An Assessment of Input Cost At Different Stages of Rice Growth and Its Effect on Production Cost on Cobb-Douglas Function in Cambodia

: The data analyzed in this study was obtained through a household survey from the three provinces in Cambodia. The sampling was done through which 540 farmer households were randomly selected. It applied Cobb-Douglas cost to examine the effect of input cost in different stages of rice growth on the total production cost. The result reveals that dry paddy, a 1% increase in the cost of the seedling stage would increase the rice production cost by approximately 25%. A 1% increase in input cost of jointing and booting stages would increase rice cost to 15%. And a 1% increase in farm size would increase output cost by roughly 17%. It means that the percentage change of the input cost of dry paddy would change output cost by 1%. In wet paddy, a 1% increase in input cost of the tillering stage would increase the rice cost by 28%. A 1% input cost of popular and milk stages would affect the output cost to approximately around 24%. A 1% increase in income off-farm jobs would increase rice costs by 11%. The elements of cost inputs of rice growth stages include fertilizer, pesticides, herbicides, irrigation, hired labor; land preparation and transportation stand out as the most crucial factors to contribute to the increment of cost output in wet paddy. These findings have a significant impact on how to boost rice production in Cambodia. Farmers are likely to benefit the most from improved agricultural productivity and technology. The study emphasizes that Cambodian farmers need to focus on agriculture to achieve increased rice production and poverty reduction in rural areas. As most of Cambodia includes poor people who live in rural areas and depend on agriculture, high agricultural growth will provide food security by increasing supply, reducing prices, and increasing households’ income.


Introduction
Cambodia is located in South-East Asia and has a tropical monsoon climate of two seasons, dry season, and wet season [3]. Agriculture is the top priority for the national development agenda. The poverty reduction through improving food security, household income, and employment-based on agricultural development was expected by the royal government. Economic growth and macroeconomic stability were contributed by agricultural development [15]. The leading agrarian activities are rice, subsidiary and industrialized crops, livestock, and poultry. The ecosystems for growing rice are four in Cambodia including dry season paddy, floating paddy, rainfed lowland rice, and rainfed upland rice [3]. Climate change affects rice production and other crops in the wet season. Moreover, a short drought happens in late July and early August during the wet season.
In Cambodia, rice is a staple food, the leading crop, and a valuable source of income for 85% of rural households. It contributes to approximately 4.5% of GDP, 20% of the total family income, and the rice revenue accounts for more than 50% of gross domestic product [6]. Income from crops has increased annually because of yield increase, thus, the cost of production is high. The rapid poverty reduction in rural areas, from 59% in 2004 to 24% in 2011, was driven by higher rice prices, high rice production, high returns from non-farm businesses, high rural salaries, and job growth in urban areas. Almost half of the poverty reduction is directly attributable to unaffordable prices 24% and rice production 23% [22].
Rice production alone accounted for half of the total crop production and grew significantly from about 1.7 million tons in 1980 to 9.3 million tons in 2015. Cultivated varieties include traditional non-aromatic rice, IR rice (mostly dry season paddy), and fragment rice (wet season paddy). Official statistics are scarce. However, it is currently estimated that the IR varieties account for about one-quarter to one-third of the total output. From 1980 to 1992, most agricultural fields were rice fields. Dry season rice production began to increase in 1994, up from just 0.4 million tons in 1980 to 2.2 million tons in 2015, equivalent to 23% of total paddy production [2]. Furthermore, the key inputs of rice production are seeds, fertilizers, pesticides, insecticides, farmland, and hired labor, and some may include irrigation infrastructure and machinery rentals. Early rice varieties are demanded the most in kilograms per hectare, while the late maturing rice is requested at the lowest demand. Similarly, those farmers used the highest amounts of basal fertilizer. The use of fertilizers is remarkably high in short-term farming compared to medium-and longterm agriculture. Farmers can not estimate the exact amount of agricultural pesticides they have applied to their fields. However, they were reminded of the higher spending on shortterm rice [6].
In the current year, although the studies of cost production in difference stages of rice growth is rare, but there are some research agencies such as Cambodia Development Resource Institute (CDRI) and Cambodian Agricultural Research and Development Institute (CARDI) are working on rice policies and rice productivities [21]. Thus, this study attempts to contribute to rice production literature of Cambodian agriculture by assessment of inputs cost at varies stage among rice production in the South-East region (specifically Takeo, Kandal and Kampong Speu provinces) which are the high potential regions of rice production.

Data Collection
The data analyzed in this study was obtained through a household survey conducted in 2020 from the three stated provinces in Cambodia. Random sampling was done through which 540 farmer households were randomly selected. The authors lead data collection and were accompanied by some postgraduate students from AII-CAAS, graduate students from Regional Polytechnics Institute Techo Sen Takeo (RPITT), and from the University of Management and Economics (UME). The data collection covered several aspects of the rural farmers encompassing Household conditions such as income from farming, daily expenditure, inputs of rice production, and agricultural technology information. The data collection was preceded by contacting the local authorities (chiefs of the ward, commune, and village) and then conducting a face-to-face interview with farming households and stakeholders. The rice inputs of dry season rice included seeds, pesticides, herbicides, fertilizer, irrigation, household labor, hired labor, transportation, and others. An increase in inputs affected the production of rice in the wet season and in the dry season rice production had increased yield to about 7.637 million tons and 2.315 million tons respectively in 2016. The increase in rice production is mainly due to the support offered by the Royal Government of Cambodia, relevant ministries and institutions, development partners, national and international organizations, sub-national authorities, and farmer participation. Based on our research, only farming households were selected for analysis. Mixed farmers, paddy producers, and other crops are not included in the data to be analyzed to minimize sample bias options. Data modification and filtering were performed to ensure that the unit of measurement for each variable is consistent with the academic goals and the quality of the data is satisfactory.

Constraints of Rice Production Cost
To assess the rice production constraints in this study we categorized three species which include biotic, abiotic, and socioeconomic constraints. The biotic constraints are related to all living factors including plants, animals, and humans, while the abiotic constraints are associated with non-living factors such as weather, temperature, geography, wind, rain, or natural disasters. Likewise, socioeconomic constraints deal with social issues and economic factors [1]. Data analysis was classified into four rankings (from 0 to 4) each of the classification constraints is relevant to the level of occurrence to influence the rice production. Zero (0) ranking presents that the respondents didn't know the constraints, while one (1) ranking appoints that it is the constraints none existing or not significant to affect the rice production. Furthermore, two (2), three (3), and four (4) ranking are modified about the low, medium, and high constraint, respectively.

Biotic Constraints
The biotic constraint factor in figure 2 illustrates the average ranking divided into 4 ranks (1=non-existing, 2=low, 3=medium, and 4=high) and separate three categories namely: weed, disease/insects, and rodents in rural Cambodian. Weed is a major constraint factor to influence rice production with an average ranking, while disease or insects have an average ranking above 3; it means that disease or insects are the medium constraints factor to the rice production. On the other hand, the average ranking of rodents is around 2, which changes that rodents are low constraints factors. As mentioned, the constraint factors are most affected by the rice production of Cambodian farmers, if farmers prevent the constraints they could increase the rice yield.

Abiotic Constraints
The abiotic constraint factor in figure 3 is related to weather conditions or a natural phenomenon. In the study area, the interviewed farmers were affected by abiotic constraints according to the occurrences rate and damage of drought, flood, soil erosion, wintry weather, soil quality, and heat stress. The average opinion of the farmer to rice production constraints affected by abiotic constraints includes heat stress, poor soil quality, and drought (on average rank about 3), while low constraint factors include flooding, soil erosion, and cold temperature.

Socioeconomic Constraints
The socioeconomic constraints are related to the excessive cost and unattainability or difficulties to access critical factors to rice production including credit cost, seed cost, land cost, labor cost, fertilizer cost, agrochemical cost, mechanization, market, transportation, road facilities, technology, and irrigation infrastructure. Figure 4 depicted an average ranking of socioeconomic constraints. The market and agrochemical cost constraints are high-ranking constraints to rice production. During the conducted field research, most of the farmers complained about the low market price and price volatility due to intermediary findings their low price and lack of government or stakeholder interventions worsened these challenges. In addition, the inflated cost of agrochemicals is of major concern to farmers as they overspend to meet the high cost of agrochemical to prevent crop diseases prevent diseases, or insects and increase their output. Other factors (credit cost, seed cost, labor cost, fertilizer cost, mechanization cost, transportation cost, road facilities, technology, and irrigation infrastructure) are medium constraint factors to the farmers' feeling of the production. Besides, socioeconomic factors also show the confronting of farmers who didn't increase output or productivity.

Research Methodology
The study applied the Cobb-Douglas cost production function, using STATA software to analyze cost input in different growth stage rice and its effect on the production cost of rice. This study is a buildup on new production function with technological innovation using cobb-douglas production function applied in China by Qian  Therefore, the study will contribute to increasing the rice production cost in rural Cambodia to surge household income and reduce poverty reduction.

Results and Discussion
Cambodian farmers usually applied different costs of inputs at various stages of rice cultivation. The inputs cost of the dry season rice is included seed, fertilizer, pesticides, herbicides, land preparation, hired labor, irrigation system, transportation, harvesting, and others. The Cobb-Douglas cost production function was carried out to estimate the parameter in this study. Table 1 presents the estimated parameter of the cost of the inputs of the dry season paddy. The coefficient of the cost seedling stage, jointing-booting stages, and plot size are significant to change cost output in the south-eastern in Cambodia. The cost of the tillering stage, poplar stage, milk stage, ripening stage, and other factors are not more effective with the production cost of dry season paddy. The influence on the cost of inputs during the seedling stage in the production cost is highly significant at 1% with a coefficient of 0.25. On the other hand, a 1%increase in the cost of seedling stage applications would increase the output cost by approximately 25%. The cost of jointing-booting stages presents a positive impact on the cost of rice yield and is significant at a 1% level with an estimated parameter of 0.15, while a 1% increase in the cost of the inputs at jointingbooting stages would increase the production cost by around 15%. Besides, plot size enlargement supplies an extreme impact on the production cost of the dry season paddy, while farm size is significant at a 1% level and the coefficient is roughly 0.17. In the past, Cambodia enjoyed agricultural land abundant, thus, increasing cultivated land might be a shortterm solution in attaining food security. But in the long-term improvement in productivity is one possible method for maintaining stable growth [26].
As shown above, the Cobb-Douglas cost production function inspects the cost of inputs in various stages of the rice growth, which means that the percentage change of the production cost if all cost factors are increased by 1%. Furthermore, the cost of seed, fertilizer, pesticides, herbicides, land preparation, hired labor, irrigation, and transportation are highly significant for the seedling stage, jointing, and booting stages, respectively, while the plot size is also extremely significant in all stages of rice growth. Rice production in Cambodia is separated into two categories: the wet season paddy and the dry season paddy, and within the wet season rice production, there are five species of rice, namely, early, medium, late, upland, and floating rice. Likewise, the growth stage of the wet rice is not different from the growth stage of the dry rice but the period of the wet rice is normally longer than the dry rice. Thus, we employed the Cobb-Douglas cost production function to estimate the cost of inputs in various stages of rice growth. Table 2 is depicted in the coefficient of the wet rice. The cost inputs of the tillering, poplar, milk, and drought stages involved in the production cost were positively affected by the output and it was highly significant at a 1% level for the tillering stage, while the poplar, mike, and dough stages were significant with 5% level. Moreover, the income off the job is also highly significant at the 1% level. In other words, a 1% increase in the cost of the tillering stage would increase the production cost by around 28%, while a 1% increase in the cost of poplar, milk, and dough, respectively would increase the output cost by roughly 24%. On the other hand, if a 1% increase in income off the job would increase by about 11%. The elements of cost inputs of rice growth stages include fertilizer, pesticides, herbicides, irrigation, hired labor; land preparation and transportation stand out as the most crucial factors to contribute to the increment of cost output.
As mentioned above, the research carried out a Cobb-Douglas cost production function to examine the variation between the cost of inputs and the cost of outputs during the wet season paddy. If the percentage change of the cost output if all factors of cost inputs are increased by one percent.

Conclusion
This study carries out the Cobb-Douglass Cost Production Function to inspect the cost of inputs at different stages of rice growth in rural farming Cambodia. It proves that the coefficient of some factors of wet and dry paddy was significant with rice cost. Rice production in Cambodia was influenced by three constraints including biotic constraints, abiotic constraints, and socio-economic constraints. The biotic constraint was separated into three factors namely: weed/ disease, insects, and rodents. Weed is a major constraint to influence the rice production cost, while disease or insects is secondly affected, and rat is thirdly influencing rice production. The abiotic constraint factors change the weather and ecological condition to effects crop growth. It is related to flooding, drought/scarcity of water, cold temperature, heat stress, and poor soil quality. Socioeconomic constraints are related to the prohibitive cost and unattainability or difficulties to access critical factors to rice production such as credit cost, seed cost, land cost, labor cost, fertilizer cost, agrochemical cost, mechanization, market, transportation, road facilities, technology, and irrigation infrastructure.
Based on the results for dry paddy, a 1% increase in the cost of the seedling stage would increase the rice production cost by around 25%. A 1% increase in input cost of jointing and booting stages would increase rice cost amount 15 percent. And a 1% increase in farm size would increase output cost by roughly 17%. In wet paddy, a 1 percent increase in input cost of the tillering stage would increase the rice cost by 28%. A 1 percent input cost of popular and milk stages would affect the output cost around 24%. Moreover, a 1 percent increase in income off-farm jobs would increase rice cost by 11 percent.
These findings have an important effect on how to boost rice production in Cambodia. The farmers are likely to benefit most from improvement in agricultural productivity and technology. It is clarified that Cambodian farmers ought to focus on the agriculture sector to achieve rice production growth and poverty alleviation in rural areas. Due to most of Cambodia's poor people living in rural areas and relying on agriculture, high agricultural growth will provide food security through increased supply, reducing prices, and rising incomes of the poorer farm household. To facilitate this response and achieve food security, neglected agriculture has been included in the political agenda. Firstly, there is significant scope for improving rice production in Cambodia. It is possible to increase Cambodian rice output to the level of its neighbor countries if appropriate inputs (fertilizer, irrigation) and infrastructure (electricity markets, agricultural extension, and education) are provided. Given the high awareness of fertilizer, farmers could noticeably increase their yield and revenue from more market sales [27].
Secondly, the promotion of advanced technologies and crop diversification should be organized according to local conditions. Nevertheless, poor road and market conditions prevent local producers from benefiting from the comparative advantage of rice production. Greater investment infrastructure enables farmers to gather the latest market information and ship their produce to Phnom Penh and other regional markets. Rural investment roads have high yields returns on poverty reduction in developing countries [26]. Improving rural roads will enable rural people to access essential services.