1 Introduction

Since the green revolution began in the 1950s, increasing inputs of inorganic fertilizers, organic manures and pesticides have become the principal means of attaining yields and indirectly, greater production of livestock, both globally and in China (Sun et al. 2012). In 2013, yield of crops of cereals in China reached 6.02 × 108 t (tonnes), which is twice as great as the production of 3.03 × 108 t that was achieved in 1978. During the same period, application of inorganic fertilizers increased 6.7-fold from 8.84 × 106 to 5.84 × 107 t, with average applications of 486 kg/ha of cropland in 2013. Rapid increases in economic activities as measured by the gross domestic product (GDP) have provided the fiscal means for farmers in China to buy more inorganic fertilizers to improve yields of crops. China is now the largest producer and user of synthetic fertilizers in the world. It consumed one-third of all of the inorganic fertilizers applied in the world. The mass of fertilizer used per unit area in China is more than three times greater than the average for the rest of the world (Ding and Zang 2009). However, this agro-chemical-based intensive agriculture has contributed substantially to emission of greenhouse gases CH4 and N2O, and the entry of pollutants (excessive nitrogen and phosphorus) into soils and water bodies, which has resulted in serious degradation of the natural surface waters due to cultural eutrophication (Smil 1997; Diaz and Rosenberg 2008; Gilbert et al. 2010). Concentrations of nitrogen (N) and phosphorus (P) in larger rivers, especially the Yangtze, Yellow and Huai, have been increasing during recent years (Li et al. 2007; Yu et al. 2010; Zou 2011). The first national pollution census bulletin for China, which was published in 2010, reported that the total mass of N from agricultural non-point source pollution was 2.7 × 106 t, while that of P was 2.84 × 105 t, which accounted for 57.19 and 67.27 % in total emissions of these two nutrients, respectively. Surveys conducted in 2012 by the Chinese government found that 70 % of river systems in China suffered from slight or moderate pollution, and eutrophication of lakes was a serious problem in some regions (State Environmental Protection Administration 2013).

Anhui is a province of China, rich in agricultural resources. It is a national fundamental region for production of grain, cotton, food oil, meat and fresh water products. In 2012, total output of grain was 3.3 × 107 t. A total of 3.3 × 106 t of inorganic fertilizer was used at an average rate of 797.1 kg/ha, which is 1.66-fold greater than the national average. While several studies on non-point pollution of farmland and surface waters in Anhui have focused on trace metals (Zhu et al. 2007; Xu and Chang 2008; Fan et al. 2010), little has been done relative to hazards posed by chemical fertilizers. Here, the concepts of Fertilization Environmental Hazard Index (FEHI) and fertilization environmental safety threshold (FEST) are presented and used to evaluate hazards of farmland fertilization in order to identify serious eutrophication due to agriculture that is not sustainable.

2 Materials and methods

2.1 Study area

Anhui Province is located in eastern China with latitude from N29o41′ to N34o38′ and longitude from E114o54′ to E119o37′, and covers 1.4 × 105 square kilometers accounting for 1.45 % of total surface area of China. The province is crossed in the north by the Huai River and in the south by the Yangtze River, with alternating areas of plains, hills, mountains, lakes and low-lying areas. The north of the province is part of the North China Plain, while the north-central areas are part of the Huai River watershed. Both of these regions are flat and densely populated with intensive, advanced agriculture. The land becomes more uneven further south, with the Dabie Mountains occupying much of southwestern Anhui and a series of hills and ranges cutting through southeastern Anhui. Chao Lake, the fifth largest fresh water lake of China, with an area of about 800 km2, is located in the center of the province,

Compared to its eastern neighbors, Zhejiang and Jiangsu Provinces, Anhui has lagged in economic development, specifically industrialization, with a per capita GDP in 2012 of ¥ 25,920 ($4,249 USD). It is also a primary agricultural region with cultivated land of 4.2 × 106 ha and rural population of 53 million people, which accounts for 77 % of total population of Anhui. There are 16 sub-administrative regions, each with distinctive geographic and economic conditions.

2.2 Collection of data

Most of the data used in this analysis came from the 2013 Anhui Statistical Yearbook (Bureau of Statistics of Anhui 2013), which is compiled by the Bureau of Statistics of Anhui Province, and the document of Eco-county, Eco-city, Eco-province Construction Indexes (Revised Draft) from the former State Environmental Protection Administration issued in 2007. Some of the data were compiled from the 2013 China Statistical Yearbook (National Bureau of Statistics of China 2013) and 2013 Anhui Statistical Yearbook.

2.3 Methods

Assessment of hazards posed by application of inorganic, chemical fertilizations was based on an evaluation of the status and trends in potential damage and threats to human health, economy and ecological system, and the decision of management. Here, the concept of total Fertilization Environmental Hazard Index (FEHI t ) is presented (Eqs. 1–2).

$${\text{FEHI}}_{t} = \sum\limits_{i = 1}^{n} {W_{i} \cdot {\text{FEHI}}_{i} }$$
(1)
$${\text{FEHI}}_{i} = \frac{{{\text{FI}}_{i} }}{{{\text{FI}}_{i} + {\text{FEST}}_{i} }}$$
(2)

where FEHI t denotes the total Fertilization Ecological Hazard Index, which is the sum of component hazard factors multiplied by weighting factors; FEHI i represents a single factor (i) for an individual constituent of fertilizers, such as N, P or K; W i is the weight of each factor with values between 0 and 1. FI i is the fertilization intensity of i factor, that is the mass of fertilizer i applied on the per unit of cultivated land area (kg/ha); FEST i is the fertilization ecological safety threshold of a single factor, which means the maximum mass of a fertilizer applied to soil to maximize productivity without adverse effects on the environment (kg/ha). The net volume of fertilizer is the mass of N, P or K in the forms of N, phosphate (P2O5), potash (K2O), respectively.

Values of FEHI t (or FEHI i ) range from 0 to 1.0. When FEHI t is equal to 0.5, FI i is equal to FEST i , where fertilization of cropland is at the critical point of environmental safety, above which adverse effects would be expected to occur. When FEHI t is nearly 1.0, fertilization intensity (FI i ) of fertilizer greatly exceeds the environmental safety threshold (FEST i ). That is, pollution due to excess application of fertilizer would be extremely serious. When FEHI t approaches 0, use of inorganic fertilizer is nearly 0 and FI i is less than the FEST i . This is referred to as organic agriculture, in which addition of inorganic fertilizer is not contributing to cultural eutrophication. Environment hazard (or safety) can be assessed by the magnitude that FEHI t deviates from 0.5. According to the folds of fertilizer mass greater or less than the FEST, classification of environmental hazards from “safety” to “extreme hazard” can be divided into 6 classes (Table 1).

Table 1 Classes of Fertilization Environmental Hazard Index (FEHI)
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3 Results and discussion

3.1 Temporal trends in indexes due to use of fertilizer in Anhui Province

Before calculation of Fertilization Environmental Hazard Indexes (FEHI), the threshold FEST must be determined. In this assessment, 250 kg/ha was used as the threshold FEST t , because the Chinese government considers it to be the standard for assessment of eco-county in China (Ministry of Environmental Protection of P.R.C. 2009). Because the appropriate proportions of N, P and K for most crops is 1:0.5:0.5, values of FEST i for N, P and K are 125, 62.5 and 62.5, respectively. According to their magnitudes of harm to the environment when overused, 0.35, 0.55 and 0.10 are defined as Wi for N, P and K, respectively. Using models of fertilization environmental hazard assessment, yearly fertilization intensities (FI i ) were calculated for Anhui Province for the period 1990–2012. This information was then compared with annual yields of grain, cotton and food oil (Fig. 1).

Fig. 1
figure 1

Trends of fertilization intensity and sum yields of grain, food oil and cotton products

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Amounts of fertilizer applied, expressed as both the total and normalized to area, has been steadily increasing in Anhui Province from 1990 to 2012. The total amount of fertilizer used increased from 1.45 × 106 t in 1990 to 3.3 × 106 t in 2012. Fertilization intensity (FI), where the total amount of fertilizer applied was normalized to the area farmed, increased from 333 to 797 kg/ha in the same period. Both total amount of fertilizers and FI t increased, while the sum of yields of grains, food oil and cotton products increased by 38 % from 6,123 to 8,475 kg/ha (Fig. 1). This analysis suggests that it is likely that the amount of fertilizer used will continue to increase into the future, a result that is consistent with the conclusions of other studies (Hu and Zhao 2007; Zhao and Cheng 2011; Sattari et al. 2012).

Due to the “law of diminishing returns” of land, increasing rates of use of fertilizer have been greater than rates of production of grain, food oil and cotton. Efficiency of use of fertilizers, which is the product yield per unit of fertilizer, has been decreasing, while the FEHI has been increasing (Fig. 2). The FEHI increased from 0.57 (“minimal hazard”) through 0.65 in 1995 (“medium hazard”) to 0.77 (“serious hazard”) in 2012. According to the current trend of fertilizer use, FEHI will soon exceed 0.8, which indicates “extreme hazard.”

Fig. 2
figure 2

Trends of fertilizer effect and Fertilization Environmental Hazard Index (FEHI)

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3.2 Spatial variation of FEHI in Anhui Province

Using the models of fertilization environmental hazard assessment, FEHI t and FEHI i (FEHIN, FEHIP, FEHIK) were calculated and ranked for each region of Anhui (Table 2).

Table 2 Fertilization Environmental Hazard Index (FEHI t ) among regions of Anhui Province in 2012
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Two regions, Tongling and Huainan of Anhui Province, were classified as being at “extreme hazard” from over-fertilization. Seven regions, Bengbu, Hefei, Xuancheng, Chuzhou, Wuhu, Anqing and Liuan were classified as being at “serious hazard.” Hazards of the rest six regions were classified as “medium hazard” (Fig. 3). Two regions of Huainan and Huangshan were classified as being “extreme hazard,” and nine regions were classified as “serious hazard” due to pollution with N (Fig. 4). Three regions, Huainan, Tongling and Bengbu, were classified as being “extreme hazard,” due to pollution with P (Fig. 5). No regions were classified as being “extreme,” but eight regions were classified as being “serious,” and the rest of eights regions as being “medium” due to pollution with K (Fig. 6). Hazards posed by non-point pollution, due to use of inorganic, chemical fertilizers in Anhui Province, are serious, especially for P due to its cause of entrophication of lakes. This causes undesirable changes in ecology, resulting in a decline in the provision of eco-services, often with serious economic consequences (Syers et al. 2008).

Fig. 3
figure 3

Distribution of hazards (FHRI) due to NPK pollution

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Fig. 4
figure 4

Distribution of hazards (FEHIN) due to N pollution

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Fig. 5
figure 5

Distribution of hazards (FEHIP) due to P pollution

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Fig. 6
figure 6

Distribution of hazards (FEHIK) due to K pollution

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3.3 Effects of overuse of chemical fertilizers on the environment of Anhui Province

Excess fertilization can eventually cause deterioration of soil, pollution of air and water, poor quality agricultural products and in some cases result in adverse effects on health of people, such as methemoglobinemia caused by nitrite (NO2 −). Excess N in surface and groundwater mainly originates from farmland, on which excess inorganic fertilizers are applied (Zou 2011). According to monitoring of soils in Mengcheng County in Bozhou, Anhui Province, sponsored by the local government, pH of soil has been decreasing since 1985. On average, pH of soil decreased from 8.2–8.4 in 1985 to 7.2–7.7 in 2003 with the least pH of 6.1. Thus, pH has decreased 0.7–1 units within 8 years. By 2006, the mean pH of soil was 6.56, with a minimum of 4.57, which is a decrease of 1 U within 3 years (Table 3). This trend in pH is mainly due to overuse of fertilizer (Zhang and Hu 2008).

Table 3 Changes of nutrients and pH values of soils in Mengcheng, Bozhou, Anhui Province (Zhang and Hu 2008)
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The main reason for the decreasing pH is the use of inorganic, chemical fertilizers which contain chlorine (Cl), sulfur (S) and P. These elements can result in leaching of ions, including Na+, K+, NH4 +, Mg2+ and Ca2+ from soil, which affects ion balance and results in excessive H+. Another reason for acidification is increasing rates of use of fertilizer and lesser efficiency of assimilation by plants. For example, in the vicinity of Chao Lake, the mass of N from fertilizer was 75, 750 and 960 kg/ha in 1960s, 1980s and 2000s, respectively, with the greatest amount of 1,200 kg/ha in 2008 in some areas (Wang et al. 2008). According to the Environmental Protection Bureau of Anhui Province (Bureau of Environmental Protection of Anhui Province 2013), water quality of tributaries to the Huai River in Anhui Provence is moderately polluted. Of the 19 tributary rivers, there were 4 tributaries with minimal water pollution, 3 tributaries with moderate pollution, 12 tributaries with severe pollution. Water quality of Chao Lake was grade IV, with minimal pollution and moderate eutrophication. Among 11 rivers which flow into the Chao Lake, there were 2 rivers that were classified as being moderately polluted, 5 rivers were seriously polluted, and only 4 rivers were deemed to not be polluted. According to the survey on 740 farm families in watershed of Chao Lake (Liu et al. 2008), 90 % of them overused nitrogen fertilizers with unsuitable methods of fertilization, such as spreading fertilizers on the surface of soil, fertilizing crops once a year with unreasonable amounts, which results in non-point source pollution due to runoff, leaching and evaporation.

3.4 Responsibilities of governments

Excess fertilization has resulted in severe acidification of soil, moderate pollution of the Huai River and entrophication of Chao Lake in Anhui. Thus, overuse of fertilizers is a significant environmental problem there. One reason for the overuse of fertilizers is that farmers do not know how much fertilization is suitable for their crops. Most of them have the misperception that the more fertilizers the greater production. So it is the responsibility of local jurisdictions to offer many kinds of training programs to farmers. Government agencies should send agricultural technicians to the countryside to guideline fertilization applied by farmers. They should inform farmers of the optimal amounts and types of fertilizers to apply, based on the regional soil types and crops. For example, the northern area of Anhui is mostly located in the Yellow-Huai River alluvial plain. There are various types of yellow alluvial soils, most of which have lesser quantities of organic matter should be used with more organic fertilizers to improve soil structures. In the southern part of Anhui, where rice is cultivated along the Yangtze River Plain, it is recommended to use fertilizers such as urea, ammonium chloride, rather than sulfate and nitrate N. There were some successful practices that government helped farmers with technology of fertilizer prescription via soil measurement since 2005. It has been demonstrated that optimal rates of applications of fertilizers would reduce rates of application by 28 kg/ha, which would also maintain optimal productivity. In fact, based on a reduced cost of fertilization while maintaining maximum productivity would result in a net increase in profit of approximately 838 ¥/ha (136.3 $/ha) (Zhao and Cheng 2011). As farmers learn better fertilization practices, they will be better able to assist in protection of the environment, reduce environmental hazards and ensure sustainability of their agricultural practices.

Government agencies should also persuade and assist fertilizer producers to pay more attention to technological innovations by providing farmers with better quality, more effective, slow-releasing fertilizers, such as organic compound fertilizers. Application of mixed organic and inorganic fertilizers is good for quality of both soil and products. Also straws and other residues of crops could be used.

4 Conclusions and suggestions

  1. 1.

    Models of evaluating the environmental hazard by over-fertilization, initially set up by authors were applied to assess Anhui agricultural environment. The FEHI increased from 0.57 (minimal hazard) in 1990 through 0.65 (medium hazard) in 1995 to 0.77 (serious hazard) in 2012. According to the current trend in use of fertilizer, the FEHI will soon be over 0.8, which is extreme hazard. Thus, the rural ecological environment situation of Anhui Province faces serious challenges.

  2. 2.

    Fertilizers were found to be over-used in most sub-administrative regions of Anhui Province. Among 16 regions, two were classified as being extremely at hazard from over-fertilization, seven were classified as being serious, six were classified as being moderate. Two regions were classified as being extremely at hazard due to pollution with N, three were classified as being serious at hazard due to pollution with P, and no regions were classified as being extreme at hazard due to pollution with K. Based on the results of this assessment, environmental hazard posed by non-point source pollution from use of chemical fertilizers in Anhui Province is very serious.

  3. 3.

    Models of assessing fertilization environmental hazard need further improvement in the future. Determination of threshold guidelines for application of inorganic fertilizers should consider the social, ecological and economic factors of agricultural production of various regions in China. The 250 kg/ha of fertilization environmental safety threshold suggested by the Chinese government is very general, but is useful for the control of total amount of fertilizers at provincial or county levels. It gives references of fertilization for policy makers, agriculture producers or farmers. In fact, the situation varies between regions, sites and also between crops, so the FESTs should be different in different places where the amounts of fertilizer used could be higher or lower than 250 kg/ha according to local conditions. And the classifications of fertilization environmental hazard can also be adjusted according to local conditions and requirements for the quality of environment.