فصلنامه اقتصاد کشاورزی
سال سیزدهم شماره 2 (تابستان 1398)

Extended Abstract
 
1-The issue of forest depletion in the north of Iran has always been a subject of debate, especially in recent years, and the need for sound planning and proper management has been increasingly emphasized. In order to determine the optimal forest management strategy in northern Iran under uncertainty, this study has attempted to estimate forest growth model, ARIMA model for predicting wood price, Harvesting Cost Model and a Dynamic Planning Model, Management Strategies in Three Scenarios, Maximizing Net Present Value, Maximizing timber harvesting and maximizing growing stock. It is worth noting that the present study aims at selecting different management strategies in order to determine optimal harvesting strategy and evaluation of sustainability of simulated strategies is a new step in choosing appropriate management policy in northern forests.
2-Materials and Methode
In order to simulate forest management strategies, firstly it needs to estimate the price equation, the growth equation, the cost equation, and the net present value equation. ARMA models are a combination of Autoregressive (AR) and moving average (MA) variables. This model was applied to predict timber price and estimate price equation. The quadratic cost equation with intercept is assumed to be the function of the harvest cost and the squared of the harvest variable. In order to estimate the forest increment equation, we used a logistic growth model. This model, despite the low observations, shows well the relationship between growing stock and growth rate, and theoretically and mathematically describes the model well. Given the equation of price, cost equation, growth equation and net present value equation, we evaluated the defined strategies in the dynamic programming model using GAMS software. After simulating strategies to maximize timber harvest, maximize net present value, and maximize forest timber inventory, a hierarchical analysis model was used to evaluate the sustainability of forest resources in each strategy.
3-In the strategy of maximizing harvest, there was an almost decreasing trend for the growth variable, with a slight decrease, and some variations were observed for the harvest variable. Changes in harvest rate per hectare and growth rate per hectare follow each other in this strategy, which means that the harvest rate should be determined by the rate of growth per hectare. In the strategy of maximizing the net present value, the growth rate is at an acceptable level and therefore the forest is not damaged. By applying this strategy, the harvest rate will increase in the early years and then continue to be somewhat steady until the end of the period. This means that in this case, the situation of the stakeholders will improve economically, which is one of the goals of sustainability. In the second strategy Harvest rate follows the growth rate in this strategy, and there is a correlation between harvest rate per hectare and stock availability per hectare. In the third strategy of maximizing forest stock, the amount of growth was acceptable. Harvesting variable during the period of study has an increasing trend. The stock per hectare increased at the beginning of the study period and has been somewhat steady since the first few years. It is remarkable that in this strategy, which aimed to maximize the amount of growing stock per hectare, the growth rate was almost acceptable and the harvest rate per hectare followed the pattern of stock availability per hectare.
4-Suggestion
In general, it is suggested that dynamic planning methods be used in forest management, especially those of commercial and economic importance in the northern forests, to achieve appropriate management strategies. As the results showed, economic and environmental objectives will be achieved simultaneously with dynamic planning and proper management of forest resources.
JEL Classification: C61, C63, Q23

Clustering is one of the most important operations in data mining and its results are useful for researchers and policy makers in various fields for analysis and planning. Since in recent years, the knowledge based economy has been developing with the support of knowledge-based companies in Iran, the analysis of the characteristics of these companies and their segmentation for effective planning provides an appropriate perspective for policy makers.
In this article, Iranian knowledge based companies of agriculture using 2017 data have been clustered based on the field of technology, the number of products and value of product sales. Three clustering methods, simple K-Means and K-Means in combination with hierarchical and ant colony algorithms by using MATLAB 2016a software were applied for clustering. Then, results of three algorithms have been compared and the best one for this data have been selected.
According to the results, the clustering using K-Means in combination with the ant colony algorithm, in comparison with the other two methods, shows a more balanced distribution of the firms among six clusters, and the average Silhouette width value of the 0.7 confirms the validity of this clustering. The highest number of companies and products are in first cluster and the lowest are in 4th and 5th clusters which have the highest average sales per company with 27293 and 5404 million Rials, respectively. The reason for the small number of members in these clusters is that few companies have a large number of knowledge-based products with high sale. In contrast, most companies have acquired a small market share with few number of products. The variety of products and sales of companies indicates the flexibility of the company in different markets, the size of the market and the ability to participate in market development.
Suggestion
Based on the results, it is suggested that similar support programs be designed for companies that are due to similar characteristics in a cluster in order to be effective and avoid losing budget. For knowledge based companies with low average sales that are in a cluster, market support programs and for companies with products diversification and high average incomes, export market development programs are recommended. Providing banking facilities to agricultural knowledge-based companies can not have the same model for every company, and It is necessary to determine the amount of facilities provided and the method of repayment based on the results of the clustering..
JEL Classification: C81, L2, M13, O31, Q16

Whole Farm Insurance (WFI) is a new policy that could solve most of the problems involving the traditional insurance. This program protects farmers against loss of revenue in a single policy instead of insuring the crops separately. This paper aimed firstly to design the WFI and then calculate premium rate, sum insured and aggregate limit of indemnity in the case of single-crop and multi-crop choices for farmers in Zanjan city.
 
The purpose of this study was to introduce and design a Whole Farm Insurance for the wheat, barley and alfalfa crops in Zanjan city. Required information including times series data of yields and prices were collected for the period 1982-2014, in addition to farm-level yield data for the period 2008-2014. A two-step method was used for modeling the PDF and CDF of the crops, in order that in the first step, the data were detrended using an appropriate regression model and in the second step, detrended data were used to simulate the probability density functions. In order to model the price series, the real prices of the products were calculated using the producer price index and then detrended. Afterward, the distribution of the prices was estimated using the detrended data. Meanwhile, the DF-GLS and KPSS tests were used for examining the stationarity of the yield and price series.
Then the guaranteed incomes for the products were estimated at different coverage levels using the joint distribution of the yields and prices. In the next step, the expected indemnity, premium rate, insurer’s liability and sum insured were calculated in the single-crop, two –crop and multi-crop cases by employing the PQH simulation method, Cholesky decomposition and Simetar package.
 
The primary analysis of the data indicated that the yields are trend stationary process (TSP) and the prices are difference stationary process (DSP). Furthermore, the premium rates for wheat, barley, alfalfa, wheat-barley, wheat-alfalfa, alfalfa-barley and wheat-barley-alfalfa cases were calculated 20.9, 0.5, 5, 6.7, 1.9, 1.8, and 3.7 percent at the 75 percent coverage level, respectively. The results indicated that the whole farm insurance offers lower premiums in comparison to insuring the crops separately as well as it has less administrative costs. Therefore, it could be an appropriate tool for risk management in agricultural sector.
 
Suggestions
According to the results, it is recommended to the Agricultural Insurance Fund to put the whole farm income insurance in the priority of his administration or to use it as a supplement or substitute for the existing insurance programs.
 
JEL Classification: C15, C53, C63, G22, Q18

The paradigm transmission from traditional economic to knowledge-based economic is based on the production, distribution, and use of knowledge as a principal factor in all aspects of society.
Improving and increasing agricultural productivity is the result of transferring from resource-based production systems to knowledge-based production systems. In the new patterns of agricultural development, science and technology play an important role in sustainable agricultural growth and development, and these patterns are referred to as scientific agriculture, knowledge-based agriculture and technology and knowledge agriculture. in this study, it tried to study the role of knowledge-based economic in agricultural growth of some selected countries with emphasis on Iran.
 
 
In this study, we tried to study the role of knowledge-based economic in agricultural growth of some selected countries with emphasis on Iran, using fixed effects method and knowledge assessment methodology of the World Bank during the period of 2008-2017.To calculate the knowledge-based index was used the methodology of knowledge economy assessment by the World Bank Institute. Since the main purpose of the present study is to investigate the role of knowledge-based economy in the agricultural sector of selected countries with emphasis on Iran, besides considering the factors of capital and labor force which are also used in Solo growth model, Endogenous Growths in Explaining the Residual Component of Growth, The Role of Components of knowledge-based economy was been investigated. fixed effects method was used to investigate the role of knowledge-based economic in the agriculture growth of selected countries with an emphasis on Iran.
The results showed that during 2008-2009, the average of knowledge-based economy index increased from 4.07 to 5, indicating a relatively "poor performance" of Iran in knowledge-based economy index. also, the results showed that the variables of capital stock, employment, and knowledge-based economic index have a significant and positive effect on the agricultural growth of selected countries. Out of the elasticities of capital stock (0.26), employment (0.075) and the of knowledge-based economics index (0.90), the most significant is related to the knowledge-based economy index, and it shows the importance of knowledge-based agriculture is important.
Suggestion
According to the result, science knowledge-based economic is one of the components of the resistance economy, Coordination between agricultural education and research activities is essential in order to move from resource-based agriculture to knowledge-based.
 JEL Classification: O1, O4, O41.

Wheat as a staple food of the Iranian people plays a special and essential role in ensuring the food security of the country. Therefore, due to the importance of wheat consumption in the country, several protection policies have been implemented to improve the self-sufficiency of this crop. However, official statistics show that despite the efforts made, the stable production of wheat in Iran remains far from reliable. Hence, for many years a significant portion of the country's wheat consumed is supplied by imports. Therefore, considering the importance of identifying dynamic processes in the wheat production and wheat supply chain in Iran such as climate change and population growth, this study aimed to evaluate the effectiveness of a guaranteed purchase policy in stabilizing wheat production for the time horizon of 2025 as a long-term period.
In this study, by designing a dynamic partial equilibrium model, the processes in the production and supply chain of wheat in Iran were simulated. Dynamic partial equilibrium models are among mathematical programming models and have the capability of simultaneously simulating different aspects of production and trade of goods with respect to dynamic processes in the field. Therefore, in this study, various components of wheat production and different dimensions of supply chain of this product from the beginning of inputs demands to the end of wheat storage were simulated for the period. The demand functions of inputs was estimated by using the profit function approach and the irrigated seemingly unrelated regression estimation method (ISUR). The econometric functions specified for yield, area under cultivation, import and export of wheat were also estimated using the autoregressive distributed lag model (ARDL). After estimating the required parameters, the dynamic partial equilibrium model was first calibrated to reproduce the mean value of the data for the years 2014 to 2016 as the base year. Then, the exogenous variables in the model were predicted using double exponential smoothing and additive Holt-Winters methods for the years 2017 to 2025 and the dynamic partial equilibrium model was simulated for this time period.
The results showed that the adoption of a guaranteed purchase policy in addition to encouraging farmers to allocate arable lands to wheat planting also influences their derived demand for allocating production factors. In this case, with the proper implementation of the policy, in addition to a minimal fluctuation of the area under cultivation, the limitation of the demand for production factors by the farmers is minimal and has the least possible fluctuation. Therefore, the results showed that the wheat yield fluctuation would also be as low as possible under this condition. In the following, the results showed that the total volatility of wheat production in the country will be minimal with the proper implementation of this policy and in the time horizon of 2025 if the guaranteed purchase policy is properly implemented, the average wheat production in the country will be about 12 million tons per year. Based on the results, according to the country's population growth process in the 2025 time horizon, an average of about 9.8 million tons of wheat is needed each year for bread production. In addition, about 2 million tons of wheat will be needed each year for the industrial sector. Thus, in the time horizon of 2025, an average of about 12 million tons of wheat would be needed each year. However, domestic production of wheat after deducting self-consumption, seed production, and process loss would eventually cover about 9.5 million tons of total demand. In this condition, on average, about 84 percent of the country's total consumption of wheat would be provided from domestic production per year.
Suggestion
According to the results, focusing on improving productivity in wheat production in the country with the aim of enhancing the yield of this crop is an important goal that by investing more in agricultural research policies as a complement to the purchase policy can guarantee a stable self-sufficiency. Therefore, in this study, it is suggested that in order to stabilize wheat production in the country, first, the maximum potential of guaranteed purchasing policy should be implemented and, secondly, policies related to wheat yield improvement should be taken into consideration. In this context, future research needs to address the question of how much production elasticity and supply of wheat and the index of self- sufficiency of this product will be due to technological and research changes in yield improvement.
JEL Classification: C02; Q18

Considering that the agricultural sector is strongly dependent on climate parameters of temperature and precipitation, it reacts rapidly related to climate change. Farmers are not able to control the climatic conditions, but management and optimization of the cropping pattern according to the region's climate can reduce the effects of climate change on the yield of agricultural products.
In this research, the effects of climate change on the yield, gross margin and Cropping Pattern of Gorgan County were investigated. For this purpose, at first, by using the regression analysis, the effects of climate variables on temperature and annual precipitation on the yield of selected products during the period of 1367-1396 were investigated. Then, the climate change of the study area was predicted for the upcoming periods (2021-2040), the near future (2051-2070) and the far future (2081-2100) by General Circulation Model HadGEM2. in the end, the region's cultivated area was stimulated by the application of Positive Mathematical Programming (PMP) and the effects of climate change on the cultivated area in the mentioned periods were investigated.
The results showed that climate parameters such as temperature and precipitation have a significant effect on the yield of selected products. Also, by applying predictions of climate change in the cropping pattern model, Potato with 0.27 and 71.7 percent increase, the highest increase in yield and cultivated area respectively, and High-quality long-grain rice with 0.17 percent reduction have the highest decrease in yield and barley with 89.1 percent reduction have the highest decrease in the cultivated area. and the gross margins of farmers were increased in all three periods.
Suggestion: As a result, it could be mentioned that consideration of the effects of climate change and improving the productivity of agricultural products, can decrease the negative effects of this event.
 JEL Classification: C22, C02, Q25, Q54