels, progeny C4 stood out with a significantly higher K amount (286 g palm-1) compared to the other progenies, which exhibited statistically similar values between 185 and 205 g palm-1 (Figure 1b).
Progeny C3 absorbed the highest Mg amount (0.44 kg palm-1), while progeny C1 had the lowest (0.34 kg palm-1) (Figure 1c). In the above-ground organs, Mg distribution was 90% in C1, 89% in C2, 92% in C3, and 88% in C4. The palm trunk exhibited equal Mg stocks across all progenies, averaging 89 g palm-1. The petiole bases stored substantial Mg amounts, with progeny C3 having the highest Mg content (128 g palm-1 or 32% of the total Mg in above-ground organs). The latter was significantly higher than the levels in progenies C2 (96 g palm-1, 30%) and C4 (95 g palm-1, 28%) (Figure 1c). The high Mg levels in progeny C3 can be partly attributed to its elevated leaflet Mg content (78 g palm-1 or 19% of the above-ground Mg), compared to 47 g palm-1 in C1 (15%), 51 g palm-1 in C2 (16%), and 64 g palm-1 in C4 (19%). Additionally, progeny C3 displayed a higher Mg amount in the rachis (46 g palm-1 or 16% of above-ground Mg), compared to C1, C2, and C4 (Figure 1c).
Overall, mineral distribution varied across different organs in the oil palm progenies. Potassium was more concentrated in the trunk, rachis, petiole base, and petiole, while magnesium was predominantly found in the petiole base, trunk, and leaflets.
Oil palm reproductive biomass
No significant differences were observed in total bunch biomass among progenies (p = 0.08). However, significant variations were found in the biomass of bunch sub-organs, including peduncle + spikelets (p = 0.05), kernel (p = 0.001), and shell (p = 0.0001) (Figure 2a). The peduncle + spikelet biomass constituted 65%, 61%, 60%, and 65% of the total bunch biomass for progenies C1, C2, C3, and C4, respectively. Progeny C3 exhibited the highest peduncle + spikelet biomass (1.21 kg DM bunch-1), while progeny C1 showed the lowest (0.93 kg DM bunch-1) and progenies C2 and C4 had intermediate and statistically similar values. Progeny C4 recorded the highest kernel biomass (0.53 kg DM bunch-1), while progenies C1 and C2 had the lowest and statistically similar kernel biomass values (0.40 kg DM bunch-1 and 0.39 kg DM bunch-1, respectively) (Figure 2a). Shell biomass was statistically similar among progenies C1, C3, and C4, which exhibited the highest values ranging from 0.44 to 0.50 kg DM bunch-1. No significant differences were observed among the progenies for mesocarp’s fibre biomass, which was 0.80 kg DM bunch-1, on average (Figure 2a).
Figure 2. Oil palm reproductive biomass (a), K amounts (b), and Mg amounts (c) according to progenies at 7.5 years after planting (YAP). Peduncle + spikelets (square ware-netting bars), kernel (horizontal hatch bars), shell (cross dot-line bars), and mesocarps’ fiber (white bars). Upper-case letters indicate differences among progenies and lower-case letters differences among sub-organs (peduncle+spikelet, kernel, shell, and mesocarps’ fiber) for each progeny as revealed by the Tukey test. The error bars stand for standard deviation. Progenies (C1, C2, C3, and C4) were classified in two categories for each mineral (K and Mg). Category (+): leaflet mineral concentration (lmc) > almc and category (−): lmc < almc; where almc is the average leaflet mineral concentration of all progenies (Dassou et al., Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Damme2022b).
K and Mg distribution pattern in bunch and mineral export
Although total reproductive biomass was similar across all progenies, progeny C3 exported the highest amounts of K (p = 0.03) and Mg (p = 0.0001) from the field. Progeny C3 exported approximately 46 g K bunch˗1, while progeny C1 exported the least (37 g K bunch˗1). Progenies C2 and C4 had statistically similar K export levels, about 40 g K bunch˗1 (Figure 2b).
Based on the average fresh fruit bunch (FFB) yield per progeny from ages 3 to 8 years, progeny C3 exported around 91 kg K ha-1 y-1, significantly higher than that of progeny C4, which exported the least (68.3 kg ha-1 y-1). Among the bunch sub-organs, only kernel (p = 0.0001) and mesocarp’s fibre (p = 0.001) K contents differed significantly among progenies. Progeny C4 had the highest kernel K content (30 g bunch˗1), while progenies C1 and C2 exhibited the lowest and statistically similar values (1.7 g and 1.6 g bunch˗1, respectively). Similarly, progeny C4 showed the highest mesocarp’s fibre K content (9.1 g per bunch), while progenies C1 and C2 had the lowest and statistically similar values (6.8 g and 7.3 g bunch˗1, respectively). Again, progeny C3 exhibited an intermediate mesocarp’s fibre K content (Figure 2b). The peduncle + spikelets were the primary organs for K accumulation, accounting for 73%, 75%, 76%, and 68% of total K per bunch in progenies C1, C2, C3, and C4, respectively. No significant differences were observed between progenies for K content in the peduncle + spikelets, with an average K content of 30 g per bunch. Similarly, shell K contents were also similar across progenies, averaging 0.7 g per bunch (Figure 2b).
Progeny C3 exported significantly more Mg (7.5 g bunch˗1) than the other progenies (Figure 2c). Considering the average annual FFB production for progenies aged 3 to 8 years, progeny C3 exported the highest amount of Mg, estimated at 15.1 kg ha-1 and progeny C4 exported the least Mg (9.66 kg ha-1 y-1). Among the bunch sub-organs, Mg content differed significantly in the peduncle + spikelets (p = 0.02), shell (p = 0.009), and mesocarp’s fibre (p = 0.0001). The mesocarp’s fibre was the sub-organ with the highest Mg content, accounting for 40% to 49% of the total bunch Mg content in progenies evaluated herein. Progeny C3 exhibited the highest mesocarps’ fibre Mg content (4 g bunch˗1) and also had the highest Mg content in the peduncle + spikelets (3 g bunch˗1), as shown in Figure 2c. Mg levels in the shell were minimal, with progeny C3 having the highest Mg content (0.24 g bunch˗1) and progeny C2 the lowest (0.16 g bunch˗1). The average Mg content in the kernel was 1 g bunch˗1, with no significant differences observed among progenies (Figure 2c).
K and Mg effects on total oil palm biomass, bunch biomass, and K/Mg contents
Applications of KCl (p = 0.79) and MgSO4 (p = 0.78) did not significantly affect the total biomass or bunch biomass of the oil palm progenies. However, KCl applications had a highly significant effect on the total K content across all progenies (p < 0.0001). Kieserite applications significantly influenced total Mg content, but only in progenies C1 (p = 0.05) and C3 (p = 0.03) (Figure 3a,b).
Figure 3. KCl and kieserite fertilisation effects on total K amounts (a) and total Mg amounts (b) in oil palm progenies sub-organs: leaflet (black bars); petiole (grey bars); rachis (dotted bar); petiole base (cross hatch bars); trunk (slanting brick bars); root (vertical hatch bars); and bunch (slightly dotted bar). Lower-case letters indicate differences among mineral contents for each progeny according to fertilisation levels, as revealed by the Tukey test. The error bars stand for standard deviation. Progenies (C1, C2, C3, and C4) were classified in two categories for each mineral (K and Mg). Category (+): leaflet mineral concentration (lmc) > almc and category (−): lmc < almc; where almc is the average leaflet mineral concentration of all progenies (Dassou et al., Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Damme2022b).
Discussion
Oil palms require large amounts of nutrients to maintain their high-standing biomass and therefore need substantial nutrient inputs to sustain their high biomass and productivity (Dubos et al., Reference Dubos, Hernán, Jesùs, Lòpez and Ollivier2010). The mineral requirements of oil palms are largely driven by the development of aerial organs and the yield characteristics specific to each progeny, which represent key sinks for these nutrients.
Oil palm biomass
In our study, average oil palm biomass varied among genetic provenances, with differences also observed in the biomass of individual organs within the same progeny. In Indonesia, Legros et al. (Reference Legros, Mialet-serra, Caliman, Siregar, Clement-Vidal, Widiastuti, Jourdan and Dingkuhn2006) estimated the total biomass of a 9-year-old oil palm (including roots) at 645 kg palm˗1, equivalent to 92 Mg ha-1, or an annual increase of 10 Mg ha-1 y-1. The trunk accounted for 49% of this total (∼315 kg), while the leaves, petiole bases, and root system contributed 26%, 14%, and 11%, respectively. This estimate by Legros et al. (Reference Legros, Mialet-serra, Caliman, Siregar, Clement-Vidal, Widiastuti, Jourdan and Dingkuhn2006) is approximately twice as high as our average biomass estimation for the tested progenies, which was 36 Mg ha-1 (including roots) or an annual increase of 4.8 Mg ha-1 y-1. Such discrepancy could be attributed to differences in age, genetic material (Durand Gasselin et al., Reference Durand-Gasselin, Blangy, Picasso, De Franqueville, Breton, Amblard, Cochard, Louise and Nouy2010; Cochard et al., Reference Cochard, Amblard and Tristan2005), or environmental conditions, as the study by Legros et al. (Reference Legros, Mialet-serra, Caliman, Siregar, Clement-Vidal, Widiastuti, Jourdan and Dingkuhn2006) was conducted in Indonesia, where precipitation is generally more favourable for oil palm cultivation than in Nigeria.
Khalid et al. (Reference Khalid, Zin and Anderson1999) estimated the biomass of two organs (trunk and leaves) at 85 Mg ha˗1 in Malaysia for oil palms about 23 years after planting, corresponding to an annual increase of 3.7 Mg ha˗1 y˗1. The latter estimate exceeds the findings of our experiment and may be explained by differences in genetic provenance (e.g., Deli x Avross palms with higher growth potential) compared to the plant material in our study (Durand Gasselin et al., Reference Durand-Gasselin, Blangy, Picasso, De Franqueville, Breton, Amblard, Cochard, Louise and Nouy2010; Cochard et al., Reference Cochard, Amblard and Tristan2005), as well as difference in age or in environmental conditions. In Côte d’Ivoire, where environmental conditions are similar to those in Nigeria, Dufrêne (Reference Dufrene, Ochs and Saugier1990) estimated trunks and leaves biomass at 42 Mg ha˗1 for oil palm after 10 years of planting (YAP), equivalent to an annual increase of 4.2 Mg ha˗1 y˗1. This estimate is close to our findings which included roots. However, the difference in biomass estimation could also be attributed to the 3-year age gap or variations in soil fertility. Another study in Côte d’Ivoire reported a maximum above-ground biomass of 50 Mg ha˗1 for oil palm plot planted at a low density of 130 palm ha˗1, with a yearly increase of 3 Mg ha˗1 y˗1 between 15 and 20 years after planting (Jaffré, Reference Jaffré1983). The lower planting density in that study likely enhanced plant canopy development and growth by increasing light available for photosynthesis (Bonneau and Impens, Reference Bonneau and Impens2022). Moreover, the palms were 2 to 2.7 times older than those in our study, resulting in higher growth rates.
The latter findings suggest that the biomass of oil palm plants and that of their organs increase with age and are affected by environmental conditions, soil fertility, genetic provenance, and planting density. The relatively low average oil palm biomass (36 Mg ha˗1 in average, including roots) observed in our study can also be explained by ongoing breeding programmes focused on developing more compact oil palm materials with low trunk growth rates to improve economic return. Compact palms are easier and less costly to harvest (Cochard et al., Reference Cochard, Amblard and Tristan2005; Konan et al., Reference Konan, Allou, Diabate, Konan and Koutou2014; Dassou et al., Reference Dassou, Bonneau, Aholoukpè, Vanhove, Ollivier, Impens, Flori, Durand-Gasselin, Mensah, Sinsin and Van Damme2022c).
According to Corley and Tinker (Reference Corley and Tinker2016), most oil palm biomass is concentrated in the trunk, leaves, and bunches, which together represent up to 96% of annual above-ground oil palm biomass production. Oil palm leaf biomass increases from 2.5 kg during the pre-adult stage to 3.3 kg at maturity (Aholoukpè, Reference Aholoukpè2013). Yearly biomass production in our experiment is higher than that of the earlier cited studies because they did not consider petiole base biomass. According to Henson et al. (Reference Henson, Betitis, Tomda and Chase2012), petiole base biomass is significant, accounting for 20% of total oil palm biomass. In our study, the petiole base contributed a higher biomass proportion (approximately 29% of aerial total biomass) compared to the findings of Henson et al. (Reference Henson, Betitis, Tomda and Chase2012). We also observed that petiole base biomass is similar to the trunk biomass, a possible consequence of our methodology. Here, petiole base biomass was extrapolated from samples measured at 1.10 m above ground, potentially overestimating contributions from younger fronds (ranks 1 to 13). It was further difficult to assess functional frond petiole base without affecting the palm heart. This approach was used to avoid damaging the palm heart, which could lead to palm death. Moreover, oil palm trunk biomass was estimated only from the portion extending from frond 33 to the ground, excluding the palm heart and emerging new leaves (Dassou et al., Reference Dassou, Bonneau, Aholoukpè, Vanhove, Ollivier, Impens, Flori, Durand-Gasselin, Mensah, Sinsin and Van Damme2022c). This bias was replicated on all progenies for the comparison of their biomasses and mineral contents. Petiole base abscission was not observed in our experiment due to the young age of the palms (7.5 years after planting, YAP). According to Corley and Gray (Reference Corley, Gray, Corley, Hardon and Wood1976), oil palm petiole base shedding typically begins between 11 and 15 YAP, although in some cases, palms of 19 YAP have been found to have completely shed their petiole bases. In Papua New Guinea, petiole bases shedding was rare until palms reached 14 YAP, whereas in Malaysia, shedding was observed in palms as young as 12.5 YAP (Goh et al., Reference Goh, Rolf, Fairhurst and Chee1994). Annual frond pruning as well as petiole bases shedding contribute to improve soil health and its sustainable management by providing organic matter and therefore minerals. As fronds and petiole bases decompose, they enrich the soil with humus, which enhances soil structure, aeration, and water retention (Aholoukpè et al., Reference Aholoukpè, Amadji, Blavet, Chotte, Deleporte, Dubos, Flori and Jourdan2016). During decomposition, the minerals stored in their tissues are released into the soil, making them available to other plants. This process also stimulates soil biota, increasing biodiversity and promoting nutrient cycling, as microbes, fungi, and invertebrates feed on the decaying material (Rees and Tinker, Reference Rees and Tinker1963; Ng et al., Reference Ng, Thamboo and de Souza1968). Root biomass also varied with age. Dassou et al. (Reference Dassou, Nodichao, Aholoukpè, Cakpo and Jourdan2021) estimated root biomass at 22.23 ± 0.81 Mg ha˗1 in 16-year-old oil palm while it was 0.86 ± 0.03 Mg ha˗1 for immature palms after 2 YAP. Genetic differences in oil palm root system development have been reported (Ruer, Reference Ruer1968; Cornaire et al., Reference Cornaire, Daniel, Zuily-Fodil and Lamade1994), with oil palms derived from DA 8D and DA 10D parents, exhibiting more developed root systems (Cornaire et al., Reference Cornaire, Daniel, Zuily-Fodil and Lamade1994; Nodichao, Reference Nodichao, Aké and Jourdan2008). These palms were qualified as drought-tolerant materials (Nodichao et al., Reference Nodichao, Aké and Jourdan2008) because they have ability to access water and mineral resources in deep soil layers. In our study, no differences in TRB were observed among progenies, likely because the palm trees of these progenies were grown in the same favourable environment, where genetic traits and fertilisation effects were not prominent growth (Bonneau et al., Reference Bonneau, Vandessel, Buabeng and Erhahuyi2014).
The progenies tested in our study exhibited similar bunch biomass but differed in average bunch weight (ABW) (Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a). It means that variations in ABW likely reflect differences in the number and weight of FFB produced by each progeny, influencing their specific total amount of oil produced (Table 2). Thus, progeny C1 produced the highest number of bunches, while progeny C3 produced fewer, but much larger bunches (Table 2), resulting in comparable bunch biomass (Figure 2a).
Mineral mass and uptake in vegetative and reproductive organs
Oil palm mineral mass refers to the mineral content in the oil palm’s tissues, reflecting the nutrient stock within the plant at a given time and the pattern of mineral distribution across its organs (Aholoukpè, Reference Aholoukpè2013). At the end of plantation life cycle, assessing mineral mass can indicate the potential for recycling nutrients into the soil through organic matter decomposition, thus maintaining soil fertility and reducing mineral fertiliser costs for producers. In an Indonesian oil palm plantation with a density of 136 palm ha˗1, recyclable aerial organs’ biomass contained 1255 kg K (50 kg K ha˗1 y˗1, considering 25 years for an oil palm life cycle), 285 kg Ca (11 kg Ca ha˗1 y˗1), and 141 kg Mg (6 kg Mg ha˗1 y˗1) per ha at the end of its life cycle (Khalid et al., Reference Khalid, Zin and Anderson1999). These figures exceed the results obtained in our experiment and can be explained by the fact that our results were obtained by assessing palms’ mineral contents at 7.5 YAP whereas the study of Khalid et al., (Reference Khalid, Zin and Anderson1999) was done 30 YAP, at the end of the plantation life cycle. However, yearly uptake in our experiment is higher than that reported by Khalid et al. (Reference Khalid, Zin and Anderson1999), suggesting that recent planting material seems more efficient in mineral uptake. The latter can therefore explain differences in mineral requirements which are specific for each planting material and also differ among environments (Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a,Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Dammeb). The lower mineral contents values observed in our study compared to those of Khalid et al. (Reference Khalid, Zin and Anderson1999) may be due to environmental factors (Prabowo et al., Reference Prabowo, Foster, Nelson, Sitepu and Nelson2012; Corley and Tinker, Reference Corley and Tinker2016; Dassou et al., Reference Dassou, Ollivier, Vanhove, Aholoukpè, Impens, Bonneau, Flori, Durand-Gasselin, Sinsin and Van Damme2022b) or the genetic background of the planting material (Aholoukpè, Reference Aholoukpè2013; Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a).
Furthermore, petiole and rachis K concentrations were higher in progenies C2 and C3 than in progenies C1 and C4, in which petiole and rachis K concentrations were higher than in the leaflets. Leaflet potassium (K) plays a key role in metabolite production (sugars and starch) through photosynthesis. The high amount of K found in the petiole and rachis results from its translocation from older to younger leaves. This translocated K ensures the transport and storage of metabolites from the site of photosynthesis (the leaflet) to different plant organs (Marschner, Reference Marschner1995; Mirande-Ney et al., Reference Mirande-Ney, Tcherkez, Gilard, Ghashghaie and Lamade2019; Naqiuddin et al., Reference Naqiuddin, Ling and Ong-Abdullah2020). Also, progenies’ petiole and rachis exhibit a well-contrasting K concentration than in leaflet. This means that, in the context of managing potassium (K) nutrition in oil palm, petiole and rachis K contents are less influenced by genetic origin than leaflet K content. Hence, petiole and rachis provide a better prediction of K nutrition and appear to be relevant tools for plantations that use multiple planting materials (Ollivier et al., Reference Ollivier, Flori, Bonneau, Vrignon-Brenas, Surya and Dassou2023).
On average, K and Mg levels in the whole oil palm DM were estimated at 1.31 ± 0.16% and 0.18 ± 0.02%, respectively (Ng et al., Reference Ng, Thamboo and de Souza1968). However, Teoh and Chew (Reference Teoh, Chew, Hj Hassan, Chew, Wood and Pushparajah1988) found a slightly higher mean K concentration of 1.48 ± 0.05% in 12.5- to 19-year-old Tenera oil palms. According to Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017), K concentrations follow a gradient in the oil palm, decreasing from the trunk to the petiole, rachis, and leaflet (with the lowest value). For example, K concentrations in the trunk of 10-year-old palms of Dura and Tenera progenies varied from 2.16 to 2.73% and 1.92 to 3.59%, respectively (Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). In an 11.5-year-old Dura oil palm, Ng et al. (Reference Ng, Thamboo and de Souza1968) found 2.13% K in the trunk. Teoh and Chew (Reference Teoh, Chew, Hj Hassan, Chew, Wood and Pushparajah1988) found that K concentrations in the trunk varied between 1.19% and 2.33% for 12.5- to 19-year-old Tenera trees grown on varying soil types. Taken together, those results revealed that the amount of K stored in palm organs increases with age and varies according to the genetic provenance of the oil palm. These findings are consistent with the higher K amounts found in our study and confirm the plant’s capacity to stabilise its internal K mechanisms (such as K storage in vacuoles or K translocation between organs) when external K supply fluctuates. This buffering ability prevents sudden nutrient deficiencies and ensures steady metabolic activity (Steingrobe et al., Reference Steingrobe, Claassen and Syring2000).
Unexpectedly, progeny C4 with the highest leaflet K concentration did not have the highest whole-palm K uptake, highlighting the dilution phenomenon and uneven mineral distribution pattern across oil palm organs (Dassou et al., Reference Dassou, Bonneau, Aholoukpè, Vanhove, Ollivier, Impens, Flori, Durand-Gasselin, Mensah, Sinsin and Van Damme2022c). Progenies C2 and C3 absorbed the most K overall, compensating for lower leaflet K with higher concentrations in other organs (Figure 1b). The latter underscores the importance of considering whole-palm mineral uptake capacities, rather than solely relying on leaf diagnostics for assessment of oil palm mineral requirements. However, progeny C3 which had the highest Mg concentration in the leaflet still had the highest Mg uptake overall, primarily due to substantial Mg contributions from the petiole base and rachis. These findings align with observations by Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017), who reported significant differences between progenies in the nutrient allocation to vegetative and reproductive organs. According to Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017), K was the most critical nutrient required in oil palm cultivation, with annual uptake averaging 2.35 kg palm˗1 y˗1, of which 56% is allocated to leaf renewal, 17% to reproductive organs, and 27% for the trunk storage. They also state that the amount of K annually absorbed for trunk growth among the oil palm origins tested contrasts greatly and varies from 634 to 896 g K palm˗1 y˗1 for Dura and 570 to 959 g K palm˗1 y˗1 for Tenera. Magnesium uptake averaged 358 g palm˗1 y˗1, of which 58% was used for leaf renewal, 24% for reproductive organs, and 17% for trunk growth (Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). Our results showed higher K and Mg uptake capacities than those reported by Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017) because we included total mineral uptake and accounted for annual mineral uptake per bunch produced by each progeny. Furthermore, the differences are also due to genetics, which influence optimal mineral concentrations in the entire palm (Dassou et al., Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a).
Lack of Mg in the leaflet is replenished by Mg reallocation from the trunk (main organ of mineral storage) or from old to more recent leaves. However, it is used in the chlorophyll production (up to 25% of total leaflet Mg), essential for photosynthesis (Dubos et al., Reference Dubos, Caliman, Corrado, Quencez, Siswo and Tailliez1999), which making it become again low. The latter can explain relatively low Mg concentrations observed in our study for oil palm tissues, especially in leaflets.
The variations in K and Mg concentrations and amounts across the progenies’ bunch components found in our study align with findings from previous studies (Ng and Thamboo, Reference Ng and Thamboo1967; Tarmizi and Mohd, Reference Tarmizi and Mohd2006; Prabowo et al., Reference Prabowo, Foster, Nelson, Sitepu and Nelson2012 and Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). DM analysis revealed that bunches contain approximately 0.65% K (Ng et al., Reference Ng, Thamboo and de Souza1968; Dubos et al., Reference Dubos, Hernán, Jesùs, Lòpez and Ollivier2010). With similar bunch biomass between the progenies tested in our study, progeny C3 mobilised the highest amount of K and Mg in the bunches. As bunches are removed from fields during harvest, plantations of progeny C3 would experience greater nutrient loss compared to other progenies. To address this, it is therefore recommended to return peduncle and spikelets, which are rich in K and Mg, to the plantation soil. According to our experiment, an EFB of 7.5-year-old palm tree weighted in average 1.05 kg DM (composed of peduncle and spikelets only). This corresponds to 1.8, 2.03, 2.22, and 1.55 Mg DM ha˗1 y˗1 for progenies C1, C2, C3, and C4, respectively. During decomposition in Malaysia environmental conditions (tropical area as in Nigeria, but with more rainfall), the EFB DM loss followed an exponential model, with 50% loss in DM in the initial 3 months and 70% loss after 8 months (Lim and Zaharah, Reference Lim and Zaharah2000). On the other hand, Rosenani and Hoe (Reference Rosenani, Hoe and Van Cleemput1996) reported that the EFB biomass reduced to 50% after 7.5 weeks in the double-layered and 8.5 weeks in the single-layered EFB. After 15 weeks, only 32% and 29% of the EFB initial DM were left in the single-layered and double-layered, respectively. The C/N ratios had reduced from 57 to 31 in the single-layered and from 55 to 24 in the double-layered EFB.
Interestingly, nutrient concentrations in the mesocarp (mesocarps’ fibres) were also found to be high, with oil palm mesocarps’ fibre containing the highest Mg concentrations among the bunch components. Our research therefore highlights oil palm mesocarps’ fibre as a new source of Mg that can be recycled within oil palm plantations. Alternatively, it could be applied in small quantities in pre-nurseries or nurseries, as an organic Mg fertiliser, offering a sustainable means of enhancing soil fertility. Unlike mineral fertilisers, the organic approach would avoid adverse environment effects such as harm to soil microorganisms or groundwater pollution. However, on most oil palm plantations, oil palm mesocarps’ fibre is currently burned as a feedstock in boilers to process FFBs. According to Ollivier et al. (Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017), Tenera bunches had significantly higher K and Mg concentrations in their mesocarp compared to Dura and Tenera parents’ bunches. The more recent genetic material contains higher levels of these minerals than older varieties (Ollivier et al., Reference Ollivier, Flori, Cochard, Amblards, Turnbull, Syahputra, Suryana, Lubis, Surya, Sihombing and Durand-Gasselin2017). Ng and Thamboo (Reference Ng and Thamboo1967) reported 0.399% K and 0.11% Mg in the mesocarp of Dura bunches, while Tarmizi and Mohd (Reference Tarmizi and Mohd2006) found 0.401% K and 0.138% Mg in the mesocarp of Tenera bunches. In Indonesia, Prabowo et al. (Reference Prabowo, Foster, Nelson, Sitepu and Nelson2012) observed 0.42% K and 0.14% Mg in the mesocarp. Since progeny C3 is the highest producer of FFBs compared to the other progenies and also contains more K and Mg in its bunches, it can be concluded that C3 oil palms require more nutrients to support fruit bunch production than the other progenies studied as also found by Dassou et al. (Reference Dassou, Adjanohoun, Vanhove, Impens, Aholoukpè, Bonneau, Flori, Cochard, Sinsin, Van Damme and Ollivier2022a).
Conclusion
The main purpose of this research was to assess the K and Mg uptake in four oil palm genotypes with varying origin by evaluating the mineral content of reproductive and vegetative biomass and examining mineral distribution patterns within various oil palm organs. As mineral uptake capacity varies among oil palm progenies, fertilisation should be adapted accordingly. Although progeny C4 exhibited the highest leaflet K concentration, it did not have the highest total K content in the whole palm, underscoring the phenomenon of K-dilution and uneven mineral distribution across palm organs. This finding questions the validity of the leaf diagnostic as tool for assessing the oil palms’ mineral requirements, as other organs may get higher amount of a given nutrient and compensate differences found in leaves. Progeny C3 emerged as the most efficient planting material, producing the highest vegetative biomass and absorbing the largest amounts of K and Mg from the soil. Identifying plant materials with superior K and/or Mg uptake efficiency holds significant potential for breeding. However, the specific traits driving such high efficiency remain unclear. Unveiling these traits will provide breeders with valuable insights for selecting the best-performing progenies for the next generation of commercial oil palm varieties.
Acknowledgements
The authors sincerely thank the Islamic Development Bank (IsDB) and the Belgium government thought Bijzonder Onderzoeks Fonds (BOF) for providing a PhD scholarship to the first author with which the present research could be performed. The authors further thank INRAB, CIRAD, PRESCO, and UGent for their technical and financial support. To be able to write this article, field data collection was organised and achieved by the technical staff of the PRESCO R&D department to whom we express our sincere gratitude.
Authorship contributions
Olivier S. DASSOU: Project conception, Data collection and curation, Data analysis, Writing original draft, and Writing – review and editing. Hubert DOMONHEDO: Writing – review and editing. Jean OLLIVIER: Project conception, Supervision, Investigation, Methodology, and Writing – review. Wouter VANHOVE: Supervision, Writing – original draft, and Writing – review and editing. Albert FLORI: Conceptualisation, Data curation, and Formal analysis. Michel CAZEMAJOR: Writing – review and editing. Brice Augustin SINSIN, Patrick VAN DAMME, Eduardo DE LA PEÑA: Project conception, Supervision, Project administration, and Writing – review and editing.
Ethics approval and consent to participate
The paper content has not been previously published, nor is it under consideration for publication elsewhere. The authors have contributed to the paper and have agreed to be listed as co-authors.
Consent for publication
The authors have read and commented on this manuscript and have agreed to submit this manuscript to the journal.
Competing interests
The authors declare no competing interests.
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