Fruitset quality of oil palm fresh fruit bunch over eight years in acid sulphate soil, Central Kalimantan

The low-quality fruitset of oil palm fresh fruit bunch (FFB) has occurred in 2014 in the acid sulphate soil of PT Kalimantan Sawit Abadi, Central Kalimantan. It was known that the FFB quality has a very low percentage of fruitset about 17.4% on January 2014. The objective is to examine the historical quality of oil palm FFB fruitset for more than eight years (2014 – 2022) on acid sulphate soil and the factors that influenced it. Routine observations were conducted monthly with the variables fruitset value, number of male inflorescence anthesis (MI), and population of Elaeidobius kamerunicus. The data was carried out in a historical descriptive analysis (paired T comparison test). For eight years, the trend of fruitset quality in the observation sites has increased. The fruitset value on September 2022 reached 57% and was significantly different compared to 2014. It was known that the population of E. kamerunicus/ha significantly increased in the same period. The number of MI/ha each year tends to decrease (R2 = 0.151) with changes in plant age, ie. 5 – 13 years. Plant age development had a strong Pearson correlation (0.945) with the FFB quality.


Introductions
Development in addition to expanding the planting area, the oil palm commodity was also influenced by the successful introduction of the oil palm pollinating insect, namely Elaeidobius kamerunicus Faust (Coleoptera: Curculionidae).The introduction of E. kamerunicus to Indonesia in 1983 has led to an increase in the productivity of oil palm fresh fruit bunches (FFB) [1].Fruitset value is one of the FFB quality parameters that can indicate the plant and pollinating insect's interaction.The important role of the presence of E. kamerunicus in improving the quality of FFB is shown by an increase in fruitset value of 26% after the first introduction [2].However, this condition cannot always be positively correlated with an increase in the population of E. kamerunicus and optimum FFB quality.The dynamics of fruitset value after the introduction of E. kamerunicus began to decline in the 21 st century.Purba et al. [3] and Lubis [4] reported the incidence of low-quality FFB with an average fruitset value of <50% in West Java, South Sumatra, and Central Kalimantan.
The incidence of low-quality FFB in Central Kalimantan began in 2013 with a fruitset value of <20% (Figure 1) and caused the average long-term weight to decrease to 33% [5].Lubis et al. [6] reported the results of an evaluation of efforts to increase the value of the fruitset from the 2013 incident which took place in Central Kalimantan.Based on improvement efforts carried out using the assisted pollination (aspol) method, hatchery system, and re-introduction of E. kamerunicus, it is known that there was an increase in fruitset values four times from the initial incident, namely 8% to 35% from 10 months of observation (June 2013 -April 2014).The dynamics of fruitset values can occur due to various factors, including soil type [4], nutrition, water, availability of carbohydrates, pollination [7], and climate [8].Lubis [4] reported differences in fruitset values for three soil types, namely mineral, sandy, and peat, respectively 58.9%, 49.8%, and 46.4%.Other types of soil can be found in Central Kalimantan, namely acid sulphate which is classified as suboptimal soil.The key problem in acid sulphate soil types is the presence sulfidic materials, which contain pyrite (FeS2) which can interfere plant growth [14].The pyrite layers characterize the acid sulphate soil type in the observation site as reddish-orange above ground level (Figure 2).It is suspected that there is a dynamic or change in the pattern of fruitset values after a long period of effort with the inhibiting factor of soil type.The objective is to examine the historical quality of oil palm FFB fruitset for more than eight years (2014 -2022) on acid sulphate soil and the factors that influenced it.

observation method
The data collection method was carried out through routine observations every month for around 84 months or more than eight years (2014 -2022).Observations were made randomly in the research location.The observed variables were the fruitset value, the male inflorescence anthesis (MI) and receptive female inflorescence (FI) to get the sex ratio in the planting area, and the population of E.kamerunicus.

The value of the fruitset.
Observation of the fruitset value was carried out by taking random samples from the yield collection point (YCP) of fresh fruit bunches (FFB).A total of six FFBs as a sample for observing fruitset values.Each FFB counted the number of normal and abnormal fruit (parthenocarpy) by dividing it into three parts, namely top, middle and bottom (Figure 4).In addition to observing the state of the fruit (fruitset).The calculation used to determine the fruitset value is with formula (1) as follows.

The number of blooms (sex ratio).
Observation of the number of MI and FI or census sex ratio was carried out by observing a sample area of observation blocks.Selection of representative samples, namely at every five rows with an observation area of ±5 Ha.The criteria for the efflorescence of inflorescence are those with a rate of ≥ 75% (Figure 5).The observer will walk in the observation area by paying attention to the state of each type of inflorescence that blooms on each tree that is passed in the observation line.Then the blooming inflorescence will be recorded in a census format to obtain sex ratio data and the number of each type of blooming inflorescence.The formula to find out the value of the sex ratio is by formula (2) as follows.

Population of Elaeidobius kamerunicus
The population census of E. kamerunicus in the observation area was carried out by taking six samples of male anthesis inflorescences from the sex ratio census.The observation of the population of E. kamerunicus was carried out at 09:00 am or earlier because at that time the activity of the weevils on the average was still on the male inflorescences, whereas in the afternoon, after 10:00 am there would be many weevils flying toward the female inflorescences [9].For each inflorescence sample, the number of E. kamerunicus weevils present in each spikelet was counted (3).The observation spikelets were randomly selected from three parts of the inflorescences bunch, namely top, middle, and bottom with three spikelets for each part so that a total of nine spikelets were observed.The total number of spikelets from each sample bunch was also counted to obtain data on the number of E. kamerunicus in one bunch using formula (4).Then, from these data, it will be known the estimated population of E. kamerunicus per Ha contained in the observation area with the following formula (5). (

Data analysis
The data obtained from the observations were the fruitset value, the number of anthesis MI, receptive FI, the sex ratio, and the population of E. kamerunicus.Observational data were obtained for more than eight years, namely from 2014 to 2022.The data were then subjected to historical descriptive analysis using paired t-test comparison.In addition, the correlation value between the fruitset variables and each other observational data is obtained by the correlation test.

Results and Discussion
The productivity quality of oil palm in the form of FFB can be assessed quantitatively based on the fruitset value parameter.The FFB fruitset value was observed at the age of the fruit bunches about five months after pollination of the blooming flowers [10,6].This means that the FFB samples harvested in the month of observation were the result of pollination about five months earlier.Monitoring of the quality of FFB in the acid sulphate area of research location was carried out based on cases of low fruitset values in 2013 [6].After efforts to improve the quality of FFB until 2014, monitoring of the development of fruitset values will continue until 2022, for eight years.The fruitset value of monitoring results for eight years shows an increasing trend (Figure 6).In 2017 and 2018, the average observed fruitset value showed a decrease compared to 2016 which then increased again in 2019.So it is known that the quality of FFB after the efforts to increase the fruitset value eight years ago can change to be higher or lower, but no results were obtained lower than in 2014.The quality of FFB in 2022 (Figure 7) seen better from 2013 (Figure 1) visually.Figure 8 shows the trend of fruitset value from January to December at the beginning (2015) and end (2022) of observations.The fruitset value in 2015 and 2022 is in the range of 30 -46% and 44 -58%.The results of the T-test analysis of fruitset values and the population of E. kamerunicus at the start and end of monitoring for eight years showed significant differences with significantly less than the P-value (Table 1).The trend of the dynamics of fruitset values experiencing differences at the beginning of the year tends to be higher than at the end of the year.Pollination results can change because it is influenced by various factors.The Figure 9, 10 and Table 3 show some of factors that affect the fruitset quality are anthesis male inflorescences per Ha, population of E. kamerunicus per Ha, and plant age.Factors that can affect the quality of FFB include soil nutrients [11] and the pollinating insects ie.E. kamerunicus population levels, pollination success, availability of male anthesis inflorescences, natural enemy populations of E. kamerunicus also climatic conditions [6,12,4,13].The area of observation had acid sulphate soil type in the subgroup namely Sulfic Endoaquepts.Acid sulphate soil as suboptimal soil is classified as marginally suitable (S3) from the analysis of land evaluation.Marginally suitable land has a severe limiting factor (pyrite depth) and will affect crop productivity.R&D report of CBI [20] reported that the soil type in this observation site has a layer of pyrite at a depth of 50-100 cm with poorly drained and permeability.The acid sulphate soil is areal or land which has pyrite layers in 0-50 cm from the above ground level.The key problem in acid sulphate soil types is the presence sulfidic materials, which contain pyrite (FeS2) of more than 2% which can interfere plant growth [14].The potential of soil fertility is determined by the levels of nutrients in the soil.Meanwhile in acid sulphate soil types, direct absorption of nutrients will be hampered.Lubis et al. [16] reported the quality of FFB in three different soil types, namely clay, sand, and peat with a fruitset value of 58.9% each; 49.8%; 46.4%.So it is known that the quality of FFB in the acid sulfate soils of West Kotawaringin, Central Kalimantan, is not much different from production in other plantations.
Monitoring results for eight years showed the highest fruitset value, namely 70% in August 2019 (Table 2).The lowest fruitset value from the monitoring results was obtained from the FFB sample in July 2019, namely 21% (Table 2).The average fruitset value from monitoring results for eight years is 45%.Lubis et al. [6] reported the quality of FFB after treatment with the highest fruitset value of 40.4%.This shows an effort to increase the value of fruitset in the period 2013 -2014 by re-introducing E. kamerunicus [6] to experience the success and dynamics of FFB quality until eight years later still showing good results.The average fruitset value from the monitoring results is not much different from the report [3], which is 49.90%.The decline in the quality of FFB based on the value of the fruitset apart from the possibility of being caused by the soil type factor is also thought to be caused by the reduced population of pollinating insects of E. kamerunicus in the oil palm plantation area.Purba et al. [3] and Susanto et al. [17] reported a decrease in the population of E. kamerunicus followed by a lower value of the FFB fruitset.Further reported by [21] about the decline in the value of fruitset in North Sumatera by ± 16% after 17 years after the initial introduction of E. kamerunicus.Figure 9 shows the declining population trend of E. kamerunicus, accompanied by an increase in fruitset value and plant age.This shows that the decline in the population of E. kamerunicus is not always accompanied by a decrease in the quality of FFB.The population of E. kamerunicus has a role in increasing the effectiveness of pollination.Donough and Law [1] also Susanto et al. [18] stated that the standard population value for E. kamerunicus was 20,000 beetles to get pollination results with a fruitset value of more than 75%.Monitoring for eight years showed that the highest population of E. kamerunicus and close to the standard value occurred in 2014 (Figure 9), but the fruitset values obtained were close to the standard occurring in 2019 (Figure 6 and Table 2).The high population of E. kamerunicus in 2014 was because it was still in the period of efforts to improve the quality of FFB (re-introduction of E. kamerunicus and hatchery) and the number of male anthesis inflorescences per hectare was higher compared to the following years of observation (Figure 10).Monitoring results at other times showed lower populations of E. kamerunicus and fruitset values.[19] stated that the decline in pollinator insect populations did not affect plantation yields on a global scale.In addition to the presence of pollinating insects, good quality fruit development can be influenced by the nutrients obtained by oil palm, water, and carbohydrate fulfillment [7].x-axis which is 1 to 9 is for the year of observation Improvement in the quality of FFB can occur due to the effect of increasing the age of the plants which continue to enter their physiological maturation phase.Susanto et al. [17] reported that the fruitset value of oil palm plants with different planting years showed higher yields at older plant ages, namely yop.2010, 2006, and 2000 respectively valued at 66.7%; 72.9%; and 81.1%.Monitoring results (Figure 9) show a trend of increasing fruitset value with the equation y = 2.1306x + 34.292 and increasing plant age with the equation y = x + 4. The model for improving FFB quality and plant age is linear.Figure 10 shows the trend in the number of antheses male flowers tends to decrease with increasing plant age (y = -0.2155x+ 3 .1805and R² = 0.151).The highest number of anthesis male flowers was found in 2014 and 2019 (5 and 4) with the number meeting the standards to obtain a high fruitset value as a good quality FFB.The standard number of anthesis male inflorescences per hectare to get fruitset value ≥ 75%, that is 3 bunches of flowers [17].Male inflorescence types on young oil palm plants will appear more with the sequence and proportion of irregular inflorescence production [15].However, Kevan et al. [11] stated that the value of the fruitset and the sex ratio were high in young oil palm plants.
The trend line models in Figures 9 and 10 from the monitoring data show that the results of the correlation analysis of the data variables are appropriate and varied, namely, the relationship is very weak to very strong (Table 3).The concordance of the analysis results (positive and negative correlations) in Table 3 was obtained based on the research report [17,15], namely an increase in plant age along with an increase in fruitset value and inversely proportional to the number of anthesis male inflorescences.The result of analysis in Table 3 shows that the fruitset value had a very strong correlation (0.945) with the plant age and a very weak correlation (0.017) with the male inflorescences anthesis per Ha.Plant age had a negative correlation with the population of pollinators and the male inflorescence per Ha.

Conclusion
For more than eight years, the trend of fruitset quality in the observation sites has increased.The fruitset value at the end of the observation (December 2022) reached around 5.9% and was significantly different compared to 2014 (39.7%).It was known that the population of E. kamerunicus per hectare had significantly increased (P = 0.00) in the same period.

Figure 1 .
Figure 1.FFB with low fruitset quality in yield collection point (a) and a bunch (b) on 2013[5]

Figure 4 .
Figure 4. Calculation of the fruitset value by sampling 10 spikelets from each part of the observed fruit bunches

Figure 6 .
Figure 6.The trend of average fruitset value from FFB quality monitoring for eight years at acid sulphate soil area in West Kotawaringin

Figure 9 .
Figure 9. Population trends of E. kamerunicus and the average fruitset value from monitoring the quality of FFB with the age of the plants during observation on 2014 -2022 in the West Kotawaringin; x-axis which is 1 to 9 is for the year of observation

Table 1 .
The results of the comparative T-test analysis of monitoring data on fruitset values and

Table 3 .
The trend of the number of antheses male infloresccence per hectare with the age of the plants from monitoring observations for years in the West Kotawaringin Analysis results of the correlation level between the two observational variables from monitoring data on fruitset values in the acid sulphate area of West Kotawaringin for more than eight Correlation value with a negative sign (-): indicates an increase in one variable can cause a decrease in other variables. * The number of male inflorescence anthesis per hectare each year tends to decrease with changes in plant age.Plant age development had a strong Pearson correlation with FFB quality.