Response of Immature Oil Palm Growth and CO2 emission on Intercropping System After Replanting

One of the problems in smallholder oil palm plantations was the financing for replanting and loss of revenues during immature oil palm period. One alternative to the problem was the development of an adaptive plant system through intercropping crops planted among immature oil palm crops. The research was conducted in banjar seminai village, dayun subdistrict, siak regency, Riau Province on May to October 2017. The study used a factorial randomized block design with three replications. Annual crops treatment consists of corn, soybean, eggplant and chili. The results showed that there was positive response of oil palm height on intercropping systems. Corn intercropping plants increased the height of oil palm crops. The intercropping plants had no significant effect on the number of leaf midrib and the width of oil palm canopy. Monoculture oil palm crops without intercropping produced average emissions of 8.78 t CO2 ha-1yr-1. Oil palm intercrop with eggplant and soybean produces the highest CO2 emissions of 10.4 and 10.2 t CO2 ha-1yr-1, while oil palm in intercrop with chili produced the lowest CO2 emissions of 8.66 t CO2 ha-1yr-1.


INTRODUCTION
The palm oil industry was one of the main industries that drived economic and strategic wheels in Indonesia. Economically oil palm crop began to be replanted after 25 years age and above. At this time some oil palm plantations in Riau Province have been more than 25 years old. Therefore, oil palm plantation replanted activities need to be done. According Manurung et al. (2015), around 53% of the total area of oil palm plantations in Riau Province is still awaiting rejuvenation due to capital constraints and replanting plant material. Replanting was an unproductive old crop replacement with new plants. Replanting become very important to maximize production. According to PPKS (2008), the main consideration for oil palm replanting were: (1) The age of the plant that will and has reached the economical age of about 25 years old, with low productivity or under 13 tons of FFB ha -1 year -1 ; (2) The higher of oil palm tree the more difficult to harvest; (3) With new plants, new production will be higher. According to Pahan (2012) and Manurung et al.( 2015), the problems faced by farmers to do the replanting was related to the need for investment and operational costs. The constraints faced by smallholders in replanting were limited capital for replanting, fear of losing income sources during replanting, lack of knowledge of farmers about replanting techniques and lack of access to certified seedlings.
The problem of financing and loss of income during the oil palm replanting, it need to find a solution. One alternative was the development of an adaptive plant system through intercropping plants grown among immature oil palm plants. According to Suwondo dan Saputra (2012), rejuvenation with the intercropping model is to combine oil palm plants with annual crops as a substitute for land cover crops. This model will provide beneficial added value (Armaini et al. 2012). According to (Manurung et al. 2015), intercropping models after replating can increase income before oil palm plants produce (0-3 years). Furthermore Suherman et al. (2018), the application of intercropping after replanting is an effort to optimize land by utilizing open space between oil palm plants.

MATERIALS AND METHODS
The research was conducted in banjar seminai village, dayun subdistrict, siak regency, Riau Province on May to October 2017. Raw materials used were 1 year old of immature oil palm, seeds of corn, soybean, eggplant and chilli, manure, fertilizer (Urea, TSP and MOP). The tools used were farming tools, GPS, Infrared Gas Analyzer (IRGA) LI-820 model, LICOR Inc. computer.
The study used a factorial randomized block design with three replications. The intercropping treatment consists of corn, soybean, eggplant and chili. Each experimental unit consisted of 10 plant samples. The experimental area was 4 800 m² with 400 m² of each experimental plot ( Figure 1). The design model used was: (1) with: Y ijk = observation response on i-level of plant type treatment, and j-level of repeat µ = average Ai = influence response of i-level of plant type treatment Ƭj = influence response of j-level of repeat € ijk = error

Hariyadi et al. Int J Oil Palm
and measurements of oil palm growth were carried out on variables: plant height, number of leaf midrib and canopy width.
Measurements and observations of CO2 emissions were carried out using the infrared gas analyzer (IRGA) device model LI-820, LICOR Inc. USA with a covered chamber. The chamber used was made of PVC pipe with 25 cm diameter and 25 cm height. Emission measurements were conducted once a month in the morning and afternoon. The length of measurement for each point was ± 150 seconds (2.5 minutes). The linear relationship between measurement time and CO2 concentration was used to calculate the CO2 flux according to Madsen et al. (2009).

Growth of Oil Palm Crops
The growth of oil palm plantations, until the third month of observation showed good results. Growth of immature oil palm plants in the intercropping model is shown in Figure 2-5. There was positive response of oil palm height on intercropping systems. The intercropping of corn significantly affected the plant height of oil palm. The planting of the intercrops did not significantly affect the addition of palm leaf and wide palm oil canopy (Table 1, 2, 3). These results are supported by the results of the study of Syakir et al. (2015) that the rejuvenation model with intercropping in the form of corn had a significant effect on the height of young oil plants aged 3 and 6 months after planting.
The high response of oil palm plants through the pattern of intercropping with corn is caused by the activity of microorganisms in the roots of corn plants that can support the growth of oil palm plants. Corn root contains endophytic microorganisms which can help provide plant phosphorus (Hafsan et al. 2017), and produce IAA growth hormone that can be used for plant growth (Retnowati et al. 2018). Furthermore Misbahuddin et al. (2018), states that the increased activity of microorganisms in the rhizosphere region is strongly supported by optimum soil    temperature conditions. The corn plant used in the intercropping system has a wider canopy compared to other commodities so that it can improve the microclimate around the oil palm plantations. According to Manurung et al. (2015), replanting with intercropping models using corn plants will produce oil palm plants with equitable growth.

The Effect of Intercropping on CO2 Emissions in Oil Palm Plantations
The planting of monoculture palm oil without intercropping plants resulted in average CO2 emissions of 8.78 t CO2 ha -1 yr -1 . Planting intercrops can increased CO2 emissions in oil palm plantations. Oil palm intercrop with eggplant and soybean produces the highest CO2 emissions of 10.4 and 10.2 t CO2 ha -1 yr -1 . While oil palm in intercrop with chili produced the lowest CO2 emissions of 8.66 t CO2 ha -1 yr -1 ( Table 4).
Increased of CO2 emissions in oil palm crops with intercropping plants can be attributed to root activity from intercropping plants. Roots were a preferred place for

Int J Oil Palm
Hariyadi et al.  Oil palm 9.2 11.9 13.7 1.5 Oil palm + chili 9.2 11.8 13.8 1.5 Oil palm + eggplant 9.2 11.8 13.6 1.5 Oil palm + corn 9.2 12.1 13.8 1.5 Oil palm + soybean 9.2 11.9 13.8 1.5 many microbs compared to bulk soil (Peterson 2003). It increased microbial population and microbial activity around roots. This increased as a result of high concentrations of nutrition, C-labile and the influence of root exudates (Kuzyakov et al. 2000;Misbahuddin et al. 2018). Increased of population and microbial activity resulted in increased microbial respiration and CO2 production (Subke et al. 2004).

CONCLUSION
There was positive response of oil palm height on intercropping systems, intercrops did not significantly affect the number of midrib and the width of oil palm canopy and intercrops had affected on increasing CO2 emissions in immature palm plantations