Nutrition: Materials and Methods
[addw2p name=”oilPalmNutrition”]
Experimental sites
The oil palms selected for study came from the optimal NPK treatments of two factorial, fertilizer response trials. Both experiments were conducted on Munchong series (Typic Hapludox) soil which was derived from shale. In the first experiment, destructive samplings of the palms were carried out at six palm ages to study the B requirements of growing palms. Two palms were sampled at 20, 37 and 71 months after field planting whereas three palms were sampled at 46, 57 and 82 months after field planting. At each sampling, the palms were chosen from different replicates and where possible, palms from the same replicates were taken across the months. Sodium borate was applied at an average rate of 3.1 kg B ha-1 yr-1.
In the second experiment, two 16 years old palms, the interrow vegetation and the frond stacks were sampled to examine the B distribution in an oil palm field at the steady state condition. Sodium borate was applied at an average rate of about 1 kg B ha-1 yr-1.
In both experiments, the number of leaves produced by each sampled palm were measured at half yearly intervals, the fresh fruit bunch (FFB) yields at 10 day intervals and the male inflorescences at quarterly intervals. These data were then summarized on an annual basis to estimate the yearly B requirements of oil palm.
Palm destructive sampling and B analysis
The oil palm can be divided into unambiguous morphological components (Tinker and Smilde, 1963). These are: leaf, which can be further separated into leaflets, leaf rachis and leaf petiole, unopened spear leaves, growing point or “cabbage”, stem, roots, male inflorescences and fresh fruit bunches. In this paper, the stem included the petiole bases, which were attached to it after pruning the leaves, and the root bole, which was the growing point for the roots.
Each fresh leaf was cut down (“fresh” being taken to mean that over half the total leaflet area was still green) and counted. Each leaf was then separated into the leaflets, petiole and rachis. The leaflets for nutrient analysis were sampled systematically by taking 1 in 10. The balance of the leaflets was then sampled for determination of fresh and dry weights. The rachis was cut into three equal sections. Each section was divided into three equal parts and a 10 cm section was cut from the middle of each part. One longitudinal half from each section was bulked for fresh and dry weight determination. Leaf petioles from leaves 1 to 6 were divided into two equal parts whereas the older ones into three equal parts. Leaf 1 was the youngest fully opened leaf. A 10 cm section was cut from the middle of each part. One longitudinal half was then taken from each section and bulked for fresh and dry weight determination. For B analysis, the leaflets, rachis and petiole were each bulked for various groups of leaves in the ratio of their dry weights. In the oil palm, each group or whorl of leaves consists of eight leaves i.e. leaves 1 to 8, 9 to 16, 17 to 24, 25 to 32, 33 to 40, 41 to 48 and 49 to 56. The unopened spear leaves were sub-sampled in the same manner as the leaf but their rachis and petiole were not separated because most of them had very short petioles.
The primary roots around the stem were cut to facilitate its felling at ground level. The cabbage was then cut off from the apex of the stem. Two 1/16th sections were sampled. The rest of the stem was divided into six equal sections. The middle 15 cm of each stem section was sampled and two 1/16th sections sub-sampled.
The roots were sampled using the trenching method. Since the palms were planted in an equilateral triangular pattern of 9.1 m and 8.9 m apart for experiment 1 and 2 respectively, the palm area was divided into three sections as follows: palm to palm of the same row, palm to palm of another row and palm to interrow area. In each section, a trench 30 cm wide and 90 cm depth was dug to the middle of the planting row or interrow area. The roots that were dug up were sieved out and collected for every 30 cm by 100 cm by 30 cm depth section and then bulked for each palm
The male infloresecences on the palms at the time of sampling were separated into immature inflorescences, mature inflorescences and old inflorescences. The FFB for B analysis were collected from the second experiment only. A total of 26 bunches were collected over a three month period. In the laboratory, each bunch was weighed, stripped and divided into its major unique components of fruit, stalk, spikelets and parthenocarpic fruits. The fruit was further separated into the shell and kernel. Fresh weight of each component was taken. Two 100 g samples of each of the chopped and ground stalk and spikelets were collected for fresh and dry weight determination. The oil in the fruits were extracted using hexane following the modified Blaak’s method (Rao et al ., 1983).
The aerial parts of the interrow vegetation in each palm area were cut and weighed. The vegetation on the palm stem was also sampled, weighed and bulked with the interrow vegetation. Only one eighth of the fresh weight was taken for analysis.
All sub-samples of the vegetative and reproductive parts were sent to the laboratory for fresh and dry weight determination and B analysis. The latter followed the Azomethine-H method (John et al ., 1975). Briefly, 1 g of plant sample was dry ashed at 530 ° C and digested with 10 ml of 1.4 M H2 SO4. The solution was then filtered through Whatman No. 1 paper. 0.5 ml of 0.05 M EDTA, 1 ml of 0.5 M ammonium acetate and 1 ml of Azomethine-H solution were than added to 1 ml of the filtrate to prevent interferences and developed the colour. The B concentration in the filtrate was then read using a UV/VIS spectrophotometer.
Computing the annual B requirements from the data
In the first experiment, the time intervals were not fixed. Therefore, the cumulative B accumulation or uptake by the palm in each component at each sampling time has to be computed and the results modeled using non-linear regression. The gradient of the model at each yearly time period gave the annual B requirement for the component.
The B requirement of canopy between two sampling periods (t1 and t2) was: B content of new leaves produced between t1 and t2 plus B content accumulated by the older leaves between t1 and t2. It was also assumed that the B content in the canopy at the first sampling represented a continuous accumulation of B from the time of field planting since pruning of the leaves had not commenced then.
The B requirement of roots between two sampling periods (t1 and t2) was computed as follows:
B content at t2 – B content at t1 + a B content at t2
where a is the percentage of self-pruned roots. The a value for each time period was obtained from Jourdan and Rey (1997). It was also assumed that the root biomass continued to grow in the first 36 months after field planting with minimal self pruning following the logistic root model of Jourdan and Rey (1997).
The annual B requirements for fresh fruit bunches and male inflorescences were estimated based on their annual dry matter production multiplied by their average B concentration for the year.
Statistical analysis
Descriptive statistics, means and standard deviations, were calculated using Statistica Ver. 7.0 (StatSoft, 2004). Separate one factor analysis of variance (Anova) was computed for the B distribution within the vegetative components of the palm and the fresh fruit bunches. Non-linear regression was used to model the cummulative vegetative data using CurveExpert 1.38 (Hyams, 2001).