Effects of EFB mulch application during extreme drought conditions (2014-2015) on FFB yield of oil palms planted on lateritic soil in Belitung Island, Indonesia

Oil palm is a perennial crop whose vegetative growth and yield production are affected by many factors, including climate. The climate could limit the potential yield of oil palm. Extreme drought occurred in 2014-2015, resulting in a drop in FFB yield in almost every region, particularly in the Belitung region. The observation of the effect of EFB application on FFB yield during extreme drought conditions in 2015 was conducted in the EFB and Fertilizer trial plot. The study was conducted in 2004 planting, planted on lateritic clay soil (Lithic Hapludult/Tampin Series) in Belitung Island, Indonesia. The design of the trial was a split-plot factorial trial design with the main plot was EFB mulching with three rates, E1=0 ton/ha, E2=30 ton/ha, and E3=60 ton; the subplot was N and K fertilizer, three rates of N (N1=0 kg of Urea/palm, N2=2 kg of Urea/palm, and N3=4 kg of Urea/palm) and two rates of K (K1=0 kg of MOP/palm and K2=4.5 kg of MOP/palm). Application of pressed EFB mulching on lateritic soils increases cumulative FFB yield significantly by 13-19% higher after 6 years of continuous application. Pressed EFB mulch has a significant effect after 3 years of constant application. There was an interaction between EFB mulching and N treatments, which implied that the presence of both treatments had significantly shown better results. Coincidentally, as the trial period went through a severe drought period, EFB mulch could sustain the FFB yield after the drought and reduce the effect of severe drought significantly between 25-44% (30 ton/ha) and 35-58% (60 ton/ha) higher than without EFB mulch within 2-3 years after the drought.


INTRODUCTION
Oil palm is a perennial crop whose vegetative growth and yield production are affected by many factors, including climate.The climate could limit the potential yield of oil palm (Goh, 2000).The optimum climate condition for oil palm to grow and produce good yield has been defined by many oil palm experts.The optimum temperature for oil palm ranges from 240C to 280C (Corley & Tinker, 2016).The optimum annual rainfall is between 2000 to 2500 mm; its monthly rainfall distribution is evenly throughout the year and more than 100 mm.The optimum sunshine hour for oil palm is 5-7 h/day, with 15 MJ of solar radiation and low VPD (Hartley in 1988 andGoh in 2000, in Corley, 2016, p.64).
The difference in climatic conditions could lead to different growth, FFB yield production, and cropping pattern of oil palm in particular locations (Corley, 1976;Ooi et al., 2004;Lim, 2011, p.6). Rainfall is one of the most important climatic factors because many past research has used rainfall data to see the correlation with the FFB yield.Rainfall (in terms of water deficit) has been recognized to be closely associated with various physiological and developmental processes of oil palm, such as flowering and bunch production (Lim, 2011).During very dry conditions, the production capacity of oil palm could be reduced by up to 10-30%, as Patterson (2018) reported.Another study reported that for every 100 mm of water deficit, the production was lower by 10% of its potential yield (Corley, 2016).
El Nino is the term for a climatic phenomenon where there is a reversal of normal weather in which the temperature is higher in the Western Pacific than in the Eastern Pacific, which affects the rainfall distribution, with less rainfall in the former and more rainfall in the latter (Lim, 2011).The occurrence of El Nino has been recorded since 1983, and the most recent was in 2015.According to Azlan et al. (2016), El Nino in 2015 was one of the strongest El Nino besides in 1983 and 1997/1998.They also reported that the plot with irrigation had 44% to 95% higher FFB yield compared to the non-irrigated plots after 1997/1998 El Nino and the effect on FFB yield reduction could be up to 2 years after the El Nino, which had been reported earlier by Caliman and Southworth (1999) on the lagged of FFB production due to water stress.El Nino is unavoidable, but we could minimize the effect by implementing some best management practices such as irrigation (high cost), good nutrition input, by-product application, and maximizing soil cover.EFB, or empty fruit bunches, is one of the by-products of oil palm used as mulching to provide organic matter and nutrients and retain soil moisture.EFB production could be up to 25% of FFB production, depending on the mill's efficiency.Since EFB contains nutrients, primarily N and K, it has been treated as organic fertilizer.Some past study shows that applying EFB could improve FFB yield and soil properties (Che, 2020).
In Belitung, an extreme drought occurred in 2011, 2014, and 2015 and affected the region's oil palm growth and yield.The study was originally conducted to determine the effect of EFB mulching and N, K fertilizer application on the growth and yield of oil palms planted on lateritic soil.However, since the extreme drought during the trial period, a study on the effect of EFB mulching application on withstanding the extreme drought is more relevant and discussed in this paper.

Study site:
The trial was carried out on oil palm (DxP), planted in 2004 on lateritic soil (Typic Hapludult) on flat to undulating terrain in Belitung Island, Indonesia.

Treatment:
The study design was split plot factorial with EFB mulching as main plots and N and K fertilizer as subplots.The main plot consists of 3 level treatments namely E1 (0 ton/ha of EFB), E2 (30 ton/ha of EFB), and E3 (60 ton/ha of EFB), while subplot consists of 3 levels N (N1 = 0 kg/p, N2= 2 kg/p, N3= 4 kg/p of Urea) and two levels of K (K1=0 kg/p, K2=4.5 kg/p of MOP).The detail of the treatment is presented in Table 1.EFB mulch used in the trial is pressed EFB.

Yield Response
The yearly FFB yield from 2012 to 2017 is presented in Table 2.The result showed that the response of EFB mulching on FFB yield was noted after three consecutive years of EFB applications.This result was slightly different from previous findings by Loong et al. (1988), which reported the response of EFB mulching on FFB yield after two consecutive years of mulching.The slower response to EFB might be due to the use of pressed EFB, which has lower nutrient content than normal EFB used in other trials.
In addition, the occurrence of dry weather before (in 2011) and during the trial (in 2014 and 2015) might also contribute to the slower response of EFB mulching.The cumulative FFB yield data is presented in Table 3.The result shows a significant increase in FFB yield with the application of EFB or N fertilizer.However, a significant interaction between EFB and N fertilizer was noted in response to FFB yield (Graph 1).Graph 1 shows that although both EFB mulching and N fertilizer treatment significantly responded to FFB yield, a substantial result was achieved when both N and EFB were applied.This is probably related to the fact that the decomposition of EFB requires some amount of N. For other yield parameters, the application of N fertilizer and EFB mulching gave a significant response to bunch number; application of N fertilizer significantly increased the bunch number, although there was no significant difference in different rates of N. Similarly, the application of EFB mulching significantly responded to bunch numbers.This result indicates that the application of EFB mulching and or N fertilizer influenced more bunch number than bunch weight.

Effect of drought on FFB yield
Graph 2 shows the annual rainfall and potential moisture deficit of 2011-2018.The potential moisture/water deficit was calculated using the established equation by Lim et al. (1994); the calculation was based on AWC of 100mm/m and PET of 150 mm/month.Graph 2 shows that drought periods were noted before and during the trial.The drought period with more than 100mm of potential water deficit occurred in 2011 (251mm), 2014 (309mm), and 2015 (335mm).The highest potential water deficit was noted in 2014 and 2015, categorized as severe El Nino.As expected, the drought period affected the production of FFB yield, as presented in Graph 3. The FFB yield dropped from an average of 26.81 tons/ha in 2012 to 20.33 tons/ha in 2013.These were likely due to drought in 2011 and 2012, as Caliman and Southworth (1999) reported that water stress pronounced lagged FFB production.They reported that water stress would affect three stages of the FFB production process, namely abortion (about 8-11 months after drought), sex differentiation (about 19-25 months after the drought), and floral initiation (about 33-36 months after drought).The drop in FFB yield was also noted in 2016, after the severe drought in 2014 and 2015.The effect of the 2014 and 2015 drought continued in 2017; the yield was stagnant.
Despite the drop in FFB yield, Graph 3 shows that application of EFB reduces the effect of drought on FFB yield.Plot with EFB application had significantly higher FFB yield than non-EFB plots after three years of continuous EFB application.Based on Table 4, during the drought (2015), the FFB yield in plots with EFB application had 25-34% higher FFB than in non-EFB plots.After the drought (2016-2017), the FFB yield of EFB plots was 58% higher than non-EFB plots.Cumulatively (Table 3), plots with EFB mulch had 13-19% higher cumulative FFB yield than plots without EFB mulch.

CONCLUSIONS
Application of pressed EFB mulching in 6 consecutive years on lateritic soils increases cumulative FFB yield significantly by 13-19% higher.Pressed EFB mulch has a significant effect after three years of continuous application.There was an interaction between EFB mulching and N treatments, which implied that the presence of both treatments had significantly shown better results.
Coincidentally, as the trial period went through 2-3 years of the severe drought period, EFB mulch could sustain the FFB yield after the drought and reduce the effect of severe drought significantly between 25-44% (30 ton/ha) and 35-58% (60 ton/ha) higher than without EFB mulch.

Graph 3 .
Annual FFB yield of EFB mulching Treatment and Control.

Table 3
Cumulative FFB yield and Bunch Number and mean bunch weight 2012-2017

Table 4 .
The comparison of FFB Yield in EFB vs. Non-EFB Plot