Estimation of Weed Biomass as Forage Production under Oil Palm Plantation

Perkebunan


Introduction
Oil palm or Elaeis spp.Plantations covering extended areas in Indonesia reach 14 456 611 ha (BPS 2019).In the oil palm plantation, the standard spacing resulted in weed invasion under the oil palm trees (Kothari and Schweiger, 2022).Weeds compete with the main crops for nutrients, water, and sunlight which reduces in main crops quality and animal products quality (Iderawumi and Friday 2018).The effective control methods for weeds that are a problem in forage crops are still not available, unfortunately.Most weed control using herbicides that are costly and effects on environmental health (Ryadin et al 2022).
Recent research revealed that weed vegetation under oil palm plantations could be one of forage resources for ruminants (Ramdani et al 2017;Kumalasari 2020).Weed control using ruminant could optimize land use as integrated beef cattle in oil palm plantations to fulfill the animal forage needed (Sandiah et al 2021).
Proper management in integrating beef cattle under oil palm plantations can reduce weeding and fertilization cost (Darras et al 2019).
In order to optimize the weed utilization as forage, weed vegetation analysis is needed to identify the botanical composition and forage production.In the previous research, the number of weed diversity under oil palm plantations was varied that ranged from 16 to 36 with the average of total fresh biomass production was 13.37 ton ha -1 without palatability consideration (Akbar et al 2021).This research was conducted to evaluate the botanical composition, diversity level and estimate the weed production under oil palm plantation as ruminant forage based on plant palatability.

Method 2.1. Study area
The research was located at Cikabayan oil palm plantation from January to April 2019.The vegetation identification and processing were conducted at the Laboratory of Agrostology, Faculty of Animal Science IPB University.

Procedure
Sampling plots were carried out on different ages of oil palm plantation, i.e.: 6 and 8 years old.Vegetation was sampled using quadrants in size 50 cm x 50 cm, 10 times randomly.Weed samples were identified and then confirmed by Global Biodiversity Information Facility (GBIF) as reference.
Forage was collected from each plot and harvested ±5 cm above soil area.Fresh weight was measured at each plot after harvesting.Dry weight was measured after sample drying in an oven with a temperature of 60 o C in 48 hours.

Data Analysis
Botanical composition analysis by following the Dry Weight Rank methods (Mannetje dan Haydock 1963).Weed dominance was calculated using data of density, relative density, frequency and relative frequency (Kainde et al. 2011), Important Value Index (Brower et.al 1990), and Summed Dominance Ratio (SDR) (Mueller-Dombois and Ellenberg 1974).
Forage production potency was calculated using equation as follows P = C x (10.000 -(LP x JS)), where P was weed production (kg hectare -1 ), C was weed fresh weight per m 2 , LP was plate width area of oil palm tree and JS was number of oil palm tree in a hectare (Daru et al. 2014).Carrying capacity calculation based on forage production in a year that assumed there were 6 harvest times with 60% proper use factor.Diversity index (H') was analysed using the Shanon-Wiener method (Brower et.al 1990).
Data was computed using Microsoft Excel and the results were presented in tables.Forage diversity level was statistically analyzed using Analysis of Variance (ANOVA).The LSD test was applied as the post hoc test using software R.3.5.3 to determine homogenous groups.Forage palatability was investigated using secondary data.

Environmental condition
Based on Meteorological, Climatological, and Geophysical Agency data, the average temperature in January until April 2019 were in the range 23 0 C -27 0 C, with humidity being 70-90%.The 6 years old of oil palm plantation has latosol type with pH 4.94, while at 8 years old it was 4.52.Land was maintained with fertilizer every 6 months.Sunlight intensity was measured using a lux meter on each area.The average light intensity in the 6 years old oil palm plantation was 12170 lux, while in the 8 years old it was 2100 lux.

Botanical composition
Based on the result (Table 1) showed that different oil palm plantation ages affect the weed botanical composition under the trees.There were 19 weed species belonging to 11 families under oil palm plantation.Thirteen weed species belonging to 9 families were found only in the 6 years old oil palm plantation.There were less species under 8 years old palm plantation, i.e. 10 species belonging to 5 families.These were herbs, herbaceous climbers, shrubs, climbing shrubs, trees, small trees, ground and epiphytic ferns.
The low IVI values on the older oil palm plantation could be due to the sharing of resources, especially spaces that limited plant dispersal and minimize plant interaction among the species (Liao et al 2013).Furthermore, the low IVI values could be due to low light intensity on the 8 years old oil palm plantation (2100 lux) compared to the 6 years old (12170 lux).Dormann et al (2020) reported that the reduced light availability would decrease the plant species richness.

Weed diversity index
The high diversity of weed species represented by Shanon's (3.14) for the 6 years old oil palm plantation (Table 3).The higher diversity of weed species on the 6 years old oil palm plantation than 8 years old occurred in response to transmitted gap light (Jia et al 2015).Oil palm plants can cause light limitation in shade-intolerant species that suppress the plant growth while increasing growth of the tolerant species.The different seed remnant species may have varying responses to the radiation gradient that stimulates seed germination and plant growth (Kothari et al 2021).
In each plot (0.5 m 2 ) the number of weed individuals ranged from 9 to 75.The number of weed individuals in the 6 years old oil palm plantation ranged from 22 to 75, with mean value of 53.60.This number of individuals is higher than the 8 years old oil palm plantation that ranged 9 to 39, with a mean value of 24.10 (Table 3).This result was similar to Hilwan and Santosa (2019) that reported the oil palm plantation caused biodiversity loss up to 60% than the prior plants and the older plantation would reduce more.In the older oil palm plantation, the main plant would grow rapidly and take more space that the combining several cover crop species with partitioning of physical space could govern the other number of individuals (Liao et al 2013).
The number of individuals in each plot affected the biomass production in the oil palm plantation.The biomass production on 6 years old oil palm plantation (7845.50kg/ha) was higher than 8 years ol oil palm plantation (6264.00kg/ha).The result was higher than Ramdani et al (2017) that reported the biomass ranged 6.10 ton ha -1 to 6.49 ton ha -1 .The biomass production decreases in older oil palm plantation age related with the micro environmental changes in the oil palm plantation, especially soil characteristics (Le et al 2023), light and shade trees degree (Akbar et al 2021).

Forage potential
Based on the botanical composition, there are several types that can be consumed by livestock including Paspalum conjugatum P.J. Bergius, Digitaria ciliaris (Retz.)Koeler, Axonopus compressus (Sw.)P. Beauv and Cynodon dactylon (L.) Pers (Table 4).Paspalum conjugatum has the highest important value index at several plantations, such as coffee (Hartoyo et al 2023) cassava (Qomariyah et al 2014) and coconut plantation (Ngawit and Farida 2019).Roba et al (2017) reported that shade plants have an effect on increased pH, organic carbon, total nitrogen, cation exchange capacity, and kalium.The high tolerance of P. conjugatum on highly acidic soil conditions is commonly found amongst cover crop plants (Lestari et al. 2019).The weed rank as forage was determined based on plant palatability for ruminants that the highest palatable was grasses, legume, than other plants (Treydte et al 2013).Another consideration are the concerns of bloat and some plant toxicities (Marsalis et al 2020).

Conclusion
The weed botanical composition and diversity level were affected by oil palm plantation age.The older oil palm plantation reduces the number of weed species and diversity level.The estimation of weed production ruminant forage was dominated by grass that had up to 1.87 ton ha -1 of fresh biomash.

Table 1 .
Weed botanical composition of under the different age of oil palm plantation

Table 2 .
Weed species distribution

Table 3 .
Weed diversity and biomass production

Table 4 .
Potency of fresh forage production