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Journal of Resources and Ecology >

2019 , Vol. 10 >Issue 3: 265 - 274

DOI: https://doi.org/10.5814/j.issn.1674-764X.2019.03.004

Cultivated Land Resources and Land Use

Temporal Variations and Driving Factors of Cultivated Land Use Intensity in Shandong Province from 1980 to 2015

  • LI Zijun ,
  • YU Yuanhe ,
  • JIANG Aixia , *
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  • College of Geography and Environment, Shandong Normal University, Jinan 250358, China
*Corresponding author: JIANG Aixia, E-mail:

*First author:

Received date: 2018-11-02

  Accepted date: 2019-02-18

  Online published: 2019-05-30

Supported by

Humanities and Social Sciences Research and Planning Fund of Ministry of Education of China (17YJAZH050)

National Natural Science Foundation of China (41101079).

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Abstract

Based on the cost-income data of agricultural products and relevant statistical data, taking major grain crops and economic crops in the process of cultivated land use as study cases, we studied characteristics of the temporal variation of cultivated land use intensity and its composition in Shandong Province from 1980 to 2015, and then analyzed its main driving factors. The results showed that: (1) The total intensity of major crops in Shandong Province showed a rising trend from 919.73 Yuan ha-1 in 1980 to 3285.06 Yuan ha-1 in 2015, and the average annual intensity of economic crops was higher than that of grain crops. The labor cost and material cost of major crops both showed an increasing trend, but the material input was much higher than labor input for grain crops, while the labor input was much higher than material input for economic crops. (2) The labor intensity of major crops in Shandong Province showed a decreasing trend from 501.75 man-day ha-1 in 1980 to 161.93 man-day ha-1 in 2015. The labor intensity of grain crops was lower than that of economic crops and its decline rate was fast. On the contrary, the capital intensity showed an increasing trend from 518.33 Yuan ha-1 in 1980 to 1159.95 Yuan ha-1 in 2015. In the internal composition of capital intensity, the proportion of yield-increasing inputs such as seed, farmyard manure, fertilizer, pesticide and drainage and irrigation decreased gradually, while the proportion of labor-saving inputs such as agricultural machinery increased significantly. (3) The cultivated land use intensity in Shandong Province had significant negative correlations with the amount of agricultural labor and cultivated land area per capita. The primary direct driving factor was the net income per unit cost of major crops, but the time response lagged by 1-3 years. The main indirect driving factor was the reform of agricultural policy.

Key words： cultivated land use intensity; temporal variation; driving factors; Shandong Province

Cite this article

LI Zijun , YU Yuanhe , JIANG Aixia . Temporal Variations and Driving Factors of Cultivated Land Use Intensity in Shandong Province from 1980 to 2015[J]. Journal of Resources and Ecology, 2019 , 10(3) : 265 -274 . DOI: 10.5814/j.issn.1674-764X.2019.03.004

1 Introduction

As an important part of the terrestrial ecosystem on the earth’s surface, cultivated land is a major form of land resource use and a material basis for human survival and development. With the rapid development of the social economy, the acceleration of urbanization and the increasing demand for ecological environment construction, the contradiction between humans and land becomes even more acute, and the pressure on cultivated land resources is increasing. The changes in cultivated land use have become an important part of land use and land cover change (LUCC) research (Li, 1999; Yang et al., 2000; Li et al., 2003; Liu et al., 2006), which is related to food security, economic development, social stability and security of the ecological environment of a country or a region. The cultivated land use changes include land use transfers and intensity changes (Li et al., 2008; Theo et al., 2016). The cultivated land use intensity change is an important aspect of the cultivated land change process, which may threaten food security more seriously than the shrinkage of cultivated land area caused by land use transfer (Li et al., 2003; Kilic et al., 2009; Hao et al., 2013; Kehoe et al., 2015). Given that the decreasing trend of cultivated land area is difficult to reverse, even within a long period in the future, the present cultivated land use intensity and its changing tendency will be important factors affecting national food security as well as sustainable social and economic development (Zhu et al., 2008; Chen et al., 2009; Xie et al., 2015). Therefore, research on the characteristics of the temporal variation of cultivated land use intensity can not only provide a deeper understanding of the cultivated land use intensity status in a region, but also further reveal the driving mechanisms and effects of cultivated land use intensity, and lay a foundation for promoting rational intensification of cultivated land use (Hao et al., 2011; Guo et al., 2014; Smith et al., 2016).
Due to differences in natural conditions and economic and social development levels in different regions, the cultivated land use intensity presents obvious regional characteristics (Liu et al., 2016; Li et al., 2017). Thus, revealing the characteristics of the variation and the laws pertaining to cultivated land use intensity in different regions can provide an important basis for scientifically formulating differentiated cultivated land use and protection policies, improving the regional cultivated land use intensity level, ensuring regional food security and promoting sustainable development of the social economy. At present, many domestic scholars have studied the temporal changes (Li et al., 2003; Liu et al., 2006a; Zhu et al., 2007; Pang et al., 2007; Lambin et al., 2011; Yao et al., 2014; Xie et al., 2015; Ding et al., 2015; Xie et al., 2016), regional differences (Zhang et al., 2008; Yan et al., 2009; Yao et al., 2014), structural characteristics (Liu et al., 2006b; Chen et al., 2009) and influencing factors (Zhao et al., 2010; Du et al., 2013; Xie et al., 2015; Wang et al., 2015) of cultivated land use intensity in China and some of the main grain producing areas. These studies provide a basis for objectively understanding the macroscopic changes in cultivated land use intensity in China and some individual regions. However, the measurement indexes and methods of quantifying intensity are different, and the attention that is given to the internal structural changes of intensity is still insufficient. Most studies adopt the methods of multiple crop index (Li, 2003; Zhu et al., 2007; Xie et al., 2015; Ding et al., 2015), labor input and various forms of capital input (Liu et al., 2006a; Zhang et al., 2008; Chen et al., 2009; Yao et al., 2014; Wang et al., 2015), or various kinds of production material inputs combined with energy analysis to measure cultivated land use intensity from the investment aspect (Yao et al., 2014; Xie et al., 2016). There are also some studies that evaluate the cultivated land use intensity by establishing an evaluation index system and using a comprehensive index evaluation method (Zhao et al., 2010; Du et al., 2013; Wang et al., 2014). The intensive use of cultivated land occurs essentially to improve the output efficiency and economic benefits in cultivated land per unit area by increasing the other element inputs (such as capital, labor or agricultural technology) to replace the expansion of cultivated land area (Brookfield, 1972; Verburg et al., 2011; Wu et al., 2012).
As a large populous, agriculture-rich province in China, Shandong Province is also one of the 13 main grain production areas (Fig. 1). With the rapid growth of the population, fast development of the social economy and quick advancement of urbanization, much of the cultivated land has been permanently occupied (Deng et al., 2017). The total amount of cultivated land resources and the per capita occupancy rate have been decreasing gradually, and the cultivated land per capita has decreased from 0.099 ha in 1980 to 0.078 ha in 2015, which has led to a sharp contradiction between humans and land. Moreover, the reserve resources of cultivated land in Shandong Province are very limited. According to the second land survey data, the reserved cultivated land resources of the entire province are only 0.34 million ha. Furthermore, most cultivated land use patterns in developed areas of Shandong Province are still extensive (Pang et al., 2007), which further aggravates the contradiction between population, cultivated land and grain. In this context, it is of great practical significance to explore the efficient and intensive use of cultivated land resources in Shandong Province, and its driving factors, to ensure the food security of the whole province and even the country, as well as the sustainable development of the regional social economy. The proportions of sown area of wheat and maize as grain crops in Shandong Province were relatively large, accounting for 34.46% and 28.78% of the total sown area of crops, respectively, in 2015. The proportions of planting area of peanut and cotton as economic crops in Shandong Province were relatively large, accounting for 6.72% and 4.68% of the total planting area of crops, respectively, in 2015. Therefore, we took these two major grain crops and two major economic crops in the process of cultivated land utilization in Shandong Province as examples, and systematically analyzed the temporal characteristics of cultivated land use intensity and its internal structure changes from the perspective of input changes in the agricultural production processes, then discussed the main factors influencing cultivated land use intensity in Shandong Province. This research will provide certain reference values for the reasonable utilization of cultivated land and guaranteeing regional food security in Shandong Province.
Fig. 1 The location of Shandong Province

2 Materials and methods

2.1 Data sources

In this study, two major grain crops (wheat and maize) and two major economic crops (peanut and cotton) were taken as research objects. Some indices for the four crops (all “per unit area”), including labor employment amount, labor cost, material cost, seed cost, farmyard manure cost, fertilizer cost, pesticide cost, machinery cost and drainage and irrigation cost, were selected to establish an analysis database of cultivated land use intensity from 1980 to 2015. Data used in this study were from Agricultural Products Cost-income Data Compilation of China and Shandong Statistical Year Book. The time spanned from 1981 to 2016.

2.2 Study methods

In order to examine the change in cultivated land use intensity in Shandong Province, total intensity, labor intensity and capital intensity of the four kinds of crops were analyzed from the perspective of production investment in cultivated land. The total intensity of cultivated land use is the sum of the labor cost and the material cost invested per unit land area, which can be calculated from the following formula:
I=(A+K)/S(1)
Where I is the total intensity of cultivated land use; A is the amount of labor cost invested in cultivated land (the sum of the cost of domestic workers and employees); K is the amount of material cost invested in cultivated land (direct production cost), including yield-increasing input and labor-saving input; and S is the area of cultivated land.
The labor intensity is the amount of labor input per unit planting area, and is expressed as the material form of labor input per unit planting area. The formula is given as follows:
L=E/S (2)
Where L is the labor intensity; E is the amount of labor invested in cultivated land; and S is the area of cultivated land.
The capital intensity is the total amount of capital input per unit planting area, and is analyzed in the value form of various agricultural production materials consumed per unit planting area during the direct production process of the crops. The formula is given as follows:
C=M/S (3)
Where C is the capital intensity; M is the amount of material invested in cultivated land; and S is the area of cultivated land.
In this paper, the internal composition variation of capital intensity was analyzed by choosing value forms of seed cost, farmyard manure cost, fertilizer cost, pesticide cost, machinery cost and drainage and irrigation cost. The total of the above six input types accounted for 95.43% of the total capital intensity in 2015, so collectively they could represent the overall development trend of the internal structure of capital intensity. According to the main purposes of different capital input types, they are subdivided into yield- increasing inputs and labor-saving inputs. Seed, farmyard manure, chemical fertilizer, pesticide and drainage and irrigation inputs are yield-increasing inputs for the purpose of increasing grain yield per hectare. Machinery input is the labor-saving input for the main purpose of substituting labor forces. In order to eliminate the effects of rising prices and inflation among the different years, the total intensity and all types of capital intensity were modified using the price index for agricultural means of production according to the base year of 1980. The net income from tax reductions of the four kinds of crops were all modified by adopting the price index for purchasing agricultural products using 1980 as the base year.
The change in cultivated land use intensity is affected by many factors. In this paper, we mainly consider the factors of population, cultivated land resources endowment, social economy and policy. Moreover, the numbers of practitioners in agriculture, forestry, animal husbandry and fishery, the cultivated land area per capita, the net income from tax reductions of crops and the agricultural policy were selected as independent variables, while the average intensity of the four kinds of crops was taken as the dependent variable. On this basis, reasons for the changes in cultivated land use intensity in Shandong Province were analyzed qualitatively and quantitatively in order to provide a scientific reference for the farmland management in this region.

3 Results

3.1 Temporal variations of cultivated land use intensity in Shandong Province

Two major grain crops, wheat and maize, and two major economic crops, peanut and cotton, are the main crop types in Shandong Province. By analyzing the changes in production intensity of these main crops, the characteristics of the interannual macroscopic variation in cultivated land use intensity in Shandong Province on the whole can be reflected.
3.1.1 Variations of total intensity
Fig. 2 shows the changes in total intensity for wheat, maize, peanut and cotton from 1980 to 2015. The total intensities of the two kinds of grain crops and the two kinds of economic crops each show an increasing tendency since 1980. The mean of the total intensity of the major crops increased from 919.73 Yuan ha-1 in 1980 to 3285.06 Yuan ha-1 in 2015, with an average annual growth rate of 3.70%. Of the fourcrops, the total intensity of cotton maintained the highest level, and the average annual intensity was 2696.48 Yuan ha-1. The total intensity of peanut took second place with an average annual intensity of 1747.26 Yuan ha-1. However, the total intensities of wheat and maize remained at lower levels with average annual intensities of 1326.25 Yuan ha-1 and 1068.16 Yuan ha-1, respectively. From 1980 to 2015, the average annual intensity of the economic crops was 2221.87 Yuan ha-1, which was 1.86 times that of the grain crops and reflects the higher economical returns of economic crops.
Fig. 2 Variations in total intensity for four major crops in Shandong Province from 1980 to 2015
In order to further analyze the changes in cost composition of the major crops in Shandong Province, the variations in labor cost and material cost averaged for the four kinds of crops from 1980 to 2015 are presented in Fig. 3. Since 1980, both the labor cost and material cost of the major crops, have increasing trends. The labor cost increased rapidly from 401.40 Yuan ha-1 in 1980 to 2125.11 Yuan ha-1 in 2015, with an average annual growth rate of 4.61%. The material cost increased from 518.33 Yuan ha-1 in 1980 to 1159.95 Yuan ha-1 in 2015, with an average annual growth rate of 2.09%. The material cost was higher than the labor cost from 1980 to 1995, while the labor cost was higher than the material cost from 1996 to 1998. From 1999 to 2009, the material cost exceeded the labor cost once again. However, the labor cost has increased rapidly since 2008 and has far exceeded material cost since 2010. This is mainly because the Lewis Turning Point appeared in advance in China, and the phenomenon of a shortage of peasant workers occurred, indicating that the demographic dividend is gradually disappearing.
Fig. 3 Cost variations averaged for the four major crops in Shandong Province from 1980 to 2015
By further analyzing the cost composition of the grain crops and economic crops from 1980 to 2015, we found that the average annual material cost of the grain crops was 705.96 Yuan ha-1, while the average annual labor cost was 491.24 Yuan ha-1, so the material input was much higher than the labor input. The average annual material cost of the economic crops was 989.22 Yuan ha-1, but the average annual labor cost was 1232.64 Yuan ha-1, so the labor input was much higher than the material input. This difference between the crop types was mainly determined by the crop production processes. The production processes for grain crops, such as ploughing, fertilization, sowing and harvesting, resulted in higher material cost because they are amenable to the use of agricultural machinery. However, many production steps for the economic crops, such as sowing and picking, can only use labor forces, ultimately leading to higher labor costs.
3.1.2 Variations of labor intensity
Fig. 4 shows the changes in labor intensity of wheat, maize, peanut and cotton from 1980 to 2015. Since 1980, the labor intensity variations of the four crops show fluctuating descending tendencies and they can be divided into two stages. From 1980 to 1995, the labor intensities of the four major crops showed fluctuating declining trends, and the average labor intensity decreased from 501.75 man-day ha-1 in 1980 to 355.99 man-day ha-1 in 1995, with an average annual descending rate of 2.26%. From 1996 to 2015, the labor intensities of the four major crops decreased continuously, and the average labor intensity decreased from 342.75 man-day ha-1 in 1996 to 161.93 man-day ha-1 in 2015, with an average annual descending rate of 3.87%. These trends show that the labor input as an agricultural production cost was continuously decreasing with the increasing of agricultural labor opportunity cost. The labor intensity of cotton had remained at a high level, and the average annual amount of labor input was 553.46 man-day ha-1 with an average annual declining rate of 2.45%. The labor intensity of peanut was also relatively high, and the average annual amount of labor input was 270.08 man-day ha-1 with an average annual declining rate of 2.94%. However, the labor intensities of wheat and maize remained at lower levels, and the average annual amounts of labor input were 180.32 man-day ha-1 and 181.99 man-day ha-1, respectively, with average annual declining rates of 4.81% and 4.16%, respectively.
Fig. 4 Labor intensity variations of the four major crops in Shandong Province from 1980 to 2015
The average annual amount of labor inputs for grain crops and economic crops were 181.15 man-day ha-1 and 411.77 man-day ha-1, respectively. Compared with economic crops, the labor intensity of grain crops was lower while the rate of decline was higher. On the one hand, the input of large-type farm machinery in the production process of grain crops have made it possible to reduce the labor forces required, indicating that farmers are increasingly dependent on machinery (Huang et al., 2009). On the other hand, farmers prefer to input labor forces to grow crops with higher economic benefits.
3.1.3 Variations of capital intensity
The changes in the capital intensities of wheat, maize, peanut and cotton from 1980 to 2015 can be seen in Fig. 5. Since 1980, the capital intensities of the four crops have followed upward trends on the whole, which is the opposite of the changing trends of labor intensity. The average capital intensity increased from 518.33 Yuan ha-1 in 1980 to 1159.95 Yuan ha-1 in 2015 with an annual growth rate of 2.33%. In the past 30 years, the average capital intensity of cotton was the highest, reaching 1023.35 Yuan ha-1. The average capital intensities for peanut and wheat were intermediate, at 955.10 Yuan ha-1 and 847.81 Yuan ha-1, respectively. The average capital intensity of maize was the lowest, at 564.12 Yuan ha-1. Among the four kinds of crops, the annual growth rate of capital intensity for maize was the highest, reaching 3.56%, followed by those for wheat and peanut at 2.73% and 2.71%, respectively, while cotton was the lowest at 0.96%. Moreover, the capital intensity of peanut has exceeded that of cotton since 2007, and the capital intensity of wheat has also exceeded that of cotton since 2013. The average annual capital intensity of the economic crops was 989.22 Yuan ha-1, which was 1.40 times that of the grain crops.
Fig. 5 Capital intensity variations of the four major crops in Shandong Province from 1980 to 2015
In order to further study the internal structure characteristics of capital intensity for cultivated land use in Shandong Province and capture the changing direction of intensive utilization of cultivated land more specifically, the changes of various capital input types for major crops from 1980 to 2015 were analyzed (Fig. 6). From 1980 to 2015, the total amount of capital intensity for major crops in Shandong Province was rising constantly. Among the six capital input types, the proportion of yield-increasing inputs in the form of seeds, farmyard manure, fertilizers, pesticides and drainage and irrigation decreased gradually from 96.02% in 1980 to 75.06% in 2015. On the contrary, machinery was used as a kind of labor-saving input whose proportion increased rapidly from 3.98% in 1980 to 24.94% in 2015, indicating that the internal structure of capital inputs for major crops in Shandong Province has changed tremendously.
Fig. 6 Capital intensity structure variations for major crops in Shandong Province from 1980 to 2015
In the past 30 years, among the capital input types for major crops in Shandong Province, fertilizer has consistently represented the largest proportion of all capital input types with an average input level of 314.05 Yuan ha-1. On the whole, the input level of fertilizer showed a rising trend, increasing from 154.39 Yuan ha-1 in 1980 to 411.48 Yuan ha-1 in 2015. Secondly for seeds, the average input level was 145.53 Yuan ha-1, and the annual input level also showed an upward trend, increasing from 68.89 Yuan ha-1 in 1980 to 191.76 Yuan ha-1 in 2015. The average input level of machinery was 100.29 Yuan ha-1, and it increased rapidly from 18.49 Yuan ha-1 in 1980 to 275.61 Yuan ha-1 in 2015 which represents a 14.91-fold enhancement. After 2008, the input level of machinery exceeded that of seeds and it became the second largest capital input type. The average input level of farmyard manure was 78.25 Yuan ha-1, and the annual input level has shown a rapidly declining tendency, decreasing from 170.55 Yuan ha-1 in 1980 to 43.40 Yuan ha-1 in 2015. The average input level of pesticides was 78.08 Yuan ha-1, and the annual input level showed a trend of rising initially and falling later, increasing from 35.89 Yuan ha-1 in 1980 to 130.74 Yuan ha-1 in 1992 and then decreasing to 91.16 Yuan ha-1 in 2015. The average input level of drainage and irrigation was the lowest, but the annual input level showed a rapid rising trend, increasing from 16.16 Yuan ha-1 in 1980 to 91.86 Yuan ha-1 in 2015, a 5.68-fold increase.
According to the changes in the six types of capital inputs, the average annual increments and change rates from 1980 to 2015 were seeds (3.41 Yuan, 2.97%), farmyard manure (-3.53 Yuan, -3.83%), fertilizers (7.14 Yuan, 2.84%), pesticides (1.54 Yuan, 2.70%), machinery (7.14 Yuan, 8.03%) and drainage and irrigation ( 2.10 Yuan, 5.09%) (Table 1). The machinery cost had the largest average annual growth rate (8.03%) and increment (7.14 Yuan yr-1), indicating that as a kind of labor-saving input, machinery has been chosen as an important means for replacing labor forces input by farmers with the advancement of science and technology. As an important yield-increasing input, the fertilizer cost also had largest average annual increment (7.14 Yuan yr-1), although its average annual growth rate was only 2.84%, indicating that farmers are relatively dependent on fertilizers. The average annual growth rate of drainage and irrigation cost (5.09%) was second only to that of machinery though its average annual increment was small (2.10 Yuan yr-1), indicating that the importance of drainage and irrigation for agricultural development has been relatively modest but continuously increasing. At the same time, the input of farmyard fertilizer was constantly decreasing as the input of fertilizer was continuously increasing. During the period of 1980-1995, the average annual increments of inputs for fertilizer, pesticides and seeds were larger. Among them, the average annual increment of fertilizer was 8.25 Yuan yr-1, and that of machinery was only 1.51 Yuan yr-1, indicating that the primary purpose of agricultural capital input in this period was to increase production. From 1996 to 2015, the average annual increment of machinery input reached 10.71 Yuan yr-1, while that of fertilizer input decreased to 2.10 Yuan yr-1, or only 19.63% of the machinery input, indicating that agricultural capital input in this period was mainly aimed at replacing labor forces.
Table 1 Annual change and average annual changing rates of capital inputs for the main crops in Shandong Province from 1980 to 2015
Capital input type Annual change during
1980-2015 (Yuan yr-1)		 Annual change during 1980-1995 (Yuan yr-1) Annual change during 1996-2015 (Yuan yr-1) Average annual
changing rate (%)
Seed cost 3.41 4.29 3.11 2.97
Farmyard manure cost -3.53 -5.20 -1.10 -3.83
Fertilizer cost 7.14 8.25 2.10 2.84
Pesticide cost 1.54 5.76 -0.25 2.70
Machinery cost 7.14 1.51 10.71 8.03
Drainage and irrigation cost 2.10 1.53 2.22 5.09
To sum up, the labor input level of major crops in Shandong Province has been declining, while the overall capital intensity has shown an increasing tendency, but the changing trends of various capital input types were different. With the development of the social economy and the advancement of science and technology, the input of material capital has liberated rural labor forces, resulting in the gradual transition from labor intensity to capital intensity for agricultural production.

3.2 Driving factors for cultivated land use intensity variation in Shandong Province

3.2.1 Socio-economic factors
There are many factors driving the changes of cultivated land use intensity, but the most essential deeply-rooted cause is closely related to the net income variation of cultivated land use. As shown in Table 2, there was a good correlation between the average net income from tax reduction per unit cost and the average annual intensity of the four major crops in Shandong Province. For the two different crop types, the correlation coefficient (Rg) between net income from tax reduction per unit cost of grain crops (Pg) and the average annual intensity (Ig) was higher than that (Re) between net income from tax reduction per unit cost of economic crops (Pe) and the average annual intensity (Ie). The correlation coefficients between the average annual intensities with lag times of 1-3 years and the net incomes from tax reduction per unit cost of grain crops (Pg) and economic crops (Pe) were all higher than those of the same period. For different periods, the correlations between the average annual intensities (Ig) and the net incomes from tax reduction per unit cost of grain crops (Pg) was stronger from 1980 to 2006, while that of economic crops was not obvious in the 1980s but significant after the 1990s. From 2007 to 2015, the average annual intensities increased steadily, while the net incomes from tax reduction per unit cost of grain crops and economic crops both showed fluctuating trends, and the amplitude of variation for net income from tax reduction per unit cost of economic crops was larger than that of the grain crops. As rational economic businessmen, farmers can adjust their economic behaviors according to their own resource allocations which are driven by policies and market prices. This factor is reflected in the fact that the variations of net income per unit cost influenced the changes of cultivated land intensity largely in the process of agricultural land use. However, the variations of cultivated land use intensity lagged the changes of net income by 1-3 years.
Table 2 Correlation coefficients between the average net incomes from tax reduction per unit cost and the average annual intensities of four major crops in Shandong Province from 1980 to 2015
Period Correlation coefficients (Rg) between the net income per unit cost
of grain crops (Pg) and the average annual intensity (Ig)		 Correlation coefficients (Re) between the net income per unit cost
of economic crops (Pe) and the average annual intensity (Ie)
Ig and Pg at the
same time		 Ig lag Pg for
one year		 Ig lag Pg for
two years		 Ig lag Pg for
three years		 Ie and Pe at the
same time		 Ie lag Pe for
one year		 Ie lag Pe for
two years		 Ie lag Pe for
three years
1980-1988 0.63 0.75 0.81 0.78 -0.04 0.21 -0.09 -0.08
1989-1997 0.45 0.58 0.74 0.52 0.32 0.54 0.71 0.37
1998-2006 0.65 0.88 0.79 0.74 0.57 0.73 0.96 0.78
2007-2015 -0.31 -0.14 -0.25 -0.04 -0.49 -0.26 -0.11 0.15
3.2.2 Population factors
Population is the most active factor in human social and economic activities, and also one of the important factors leading to land use and land cover changes. Population variations include population quantity, population structure, labor force quantity and others, which can affect cultivated land use through various demands such as grain demand, inhabiting recreational space, infrastructure, etc. This is especially true for the variation of labor force quantity input in the process of agricultural production, which has a direct impact on the cultivated land use intensity.
In the past 30 years, the size of the agricultural labor force in Shandong Province had dropped from 24.67 million in 1980 to 19.53 million in 2015, with an average annual decrease of 0.15 million people. However, the average annual intensity for the four major crops increased from 919.73 Yuan ha-1 in 1980 to 3285.06 Yuan ha-1 in 2015, with an average annual increase of 67.58 Yuan ha-1. By conducting a regression analysis on the annual agricultural labor force size and average annual intensity for the four major crops in Shandong Province, the corresponding regression equation is given as follows:
$Y=-1.752X+5760.216$ (4)
$R=0.760$ $Sig.=0.000$ $F=33.725$
where Y is the average annual intensity of the four major crops; X is the annual size of the labor forces in agriculture, forestry, animal husbandry and fisheries. According to the above equation, the average annual intensity of the four major crops was negatively related to the annual size of the agricultural labor forces. The reason for this relationship was that against the background of rapid industrialization and urbanization, the opportunity cost of the labor force for agriculture increased, and a large number of young rural laborers had transferred to secondary and tertiary industries, causing the agricultural labor force to gradually become a constraining condition for agricultural production. Under the precondition of ensuring food security or grain demand, it was necessary to increase the capital input to compensate for the declining labor force. In the practical agricultural production process, the most important measures were to increase the labor-saving inputs such as machinery and yield-increasing inputs such as fertilizers, which have led to the continuous rise of the total intensity. This factor can also explain the decrease in labor intensity and the increase in capital intensity for the four major crops.
3.2.3 Cultivated land resource factors
The cultivated land area per capita represents the scale of cultivated land use, which is an important description for cultivated land resources. Generally speaking, if other conditions remain unchanged, the larger the area of cultivated land per capita, the more conducive it is to machinery usage, and the cultivated land use intensity will increase accordingly.
As can be seen from Fig. 7, the cultivated land area per capita in Shandong Province decreased from 0.099 ha in 1980 to 0.076 ha in 2015. Except for the slight increases in 2002 and 2008, the other years showed downward trends. However, the average annual intensity of the four major crops has shown an upward trend, especially since 2008, and the average annual growth rate has reached 11.2%. Regression analysis was applied to the annual cultivated land area per capita and the average annual intensity for the four major crops in Shandong Province, and the corresponding regression equation is as follows:
$Y=-47141.697X+5538.105$ (5)
$R=0.795$ $Sig.=0.000$ $F=18.830$
where Y is the average annual intensity for the four major crops; and X is the annual cultivated land area per capita. This equation shows that the average annual intensity of the four major crops was negatively correlated with the annual area of cultivated land per capita, mainly because with the rapid development of the social economy, the area of cultivated land has continued to decline under the influence of policies such as construction occupation, ecological restoration and agricultural structure adjustments. The situation where the cultivated land area is shrinking and the population is increasing will inevitably lead to the decrease of cultivated land area per capita.
Fig. 7 Variations of annual cultivated land area per capita and average annual intensity for the four major crops in Shandong Province from 1980 to 2015
In light of these trends, how can we ensure food security at the national and regional levels? It is particularly important to improve the grain output per unit area and cultivated land use intensity level. Therefore, in the past 30 years, the state has increased the economic income from agricultural production for farmers through policies which directly benefit the farmers, such as improving the prices of grain and other agricultural products, reducing or exempting taxes on agriculture and subsidizing grain-planting, thus promoting farmers' enthusiasm for material investments in land, resulting in significant increases in the yield-increasing inputs of seeds and fertilizers. After the No. 1 documents from the national central government published in 2004 and 2008, the labor-saving input such as machinery was significantly strengthened, and it has played an important role in the increasing yield and income for farmers.
3.2.4 Policy factors
Policies have profound impacts on the structure, methods and degree of cultivated land utilization, the most obvious of which is the impact on the planting structure. Since 1980, the changes of agricultural policies in China can be divided into four stages, which have impacted the cultivated land use intensity in Shandong Province to different degrees.
The period of 1980-1984 was the overall transition period of agriculture in China. The “Several Issues on Further Strengthening and Improving the Farm Production Responsibility System” issued in 1980 marked the dramatic change in the system of responsibility for production. The household contract system of responsibility spread quickly in rural areas, the rural economy cooperative organizations rose gradually and the purchase prices of agricultural products increased. These measures had aroused the enthusiasm of farmers for their production, and their incomes began to increase greatly. However, due to the weak agricultural foundation, the average annual increment of intensity in this period was only 39.12 Yuan ha-1.
The period of 1985-1997 was the period of Chinese agriculture transitioning to a market economy. The “Ten Policies on Further enlivening Rural Economy” issued in 1985 marked the end of the era of unified purchase and sale, as agricultural product circulation entered into the market system, and major agricultural structure adjustments began. The sown area of economic crops such as peanut and cotton increased rapidly, and the intensity rose even faster. With the deepening of rural economic adjustments and reforms, agricultural production had recovered and increased rapidly. In 1992, agricultural production fluctuated again and the net income from crops decreased sharply. To remedy this situation, the government promulgated the “Several Policies and Measures on the Current Development of Agriculture and Rural Economy” in 1993, which increased the protection and support of agriculture. Meanwhile, the basic conditions for agricultural production had improved, and the output and income of main agricultural products had begun to increase again. The average annual increment of intensity in this period reached 63.00 Yuan ha-1.
During 1998-2001, China implemented the purchasing policy of “Grain Protective Prices” and stipulated uniform prices in all provinces and cities. The state-owned grain departments were required to purchase grain actively, and the government spent over tens of billions of Yuan on subsidies each year. However, due to the lower purchase prices and strict conditions of state-owned grain enterprises, the income of farmers did not improve substantially. In addition, with the influence of rising prices, the productive enthusiasm of farmers was baffled. As a result, the intensity of this period decreased from 1794.31 Yuan ha-1 to 1602.49 Yuan ha-1.
From 2002 to 2015, in order to relieve the burden on farmers, China gradually reduced or abolished some agricultural taxes. Since 2004, the agricultural tax was officially cancelled, which actually increased farmers’ income and, once again, their enthusiasm for agricultural production. Since then, the national central government has issued nine “No.1 Documents” consecutively from 2006 to 2015. The agricultural policies favorable to farmers, such as grain- planting subsidies, allowances for purchasing agricultural machinery, and comprehensive subsidies for agricultural means of production, have been vigorously practiced. Subsequently, the construction of rural infrastructure was gradually ramped up, and the agricultural technology input as well as agriculture financial support continued to increase. In order to improve the agricultural benefits, farmers had increased the input of fertilizers, machinery, pesticides and other materials, so the intensity continued to increase. Especially after 2008, the average annual increment reached 206.58 Yuan ha-1, and grain production achieved continuous growth.

4 Conclusions and discussion

Since 1980, the total intensity of the main crops has been on an upward trend in Shandong Province. The average annual intensity increased from 919.73 Yuan ha-1 in 1980 to 3285.06 Yuan ha-1 in 2015, with an average annual growth rate of 3.70%. The average annual intensity of economic crops was 1.86 times that of grain crops. The labor costs and material costs of the major crops all showed increasing trends. The material input of grain crops was much higher than labor input, while the labor input of economic crops was much higher than material input.
The labor intensity of the major crops in Shandong Province showed a downward trend from 501.75 man-days ha-1 in 1980 to 161.93 man-days ha-1 in 2015, and the labor intensity of grain crops was lower than that of economic crops. On the contrary, the capital intensity showed an upward trend from 518.33 Yuan ha-1 in 1980 to 1159.95 Yuan ha-1 in 2015, with an average annual growth rate of 2.33%, and the average annual capital intensity of economic crops was 1.40 times that of grain crops.
In terms of the capital input structure, the total proportion of yield-increasing inputs, in the form of six kinds of capital inputs including seeds, farmyard manure, fertilizers, pesticides and drainage and irrigation, gradually decreased from 96.02% in 1980 to 75.06% in 2015. The proportion of labor-saving inputs such as agricultural machinery increased significantly during this period. After 2008, the input of machinery exceeded that of seeds and became the second largest capital input type. The large amount of material capital input liberated rural laborers, so the agricultural production gradually shifted from being relatively labor intensive to more capital intensive.
Under the comprehensive influences of population, cultivated land resources, social economy and agricultural policies, the cultivated land use intensity in Shandong Province changed significantly. The cultivated land use intensity was negatively related to the amounts of agricultural labor and cultivated land area per capita. It was essentially influenced by the net income per unit cost of crops, but the timing of this response lagged by 1-3 years. Agricultural policies indirectly promoted the increase of cultivated land use intensity, but the impacts of agricultural policies at various periods were different. The natural, social and economic conditions at different stages had different effects on the cultivated land use intensity, so the driving factors still need to be studied further.
In the future, the input factors such as labor, machinery and fertilizer should be optimized and reorganized, agricultural machinery purchase subsidies should be strengthened, the level of agricultural mechanization and the efficiency of factor substitution should be improved, land circulation should be accelerated, and moderate-scale operation of agriculture should be promoted.

The authors have declared that no competing interests exist.

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