Keywords

1 Introduction

There is an increasing awareness of the impacts of climate change on rice production, especially, in Asian countries. There are two main reasons for this trend. The first reason is the important contribution of Asian rice farming to employment and economic growth in Asia (Bandumula, 2018; Chauhan et al., 2017). The second one is Asia the world largest rice producer and rice consumer (Chauhan et al., 2017). In turn, possible threats to Asian rice production can affect a large fraction of the world population in terms of food security, livelihoods, and economic growth (Chauhan et al., 2017).

Among Asian countries, Indonesia is the third-largest rice producer and the third-largest rice consumer in the world (Setyanto et al., 2018). As such, Indonesia is an interesting place to understand the impacts of climate factors on Asian rice production. It is also acknowledged that Indonesian temperature, as well as Asian temperature, is relatively close to rice critical temperature, leaving Indonesia’s rice production in danger under changing climate (Chauhan et al., 2017; Lobell & Gourdji, 2012; Lobell et al., 2008, 2011; Serraj & Pingali, 2018). Owing to this, some scholars have investigated several issues of Indonesian rice production. For instance, an existing study (Naylor et al., 2007) discussed the possible impacts of climate change on rice production in West Java and Bali. Other existing studies (Falcon et al., 2004; Naylor & Mastrandrea, 2009) estimated the impacts of El-Niño Southern Oscillation (ENSO) on rice production.

Other studies also discussed significant issues such as the impacts of climate on Indonesian rice yield (Amalo et al., 2017; Kinose & Masutomi, 2019; Kuswanto et al., 2018; Yuliawan & Handoko, 2016), modeling the rice production (Karim et al., 2019; Utami et al., 2019), the impacts of land-use change on rice production (Makbul et al., 2019; WorldBank, 2008), and adaptation of the rice farming to climate or seawater intrusion (Bahri, 2017; Rondhi et al., 2019; Sembiring et al., 2020; Sutrisno & Setyono, 2017; Utami et al., 2018).

Existing studies arguably provide useful information to investigate possible threats to Indonesian rice production. However, existing studies that analyzed the impacts of climate on Indonesian rice yield are very limited and none of the existing studies have analyzed the impacts of climate factors on three main rice provinces including West Java, Central Java, and East Java. Since the three Java provinces are responsible for half of the Indonesian rice production (BPS, 2020), this study specifically aims to investigate the impacts of climate factors on rice yield in the three main rice provinces.

Besides the aforementioned issues, Indonesian rice studies also discussed the perennial rice cropping system, so-called the salibu. This is important as most rice farmers have suffered from high-production costs such as labor and pesticide expenses (Budianti, 2021; Fitri et al., 2019; Marpaung et al., 2022; Yamaoka et al., 2017). Those studies explained that the perennial rice cropping system (the salibu) can increase rice yield, decrease short-duration growth, and decrease production cost (Budianti, 2021; Fitri et al., 2019; Marpaung et al., 2022; Yamaoka et al., 2017).

While several studies (Bahri, 2017; Khairulbahri, 2021; Welch et al., 2010) claimed that high temperatures associated with climate change may decrease Indonesian rice yield, the salibu method leads to higher rice yield recently (Budianti, 2021; Marpaung et al., 2022; Paiman, 2021). So, this study also aims to assess whether the salibu method enables rice farmers to escape from the negative impacts of high temperatures. In doing so, after the impacts of climate factors in West Java, Central Java, and East Java are assessed, the climatic benefit of the salibu is examined. In this study, the climatic benefit occurs once the salibu method can negate the negative impacts of climate factors on rice yield.

In fulfilling the research aim, this study first introduces relevant studies and the research aim. Next, the types of collected data and used methods in this study are described. Following this, this study discusses the results and explains important findings. In the end, some concluding remarks are described accordingly.

2 Materials and Methods

2.1 Three Indonesian Provinces: West Java, Central Java, and East Java

These three provinces are situated in Java, the most populated island in Indonesia. Together, these provinces are the main buffer rice stock in Indonesia (BPS Jawa Tengah, 2021; BPS Jawa Timur, 2021). The main buffer stock means these provinces provide rice not only for their local population but also to export their rice to their neighboring provinces.

West Java lies between 5°50ʹ–7°50ʹ South Latitude and 104°48ʹ–108°48ʹ East longitude (BPS Jawa Barat, 2021) and its capital is Bandung, so-called Paris van Java. West Java consists of 18 regencies and 9 cities with a total area and population density of about 35,377 km2 and 1,365 persons/km2, respectively (BPS Jawa Barat, 2021).

West Java has average annual rainfall between 2,000–4,000 mm/year, making this province the highest annual rainfall compared to the other Java provinces. Agriculture contributes to about 20% and 9% of the total employment and the economic output, respectively (BPS Jawa Barat, 2021) (Fig. 1).

Fig. 1
A map of Indonesia indicates three main Java provinces with the help of an arrow. These are West Java, Central Java, and East Java.

Source Google Maps (n.d.)

Indonesia and three main Java provinces (West Java, Central Java, and East Java).

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Central Java geographically stretches along the equator between 5°40’ to 8°30’ South Latitude and 108°30ʹ to 111°30ʹ East Longitude (BPS Jawa Tengah, 2021). Its capital is Semarang with a total area and population density of about 32,801 km2and 1,113 person/km2, respectively (BPS Jawa Tengah, 2021). Central Java has an annual rainfall of about 2,500 mm/year, leading to, at least, three rice growing seasons throughout the year. Agriculture contributes to 12.5 and 29% of the total economic output and the total employment, respectively (BPS Jawa Tengah, 2021).

East Java is the easternmost Java province and lies between 7.12 ‘South Latitude—8.48’ South Latitude and between 111.0 ‘East Longitude—114.4’ East Longitude (BPS Jawa Timur, 2021). Its capital is Surabaya, the Indonesian second largest city after Jakarta. East Java has a total area and population density of about 47,800 km2 and 851 persons/km2, respectively (BPS Jawa Timur, 2021). The annual rainfall is about 2,800 mm/year, and the average temperature in 2020 was 27.3 °C. Moreover, agriculture contributes to 35% and 20% of the total employment and the total economic output, respectively (BPS Jawa Timur, 2021).

Based on previous paragraphs, it can be concluded that agriculture has an important contribution to employment and economic growth in given Java provinces. So, this study can give important insights for policymakers in supporting important agricultural contributions to employment and economic output.

2.2 The Salibu and Ratoon Methods

As seen in Table 1, rice growth can be categorized into three important stages including the vegetative, the reproductive, and the ripening stages (Yoshida, 1981).The length of different stages of rice growth is varied between long- and short-duration growth varieties. But the main difference is in the length of the vegetative stage (Moldenhauer & Slaton, 2001). While the length of the vegetative stage is about 30 days for short-duration rice varieties, long-duration rice varieties have about 60 days of the vegetative stage. So, in total, the medium duration growth of rice is 115–135 days, assuming farmers apply the transplantation method (Moldenhauer & Slaton, 2001; Yoshida, 1981).

Table 1 Three stages of rice growth
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The ratoon method has been known by rice farmers for a long time (Fitri et al., 2019; Juanda, 2016). In the transplantation method, farmers need land preparation and new seed for each new growing season. In contrast, the ratoon method aims to cultivate parent rice for new growing seasons without land preparation and without new seed. Although the ratoon method may save cost and farming time, this method has been neglected due to its low yield compared to its parent yield (Adji, 2022; Fitri et al., 2019; Pasaribu, 2016; Pasaribu & Anas, 2018).

The salibu method aims to improve the ratoon methods as it can sustain or increase rice yield compared to its parent yield. The salibu method is coined by other scholars (Erdiman & Misran, 2013) when they supervised farmers in North Sumatera. After successful harvesting seasons, the salibu method has been widely applied in other Indonesian provinces (Fitri et al., 2019).

The main difference between the two is in the ratoon method, farmers would not prune parent rice as new rice plants, whereas farmers in the salibu method would prune parent plants as new rice for the next growing seasons. Usually, after 5–15 days of the harvesting seasons, farmers would prune the parent rice (Pasaribu, 2016).

Because pruning the parent rice occurs after the rice has stems, roots, and tillers, salibu method combines the vegetative and reproductive phases. In turn, the total growing seasons of rice, after the salibu method, would be less than 90 days (Fitri et al., 2019; Marpaung et al., 2022; Paiman, 2021).

2.3 Data Collection

There are two types of collected data: climatic data and non-climatic data. Climatic data such as temperature and rainfall were collected from the Indonesian Bureau of Meteorological and Geophysics (BMKG). Non-climatic data such as rice yield were collected from the Indonesian Statistics Bureau (BPS).

Collected data are statistically analyzed to estimate relationships between rice yield and climate factors. Rice yield could be affected by climate factors including maximum temperature, minimum temperature, and rainfall (Khairulbahri, 2021; Lobell & Gourdji, 2012; Welch et al., 2010). So, this study applies linear regression models to relate rice yield to temperature, rainfall, and time trends (Lobell & Burke, 2010). High-yield rice varieties are based on technological progress that is encapsulated in improved rice varieties (Bahri, 2017; Gnanamanickam, 2009; Lobell & Burke, 2010). As another study (Khairulbahri, 2021; Lobell & Burke, 2010), this study uses time variables as a representation of the technological progress of improved rice varieties. Equation 1 shows a statistical model that estimates relationships between climate, time variables, and rice yield as follows:

$${\text{Yi}} = {\text{c}}_{1} + \alpha_{1} {\text{Ai}} + \alpha_{2} {\text{Ai}}^{2} + \alpha_{3} {\text{Ti}} + \alpha_{4} {\text{Ti}}^{2} + \alpha_{5} {\text{Ta}} + \alpha_{6} {\text{Ta}}^{2} + \alpha_{7} {\text{Ri}} + \alpha_{8} {\text{Ri}}^{2} + \varepsilon_{1}$$
(1)

  • Yi = rice yield (tons/ha) in year t;

  • Ai = time variable as a representation of the technological change of rice (a year since 1993);

  • Ai2 = squared time variable as a representation of the technological change of rice;

  • Ti = minimum temperature in Celsius in year t;

  • Ta = maximum temperature in Celsius in year t;

  • Ri = seasonal rainfall in mm/year in year t;

  • c1 = constant;

  • εi = error.

For time variables, Ai and Ai2, it was set as 1 starting since 1993 (in 1993 and 2019, Ai = 1 and Ai = 27 respectively). The statistical software Eviews© version 7 was used to conduct several statistical tests assessing the adequacy of a statistical model rice yield.

The performance of selected statistical models will be obtained and assessed by Ordinary Least Square (OLS) and F-tests, respectively. Owing to this, selected statistical models must conform to normality assumptions (Greene, 2003; Gujarati et al., 2012). Furthermore, reliable statistical models have to be fulfilled relevant assumptions such as homoscedasticity, uncorrelated predictors, and no serial correlations (Greene, 2003; Gujarati et al., 2012; Lobell & Burke, 2010).

To obtain the correct model specification, the general to simple approach is applied as it is a suitable practice in modern analysis (Greene, 2003; Quiroga & Iglesias, 2009). In principle, the general to simple approach asks scientists to collect all possible independent variables and regressed them with the dependent variable step by step to obtain the best statistical model(s). By applying the general to simple approach, we can prevent ourselves from abandoning possible significant independent variables, leading to the best statistical model (Greene, 2003; Quiroga & Iglesias, 2009).

3 Results and Discussion

3.1 Observed Data

Table 2 shows the total rice production in West, Central, and East Java, the three main rice provinces in Indonesia. In general, the three provinces have similar rice production, rice yield, and harvested areas. It is also shown in Table 2 that the total rice production of the three main rice provinces is about 50% of the Indonesian total rice production, showing the importance of the three provinces in Indonesia’s rice production.

Table 2 Rice production, rice yield, and harvested areas in West Java, Central Java, and East Java
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Another similarity between the three provinces is the dominance of irrigated farming areas (95%) instead of non-irrigated areas (5%) (BPS Jawa Barat, 2021; BPS Jawa Tengah, 2021; BPS Jawa Timur, 2021). As consequence, farmers in the three provinces harvest their rice almost throughout the year. Of climate, West Java is relatively cooler than the other provinces but West Java has higher rainfall than the other provinces.

The highest maximum temperature (33.98 °C) and the highest minimum temperature (24.9 °C) are lower than rice’s temperature threshold of maximum temperature (35 °C) and minimum temperature (22 °C), respectively (Table 3). However, the impacts of temperature on rice yield are not always statistically significant as described in the following paragraphs.

Table 3 A summary of climatic data (1993–2019). Bracketed values show minimum and maximum values
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As seen in Table 4, for all rice in the three provinces, technological progress such as better rice varieties have an important role in increasing rice yield. This premise is in line with existing studies (Bahri, 2017; Gnanamanickam, 2009; Lobell & Burke, 2010), confirming the importance of technological progress in supporting rice yield. However, the impacts of high temperatures are different in the three Indonesian provinces. The following paragraphs explain the different impacts of high temperatures on rice yield.

Table 4 Statistical models for each province
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3.1.1 West Java

As 95% of total farming areas are irrigated rice areas, it is not surprising that the effects of rainfall are not statistically significant on rice yield in West Java. Likewise, the impacts of minimum temperature are not statistically significant, as the highest observed minimum temperature was 21.7 °C, lower than the threshold of minimum temperature (22 °C) (Peng et al., 2004). In another hand, a time variable, as a representation of technological progress such as better rice varieties, significantly can increase rice yield in West Java (p < 0.01). Likewise, maximum temperature has a significant impact on rice yield. Every 1 °C increase in maximum temperature tends to increase rice yield by about 3.387 tons/ha (p < 0.01).However, the maximum temperature tends to negatively decrease rice yield once the observed maximum temperature surpasses 33 °C. This is in line with other studies (Bahri, 2017; Jagadish et al., 2010; Khairulbahri, 2021), stating that maximum temperature tends to decrease rice yield by over 33 °C.

3.1.2 East Java

Farmers in East Java have experienced the negative impacts of high minimum temperature. The impacts of minimum temperature are statistically significant as the observed minimum temperature is higher than 22 °C, the threshold of minimum temperature (Peng et al., 2004). Table 4 shows that rice yield will be decreased by about 0.09 tons/ha for a 1 °C increase in minimum temperature (p < 0.05).

In contrast, farmers have experienced the positive impacts of maximum temperature as 1 °C increase in maximum temperature tends to increase rice yield by about 5.87 tons/ha (p < 0.05). However, similar to rice yield in West Java, the maximum temperature tends to decrease rice yield once the maximum temperature surpasses about 33 °C. Rainfall, conversely, has no significant impact as 95% of the total rice farming is supported by irrigation facilities (BPS Jawa Timur, 2021).

3.1.3 Central Java

Surprisingly, observed minimum temperature and observed maximum temperature tend to increase rice yield in Central Java. For every 1 °C increase in the minimum and maximum temperature, rice yield is projected to increase by about 0.149 and 0.118 tons/ha, respectively (p < 0.05). The impacts of rainfall on rice yield are not statistically significant (p > 0.1), due to a large fraction of irrigated rice land (95%) in Central Java (BPS Jawa Tengah, 1993).

The positive impacts of high temperatures are due to important reasons. The main reason is rice farmers in Central Java have applied the salibu method (Nugroho et al., 2018; Pemerintah Jateng, 2021; Sulistyono, 2019). The salibu method is local wisdom that shortens the growth duration of rice significantly without sacrificing rice yield (Jahari & Sinaga, 2019; Nugroho et al., 2018; Wahyuni et al., 2019). The salibu method can shorten rice duration growth, to less than 90 days, enabling farmers to harvest their rice for about 2–3 months (Agustina et al., 2021; Muzabi, 2021). Short growth-duration (SDG) rice varieties after the salibu method also enable rice to escape from climate extremes such as heat stress and droughts (Abdullah et al., 2008; Bouman, 2007; Yoshida, 1981). SDG rice varieties also enable farmers to escape heat stress during the night through transpiration cooling as most farming areas have sufficient irrigated water during the night (Jagadish et al., 2010; Wassmann et al., 2009).

Table 5 highlights comparisons between the salibu and non-salibu (ratoon) methods. Rice farmers who apply the salibu method tend to enjoy some benefits such as fewer farming costs (less labor cost and less seed cost), shorter duration growth, and relatively higher yield. Two advantages of the salibu method such as shorter growth duration and less water consumption are important in coping with the negative impacts of climate change (Lobell & Burke, 2010; Rosenzweig et al., 2020).

Table 5 Comparisons between the salibu and non-salibu methods
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Moreover, in the salibu method, rice farmers prune parentrice which leads to new shoots or tillers, leading to new roots (Fitri et al., 2019; Isnawan et al., 2022; Pasaribu & Anas, 2018). More roots and more tillers mean that rice has a higher coverage to capture important nutrients and higher rice yields, respectively. As parent rice is still in the farming field, parent rice and new fertilizer can be a better combination of nutrient sources for rice growth.

Differing farmers in Central Java, several studies showed that farmers in East Java (Afiani, 2018; Sayaka & Hidayat, 2015) and West Java (Dianawati & Sujitno, 2015; Rasmikayati et al., 2020; Rochdiani et al., 2017; Rohaeni & Ishaq, 2015) have sown rice varieties with relatively long growth duration (115–125 days) with limited farmers having applied the salibu method in East (Budianti, 2021) and West Java (Effendy et al., 2021). These are possible explanations for why farmers in West Java and East Java have experienced the negative impacts of high temperatures.

In tackling the negative impacts of high temperatures, rice scientists have developed heat-tolerant rice varieties (Yang et al., 2017; Ye et al., 2015; Zhang et al., 2013). However, the application of heat-tolerant rice varieties may be lagged due to costs, different rice tastes, and policymakers’ involvement (Kondamudi et al., 2012). As shown in this study, sowing SDG varieties after the salibu method should be seen as an alternative to cope with the negative impacts of high temperatures.

Existing studies (Boonwichai et al., 2019; Lobell & Burke, 2010) suggested that shifting crop seasons is one solution for minimizing the negative impacts of high temperatures. The salibu method, due to its shorter-duration growth, enables farmers to apply shifting crop seasons, preventing the rice from heat stress.

Likewise, since the rising temperature is associated with climate change, the positive impacts of the salibu method should be investigated further in higher temperatures, anticipating the negative impacts of higher temperatures beyond the observed temperatures.

4 Conclusion

This study discusses the impacts of climate factors on rice yield in the three Indonesian main provinces including West Java, Central Java, and East Java. This is important as recent temperatures in these main rice producers have reached the temperature threshold for rice growth. The importance of this study is also supported as these three regions capture about half of the Indonesian total rice production. This means that any possible threat to rice production in given provinces is likely to influence the Indonesian rice supply significantly.

In near future, the maximum temperature tends negatively affect rice yield in West Java and East Java if the maximum temperature is higher than 33 °C. Similarly, as the observed minimum temperature has surpassed the threshold of minimum temperature, farmers in East Java have experienced the negative impacts of minimum temperature on their rice. Again, since the recent minimum temperature in these three main regions has been close to the threshold of minimum temperature, changing climate is a big threat to the Indonesian rice supply.

By contrast, farmers in Central Java have experienced the positive impacts of minimum temperature and maximum temperature although both types of observed temperatures have surpassed their temperature thresholds. It appears that salibu method enables farmers to escape heat stress during rice growth, shorten duration growth, and accumulate more grain weight. Thus, this study offers a promising finding that the salibu method can minimize the negative impacts of high temperatures associated with climate change.

One of the possible mechanisms to cope with high temperatures associated with climate change is short-duration growth rice which enables rice to escape from climate extremes (Abdullah et al., 2008; Bouman, 2007; Yoshida, 1981). As the salibu method can shorten rice duration growth, rice farmers in Central Java can escape from the negative effects of high temperatures.

Another study explained other benefits of the salibu such as time saving and less production cost (Fitri et al., 2019). Owing to this, stakeholders such as policymakers/the government and rice scientists should disseminate the benefit of the salibu method as a promising farming method to get a higher profit and to cope with the negative impacts of high temperatures associated with climate change.

As precautionary measures, please bear in mind that the climatic benefit of the salibu method stated in this study is valid within observed temperatures. When the temperature rises significantly, for instance, due to climate change, the climatic benefit of the salibu method should be investigated further.

Last but not the least, the projections of the negative impacts of climate change and simulating possible options to minimize the negative impacts of climate change in the three main provinces will be the next avenue. This is important as IPCC (2013) projects that southern Indonesia will experience an increase in maximum temperature and minimum temperature by about 0.5 °C and 3 °C by 2100, respectively, depending on Radiative Concentration Pathways (RCP) scenarios.