Effect of Calcium Carbonate Application on Initial Vegetative Growth of Oil Palm Planted on Deep Peat

The main challenge of planting oil palm on deep peat is naturally acidic soil pH which affects rooting development and activity and uptake of nutrients. Considering one life cycle of oil palm can be up to ≥20 years, ensuring optimum growth of palms since its initial planting is essential. Calcium carbonate (CaCO3) application is a standard practice to increase soil pH, including on peat soils. However, the effective rate and effects of its application to palm growth are still lacking. This trial is aimed to see the effect of CaCO3 application on the vegetative growth of oil palms planted on deep peat in the initial years of planting. The trial was conducted in an oil palm plantation in Pangkalan Kerinci-Riau with a split-plot randomized complete block design. Basal application of CaCO3 for the first three consecutive years of planting with three different rates and additional rates of CaCO3 and liquid lime per palm basis were the main and sub-treatments of this trial. Significant differences were found in frond length, leaf area, leaf area index, and frond dry weight at the immature stage in which palms treated with basal CaCO3 showed better growth. At the young mature stage, significant differences were found only in leaf area, leaf area index, and the number of green fronds. A significant difference for sub-treatment was found only in the leaf area index. The result indicated that application of CaCO3 as basal application during immature stage could improve palm’s growth whereas additional CaCO3 per palm basis may not necessarily result in better growth.


Introduction
Development of oil palm plantations for the last decades has targeted peat soil and since then the possibility to get a high yield of oil palm planted on peat has become a major concern for many oil palm plantations, agronomists, and researchers.Although currently new development of oil palm on peat soil is not allowed, existing plantations that have passed the drainability assessment required by RSPO for the second cycle of planting on peat soil still face many challenges to improve the yield and sustain the period of the planting.Considering one life cycle of oil palm can be up to ≥20 years, ensuring good environmental conditions to support palm growth since initial planting is essential.One of the main challenges of planting oil palm on deep peat is naturally acidic soil pH which affects rotting development, activity, and uptake of nutrients, thus inhibiting oil palm growth.According to [1], many plantation companies apply 2-3 kg/palm limestone dust or GML, as a precautionary measure, during the first 2 to 3 years of planting to correct soil acidity and to promote better rooting and growth of palms and establishment of legume cover crops.
Many studies had reported several practices to increase soil pH, especially on peat by utilizing various liming agents.In general, the practice of applying liming makes it possible to alter chemical, physical, and biological soil, thus providing several benefits.It decreases soil acidity, toxic elements insolubilization, increases levels of calcium and magnesium, and phosphorus availability [2].The application of lime can increase plant growth by increasing soil pH and providing cations for plant intake [3].The increased soil pH can improve nutrient availability, especially N, P, K, and Mg, provide better suitability of planting conditions to support palm growth, support fast and vigorous growth of leguminous cover crops, decrease Al content in the soil, etc. Calcium carbonate (CaCO3) is a commonly used liming agent to increase soil pH on peat soil.It is also commonly applied for legume cover crops (LCC).The practice of applying CaCO3 may offer several advantages such as a low-cost option, low environmental impact, high nutrient supply, and increases nutrients [3].However, the study on the effective rate, methods of application, and effect of CaCO3 application on the initial growth of oil palms planted on peat are still lacking.
The purpose of this study is to see the effect of CaCO3 application as a liming agent on the vegetative growth of oil palm planted on deep peat at the immature and young mature stage and to determine the optimum rate of CaCO3 application that best support vegetative growth.The findings from this study can be used as a general practice for oil palm plantation especially for improving soil pH in peat soil so that maximum growth of oil palm during the initial years can be obtained, which later might result in better yield.

Materials
Oil palm seedlings of DxP Socfindo MT Gano (12 months old) were planted in 2015 on deep peat (Typic Haplohemist) in Riau.There were two types of liming agents used in the experiment i.e., commercial calcium carbonate and liquid lime, HUMIBOX REAKTIF-TE (with copper and zinc).Types of inorganic fertilizers given to supply nutrients input for oil palm throughout the experimental period consist of compound fertilizers i.e., CCM45, OPCOM32A, OPCOM65A, NK 17:30, Oxy ZinCop, and straight fertilizers i.e., BRP/ERP, MOP, CuSO4, Fertibor, and GML.All treated palms received a similar amount of nutrient input throughout the trial period.

Experimental Details
The experiment was conducted in deep Typic Haplohemists soil in Block 8, Division 4, Kebun Nilo Barat 2, PT Adei Plantation & Industry Nilo Complex, Riau, Indonesia.The experiment was done in 2015-2020 with a split-plot randomized complete block design.The main treatments were different rates of calcium carbonate application at 0 ton/ha (L0), 2 ton/ha (L2), and 4 ton/ha (L4), annually applied as a basal application by broadcasted evenly in the plot for three consecutive years (at the immature stage).Sub-treatments were different types and rates of liming agents i.e., calcium carbonate at 0 kg/palm (U1), 1 kg/palm (U2), 2 kg/palm (U3), and liquid lime 200ml/palm (U4), applied six months after basal CaCO3 application in palm circle area for three consecutive years (at the immature stage).The main plot size was 8x20 palms/treatment, and the subplot size was 6x4 palms/treatment.One main plot consists of four subplots.Measurement palms for each subplot were 4x2 palms.The experiment was run with three replicates.2.3.2.Soil pH and chemical parameters.Soil samples for analysis i.e., pH (H2O), were taken annually from six sampling points/plots (always taken from palm no 1, 7, 11, 15, and 17) in a palm circle area at 0-15 cm.The samples were then sent to the Musimmas laboratory for pH (H2O) analysis.

Data Analysis
All collected data from each plot and its replicate were analyzed using Analysis of variance (ANOVA) split plot RCBD at a 5 percent significance level.All presented data were means values from three replicates for each parameter measured.

Soil pH (H2O).
The result of soil pH in the PC area at a depth of 0-15 cm throughout the trial period, years 1 and 3 (immature stage) and 4-5 (early/young mature stage) is summarized in Table 6.Table 6.Summary of soil pH (0-15 cm) data from years 1-5.

Treatment
Year of observation 1

Discussion
Application of basal calcium carbonate CaCO3 at the immature stage of oil palm for three consecutive years gave a positive effect on the vegetative growth.The residual effect was also seen for the next two years after the application has stopped.This experiment makes it possible to see the effect of calcium carbonate-liming for a long period.
Improved vegetative growth was noted and consistent for each growth parameter i.e., frond length, number of green fronds, leaf area, leaf area index, and frond dry weight, throughout the experimental period.Significant results were mostly noted at the immature stage when calcium carbonate was applied.The frond length and frond dry weight of palms treated with calcium carbonate were significantly longer and heavier in the second and third years, as compared to the control plot.Leaf area and leaf area index were significantly higher in the third and fifth years, as compared to the control plot.The number of green fronds of treated palms was significantly higher in the fourth and fifth years, as compared to the control plot.
The percentage of improvements of vegetative growth parameters from treated versus control plot throughout the experimental period was 6.9-8.1% for frond length, 10.4-11.2% for number of green fronds, 10.7-11.9% for leaf area, 22.1-24.4% for leaf area index, and 7.4-11.2%for frond dry weight.The study result is generally in line with the result from [3], which stated that calcium carbonate amendments contribute to plant growth response, especially in plant height and total dry matter yield of oil palm seedlings.
Response of vegetative growth parameters from treatment with 2 ton/ha calcium carbonate and 4 ton/ha was mostly not significant, and most of the time better result was seen in the plot with treatment of 2 ton/ha calcium carbonate.Moreover, the application of additional calcium carbonate and liquid lime (U1-U4) were not necessarily improved vegetative growth parameters.Significant effects of subtreatments were only seen in the leaf area index in the second and third years, where an additional of 2 kg calcium carbonate gave a higher leaf area index.The finding is in line with [4] which stated a single dose of liming was found to be more beneficial than split dosage yearly.
Improvement in vegetative growth parameters was suspected to be correlated with increased soil pH especially in palm circle area at 0-15 cm, as indicated in Table 6.The study result of [3] revealed that increased plant height and total dry matter yield of oil palm seedlings grown on calcium-amended soils could be attributed to increased soil pH.The soil pH of plots treated with calcium carbonate application was higher as compared to control plots.A similar result of pH increment was stated in [3] where the result of soil chemical analysis showed that Ca 2+ -amendments residues potentially reduced the soil acidity.As the soil pH increased, the availability of nutrients was suspected to be increased as well, thus the result of better growth can be seen in this experiment.The study by [4] stated that liming improves oil palm crop output via its direct impacts on soil chemical, physical, and biological properties, which improves the availability and mobility of several plant primary nutrients.However, there were no records of the nutrient analysis from the soil samples provided in this experiment.

Conclusion
The findings of the study indicated that liming practices by continuously applying calcium carbonate (CaCO3) at 2 or 4 tons/ha annually during the immature stage of oil palms planted on deep peat soil can improve vegetative growth, especially frond length, number of green fronds, leaf area, leaf area index, and frond dry weight.The residual effect was continuously noted in the first two years of the mature stage.Improvement on the vegetative growth was suspected to be correlated with increased soil pH, as a result of liming practice.However, once the basal application of calcium carbonate is done, no additional dosage of calcium carbonate or liquid lime is needed to further improved soil pH or vegetative growth.Future studies to correlate the improvement of vegetative growth to oil palm yield are important as to whether to repeat the application of calcium carbonate in the mature stage.

3. 1 .
Result 3.1.1.Vegetative Growth Parameters.The result of each vegetative growth parameter throughout the trial period, years 1-3 (immature stage) and 4-5 (early/young mature stage) is summarized in 11 3.59 a 3.64 3.72 a U4 3.20 3.26 c 3.61 3.47 b Means with the same letter are not significantly different.

Table 2 .
Summary of number of green fronds data from years 1-5.

Table 4 .
Summary of leaf area index data from years 1-5.