Evaluation of Potential for Ethanol Production from Rice Straw Using Satellite Data

Purpose of this study is to estimate rice yield on a plot basis with use of satellite data and field investigation data and to calculate potential quantity of rice straw to be utilized as a raw material for biofuel production in Bali, Indonesia. In addition, for continuous supply of rice straw by farmers to a biofuel producer, it is absolutely necessary to investigate farmer’s interest, behavior and potential issues to solve. For this investigation, an interview was made to the subak heads. The subak is a traditional social organization consisting of farmers for managing irrigation and agriculture in the farmers’ village. The created estimation equation of rice yield had NDVI from SPOT satellite data as a predictor and was significant at 1% level. Based on the rice yield estimated through the equation and the paddy area, quantity of rice straw to be available and quantity of bioethanol to be produced were estimated. In case of Kediri, the rice straw quantity was 42,274 t/year and the ethanol quantity was 12,682 kl. On the other hand, the handling of rice straw after harvesting was leaving/putting back to soil or burning, which accounted for 76% of the rice straw. Concerning a price of rice straw, about 60% of farmers expressed their willingness to sell at 100 rupiah (1 cent US$) per kg, and about 88% including people saying high probability seemed to think this price would be as an adequate level of sales price. Through the interview work, it becomes clear that, when some issues such as price of rice straw are settled, farmers are positive to selling of rice straw for production of biofuel. For realizing bioethanol production from rice straw, there still remain some items to be studied further such as production process, transportation and storage system and costs. The result of our study suggests that a proposal for improvement of stable production can be made through rice yield estimation and monitoring using satellite data and that rice straw can be supplied as a promising resource of raw material for bioethanol production. This is considered to contribute the promotion of activity to reach the national goal of bioethanol production in future.


Introduction
Recently, use of biofuel has been actively promoted from viewpoints of reduction of greenhouse gas discharge and creation of new jobs in developing countries (Ramamurthi et al., 2016;Quispe et al., 2017;Singh, 2016).On the other hand, the biofuel from food such as grain crops has caused much controversy among various international organizations like OECD and FAO, researchers and experts in many countries about substantial influence over the agricultural market including sharp rise in price due to competitive relation between the biofuel and the food supply.This controversy and analysis of influence to change in price and production of agricultural products and also the food security are described in many reports such as De Gorter et al. (2016), Enciso et al. (2016), andMcFarlane (2016).In addition to the influence to market, production and food security, an environmental impact is pointed out as a serious problem.Biofuel production causes change of the land use which induces change of GHG discharge and change of environment.Such changes are more serious particularly in South America and Southeast Asia.For example, in Brazil, Amazon rainforest is destroyed and converted to the farm land to increase production of crops as a raw material for biofuel production, which results in serious negative influence over to the environment.
In Southeast Asia, more of plantation of oil palms and cassava and also cultivation of Jatropha change the land use and increase the environmental burden.Serious concern has been paid to this change (Almeida et al., 2016;Permpool et al., 2016).Under the above situation, more attention has been drawn to the use of by-product resources instead of food resources for biofuel production.Among several possible by-product resources, rice straw is expected to be promising from the fact that rice straw is very little used now and price is rather so inexpensive.In Indonesia having the most population in the ASEAN countries, the presidential decree was announced in 2006 relating to use of biofuel where the target was so described as 15% of total fuel to be consumed in transportation shall be bioethanol by 2025.Indonesia is the 3rd largest producer of rice in the world and, when the potential of bioethanol production from rice straw is calculated based on the Indonesian statistical information about rice planted area, the amount of biofuel to be produced accounts for 7.2%-10.7% of the national goal.This figure raises expectation to rice straw for production of biofuel, promotion of CO 2 removal and creation of new jobs.
There are several effects expected to be realized through introduction of biofuel which include reduction of environmental burden, promotion of regional economy and increase in agriculture and energy security.In order to confirm these effects, evaluation on each effect based on concrete and quantitative data and indexes is necessary.One of methods for the evaluation is, for example, LCA (Life Cycle Assessment) analysis which is widely used in the world for calculating the effect of environmental burden removal.It, however, has some isuues such as time consuming work to collect inventory data for the analysis.For the evaluation of effects, if data on actual land use situation and production volume covering wide area is available, it is expected to be able to contribute to improvement of the evaluation accuracy.
Since 2009, we have been conducting research to estimate rice production volume precisely on each plot basis with use of spatial information such as satellite data in West Java and also Bali, in Indonesia (Hongo et al., 2014;Nuarsa et al., 2012;Shikata et al., 2013).As to a rice straw, most of rice straw is left in rice field or putting back to soil or burnt in the field, so the ratio of utilization of rice straw is very low.
For promoting further the utilization of by-product resources, it is important to evaluate both abundance of the by-product resources and quantity available for utilization as precisely as possible.It is also necessary to make an appropriate arrangement and system for the utilization which carefully considers local environment and social characteristics at a site for practical utilization of the resources.Remote sensing can evaluate the abundance on each pixel basis which makes it possible to do a micro-scale evaluation and also cover wide area at the same time.In addition, in developing countries, various data and information necessary to evaluate a site for biofuel plant construction is often not fully digitized and updated.This means that cost for preparation and maintenance of the necessary data and information is not negligible.Remote sensing is expected to contribute to solution of this issue.
Moreover, in Indonesia, the agricultural insurance was started for purpose to realize the sustainable agriculture in the future.For supporting promotion of the insurance, we plan to start a research project from 2017 where new method for damage assessment of rice with use of spatial information including remote sensing data is to be developed.For the damage assessment which is a core part in the agricultural insurance, the estimation and evaluation of rice yield is conducted using spatial information.The estimated yield data can be converted to potential quantity of rice straw.In other words, the data which is obtained with use of spatial information can be used for both the realization of sustainable agriculture through agricultural insurance and the biofuel production.This multiuse of data will decrease costs relating to data acquisition and usage.
For a purpose to evaluate if there would be possibility to realize the production of biofuel from rice straw in Indonesia, particularly from viewpoint of potential quantity of rice straw and supply of rice straw to the production site, we conducted research on estimation of rice yield and calculation of abundance of rice straw to be used as raw material for biofuel production.In addition, since the supply of rice straw is so important for continuous and constant production, we conducted an interview to farmers to know their interest, intention and possible issues to be solved.

Study Area
The research was conducted in Bali, Indonesia (Figure 1).88% of this island is for agriculture and, when compared with 47% as an average of the whole Indonesia, this number is very high.In Bali, there are about 149,000 ha of paddy and an average yield is 5.8t/ha which is rather higher than that in other areas.It means that Bali can have more rice straw available as unused resources for ethanol production and has good potential for production of biofuel.Bali has 8 regencies one of which is Tabanan regency where our study area is located.The formula for estimation was verified through 10-fold cross-validation by random data partitioning and predictive error of the formula was calculated using the estimated yield and the field investigation data.Lastly, the estimation formula was applied to the SPOT data.Visualization of the result was made to show spatial distribution of yield.

Estimation of Potential Quantity of Rice Straw and Ethanol
Potential quantity of rice straw to be available in a year (DM: t/year) was calculated as below: dm = Yi × (ratio of unhalled rice to straw) × (1 -water content) (4) DM = dm × (paddy field area) × (number of harvesting per year) (5) Where, dm is a potential quantity of rice straw expected to be obtained per harvesting (t/ha), and Yi is an estimated production amount (t/ha).
Ratio of unhulled rice to straw was set as 3.19 on basis of the field investigation result, and the water content was set to be 60%.Paddy area was calculated on basis of GIS of the paddy field.
An average number of harvesting time per year is almost 3 times a year, depending of places and year, sometimes 2 times a year.Therefore, in average, 2.5 times was used for the calculation.
Potential quantity of bioethanol available from rice straw (Be: kl) was calculated through the following formula, Be = DM × (unused ratio) × (conversion efficiency) (6) Where, the unused ratio was set as 100%, considering the fact that rice straw was very little utilized and the conversion efficiency is set as 30% (This percentage is the theoretical value of ethanol production efficiency from cellulose through saccharification process).

Extraction of Paddy Field Ready for Harvesting
The study area was classified to 40 classes by the unsupervised classification method.Figure 3 shows the classified result.The 40 classes have different land use situation including paddy at panicle formation stage, heading stage, ripening stage, harvesting stage and non-paddy.The investigation work was done only in the paddy fields which were just before harvesting.So, 5 classes where the investigation was done were judged as the paddy at harvesting stage and extracted.Then, the map of paddy ready for harvesting stage was created (Figure 4).The paddy at harvesting stage was 12.5% of total paddy in the study area.
On each of pixels including this stage of paddy, estimation of rice was made as is described in section 3.2 below and, in following section 3.3 below, average potential quantity of rice straw per hectare was calculated and then, putting the rice straw quantity into an equation to get ethanol amount, estimation of ethanol to be produced was conducted.10).In addition transportin troubles or to them (F Although gave posit producers, org to this analysis So, we made an was given to th uld be acceptab s too low.Mai t 100,000 rupi g on type of jo 2).

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