Carrying Capacity of Agricultural Land in Toll Road Construction in Sragen, Indonesia, 2011–2020

Sragen Regency has enormous agricultural potential and is among one of the largest rice suppliers for the population of Central Java, Indonesia. However, since the construction of the Solo-Kertosono toll road that passes through the regency, there have been more farmlands converted for non-agricultural purposes. This study was conducted to determine the extent of land conversion into a toll road and assess the carrying capacity of agricultural land from 2011 to 2020. To identify land conversion, data from the Purwodadi Road Management Center in the regency were analyzed. Meanwhile, the mathematical formula introduced by Odum et al. was applied to the secondary data obtained from the Bureau of Statistics to calculate carrying capacity. Results show that from 2011 to 2020, rice fields were converted most extensively into toll roads, with an average of 85.28% conversion. Further, the agricultural land’s carrying capacity in affected districts fluctuated across these years due to several factors, including harvested area, rice production, productivity, and water availability for irrigation.


Introduction
Food, as the basic need of the world population, should be continuously available to fulfill the consumption demand [1].The consumption of rice, the staple food of most households in Indonesia, reached 20,685,619 tonnes, or equal to 77.5 kg per capita per year in 2019 [2].To provide a reliable supply, it is necessary to sustain one of the essential production factors of the agricultural sector, which is land.
The most common problem in farmland availability is extensive land conversion, especially from agricultural to non-agricultural, to accommodate population growth that simultaneously adds to food demand.If left unmanaged, the conversion will likely continue and reduce farmland, which can progressively, cumulatively, or permanently threaten food availability, stability, and security.Population growth, including an increase in in-migration, multiplies the need for built-up space for various purposes, such as settlements, industrial areas, and business complexes, resulting in more arable land converted into non-agricultural fields [3].1313 (2024) 012034 IOP Publishing doi:10.1088/1755-1315/1313/1/012034 2 Central Java is one of Indonesia's provinces that are rich in natural resources, including an enormous potential in the agricultural sector [4].For instance, the Sragen Regency is among the largest rice producers in the province, as evidenced by its vast rice field area.Of the 35 regencies/cities in the province, it ranked third in rice production per area in 2020 (up to 65.57 quintals/ha) [5].This potential, however, cannot be separated from the problematic agricultural land conversion due to, among others, transport infrastructure development.The construction of the Solo-Kertosono toll road has triggered massive cropland conversion in several districts: Masaran, Sidoharjo, Sragen, Ngrampal, Gondang, and Sambungmacan.Furthermore, it contributes to raising the number of housing and built-up areas for business purposes.As a direct result, the affected districts are, on the one hand, losing arable land.In the last decade, the most significant decrease was recorded at 0.71% or 286 ha from 2014 to 2015.On the other hand, the regency's population showed an upward trend or increased yearly.The year 2014 recorded the only decline in population, whereas the highest increase of 9.71% or 86,433 people was found from 2019 to 2020 [5].
While the land use conversion does not occur evenly across the regency, it affects food production and availability.Croplands are shrinking in line with population growth, potentially decreasing the carrying capacity of arable land.In addition, considering population size that changes at different rates, districts affected by the toll road construction can be used as representative units of analysis.Based on the above description, this research was intended to measure the extent of cropland conversion into the toll road in the Sragen Regency and calculate the carrying capacity of cropland in the affected districts from 2011 until 2020.

Methodology
The unit of analysis used in this study was district, i.e., all districts affected by the toll road in the Sragen Regency: Masaran, Sidoharjo, Sragen, Ngrampal, Gondang, and Sambungmacan.Secondary time-series data from 2011 to 2020 were gathered from BPS-Statistics of Sragen Regency, while the primary data were collected through in-depth interviews with the regency's Bureau of Statistics and Agriculture and Food Security Office.In addition, to determine the extent of the land use change, data on the area of land converted into the toll road were obtained from the Purwodadi Road Management Center in the regency and processed.Afterward, the carrying capacity of croplands was calculated using the formula below: where  is the carrying capacity of cropland, Lp is harvested area (ha), Pd is population size (people), KFM is the minimum amount of food (i.e., rice) one person needs (kg/capita/year), and Pr is productivity, i.e., rice production per unit of area (kg/ha).The obtained value was then used to classify each district into three classes: -Class I ( > 2.46): The district's rice production can sufficiently meet the local food demand without importing additional food (entirely self-sufficient); -Class II (1    2.46): The district's rice production can only meet some of the local food demand (partially self-sufficient); or -Class III ( < 1): The district's rice production cannot meet the local food demand at all (not selfsufficient).

Land use conversion into a toll road from 2011 to 2020
The ongoing construction of the Solo-Kertosono toll road has modified the anthropogenic landscape of the six districts observed in the Sragen Regency.Table 1 presents the total area converted into toll road segments in the affected districts by land use.Overall, Sidoharjo experienced the broadest conversion of rice fields, settlements, and fields, totaling 755,481 m² or around 30.34% of the total converted area in the regency.This extensive modification is believed to result from the toll road that traverses the district diagonally and the construction of supporting infrastructure: an exit gate and the management office of PT Jasa Marga (a stateowned company focusing on toll road operation).On the contrary, Gondang showed the least extensive conversion of up to 118,990 m 2 , accounting for 4.78% of the total converted area, because only a short segment of the toll road was planned to traverse the north of the district.1 indicates rice fields as the most extensively converted land use.Approximately 2,150,560.04m² of rice fields had been changed into the toll road, or around 86.36 % of the converted land use area in the regency, with the tremendous loss of arable land approaching 683,751.21m² in Sidoharjo.This modification stems from rice fields being the predominant land utilization type in the study area.Apart from population growth, many other factors contribute to the increasing conversion of agricultural land.For starters, croplands are assumed to be widely available in the area, thus appealing to developers to transform them for non-agricultural purposes.Also, croplands generally have a flat morphology, good accessibility, and are located close to water resources, which makes development relatively easy.In addition, unlike built-up areas, converting croplands does not require evictions, which would require greater costs and time [6].
Table 1.Land-use conversion into the Solo-Kertosono toll road in the six districts of the Sragen Regency, 2011-2020

Carrying capacity of agricultural land
In this research, the carrying capacity of existing cropland refers to the ability of a district to produce food and adequately meet the local demand⎯a condition termed food self-sufficiency.It can also be interpreted as the land's capacity to support various anthropogenic activities and needs, especially food, in different land uses [7].This concept was used to determine if croplands in the observed district could entirely, partially, or not fulfill the amount of staple food (i.e., rice) the residents needed based on conditions from 2011 to 2020.The calculated capacity was categorized into Class I ( ≥ 2.46), II (1 ≤  ≤ 2.46), or III ( < 1).The higher the degree of the carrying capacity, the more self-sufficient the region is in rice.The carrying capacity can be influenced by several indicators: total population, harvested area, rice production, and agricultural productivity for rice cultivation.The carrying capacity of each district traversed and affected by the toll road construction in the Sragen Regency from 2011 to 2020 is described in the sub-chapters below.

. Masaran District
Table 2 summarizes the calculation results of the cropland's carrying capacity in Masaran based on population, harvested area, minimum amount of rice needed per capita (KFM), and average rice production.From 2011 to 2020, the carrying capacity varied from 2.43 (2011) to 2.82 (2015).The greatest carrying capacity in 2015 was also in line with the second-highest production per area (6,740 kg/ha) after 2019 (6,761.2kg/ha).Also, the harvested area in that year was the third-highest (8,054 ha) after 2014 and 2020.In contrast, the year 2011 had the smallest carrying capacity, potentially because it had the lowest population and low rice yields, as indicated by the narrowest harvested area (7,617 ha) and the second-lowest production per area (5,935.9kg/ha) after 2014.
The Agriculture and Food Security Office in the Sragen Regency stated that the rice yield and the carrying capacity in 2011 were generally low compared to other years due to a lack of innovation and technological application in farming and suboptimal development in agricultural production.In the following years, considering water availability as a limiting factor in farming practices, a water extraction technology was introduced to withdraw groundwater using submersible well pumps.With groundwater largely available in the regency, the agricultural sector is not entirely dependent on the season; thus, crop cultivation can continue even during dry months.Another technological advancement was applied to the harvesting method.Instead of pedal trasher, rice is now harvested using combine harvesters and power threshers.After being harvested using these machines, about two-thirds of the rice stalks remain and gradually decompose into organic fertilizers.Therefore, if the allocation of subsidies for fertilizers is reduced, the soil will not lose nutrients due to the organic matter produced in the decomposition of rice stalks.This organic fertilizer is deemed capable of supplying adequate micronutrients for optimal plant growth, in addition to the macro elements obtained from chemical fertilizers.These technologies might be responsible for the generally increasing trend of carrying capacity in the district, as shown in Figure 1.Some notable fluctuations included a substantial increase of 0.23 in 2015 and a decrease from 2.82 in 2015 to 2.65 in 2016.The toll road construction in Masaran began in 2014.This was immediately followed by a decrease in the year's rice production per area, which was 355.70 kg/ha lower than the previous year.It was the most significant decrease in the district's agricultural productivity in the 2011-2020 period.Similarly, the carrying capacity decreased from 2.62 in 2013 to 2.59 in 2014.However, this figure bounced back and generally increased until the end of the observation period, except for two points of reduction in 2016 and 2018.This upward trend was potentially because the converted rice fields were smaller than the average harvested area.In other words, the toll road does not significantly affect the district's agricultural carrying capacity.Despite the dynamic carrying capacity, partially due to the conversion, the class showed improvement from Class II in 2011 to Class I in 2012 and remained so until 2020.This indicates that in 2011, the district's rice production could not adequately satisfy the local demand (partially self-sufficient).However, from 2012 to 2020, it was able to produce and supply the entire amount of rice needed by its residents without having to import additional rice (entirely self-sufficient).Figure 2 depicts the trend of the district's carrying capacity in Sidoharjo from 2011 to 2022.Overall, while some fluctuations are observed, it shows a slightly increasing pattern over the course of ten years.A significant increase was detected from 4.00 in 2014 to 4.42 in 2015, whereas a substantial decrease occurred from 4.52 in 2019 to 4.10 in 2020.The last two years also saw a sharp population growth of 6,178 people, from 51,590 in 2019 to 57,768 in 2020.An interview with Mr. Ridwan, the District Census Coordinator at the Bureau of Statistics of the Sragen Regency, revealed that the large number of people returning to the district due to the COVID-19 pandemic accounted for the local population rise in 2020.Combined with 2020 being the census year, the return migration seemed to have substantially multiplied the recorded population size compared to the previous census year.This situation also transpired in Masaran, Ngrampal, Gondang, and Sambungmacan.The toll road construction in Sidoharjo began in 2014.This was soon accompanied by a decrease of 116 ha in the year's harvested area, which became more prominent in 2015 (167 ha).Similarly, the average rice production per area in 2014 was 283.51 kg/ha smaller than in 2013.These declines in the rice production factors show the effect of land use change, especially from farmland to the toll road, on harvested area and productivity.As a result, the carrying capacity decreased from 4.25 in 2013 to 4.00 in 2014.However, while this capacity fluctuated from 2011 to 2020, it was generally higher after the toll road construction, potentially because the converted rice fields were smaller than the average harvested area.This means that, in terms of land area, the toll road construction does not significantly affect the cropland's carrying capacity in the district.Even though this capacity was dynamic over the course of ten years, it was consistently categorized as Class I, suggesting that the district's rice production sufficiently met the local food demand from 2011 until 2020 (fully self-sufficient).

Sragen District
Table 3 summarizes the calculation results of the cropland's carrying capacity and its indicators in Sragen from 2011 to 2020.It shows that the year 2011 saw the lowest carrying capacity even though the population size was the lowest among the years observed.The capacity, 1.40, was identical to that in 2014.Similarly, the rice production per area was also low, amounting to 5,935.88 kg/ha.In contrast, the highest carrying capacity (1.58) was found in 2019, with the highest rice production per area, 6,729.68kg/ha, and 4,343 ha of harvested area.
According to the Agriculture and Food Security Office, the high capacity in 2019 was because the district's enormous groundwater potential was extracted in a great amount to supply the Colo Timur irrigation using submersible well pumps.This cannot be separated from the administrative status of the Sragen District as the capital of the Sragen Regency, which potentially has more access to technological advancement than other districts in the area.Figure 3 illustrates a generally increasing trend in the carrying capacity from 2011 until 2020.A sharp increase was detected from 1.45 in 2018 to 1.58 in 2019, indicating a positive difference of 0.14.Likewise, the harvested area and rice production per area also rose substantially in 2019.On the contrary, the most significant drop was detected from 1.58 in 2019 to 1.46 in 2020.The toll road construction in Sragen began in 2015, triggering a decrease of 29 ha in the year's harvested area.However, this was not followed by a decline in rice production; instead, it increased by 424.61 kg/ha from the previous year.In 2015, the carrying capacity of croplands also showed an increase of 0.08.As seen in Figure 3, it fluctuated widely before and after the toll road construction and peaked at 1.58 in 2019.Further observation of data in Table 4 revealed that despite reductions in some years, the capacity was always categorized as Class II.It can be assumed that the district was partially self-sufficient in rice from 2011 to 2020, where its rice production could only meet some of the local demand.

Ngrampal District
Table 5 summarizes the calculation results of the cropland's carrying capacity and its indicators in Ngrampal from 2011 to 2020.Unlike Masaran, Sidoharjo, and Sragen, this district saw the lowest carrying capacity in 2020, at the end of the observation period.The harvested area also decreased from 6,850 ha in 2019 to 6,610 ha in 2020.This confirms their positive relationship, where a wider harvested area is followed by a higher agricultural carrying capacity and vice versa [8].In addition, the population multiplied dramatically from 37,563 in 2019 to 42,484 in 2020, coinciding with a plunge in the carrying capacity.The Agriculture and Food Security Office explained that the low capacity in 2020 could also be attributed to the extensive land-use conversion to factories and other supporting facilities to accommodate industrial growth.Figure 4 shows the line chart of the cropland's carrying capacity in Ngrampal from 2011 to 2020.In these years, the highest carrying capacity was identified in 2019 (4.35), when the harvested area was the secondhighest (6,850 ha) after 2013 (6,849 ha), and the productivity decreased from 6,425.44 kg/ha in 2018 to 6,326.72 kg/ha in 2019.Overall, the carrying capacity fluctuated without experiencing considerable changes in several years, such as from 2012-2014 and 2016-2019.A sharp increase was detected from 4.11 in 2015 to 4.32 in 2016, indicating a positive difference of 0.22, while the most significant decline was from 4.35 in 2019 and 3.86 in 2020.The toll road construction in Ngrampal began in 2015.This was immediately followed by a reduction in the year's harvested area, 739 ha lower than the previous year.It represents the impact of construction on landuse change, particularly from arable land to the toll road, and, consequently, on the district's harvested area.Similarly, the carrying capacity decreased from 4.21 in 2014 to 4.11 in 2015.However, this figure bounced back and became generally higher than in the years before the construction, potentially because the converted rice fields were considerably smaller than the average harvested area.Accordingly, in terms of area, the toll road development does not significantly influence the district's agricultural carrying capacity.A significant decline in the 2020 capacity is believed to be related to a substantial rise in the population.Even though the carrying capacity decreased in certain years, it was consistently categorized as Class I from 2011 to 2020.Class I suggests that the district was able to produce and supply the entire amount of rice needed by its residents without having to buy additional food (fully self-sufficient).

Gondang District
Table 6 lists the cropland's carrying capacity in Gondang from 2011 to 2020.Population, as one of the indicators, continuously grew each year.Nevertheless, while the carrying capacity fluctuated throughout the observed years, it can be concluded that the trend was generally stable.The lowest population in 2011 (41,641 people) did not necessarily correlate with the lowest capacity (3.52) because the latter was also found in 2020, with a much higher population (47,085).The district's population dramatically multiplied from 42,238 in 2019 to 47,085 in 2020, indicating an increase of 4,847 people in just one year.It was immediately followed by a decrease in harvested area (from 7,217 ha in 2019 to 6,913 ha in 2020) and a drastic reduction in carrying capacity.This corresponds to Jayadi et al. [9], who discovered that population growth has an inverse or negative relationship with agricultural carrying capacity.The highest carrying capacity was identified in 2016, with a value of 4.38, where the harvested area (7,325.7 ha) was the second-highest after 2017 (7,449.4ha), and the rice production per area was also the highest (6,670 kg/ha, increased from 6,513.81 kg/ha in the previous year).High agricultural productivity can be associated with technological advancement, irrigation improvement, proper land management, and the use of resistant seeds, which in turn positively affect the cropland's carrying capacity [10].The toll road construction in Gondang started in 2015, but it traversed only a small part of the district in the north, creating an area of 118,990 m 2 .During the construction in 2015, the harvested area and the rice production per area were higher than in the previous year.Consequently, the carrying capacity also increased from 3.82 in 2014 to 4.23 in 2015.It showed an upward trend before (2011-2015) and during the construction (2015-2016) but then continued to decline until 2020.However, the capacity was consistently categorized as Class 1 throughout the observed years, potentially because the converted rice fields were smaller than the average harvested area.Therefore, in terms of area, the toll road construction does not significantly affect the district's agricultural carrying capacity.Class I means that Gondang was fully self-sufficient in that it was able to produce and supply the entire amount of rice needed by its residents without importing additional food.

Sambungmacan District
Table 7 summarizes the calculation results of the cropland's carrying capacity based on the population, harvested area, and rice production and requirement factors in the Sambungmacan District from 2011 to 2020.Like Gondang, the population size in Sambungmacan continuously grew each year, with a substantial growth from 44,738 in 2019 to 48,466 people in 2020.Some fluctuations were observed in the carrying capacity, but the trend was generally stable.The lowest population in 2011 (44,105 people) did not necessarily correlate with the lowest capacity (3.33) because the latter was also found in 2012, 2013, and 2016, with higher populations (44,229-44,584 people).The carrying capacity varied between 3.24 (in 2014) and 3.62 (in 2015).In 2015, the rice production per area was also the highest (6,559.94kg/ha), which increased drastically from 5,899.97 kg/ha in the previous year.
Figure 6 demonstrates a widely fluctuating carrying capacity in Sambungmacan within the course of ten years.The capacity rose from 3.24 in 2014 to 3.62 in 2015, indicating an increase of 0.38, which coincided with an improvement in rice production per area from 5,899.97 kg/ha in 2014 to 6,559.94 kg/ha in 2015.It sharply reduced from 3.62 in 2015 to 3.33 in 2016, which was in line with a substantial decline of 509.10 ha in the harvested area.The toll road construction in Sambungmacan started in 2016, which was instantly followed by a reduction in the year's harvested area (by 509.1 ha) and production per area.After the construction, the harvested area increased sharply by 478.3 ha the following year, but a decrease of up to 16.94 kg/ha in productivity was recorded.Even though the cropland's carrying capacity decreased from 3.62 in 2015 to 3.33 in 2016, it fluctuated until the end of the observation period and was generally higher after the construction.This might be because the converted rice fields were small compared to the average harvested area.Therefore, in terms of land area, the toll road construction does not significantly affect the cropland's carrying capacity in the district.The significant decline in the 2020 capacity is thought to be linked to a substantial rise in the population.Even though the carrying capacity decreased in certain years, it was always categorized as Class I from 2011 to 2020.Class I indicates that the district's rice production could meet the entire amount of rice its residents needed (fully self-sufficient).

Significance of agricultural land in the toll road-affected districts
The Solo-Kertosono toll road runs through six districts in the Sragen Regency: Masaran, Sidoharjo, Sragen, Ngrampal, Gondang, and Sambungmacan, which had different agricultural carrying capacity values and trends.Therefore, their degrees or classes were mapped based on the calculation results in 2011 (Figure 7) and 2012, in which any changes remained constant until 2020 (Figure 8). Figure 7 shows four districts with Class I capacity (Sidoharjo, Ngrampal, Gondang, Sambungmacan) and the other two with Class II capacity (Masaran and Sragen).Among the observed districts, Masaran had the largest population in 2020 (77,591 people) [5].Administratively, it shares borders with the Karanganyar Regency to the south and is traversed by a primary collector road.As for Sragen, the carrying capacity of its cropland was consistently at Class II from 2011 to 2020. to others, the district tended to have a relatively low capacity because it also serves as the center of government and economic activities and the capital of the Sragen Regency.Areas located close to the center of economic growth and highways commonly have a low agricultural carrying capacity.Furthermore, Sragen is an urban area [11], which is typically developing faster than its neighboring non-urban regions.This likely leads to industrialization, in-migration, population growth, and the conversion of croplands into non-farming areas to meet the increasing demand for settlements, industrial complexes, and service facilities [3].  Figure 8 shows four districts consistently classified as Class I from 2012 to 2020: Sidoharjo, Ngrampal, Gondang, and Sambungmacan.In addition, Masaran, which was initially Class II 2011, showed an improvement in its carrying capacity and was thus classified as Class I in 2012.This condition remained the same until the end of the observation period.As an organic rice center, Masaran substantially contributes to the Sragen Regency's status as the largest organic rice producer and the first to obtain organic rice certification in the province.The government's commitment to continuously developing the agricultural sector, especially organic rice, is a factor behind these achievements [12].

Conclusion
The Solo-Kertosono toll road construction triggered land use conversions on its path, which includes six districts in the Sragen Regency: Masaran, Sidoharjo, Sragen, Ngrampal, Gondang, and Sambungmacan.The most extensive change is seen in rice fields, accounting for 81% (Sambungmacan) to 91.42% of the total converted area (Ngrampal).The cropland's carrying capacity in the six districts varied throughout the 2011-2020 period.In 2020, all the districts had a Class I carrying capacity, except for Sragen (Class II), from which It can be inferred that the rice field conversion occurred to a smaller extent than the average harvested area and thus still resulted in high carrying capacity.In other words, the construction does not significantly affect this capacity.The lowest carrying capacity in Sragen (1.46) is believed to result from its role as the capital of the Sragen Regency, where industrialization and land-use conversion to residential and industrial areas have encroached into arable land.

Figure 1 .
Figure 1.Annual trend of the carrying capacity of croplands in the Masaran District, 2011-2020

Figure 2 .
Figure 2. Annual trend of the carrying capacity of croplands in the Sidoharjo District, 2011-2020

Figure 3 .
Figure 3. Annual trend of the carrying capacity of croplands in the Sragen District, 2011-2020

Figure 4 .
Figure 4. Annual trend of the carrying capacity of croplands in the Ngrampal District, 2011-2020

Figure 5 .
Figure 5. Annual trend of the carrying capacity of croplands in the Gondang District, 2011-2020 Figure 5 illustrates a fluctuating yet stable trend in the carrying capacity of croplands from 2011 to 2020.No significant changes were identified in these years.The line chart generally shows an upward trend from

Figure 6 .
Figure 6.Annual trend of the carrying capacity of croplands in the Sambungmacan District, 2011-2020

Figure 8 .
Figure 8. Map of the carrying capacity of croplands in the six districts traversed by the Solo-Kertosono toll road in the Sragen Regency, 2012-2020

Table 2 .
Carrying capacity of croplands in the Masaran District, 2011-2020 I Source: BPS-Statistics of the Sragen Regency (Data Analysis, 2023)

Table 3
lists the cropland's carrying capacity in Sidoharjo from 2011 to 2022.The highest carrying capacity in 2016 (4.54) coincided with the highest productivity, 6,776 kg/ha.In contrast, the lowest capacity was detected in 2011 (3.89), or the same as Masaran, which might result from a combination of low population, harvested area, and productivity.Moreover, this year saw the lowest harvested area among the observed years (8,832 ha) and the second-lowest productivity (5,935.88kg/ha) after 2014.