1、 Introduction
During the 12th Five Year Plan period, although China's economy entered the "new normal" characterized by the "superposition of three phases", and economic growth was facing downward pressure, it still maintained a long-term positive development trend. Agricultural grain production has achieved "Twelve consecutive increases", the growth rate of farmers' income has exceeded the growth rate of urban residents' income, and has also achieved "Twelve consecutive increases", the income gap between urban and rural areas has narrowed, and the construction of new rural areas is making effective progress. However, new difficulties and contradictions in economic development have gradually emerged through the accumulation of a period of time. The economic growth rate has slowed down and economic structural contradictions have become prominent. The overall backwardness of agricultural production technology and the coexistence of high cost, high storage and high import of surplus agricultural products, the scale of grain imports has been rising, while the domestic grain inventory collected and stored by the city has also remained high, showing a strange phenomenon of "three simultaneous increases" in birth output, import volume and inventory, which will affect the sustainable development of China's agriculture in the long run. This puts forward a new topic for academic research in the economic circle in theory and practice. It can be said that the supply side structural reform is a theoretical innovation based on China's reform practice for more than 30 years and combined with the new characteristics of the current stage of economic development (Xiao Lin, 2016).
At present, the discussion of agricultural supply side structural reform in the economic circle mainly includes three aspects: first, the reform of land system; Second? Y structure adjustment; The third is the reform of grain price system and subsidy system (kongxiangzhi, 2016). Guozhenzong (2016) believes that the agricultural supply side structural reform is a systematic project involving institutional reform, organizational innovation, structural adjustment, factor integration, technological progress, market development, policy support and many other aspects. Therefore, the agricultural supply side structural reform must be systematically promoted, top-level design and overall planning. Xu Jingyong (2016) believes that the structural contradiction on the agricultural supply side is due to the distorted function of the market in regulating supply and demand and allocating resources, resulting in structural surplus and structural shortage. Due to the different nature of agriculture and manufacturing, the supply side structural reform of agriculture cannot be copied from the supply side structural reform of manufacturing. Jiang Weiguo (2016) interpreted the agricultural supply side structural reform from the perspective of macroeconomic demand management and supply management, and believed that at a time when the marginal effect of demand management in dealing with China's economic problems is decreasing day by day, and the implementation costs and risks have been higher than the expected results, the introduction of supply management is the general trend; It also points out that the root of the supply side structural contradictions in China's agricultural development lies in the supply side, and advocates accelerating the agricultural supply side structural reform from the aspects of labor, land, capital, innovation and institutional arrangements, so as to realize the long-term effective and sustainable supply of agricultural products in China.
Since the reform and opening up, many scholars have studied the price mechanism of China's agricultural products market. Ke Bingsheng (1991) believed that it is the free market price that restricts farmers' production in China's grain market, and the response of grain production to price is very low. Sun he et al. (1999) believed that Chinese farmers have sufficient response to the price of agricultural products, and they make investment and labor decisions according to the price changes. Therefore, it is effective for the government to use price leverage to adjust the balance between supply and demand of agricultural products. Cheng Guoqiang (2009) believes that with the formation of the mechanism that the price of agricultural products is mainly determined by market supply and demand, the change of supply and demand of agricultural products has become a direct factor affecting price fluctuations, and the cobweb fluctuation characteristics of the interaction between price and output are obvious. Cai Rong et al. (2007) analyzed the formation mechanism of the price of agricultural products wholesale market from the perspective of new institutional economics, and believed that the formation of product price was the result of the game between the trading parties in the market. Wang Chuan (2014) believed that the minimum purchase price could not reflect the real level of grain market prices, resulting in the distortion of grain prices.
Through combing the existing literature, it is found that the existing research mainly focuses on the necessity and theoretical analysis of fiscal expenditure for supporting agriculture and the performance evaluation of fiscal subsidies (Hou Shian, 2007; Jin Limin, 2007; Mu Yueying, etc., 2008). The necessity of fiscal expenditure has reached a consensus in the theoretical circle. At the same time, some scholars think about the current fiscal policy of supporting agriculture and point out the shortcomings. An Guangshi (1999) believed that China's financial investment in agriculture has problems such as insufficient investment, unreasonable investment structure, imperfect investment system and so on. An Tifu and Wang Haiyong (2005) believed that in order to solve the problems of "dislocation", "vacancy" and "offside" of financial funds, the government needs to increase financial transfer payments, especially for backward areas and western regions, and increase investment in rural compulsory education, scientific research and public health. Zhang Junwei (2006) pointed out that China's fiscal policy to support agricultural development has some problems, such as the lagging transformation of government functions, low administrative efficiency, and the lagging construction of the public finance system. Shi Hong (2011) believes that there are problems in the public finance supporting the development of modern agriculture, such as insufficient financial support scale, unreasonable investment structure and decentralized fund management system.
These literatures on agricultural product prices and fiscal support policies do not involve the structural reform of the agricultural supply side, and it is relatively rare to combine the two in such studies at present. This paper aims to discover the logical relevance between the two by analyzing the deep-seated factors of the structural contradiction of the agricultural supply side, and explain and prove them with theoretical tools and econometric analysis. Even the existing research on the structural reform of the agricultural supply side basically only qualitatively studies the structural contradictions of agricultural supply, and rarely excavates the deep-seated reasons for the structural contradictions of the agricultural supply side. The author believes that the deep-seated factor of the structural contradiction on the agricultural supply side lies in the price distortion effect of the agricultural product market, and the current fiscal policy of supporting agriculture has not achieved the expected policy effect, but deepened the degree of distortion of agricultural product prices, and to a certain extent aggravated the structural surplus in the agricultural product market.
2、 Structural contradictions and deep-seated factors on the agricultural supply side
At this stage, the structural contradictions on the agricultural supply side are mainly manifested in the contradictions of variety structure, quality structure, high agricultural production costs and backward agricultural production technology.
（1） Structural surplus of varieties of agricultural products supply
With China's economic development, people's income has increased steadily, and the consumption structure of residents has been upgraded day by day, especially the food consumption structure has been qualitatively improved. The demand for animal protein such as meat, milk, eggs and aquatic products, as well as vegetables and fruits, has increased, and the demand for grain consumption has accordingly declined. At the same time, the industrialization process and the development of animal husbandry have accelerated, and the demand for industrial grain and feed grain has increased. In the past, planting industry focused on the production of food crops, while ignoring the grass husbandry of raising cattle and sheep, and the supply of grass husbandry lagged behind the demand of animal husbandry production. As shown in Figure 1, from 2004 to 2014, the planting area of green fodder decreased from 3349.18 thousand hectares to 2018.44 thousand hectares, a decrease of 1330.74 thousand hectares, a decrease of nearly 40%; And many areas suitable for planting grass and animal husbandry have been planting food crops for a long time, which has caused certain damage to the ecological environment, and the food production is low, the income is poor, and the gain is not worth the loss. On the whole, the structural contradiction of varieties in the supply of agricultural products is highlighted in the oversupply of corn, while the gap between supply and demand of soybeans, cotton, oilseeds, sugar and other materials is expanding year by year, and imports are increasing. According to the latest statistical data of the National Bureau of statistics, in 2015, China's corn planting area reached 38116.6 thousand hectares, and the corn output was 224.58 million tons ①, while the national temporary collection and storage reached 52% ②. At the same time, the national corn subsidy policy has raised the price of corn. Compared with soybeans and potatoes with low yield and poor income, planting corn has greater benefits. Therefore, under the dual effects of the national temporary collection and storage policy and the price subsidy policy, the supply structure of agricultural products is gradually distorted, and the normal role of the market in resource allocation is disturbed.
（2） Quality structural contradiction of agricultural product supply
In the past, the agricultural subsidy policy only focused on the increase of output, and used the price "scissors difference" to distort the price of industrial and agricultural products, so as to complete the original accumulation of agricultural transmission to industrial development. This kind of inertia control thinking of "holding price by quantity" also affects the current "food security" and "farmers' income". The extensive production mode that distorts the price lever, stimulates the pursuit of output and ignores quality is rampant, thus contributing to the excessive use of fertilizers and pesticides in farmers' production, which is not conducive to the transformation of agricultural development mode. Relying on the traditional extensive agricultural production mode, in order to pursue the high yield of grain, the excessive use of chemical fertilizers and pesticides has not only pushed up the production cost of grain, but also affected the quality of grain; At the same time, it leads to the destruction of soil fertility and the pollution of water resources.
Judging from the planting area of the three main grain crops ③ in China at present, a large part of them are some varieties with low quality and low price, which are difficult to meet the current market consumption demand. On the one hand, in order to maintain the stability of the grain market and protect farmers' income, the state can only purchase and store them, resulting in a backlog of inventory; On the other hand, in order to meet consumer demand, a large number of high-quality grain are imported from abroad, which leads to the imbalance of grain import and export. The insufficient demand for low-end varieties and excess production are caused by the inversion of market prices at home and abroad, and more importantly, by the low quality and high cost of agricultural products in China.
（3） High agricultural production costs
China's agricultural development mode has been carried out in an extensive way of "high input, high energy consumption and low output". For example, the increase of grain production depends on the input of pesticides, fertilizers and other factors, ignoring the law of diminishing marginal returns of factor input. Among them, the high agricultural production cost is an important factor affecting the high price of agricultural products. China has more people and less land, and agricultural development is facing severe resource and environmental constraints. In the process of industrialization and urbanization, many local governments focus on "land finance", and a large number of cultivated land is converted to non-agricultural land; At the same time, due to the intensification of soil erosion and land desertification, the cultivated land area has decreased year by year. In addition, among the existing cultivated land, soil fertility and cultivated land quality are not optimistic. In the face of such a severe reality, in order to maintain the supply of agricultural products, we can only rely on a large number of additional material elements (especially chemical fertilizers and pesticides). It is not difficult to see that the driving force of the high cost of agricultural production lies in the relative distortion of the prices of industrial and agricultural products, which leads to the excessive investment of agricultural production factors. The price subsidy mechanism of agricultural products has prompted farmers to rely on national policies, distorted the transmission mechanism of price signals, distorted the price of agricultural products, and failed to truly reflect the driving effect of costs on price rise.
As can be seen from Figure 2, the production costs of the three main grain crops in China have increased year by year. The average cost per mu of three crops increased from 485.79 yuan in 2009 to 864.63 yuan in 2014, an increase of 77.98%. Since 2012, the number of working age people in China has begun to decline, the demographic dividend has gradually decreased, and labor costs have continued to rise. The proportion of labor cost in production cost increased from 38.78% in 2009 to 51.67% in 2014, an increase of nearly 13 percentage points. It shows that the rise of labor costs has boosted the rise of agricultural production costs. Although land rent costs and service and material costs are also increasing year by year, the overall increase is less than labor costs.
In terms of service and material costs, the expenditure on fertilizers and pesticides has been increasing. According to agricultural statistics, the use of pesticides and fertilizers in China's agricultural production has been increasing year by year (see Figure 3). Although the annual growth rate is not very large, considering the actual situation that China's cultivated land area is decreasing year by year, the average use of chemical fertilizers and pesticides per unit of cultivated land area continues to rise. Taking the three main grain crops as an example, the expenditure of chemical fertilizers and pesticides per mu accounts for more than 40% of the service and material costs ④.
（4） Backward agricultural production technology
Agricultural production technology is the important foundation of agricultural modernization and the key factor to improve agricultural productivity. Since the implementation of the household contract responsibility system, although farmers' enthusiasm for production and labor has been activated to a certain extent, the fragmentation of land scale and the decentralized management system with farmers as production units are not conducive to the promotion and application of agricultural science and technology, and have become increasingly unsuitable for the development trend of modern agriculture. The level of agricultural technology in China is generally low, lagging behind developed countries, and lacking the support of modern science and technology in the production, storage, processing, sales, transportation and other links of agricultural products, which has restricted the improvement of the comprehensive level of agricultural science and technology for a long time. Although agricultural scientific and technological achievements seem to be many, most of them can not solve the practical problems encountered in the process of agricultural production and management, and the promotion and utilization rate of scientific and technological achievements is not high. Modern human capital theory shows that the transformation of traditional agriculture needs to increase the input of agricultural science and technology elements and the training of agricultural practitioners. At present, the prominent problem of China's financial support for agriculture policy lies in the insufficient investment in agricultural science and technology and agricultural practitioners. At the same time, due to the guidance of the policy, domestic agricultural scientific research and teaching institutions have been pursuing high-rise projects with the goal of scientific research innovation and major breakthroughs, lack of understanding of the real situation of the application of science and technology in the first line of agricultural production, and neglect the practicality and diversity of agricultural science and technology, It also ignores the education, training and promotion of agricultural technology, which makes the reduction of agricultural production costs and the improvement of agricultural product quality lack of timely follow-up and support of modern agricultural technology.
The promotion and use of any science and technology also depends on the quality of workers, and "aging, feminization, low culture" is a common phenomenon of Chinese agricultural workers at present, "part-time, sideline, extensive" has become the basic trend of agricultural production and management (Chen Wensheng, 2014). The low education level of labor force limits the improvement of agricultural productivity. In addition to the impact of the long-term unbalanced development of urban and rural education, the main reason for this generally low educational level of agricultural workers is that in the rapid promotion of industrialization and urbanization for more than 30 years, the comparative income of agriculture is lower than that of industry, and many excellent talents are unwilling to work from business agriculture, and a large number of powerful rural labor force flows to cities. Therefore, the cultural quality and labor skills of workers still in agricultural production are difficult to match the development requirements of modern agriculture, which hinders the promotion of agricultural science and technology.
To solve the above-mentioned structural problems of agricultural supply side, the core is to change the mode of agricultural development. To change the mode of agricultural development is to adopt an intensive, efficient, green and environmental friendly agricultural model instead of an extensive one? Dan fan a ganche └? Safety, environmental protection, resource conservation, farmers' income increase and agricultural efficiency increase are important objectives of the structural reform of the agricultural supply side, and also the basis for the sustainable development of the national economy. At present, the transformation of agricultural development mode is not achieved overnight. It is faced with practical difficulties in resources, environment, systems and mechanisms. 3、 Theoretical analysis
At present, the deep-seated reason for the contradiction of agricultural supply side structure lies in the failure of the price mechanism of agricultural products market and the government fiscal effect. The structural contradiction on the agricultural supply side shows that: on the one hand, agricultural prices have fallen, and grain prices have hurt farmers. On the other hand, it intensifies the financial burden, and the marginal income of financial support for agriculture decreases. China is in the transition stage from traditional agriculture to modern agriculture. In this stage, the government needs to increase investment in agriculture to improve agricultural production conditions, improve agricultural production technology, update agricultural production equipment, cultivate modern farmers, and improve the price formation mechanism of agricultural products trading market. It can be seen that the government's intervention in agricultural development is very necessary, which is understandable, but how to intervene appropriately and reasonably, so as not to produce major negativity, which is a relationship between the government and the market that needs to be carefully understood and handled when solving the structural contradictions on the agricultural supply side.
（1） The price effect of agricultural products and factor markets
Under the condition of market economy, a reasonable and effective price mechanism of agricultural products is a necessary condition for the healthy development of agriculture, and it is also the key to solve the current structural contradictions on the agricultural supply side. Some experts pointed out that the catch-up strategy once implemented in China has led to the fact that the marketization process of production factors lags behind the marketization of products, artificially suppressing the price of factor input, resulting in the distortion of the factor market (Lin Yifu, 2004). The particularity of the factor market of agricultural products is very likely to cause price distortion, which will lead to the distortion of resource use structure (shengshibin et al., 1995). As a result of the externalities of the market, farmers use too much chemical fertilizers, pesticides and agricultural films in the production process to maintain the high yield of grain. They try to retain the benefits of growing grain in the downward channel of agricultural product prices, but ignore social costs and social benefits, which actually violates the law of diminishing marginal returns of factor inputs. As mentioned in the above analysis, the increase in the cost of agricultural products is the main reason for pushing up the price of products (see Table 1). The total cost and production cost of the three kinds of grain are increasing year by year, and the increase is greater than the selling price. The increase in costs directly eroded the net profits of the three grain production.
At the same time, the improper intervention of the government in the agricultural product market is another factor causing the distortion of the agricultural product price market. In the process of transition from planned economy to market economy, the government intervenes in prices through trading markets, production markets and trade mechanisms, which affects the relative distortion of industrial and agricultural product prices (Zhang Ming et al., 2014). Although the government has established a minimum protective price for the purchase of agricultural products, this mechanism that cannot sensitively reflect the changes in market supply and demand is very likely to maintain the price of a large number of agricultural products purchased and warehoused in a relatively unchanged situation. For example, the minimum purchase price of grain only considers the cost compensation of grain production, which cannot reflect the real price of the grain market, and cannot reflect the changes in market supply and demand, And the minimum purchase price of grain distorts the price mechanism of the grain market. The national minimum purchase price of grain has been maintained at a relatively stable level, which has not increased with the increase of agricultural production costs, nor has it been adjusted according to the supply and demand changes in the grain market, as shown in Table 1 and table 2. At present, the problem of high grain inventory in China is largely caused by state supported prices. The national grain "supporting the market" policy distorts the function of market allocation of resources ⑤, thus transmitting the signal of distorted agricultural product prices and intensifying the supply constraints of agricultural product production; In addition, the generally low price of agricultural products has stimulated the growth of demand, resulting in the expansion of the gap between supply and demand.
From the perspective of deeper institutional factors, the legacy of the agricultural development model left by the planned economy period largely determines that agricultural development is led by the government, and national policies have a deep impact on agricultural development. Under the original planned economic system, the government led agricultural production, which has the characteristics of excessive control and death, and its influence depends on the path transmission for a long time and far-reaching, so that in today's Chinese agricultural development model, the situation of "offside" or "dislocation" of the government can still be seen. For example, due to the unreasonable agricultural subsidy policy of the government, the growth of agricultural output depends too much on the input of factors, and the market supporting purchase policy of agricultural products further causes the price of grain market to not reflect the real changes in supply and demand; At the same time, farmers have the expectation of psychological dependence on government policies. Take corn as an example. Due to the National Trust purchase of corn, many non advantageous areas that are not suitable for planting corn, driven by interests, farmers have planted corn one after another, resulting in the continuous increase of corn planting area and output. Due to the influence of climate conditions, the quality of corn produced is low, which not only causes a large amount of inventory backlog, but also reduces the production of other crops.
（2） ?? The effect of fiscal support for agriculture is decreasing
The position of agriculture in the national economy and the weakness of agriculture are the starting points of fiscal support for agriculture policy. The government's fiscal support for agriculture policy itself helps to stabilize the price of agricultural products in a certain cycle and prevent severe economic fluctuations. It is a policy tool for the sustained, benign and healthy development of the national economy. It can be said that fiscal policy has the function of internal stabilizer, which can automatically stabilize the economic operation of an economic system and reduce the interference of external factors to the economy. The particularity of agricultural industry and the characteristics of agricultural management determine the necessity of financial support. The comparative income of agricultural production has always been lower than that of other industries. Driven by interests, not only the resources flowing to the agricultural sector are relatively reduced, but also the resources originally used for agricultural production will gradually flow out. There are still serious "sieve phenomenon" and "false investment phenomenon" in fiscal expenditure on agriculture. On the one hand, the total amount of financial support for agriculture cannot meet the needs of agricultural development, and governments at all levels have intercepted agricultural support funds at various levels, which greatly reduced the financial support for agriculture expenditure; On the other hand, unreasonable financial subsidies distort the market price of factors, increase the marginal cost of agricultural production, and reduce the marginal benefit of agricultural input, resulting in diminishing fiscal effects, or even negative fiscal effects.
In development economics, the development stage growth theory is a theory proposed by Richard A. Musgrave and Walt Whitman Rostow to explain fiscal expenditure respectively. This theory analyzes the relationship between different stages of economic growth and fiscal expenditure, and believes that the amount and role of fiscal expenditure are different in different stages of economic growth. According to the theoretical analysis of the development stage, China is currently in the middle and late stage of industrialization, and the fiscal expenditure will further increase, but the structure of fiscal expenditure will change from focusing on infrastructure construction in the past to paying more attention to education, culture, scientific and technological progress and social security. The actual situation of China's agricultural development determines the total expenditure and expenditure structure of fiscal support for agriculture policy. Although the absolute scale of fiscal expenditure on supporting agriculture has increased year by year (see Figure 4), the relative scale (the proportion of fiscal expenditure on supporting agriculture in the total fiscal expenditure) shows a trend of phased decline and phased rise (see Figure 5), and fiscal expenditure on supporting agriculture has always been biased towards agricultural infrastructure construction, paying insufficient attention to agricultural production safety that endangers food safety, and did not support the establishment of a traceability system for the safety and quality of agricultural products; The informatization degree of agricultural production is low, and the support for the construction of various agricultural socialized service systems before, during and after production is not strong; The proportion used in agricultural science and technology is low, and the investment in scientific and technological training of agricultural practitioners and the cultivation of professional farmers is ignored, which leads to the problems of poor financial support for agriculture, low utilization rate of agricultural science and technology, low education level of agricultural practitioners and low quality of agricultural products. These problems are mainly reflected in the supply and demand of agricultural products market, which is a coexisting structural contradiction between the oversupply of green high-quality agricultural products and the oversupply of polluting low-quality agricultural products.
4、 Statistical description and quantitative analysis (I) statistical descriptive analysis
1. Analysis of the impact of fiscal policy on grain production. In order to measure the impact of Finance on grain output, the elasticity theory is used to analyze the reflection degree of grain production on the productive expenditure of financial support for agriculture. The calculation formula is as follows:
E=■
M0t=■； K0t=■
Where e is the contribution rate of the productive expenditure of financial support for agriculture to the increase of grain output; MT and MT-1 are the grain output of the report period and the previous period respectively; KT and KT-1 are the productive inputs of national financial support for agriculture in the reporting period and the previous period respectively. The data of productive expenditure of financial support for agriculture adopts the expenditure of supporting agricultural production used in agricultural expenditure by the national finance in China Rural Statistical Yearbook (2015); The per capita grain output of farmers is calculated based on the total grain output in the China Rural Statistical Yearbook (2015) and the number of primary industry employees among the three industry employees in the China Statistical Yearbook (2015).
It can be seen from Figure 6 that the change in the growth rate of productive expenditure of financial support for agriculture has a great impact on the per capita grain output of farmers. Specifically, when the increase in productive expenditure of financial support for agriculture is large, the impact on the per capita grain output of farmers is small; However, when the productive expenditure of financial support for agriculture increases slightly, the per capita grain output of farmers will decline. It shows that the negative effect of the productive expenditure of financial support for agriculture on the per capita grain output of farmers is greater than the positive effect. Before 2003, the total grain output and the per capita grain output of farmers showed a continuous downward trend, which was due to the reduction of cultivated land area and the excessive non-agricultural occupation of cultivated land. After 2003, the state increased its support for agriculture, the reduction of cultivated land area slowed down, and the total grain output also increased.
The results of the impact of fiscal support agricultural expenditure on total grain output, rice, wheat, corn, soybeans and potatoes calculated according to the data of China Rural Statistical Yearbook (2015) show that, in general, the impact of fiscal support for agriculture on grain crops is structurally unbalanced. The productive expenditure of financial support for agriculture has a relatively stable impact on the output of rice, wheat and potato crops; The impact on corn and soybean fluctuates greatly, among which the impact on corn is positive, while the impact on soybean is negative.
2. Price distortion effect of agricultural products. The author uses the calculation method of Zhang Ming and Xie Jiazhi (2014) on the degree of distortion of the relative price of industrial and agricultural products under government intervention to measure the degree of relative distortion of the price of industrial and agricultural products. Its calculation formula is: η= （P1t-1/P2t-1）/（P*1/P*2）
Where η For the degree of price distortion of industrial and agricultural products, η> 1. And the larger it is, the higher the degree of price distortion is. Figure 7 shows the relative distortion of the prices of industrial and agricultural products in China from 1991 to 2014. From 1991 to 2002, there was an upward trend, and the structural upward trend of industrial and agricultural products was obvious; With the gradual improvement of China's agricultural product price system, the price distortion of agricultural products has slowed down during the 12th Five Year Plan period.
（2） Empirical analysis
1. Model setting. The variable names and data sources in the model are shown in Table 3. The production price index of agricultural products takes 1978 as the base period, and the value is 100. Due to the change of statistical caliber, the data of 2013 and 2014 in the fiscal expenditure data of "agriculture, rural areas and farmers" are from the national fiscal expenditure on agriculture, forestry and water affairs in the China Statistical Yearbook. Take the natural logarithm of the data to eliminate heteroscedasticity as much as possible.
Model 1:
lnap= β 1+ β api1lnapi+ β pfe1lnpfe+u1
Government intervention in the market has become an important factor affecting price distortion, especially in China in the transition period. Agriculture is the foundation of the national economy, and the fiscal policy of supporting agriculture is also an important factor affecting the price of agricultural products. In order to test the impact of the fiscal support for agriculture policy on the price distortion of agricultural products, the price distortion of agricultural products is fitted with the fiscal support for agriculture expenditure, and the regression equation is as follows:
lnapd= α 0+ α apdpfelnpfe+e0（1）
Taking the price distortion of agricultural products as the adjustment variable of fiscal expenditure on "agriculture, rural areas and farmers" affecting grain output, the interaction between fiscal effect and agricultural product price is included in model II, and model II is derived:
lnap= β 2+ β api2lnapi+ β pfe2lnpfe+ β pfeapd1lnpfe*lnapd+u2
Lnpfe in model 2 × lnapd? Lindp? The adjustment variable of expenditure PFE, its coefficient β Pfeapd1 measures the adjustment effect of price distortion.
The level of agricultural mechanization, as an intermediary variable of fiscal support for agriculture policy affecting grain output, has a regression equation of formula (2):
lnalp= α 1+ α pfelnpfe+e1（2）
Substitute equation (2) into model 2 to obtain equation (3):
lnap=（ β 2+ β alp α 1）+ β api2lnapi+（ β pfe2+ β alp α pfe）lnpfe+ β pfeapd1lnpfe × lnapd+（u2+ β alpe1） （3）
On the basis of model 2, add the mechanization level as an intermediary variable to obtain model 3 with regulatory effect and intermediary effect:
lnap= β 3+ β api3lnapi+ β pfe3lnpfe+ β pfeapd2lnpfe*lnapd+ β alp1lnalp+u3
In model 2, β Pfe2 is the total effect of fiscal policy on grain output after excluding price distortions, and the coefficient of lnpfe in model III β Pfe3 is the direct impact of Finance on grain production, β Pfeapd2 is a price distortion effect with intermediary effect. β alp1 α PFE is the indirect impact of fiscal policy on grain production.
2. Regression analysis. Carry out regression analysis on formula (1), formula (2), model 1, model 2 and model 3 respectively, and the results are shown in Table 4.
The regression results show that except that the fiscal effect in model 1 is not significant, the variables of other regression equations are relatively significant. The sequence correlation test was carried out on Model 1, model 2 and model 3 respectively. The results showed that only model 2 and model 3 did not have sequence correlation at the 1% significance level, while model 1 had sequence correlation problems, indicating that there was no sequence correlation problem when adding regulatory variables and intermediary variables, and its regression structure was acceptable.
Among them, the indirect effect of intermediary effect is:
β alp α pfe=-0.341 398 6 × 0.348 025 6=-0.118 815 5
3. Inspection and analysis. The test of regulation effect is relatively simple. Generally, it is only required to consider the regulation effect, R2 of the model and the coefficient of the test interaction factor. From the regression results, it can be seen that R2 in model 2 and model 3 is greater than that in model 1 and increases one by one; At the same time, the interaction factors of fiscal and agricultural product distortion in model 2 and model 3 are significant. Therefore, the degree of price distortion as a regulatory variable of fiscal expenditure affecting grain output is significant.
At present, there are three kinds of test methods for mediating effect, namely, coefficient difference method, causal step method and coefficient product method. However, because the coefficient difference method has great defects and is not suitable for complex intermediary effects involving multiple intermediary effects or regulatory effects, it is rarely used in this case (Fang Jie et al., 2012). The author tests the mediation effect with three methods. Test H0: α Pfe=0 and H0: β alp1=0。 If these two hypotheses are rejected, it means that the mediation effect is significant, otherwise, it is not significant. The main problem of this method is that when the intermediary effect is weak, the efficiency of the test is very low. According to the regression results, it is obvious that the test effect of this method is remarkable.
Test H0: β alp1 α pfe=0。 If the original hypothesis is rejected, the mediating effect is significant. The key of the original hypothesis is to calculate the standard deviation. There are many methods. The author uses Soble (1982) to obtain the approximate formula based on the first-order Taylor expansion as follows:
S β alp1 α pfe=■（4）
S in equation (4) α PFE and S β Alp1 is the standard deviation of the estimated coefficients ■ PFE and ■ alp1 respectively, and the test statistics are:
z=■，
From this, s can be calculated β alp1 α pfe=0.051 837，z=-2.292 1，
1.96 < | Z | <2.58, p<0.05, so it is significant at the 5% significance level.
Test H0: β pfe2- β pfe3=0。 If the original hypothesis is rejected, it means that the mediation effect is significant, otherwise it is not significant. The drawback of this method is that even if the intermediary effect does not exist, as long as β If alp1 is significant, the mediation effect must be significant. Therefore, this method has a high probability of making the first kind of errors. The key to this test is to calculate the standard deviation of ■ pfe2- ■ pfe3. The formula derived by Freedman (1992) has been proved to have great effect in the study of MacKinnon (2002) and others. Its calculation formula is:
s β pfe2- β pfe3=■（5）
In formula (5), sbpfe1 and sbpfe2 are the standard deviations of the estimation coefficients ■ pfe2 and ■ pfe3 respectively, R is the correlation coefficient of the variables lnpfe and lnalp, r=0.990445, and the test statistics are:
t=■，
The calculated t statistic is -1.924, 1.711 < | t | <2.064, p<10%, indicating that it is significant at the significance level of 10%.
Based on the above test results of regulatory effect and intermediary effect, model 3 better explains the price and fiscal effect in China's grain supply, in which price has a positive effect on grain production, but the distortion effect of grain price has a restraining effect on grain production; At the same time, fiscal policy is an important factor affecting grain production. Generally speaking, fiscal policy has promoted the increase of grain supply, but at present, China's fiscal support for agriculture policy distorts the price of agricultural products. The level of agricultural mechanization, as an intermediary variable of fiscal expenditure on agriculture, has a significant intermediary effect on food production. Since the reform, the main body of China's agricultural production and management has been farmers' production. Practical experience shows that the characteristics of decentralized farmers' production and management are not conducive to the improvement of the level of agricultural mechanization. Therefore, as an intermediary variable of fiscal support for agriculture policy affecting grain production, it has restrained the supply of grain production to a certain extent.
5、 Main conclusions and policy considerations
China's supply side structural reform is different from the supply side macro management policies of western developed countries in the 20th century, which are characterized by tax reduction and deregulation based on Neo liberal economics. The core of China's supply side structural reform is the adjustment of economic structure and the transformation of economic development mode. By improving the adaptability and flexibility of supply structure, we can improve total factor productivity (Hu Angang et al., 2016). The agricultural supply side structural reform is an important aspect of the supply side structural reform. It is the key to solve the new problems of the development of "agriculture, rural areas and farmers", improve the quality, efficiency and competitiveness of agriculture, and promote the sustained and rapid growth of farmers' income.
Therefore, the author analyzes the price and fiscal effect in the structural contradiction of agricultural supply side, and the research conclusion shows that the deep-seated factor affecting the structural contradiction of agricultural supply side lies in the distortion of agricultural product market price and fiscal policy. The main mistake of the price policy of agricultural products is that the minimum purchase price policy of agricultural products can not fully reflect the changes of supply and demand in the market, which often leads to the distortion of the price signal, which is contrary to the normal play of the price mechanism. The occurrence of this situation lies in the joint action of market and government failure. The price distortion of agricultural production factor market is amplified, and the price distortion of factor market is the main driver of higher costs in the structural contradiction of agricultural supply side. The failure of fiscal policy further amplifies the distorting effect of agricultural product prices and inhibits the effective supply of agricultural products.
Empirical analysis shows that although the price of agricultural products has a positive effect on grain supply, the price distortion effect of agricultural products inhibits the supply of grain. Although fiscal expenditure on agriculture promotes the increase of grain supply, the deviation of fiscal expenditure expands the price distortion effect; At the same time, the level of agricultural mechanization, as an important intermediary variable of fiscal expenditure on supporting agriculture affecting the supply of agricultural products, also inhibits the effective supply of agricultural products to a certain extent. The main reason is that the effect of the "four items" subsidy policy of national fiscal expenditure on "agriculture, rural areas and farmers" is decreasing, and the policy performance is gradually decreasing. First of all, the funds have not been implemented where they are really needed. Many farmers who have left the land can still enjoy agricultural subsidies, while some large farmers who contract the land have not been able to enjoy the care of national policies in time; Secondly, subject to the small-scale operation of scattered farmers, advanced agricultural production technology and modern management methods are difficult to be popularized and applied; Finally, there is a shortage of talents who master modern agricultural science and technology. The level of professional knowledge and labor skills of agricultural business entities are generally low. Many rural educated young people are unwilling to take root in the countryside and engage in agricultural production. A large number of elite agricultural labor forces have been transferred, and there is a tendency of "hollowing out" in the countryside.
To effectively solve the problems in the current agricultural supply side structural reform, we must systematically correct and reform the problems in the price mechanism of agricultural products and the policy of financial support for agriculture, and correctly coordinate the relationship between the government and the market in the allocation of resources.
First, we should reform the current price formation mechanism of agricultural products, eliminate the distorting effect of grain price support policies, and gradually eliminate the minimum income of agricultural products? At the same time, we should give better play to the guiding role of market signals. The minimum purchase price of agricultural products can not reflect the changes of market information in time, and only consider the compensation of agricultural production costs, which is not conducive to the increase of agricultural production income; Moreover, the state reserves a large number of low-priced and inferior grain, which increases the financial burden and is difficult to digest in a short time. In addition, the previous direct price intervention policy is aimed at increasing output, which is the direct cause of agricultural structural contradictions. Therefore, we should give full play to the basic role of market mechanism in the formation of grain prices, strive to innovate the grain market regulation system while reforming the grain price policy, and try a price mechanism based on the separation of price and subsidy and market mechanism. Its basic requirement is to seek a basic balance between supply and demand of agricultural products, so as to return grain prices to a reasonable level.
Second, to solve the distorting effect of the fiscal support for agriculture policy in the structural contradiction of the agricultural supply side, we should first increase the scale of central and local fiscal investment in agriculture, increase the proportion of fiscal support for agriculture funds in fiscal expenditure, broaden the supply channels of public fiscal support for agriculture funds, and flexibly use a variety of policy financial instruments to expand the input of agricultural support funds under the current total supply constraints of fiscal support for agriculture funds. Secondly, in the process of investment and use of financial support for agriculture funds, we should innovate the management system and mechanism, realize the refinement and accuracy of fund management and use, and implement each financial support for agriculture fund. Finally, in the process of transforming to modern agriculture, the financial expenditure for supporting agriculture should reasonably optimize the investment structure, and pay more attention to the investment in agricultural production safety, agricultural socialized service system, agricultural science and technology and human capital. For the price distortion effect of fiscal support for agriculture policy, the key is to clarify the relationship between the market and the government. We should give full play to the role of fiscal expenditure on supporting agriculture in stabilizing grain production and increasing farmers' income, reasonably guide and optimize the agricultural production structure, improve the level of agricultural science and technology, increase support for the integration of agricultural industry, and return agricultural production factors and agricultural product prices to reasonable market prices. Third, the structural reform of agricultural supply side is not only the adjustment and optimization of agricultural production structure, but also the reform of agricultural management system, especially the adjustment of producer structure. The agricultural management system of the household contract responsibility system implemented after the reform has increasingly revealed the disadvantages of decentralized management of farmers, and it is increasingly unable to meet the requirements of modern agriculture and the development of the big market. In 2016, the "No. 1 central document" specifically pointed out that on the basis of farmers' household management, we should support the development of new agricultural business entities and encourage diversified forms of operation and appropriate scale operation. Adhering to the management of farmers' families is based on the current national conditions of China, where there are more people and less land, and many rural families still make a living from agricultural production. Supporting the development of new agricultural business entities and encouraging diversified forms of operation, moderate operation is aimed at the development direction of moderate scale operation and modern agriculture, in order to solve the deep-seated contradiction between farmers' decentralized operation and the development of large markets behind the agricultural supply side structure.
Fourth, in view of the current low cultural quality and labor skills of workers engaged in agricultural production in China, we should increase human capital investment and gradually improve the quality of agricultural workers, which is an important prerequisite for improving agricultural labor productivity and solving the structural contradictions on the agricultural supply side. Because all science and technology can play its role only by people's mastery, cultivating modern agricultural business entities with culture and understanding of science and technology is an effective way to improve the creativity of workers, promote the innovation of agricultural production technology, give full play to the efficiency of resource utilization, and protect the agricultural ecological environment. All agricultural colleges and universities, higher vocational colleges and training institutions should increase the cultivation of talents who master modern agricultural science and technology and new professional farmers. The departments of finance, industry and commerce, taxation, personnel and labor should formulate supporting policies to ensure that this team can be willing to go to the countryside, stay and achieve; At the same time, the construction of system and mechanism for the cultivation and growth of new workers should also be considered in the process of agricultural organization construction.
notes:
① The data comes from the announcement of the National Bureau of statistics on grain production in 2015. http：//www.stats. gov.cn/tjsj/zxfb/201512/t20151208_ 1286449.html。
② Calculated according to wind data.
③ The "three main food crops" refer to rice, wheat and corn.
④ It is calculated according to the data of "national agricultural product cost benefit data compilation - 2015".
⑤ On June 20, 2016, the official website of the Ministry of Finance announced that the Ministry of finance, together with relevant departments, had issued the implementation opinions on establishing a subsidy system for corn producers. The document clearly stated that according to the principle of "separation of market pricing and price subsidy", the country would establish a subsidy system for corn producers in the Northeast (Liaoning, Jilin, Heilongjiang) and Inner Mongolia Autonomous Region this year, and the country would no longer conduct temporary collection and storage, giving farmers certain subsidies.