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Soil acidification in Chinese tea plantations
Science of the Total Environment 715 (2020) 136963
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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Short Communication
Soil acidification in Chinese tea plantations Peng Yan a, Liangquan Wu b, Donghui Wang a, Jianyu Fu a, Chen Shen a, Xin Li a, Liping Zhang a, Lan Zhang a, Lichao Fan c, Han Wenyan a,⁎ a b c
Key Laboratory of Tea Quality and Safety Control, Ministry of Agriculture, Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310008, China College of Resources and the Environment, Fujian Agriculture & Forestry University, Fuzhou 350002, China University of Göttingen, Soil Science of Temperate Ecosystems, Büsgenweg 2, 37077, Göttingen DE 37077, Germany
H I G H L I G H T S • In China, the average soil pH of tea plantation was 4.68 nationally and ranged from 3.96 to 5.48 in different provinces. • Compared with cereal and cash crops systems, the greatest soil acidification occurred in the tea system. • Organic management is a way to prevent soil acidification in tea plantations.
a r t i c l e
i n f o
Article history: Received 21 December 2019 Received in revised form 18 January 2020 Accepted 25 January 2020 Available online 27 January 2020 Editor: Charlotte Poschenrieder Keywords: Soil acidification Tea Agricultural management Exchangeable acidity
G R A P H I C A L
Soil pH changes from 1980s to 2010s
A B S T R A C T
Soil pH with three crop systems
Soil pH with traditional and organic management
a b s t r a c t Soil acidification is a major problem in intensive agricultural systems and is becoming increasingly serious. Most research has reported the soil acidification of cereal crops, forests, and grasslands. However, there is no information about soil acidification under tea cultivation on a national scale. Therefore, we conducted a nationwide survey of soil acidification in the major tea-planting areas of China and used two nationwide surveys in three Chinese counties to evaluate changes in soil acidity over the past 20–30 years. Finally, the acidity of soil from forests and traditional and organic tea plantations was compared to evaluate the effects of agricultural management on soil acidification in tea plantations. Our results show that: (1) the average soil pH was 4.68 nationally and ranged from 3.96 to 5.48 in different provinces. Overall, 46.0% of the soil samples had a pH b4.5, which is too acidic for tea growth and only 43.9% had a soil pH of 4.5–5.5, which is optimal for tea growth. (2) In the past 20–30 years, the greatest soil acidification was observed in tea plantations; the pH decreased by 0.47 to 1.43, which is much greater than the decrease seen in fruit and vegetable systems (0.40 to 1.08) and cereals (0.30 to 0.89). (3) Compared with forests, tea cultivation with chemical fertilizer application caused serious soil acidification, while no significant acidification was observed at organic tea plantations. In conclusion, serious soil acidification occurs nationally in China, and organic management is an adaptive choice for sustainable tea growth. © 2020 Published by Elsevier B.V.
⁎ Corresponding author at: Tea Research Institute of the Chinese Academy of Agricultural Sciences, National Center for Tea Improvement, Key Laboratory of Tea Plant Biology and Resources Utilization, Ministry of Agriculture, Hangzhou, Zhejiang 310008, China. E-mail address: [email protected] (H. Wenyan).
https://doi.org/10.1016/j.scitotenv.2020.136963 0048-9697/© 2020 Published by Elsevier B.V.
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1. Introduction Soil acidification is a serious aspect of soil degradation worldwide and has been reported across a variety of ecosystems and regions (Guo et al., 2010; Kirk et al., 2010; Yang et al., 2012; Zhu et al., 2018). Soil acidification alters the biogeochemistry of ecosystems (De Vries et al., 2015; Caputo et al., 2016), causing diversity losses worldwide and increasing the leaching loss of cationic nutrients such as K, Na, Ca, and Mg, thereby reducing plant productivity and increasing greenhouse gas emissions (Bouwman et al., 2002; Zhang et al., 2016; Dai et al., 2017). Therefore, soil acidification has attracted increasing attention from both the scientific community and the public. One challenge to agricultural sustainability is land degradation resulting from agricultural management practices. Soil acidification in intensive agricultural systems is primarily due to the inappropriate use of fertilizers, especially N (Tian and Niu, 2015; Zeng et al., 2017), but also results from the removal of products and leaching of N, P, K, and Mg from the plant root zone (Duan et al., 2004; Yang et al., 2018). Compared with forest, greater soil acidification has been observed in tea plantations (Yan et al., 2018). In tea cultivation, a large amount of ammonium-N fertilizer is applied to increase the yield (Ruan et al., 2004). Moreover, tea plants can activate and take up large amounts of Al from soil, most of which accumulates in the leaves (Ruan and Wang, 2001). The biogeochemical cycle of Al in tea and soil further accelerates soil acidification in rainy environments (Wang et al., 2010). Tea is one of the top three non-alcoholic drinks worldwide and the major cash crop in developing countries such as China, India, Sri Lanka, and Kenya. Because of its high economic value, the area of tea cultivation has been expanding rapidly in China (Su et al., 2015). In 2017, tea cultivation covered about 3.05 million ha in China, accounting for 45.9% of the tea planting area worldwide. In China, there are tea plantations in 19 provinces, mainly in tropical and subtropical areas, with high temperatures and rainfall. Highly weathered soils are
sensitive to cation leaching and subsequent soil acidification (Yang et al., 2018). High rates of N fertilization, as high as 444 kg ha−1, further accelerate soil acidification in these areas (Ni et al., 2019). Understanding the scale of soil acidification can provide valuable information for guiding tea plantation development in China. Soil acidification is ascribed to the combination of high-N fertilization, plant uptake and the removal of base cations from soil, and acid deposition. The overuse of N fertilizer is the dominant factor in agricultural systems (Guo et al., 2010; Tian and Niu, 2015). Many studies have reported that the replacement of chemical N fertilizer by organic fertilizer can prevent soil acidification or even increase soil pH (Shi et al., 2019; Ye et al., 2019), which contributes to increasing the net base cation input (Cai et al., 2015) and producing Al-organic matter complexes (Iyamuremye and Dick, 1996; Hagvall et al., 2015). Therefore, we hypothesized the organic management of tea plantations is an effective way to avoid soil acidification in tea cultivation. The objective of this study was to: (1) evaluate soil acidification at tea plantation on a national scale in China; (2) compare soil pH changes with different cropping systems (i.e. cereal, vegetable or fruit, tea) in the past 20–30 years; (3) evaluate agricultural management (i.e. traditional and organic) on soil acidification in tea gardens. We believe that this work will be useful for us to guide tea development and management in future. 2. Materials and methods 2.1. Study area The study area included all of the tea-planting provinces in China (Fig. 1), extending between latitudes 18–36 N and longitudes 94–121E. The mean annual temperature and precipitation ranged from 12 to 22 °C and 700 to 2600 mm, respectively. The main soil types related to tea cultivation are Haplic, Humic, and Ferric Acrisols.
Fig. 1. The study area and sites where soil was sampled in each province. Blue points (n = 225) indicates soil sampling counties; green points (n = 25) is soil sampling sites with forest and tea plantations; and red points (n = 10) shows the soil sampling sites with forest and traditional and organic tea plantations. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
P. Yan et al. / Science of the Total Environment 715 (2020) 136963
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Jiangsu, Shandong, Zhejiang, Henan, and Shaanxi, respectively. No province had a soil pH N5.5. The frequency distribution of soil pH in the intervals b4.5, 4.5–5.5, and N5.5 for each province varied from 4.8 to 100%, 0.0 to 88.5%, and 0.0 to 46.9%, respectively (Fig. 3). For the entire country, 46.0, 43.9, and 10.1% of the soil samples had a pH b4.5, 4.5–5.5, and N5.5, respectively. In nine provinces, N50% of the soil samples had a soil pH b4.5: 51.2, 53.2, 66.3, 77.0, 86.9, 87.3, 88.3, 89.1, and 100.0% for Guangdong, Yunnan, Hubei, Sichuan, Guangxi, Guizhou, Chongqing, Fujian, and Jiangxi, respectively. In only three provinces did N50% of the soil samples have a soil pH between 4.5 and 5.5: 66.1, 68.5, and 88.5% for Jiangsu, Zhejiang, and Henan, respectively. Six provinces had no soil with a pH N5.5, and the percentage of soil samples with a pH N5.5 was b15% for eight provinces. In Shanxi Province, N46.9% of the soil samples had a pH N5.5.
2.2. Data sources To evaluate the soil acidity at tea plantations on a national level, 2058 soil samples were collected at 0–20 cm depths from 225 teaplanting counties (the blue points in Fig. 1) in 19 provinces in China and the soil pH was measured (Fig. 1). In this study, soil pH datasets were obtained from two sources and used to evaluate the pH changes in major croplands over the past 20–30 years (Table 1). The first consisted of 61, 449, and 50 representative soil profiles obtained in Anxi, Songyang, and Wuyi Counties, respectively, from China's Second National Soil Inventory during the 1980s. The second soil pH dataset was derived from the National Soil Testing and Formulated Fertilization Project during the 2000s (2006–2009) and comprised 5062, 1423, and 719 samples from Anxi, Songyang, and Wuyi, respectively. Depending on the soil use types, the second soil dataset was subdivided into Cereal, Fruit and vegetable, and Tea groups (Table 1). To evaluate the changes in soil acidity resulting from tea cultivation, soil samples were collected at 25 sites (the green points in Fig. 1) in forests and tea plantations (Fig. 1). To understand the effect of different forms of agricultural management on soil acidity during tea cultivation, soil samples were collected at 10 sites (the red points in Fig. 1) within forests, traditional tea plantations, and organic tea plantations (Fig. 1). Soil samples were obtained at 0–10, 10–20, and 20–30 cm depths for each profile, and a suite of chemical properties, including soil pH and exchangeable acidity, was analyzed.
3.2. Topsoil pH changes in three counties with tea, cereal, and fruit and vegetable cultivation between the 1980s and 2000s There was significant topsoil acidification in three counties (average pH declines for the soil groups of 0.30 to 1.43) in the past 20–30 years (Table 1). In all soil groups, acidification was the greatest in tea systems; the pH decreased by 0.47, 1.37, and 1.43 for Songyang, Anxi, and Wuyi, respectively. Soil acidification was greater in fruit and vegetable systems (pH decrease of 0.40 to 1.08) than under cereals (pH decrease of 0.30 to 0.89).
2.3. Soil analysis and data processing
3.3. Soil pH, exchangeable acid, and its components change with tea cultivation
Soil pH was measured using a pH meter in soil water suspensions, with a soil-to-water ratio of 1:2.5 (Bao, 2005), which is the same approach used for the National Soil Inventory during the 1980s. The total exchangeable acidity (Al3+ and H+) was extracted with 1 M KCl and titrated with 0.02 M NaOH to the phenolphthalein endpoint to obtain the exchangeable H+. The exchangeable Al3+ was calculated from the difference between the exchangeable acidity and exchangeable H+ (Bertsch and Bloom, 1996). The averaged soil pH for all of China and the distribution of soil pH in the pH intervals b4.5, 4.5–5.5, and N 5.5 were analyzed using Sigmaplot 14.0. Data from the tea plantations and forests were analyzed using oneway ANOVAs at a 0.05 probability level, followed by a t-test using SPSS v. 16.0 (SPSS Inc., Chicago, IL, USA).
The difference in soil pH between tea plantations and adjacent forests was investigated (Fig. 4). Soil pH increased with soil depth in forest and tea plantations. Compared with forests, the soil pH at the tea plantations decreased 0.50, 0.66, and 0.58 at soil depths of 0–10, 10–20, and 20–30 cm, respectively (Fig. 4A). Tea cultivation significantly increased the soil exchangeable acidity, and the exchangeable H+ and Al3+ at the tea plantations were consistently higher than those in forest soil in the soil profile (Fig. 4B–D). Soil acidity was dominated by exchangeable Al3+ in both the forest and tea plantation soils, accounting for 51.0–57.8% and 63.2–70.5%, respectively. Compared with the forest soil, significantly higher soil exchangeable Ca2+, Mg2+ and K+ were observed in the forest soil (Fig. S1).
3. Results
3.4. Soil pH, exchangeable acidity, and its components change with different agricultural management systems
3.1. The averaged soil pH and distribution in three intervals for each province and the entire country
The soil pH of forests and organic tea plantations was significantly higher than that of traditional tea plantations at all three soil depths, while no significant differences were observed between the forests and organic tea plantations (Fig. 5A). The highest soil exchangeable acidity and exchangeable H+ and Al3+ were observed in traditional tea plantations. The exchangeable acidity and exchangeable H+ and Al3+ of organic tea plantations were higher than those of forest at 0–10 and 10–20 cm soil depths, while no differences were observed at
The averaged soil pH for each tea-cultivation province varied from 3.96 to 5.48 with a mean of 4.68 for China (Fig. 2). There were eight provinces with a pH b4.5: 3.96, 4.04, 4.11, 4.12, 4.23, 4.28, 4.36, and 4.37 for Jiangxi, Fujian, Chongqing, Guangxi, Guizhou, Sichuan, Hubei, and Guangdong, respectively. The other seven provinces had a pH N4.5: 4.50, 4.64, 4.67, 4.74, 4.85, 4.99, and 5.48 for Yunnan, Hunan,
Table 1 Topsoil pH changes in three countries with tea, cereal, fruit and vegetable cultivation between the 1980s and 2000s. 1980s County
Anxi Songyang Wuyi
Samples
61 449 40
2000s pH
5.59 5.56 5.83
Cereal
Fruit and vegetable
Tea
Samples
pH
pH change
Samples
pH
pH change
Samples
pH
pH change
57 759 173
5.29 (3.80–6.50) 5.43 (4.10–7.30) 4.94 (4.13–6.18)
−0.30 −0.33 −0.89
13 224 383
5.15 (4.00–7.10) 5.16 (3.74–7.23) 4.75 (3.43–6.68)
−0.44 −0.40 −1.08
4992 440 163
4.22 (3.00–6.90) 5.09 (3.24–6.23) 4.40 (3.55–5.99)
−1.37 −0.47 −1.43
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Fig. 2. The number of soil samples and average soil pH for each province and the whole of China. The white and black line in the box represent the mean and median of the data.
20–30 cm. What's more, the soil exchangeable Ca2+ and Mg2+ of forest and organic tea gardens were higher than that of traditional tea gardens (Fig. S2).
lower than the 5.74 of forest soil (Zhu, 2017), and 0.90 lower than the 5.58 of cash crop soil (Guo et al., 2010). The optimal soil pH for tea growth is 4.5–5.5 (Ruan et al., 2007). Tea growth is inhibited when the soil pH is lower than 4.0; both the quality and quantity of tea production are negatively affected (Fung et al., 2008). In our research, only 43.9% of the soil samples had a pH in the interval 4.5–5.5, while 46.0% of the soil samples had a pH b4.5. This constrains sustainable tea development in China.
4. Discussion There is serious soil acidification in tea plantations in China. The average soil pH of tea plantations for all of China was 4.68, which is 1.06
The size of circle represents The frequency (%) distribution of the averaged soil pH soil pH in the intervals <4.5, 4.5–5.5, and >5.5 pH 4.0
14
36
50
Shandong 47
49
Henan
74
Sichuan
84
22
31
Jiangxi
16 84
Fujian
Guizhou 6
Yunnan
Zhejiang
92
Hunan
6 24
pH 5.5
67
8 23 46
4
74
4847
9 23
Hubei
Chongqing
pH of 4.5–5.5
pH 5.0
pH >5.5
Anhui
60
14 2
Jiangsu
71
35
4
6
24
5 23
pH <4.5 34
63
86
Shaanxi
pH 4.5 3
104
4
5
10
44
46
Whole country
47
47
71
Guangdong
Guangxi
Fig. 3. The frequency (%) distribution of soil pH in the intervals pH b 4.5, 4.5–5.5, and N5.5 for each province and the whole country. The orange, green and blue colour represent the interval b4.5, 4.5–5.5, and N5.5, respectively. The number in each circle represents the percentage of soil samples in the intervals b4.5, 4.5–5.5, and N5.5. The size of the circle represents the averaged soil pH for each province. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 4. The soil pH (A), exchangeable acid (B), and exchangeable H+ (C) and exchangeable Al3+ (D) changes at soil depths of 0–10, 10–20, and 20–30 cm for the forests (n = 75) and tea plantations (n = 105). Different lowercase letters indicate significant differences at the p b 0.05 level. The lines and rectangles within the boxes represent the median and mean values of all data, the bottom and top edges of the boxes are the 25th and 75th percentiles of all data, and the bottom and top bars represent the 5th and 95th percentiles, respectively.
The topsoil pH changes in Anxi, Songyang, and Wuyi between the 1980s and 2000s revealed significant acidification of all crops (Table 1). This is consistent with reports of serious soil acidification in
China (Guo et al., 2010; Zhu et al., 2018), which is related to the high rate of N fertilization and low nitrogen use efficiency (NUE) (Tian and Niu, 2015; Mao et al., 2017) and the uptake and removal of base cations
Fig. 5. The soil pH (A), exchangeable acid (B), and exchangeable H+ (C) and exchangeable Al3+ (D) changes at soil depths of 0–10, 10–20, and 20–30 cm in the forests (n = 30) and traditional (n = 30) and organic (n = 30) tea plantations. Different lowercase letters indicate significant differences at the p b 0.05 level. The lines and rectangles within the boxes represent the median and mean values of all data, the bottom and top edges of the boxes represent the 25th and 75th percentiles of all data, respectively, and the bottom and top bars represent the 5th and 95th percentiles, respectively.
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by plants (Duan et al., 2004). Moreover, the acidification is greater in tea systems (pH decrease of 0.47 to 1.43) than under cash crop systems (0.40 to 1.08) or cereals (0.30 to 0.89). This could have the following two causes. First, the decrease in soil pH might be driven by the high rate of N fertilization and low NUE (Tian and Niu, 2015). The average rate of N fertilization was as high as 473 kg ha−1, while the NUE was only about 18.3% (Chen and Lin, 2016), and most of the N was lost via 2+ NO−1 and Mg2+ 3 leaching (Yan et al., 2018). Base cations such as Ca are leached with NO−1 based on the charge balance in soil solutions, 3 which further acidifies the soil (Gundersen et al., 2006; Rothwell et al., 2008). Second, the high pH decline in tea soil might be related to its physiology. The rhizosphere of tea plants can excrete organic acids, carbonic acid, and polyphenols, leading to acidification (Yang, 2005). Tea can take up large amounts of Al, most of which accumulates in the leaves (Ruan et al., 2004). The biogeochemical cycle of Al in tea litter is another factor that leads to soil acidification in tea plantations (Wang et al., 2010). The acidification of tea soil is regulated by agricultural management (Guo et al., 2010). Generally, soil acidity increased with the duration of tea cultivation and the rate of fertilization (Li et al., 2016; Yang et al., 2018; Yan et al., 2018). In our research, the pH of forest soils was consistently higher than that of the traditional tea plantations at all soil depths, while no significant differences were observed compared with organic tea plantations (Fig. 5). This is consistent with reports that soil acidification can be prevented by the application of manure (Noble et al., 1996; Zeng et al., 2017; Zhu et al., 2018; Shi et al., 2019). Tea is an NH+ 4 -fed plant, with a high cation/anion ratio, and it extrudes the net excess H+ (Ruan et al., 2004; Yang, 2005). The mechanisms involved in reducing soil acidity with manure include the specific adsorption of organic anions on hydrous Al surfaces and the corresponding release of hydroxyl ions (Wang et al., 2016), decarboxylation of organic anions (Xiao et al., 2013), return of basic cations to soil, increased soil exchangeable cations (e.g., Ca2+, Mg2+, and K+) (Cai et al., 2015), and ammonification of labile organic N in manure (Xu et al., 2006). In our research, the soil exchangeable Ca2+ and Mg2+ of the organic tea gardens were significantly higher than that of traditional tea gardens (Fig. S1, S2). The fundamental approach to alleviate soil acidification in tea plantations is to reduce N fertilizer inputs and increase the manure inputs to soil. 5. Conclusion This study assessed soil acidification in Chinese tea plantations at provincial and national levels. The average soil pH in each province varied from 3.96 to 5.48, with a mean value of 4.68 for the entire country. Only 43.9% of the soil samples had a pH in the range 4.5–5.5, which is optimal for tea growth, while 46.0% of the soil samples had a pH b4.5, indicating serious soil acidification at tea plantations. In the past 20–30 years, serious soil acidification has occurred across Chinese croplands, with the highest rate of acidification observed in soil under tea cultivation. Compared with forest soil, no significant decrease in soil pH was observed in organic tea plantations, indicating that organic management is a useful way to avoid soil acidification during tea cultivation. In conclusion, serious soil acidification occurs at tea plantations nationally in China, and organic management is necessary for the sustainable development of tea plantations. Author contributions Peng Yan and Wen-Yan Han conceived and designed the research; Liangquan Wu, Donghui Wang, Jianyu Fu, Chen Shen, Xin Li, Liping Zhang, Lan Zhang, Lichao Fan performed the experiments and analyzed the data; Peng Yan, Liangquan Wu and Wen-Yan Han discussed the data; Peng Yan wrote the manuscript with the contributions from the other authors.
Credit author statement Peng Yan: Conceptualization, Methodology, Formal Analysis, Investigation, Data curation, Validation, Writing- Reviewing and Editing. Liangquan Wu: Formal Analysis, Investigation, Data curation. Donghui Wang: Investigation, Validation, Data curation. Chen Shen: Investigation, Data curation. Jianyu Fu: Investigation, Data curation. Xin Li: Investigation, Data curation. Li-Ping Zhang: Investigation, Data curation. Lan Zhang: Formal Analysis. Wen-Yan Han: Conceptualization, Supervision, Resources, Project Administration, Funding Acquisition. Declaration of competing interest The authors declare no conflict of interest. Acknowledgements This work was financially supported by the National Key Research and Development of China (2017YFE0107500), the Science and Technology Innovation Project of the Chinese Academy of Agricultural Sciences (CAAS-ASTIP-2014-TRICAAS), the Funds for Science and Technology Innovation Project from the Chinese Academy of Agricultural Sciences (CAAS-XTCX2016015). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.scitotenv.2020.136963. References Bao, S.D., 2005. Agricultural and Chemistry Analysis of Soil. Agriculture Press, Beijing. Bertsch, P.M., Bloom, P.R., 1996. Soil pH and soil acidity. In: Sparks, D.L. (Ed.), Methods of Soil Analysis. Part 3. Chemical Methods, SSSA Book Series 5. ASA and SSSA, Madison, WI, pp. 517–576. Bouwman, A.F., Boumans, L.J.M., Batjes, N.H., 2002. Modeling global annual N2O and NO emissions from fertilized fields. Glob. Biogeochem. Cycles 2002 (16), 281–289. Cai, Z., Wang, B., Xu, M., Zhang, H., He, X., Zhang, L., Gao, S., 2015. Intensified soil acidification from chemical n fertilization and prevention by manure in an 18-year field experiment in the red soil of southern China. J. Soils Sediments 15, 260–270. Caputo, J., Beier, C.M., Sullivan, T.J., Lawrence, G.B., 2016. Modeled effects of soil acidification on long-term ecological and economic outcomes for managed forests in the Adirondack region (USA). Sci. Total Environ. 565, 401–411. Chen, C.F., Lin, J.Y., 2016. Estimating the gross budget of applied nitrogen and phosphorus in tea plantations. Sustainable Environment Research 26 (3), 124–130. https://doi. org/10.1016/j.serj.2016.04.007. Dai, Z., Zhang, X., Tang, C., Muhammad, N., Wu, J., Brookes, P.C., 2017. Potential role of biochar in decreasing soil acidification - a critical review. Sci. Total Environ. 581, 601–611. De Vries, W., Hettelingh, J.P., Posch, M., 2015. Critical Loads and Dynamic Risk Assessments: Nitrogen, Acidity and Metals in Terrestrial and Aquatic Ecosystems. 25. Springer, Dordrecht, Netherlands. Duan, L., Huang, Y., Hao, J., Xie, S., Hou, M., 2004. Vegetation uptake of nitrogen and base cations in China and its role in soil acidification. Sci. Total Environ. 330, 187–198. Fung, K.F., Carr, H.P., Zhang, J.H., Wong, M.H., 2008. Growth and nutrient uptake of tea under different aluminum concentrations. J. Sci. Food Agric. 88, 1582–1591. Gundersen, P., Schmidt, I.K., Raulund-Rasmussen, K., 2006. Leaching of nitrate from temperate forests-effects of air pollution and forest management. Environ. Rev. Lett. 14, 1–57. Guo, J.H., Liu, X.J., Zhang, Y., Shen, J.L., Han, W.X., Zhang, W.F., Christie, P., Goulding, K.W.T., Vitousek, P.M., Zhang, F.S., 2010. Significant acidification in major Chinese croplands. Science 327, 1008–1010. Hagvall, K., Persson, P., Karlsson, T., 2015. Speciation of aluminum in soils and stream waters: the importance of organic matter. Chem. Geol. 417, 32–43. Iyamuremye, F., Dick, R.P., 1996. Organic amendments and phosphorus sorption by soils. Adv. Agron. 56, 139–185. Kirk, G.J.D., Bellamy, P.H., Lark, R.M., 2010. Changes in soil pH across England and Wales in response to decreased acid deposition. Glob. Chang. Biol. 16, 3111–3119. Li, S.Y., Li, H., Yang, C.L., Wang, Y.D., Xue, H., Niu, Y.F., 2016. Rates of soil acidification in tea plantations and possible causes. Agric. Ecosyst. Environ. 233, 60–66. Mao, Q., Lu, X., Zhou, K., Chen, H., Zhu, X., Mori, T., Mo, J.M., 2017. Effects of long-term nitrogen and phosphorus additions on soil acidification in an N-rich tropical forest. Geoderma 285, 57–63. Ni, K., Liao, W.Y., Yi, X.Y., Niu, S.G., Ma, L.F., Shi, Y.Z., Zhang, Q.F., Liu, M.Y., Ruan, J.Y., 2019. Fertilization status and reduction potential in tea gardens of China. Journal of Plant Nutrition and Fertilizers. 25, 421–432 (in Chinese with English abstract). Noble, A.D., Zenneck, I., Randall, P.J., 1996. Leaf litter ash alkalinity and neutralisation of soil acidity. Plant Soil 179, 293–302.
P. Yan et al. / Science of the Total Environment 715 (2020) 136963 Rothwell, J.J., Futter, M.N., Dise, N.B., 2008. A classification and regression tree model of controls on dissolved inorganic nitrogen leaching from European forests. Environ. Pollut. 156, 544–552. Ruan, J.Y., Wang, M.H., 2001. Accumulation of fluoride and aluminum related to different varieties of tea plant. Environ. Geochem. Health 23, 53–63. Ruan, J.Y., Ma, L.F., Shi, Y.Z., Zhang, F.S., 2004. Effects of litter incorporation and nitrogen fertilization on the contents of extractable aluminum in the rhizosphere soil of tea plant (Camallia sinensis (L.) O. Kuntze). Plant Soil 263, 283–296. Ruan, J.Y., Gerendás, J., Härdter, R., Sattelmacher, B., 2007. Effect of nitrogen form and root-zone pH on growth and nitrogen uptake of tea (Camellia sinensis) plants. Ann. Bot. 99, 301–310. Shi, R.Y., Liu, Z.D., Li, Y., Jiang, T., Xu, M., Li, J.Y., Xu, R.K., 2019. Mechanisms for increasing soil resistance to acidification by long-term manure application. Soil Tillage Res. 185, 77–84. Su, S., Zhou, X., Wan, C., Li, Y., Kong, W., 2015. Land use changes to cash crop plantations: crop types: multilevel determinants and policy implications. Land Use Policy 50, 379–389. Tian, D., Niu, S., 2015. A global analysis of soil acidification caused by nitrogen addition. Environ. Res. Lett. 10, 024019. Wang, H., Xu, R.K., Wang, N., Li, X.H., 2010. Soil acidification of Alfisols as influenced by tea cultivation in eastern China. Pedosphere 20, 799–806. Wang, L., Butterly, C.R., Tian, W., Herath, H.M.S.K., Xi, Y., Zhang, J., Xiao, X., 2016. Effects of fertilization practices on aluminum fractions and species in a wheat soil. J. Soils Sediments 16, 1933–1943. Xiao, K., Xu, J., Tang, C., Zhang, J., Brookes, P.C., 2013. Differences in carbon and nitrogen mineralization in soils of differing initial pH induced by electrokinesis and receiving crop residue amendments. Soil Biol. Biochem. 67, 70–84.
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Xu, J.M., Tang, C., Chen, Z.L., 2006. The role of plant residues in pH change of acid soils differing in initial pH. Soil Biol. Biochem. 38, 709–719. Yan, P., Shen, C., Fan, L.C., Li, X., Zhang, L.P., Zhang, L., Han, W.Y., 2018. Tea planting affects soil acidification and nitrogen and phosphorus distribution in soil. Agric. Ecosyst. Environ. 254, 20–25. Yang, X.D., Ni, K., Shi, Y.Z., Yi, X.Y., Zhang, Q.F., Fang, L., Ruan, J.Y., 2018. Effects of longterm nitrogen application on soil acidification and solution chemistry of a tea plantation in China. Agric. Ecosyst. Environ. 252, 74–82. Yang, Y.H., Ji, C.J., Ma, W.H., Wang, S.F., Wang, S.P., Han, W.X., Mohammat, A., Robinson, D., Smith, P., 2012. Significant soil acidification across northern china's grasslands during 1980s–2000s. Glob. Chang. Biol. 18, 2292–2300. Yang, Y.J., 2005. Tea Plant Cultivation in China. Shanghai Scientific and Technological Press, Shanghai (in Chinese with English abstract). Ye, G.P., Lin, Y.X., Liu, D.Y., Chen, Z.M., Luo, J.F., Bolan, N., Fan, J.B., Ding, W.X., 2019. Longterm application of manure over plant residues mitigates acidification, builds soil organic carbon and shifts prokaryotic diversity in acidic Ultisols. Appl. Soil Ecol. 133, 24–33. Zeng, M.F., De Vries, W., Bonten, L.T.C., Zhu, Q.C., Hao, T.X., Liu, X.J., Xu, M.G., Shi, X.J., Zhang, F.S., Shen, J.B., 2017. Model-based analysis of the long-term effects of fertilization management on cropland soil acidification. Environ. Sci. Technol. 51, 3843–3851. Zhang, Y., He, X., Liang, H., Zhao, J., Zhang, Y., Xu, C., 2016. Long-term tobacco plantation induces soil acidification and soil base cation loss. Environ. Sci. Pollut. R. 23, 5442–5450. Zhu, Q.C., 2017. Quantification and Modelling of Soil Acidification at Regional Scale of China[D] (in Chinese with English abstract). Zhu, Q.C., Liu, X.J., Hao, T.X., Zeng, M.F., Shen, J.B., Zhang, F.S., 2018. Modeling soil acidification in typical Chinese cropping systems. Sci. Total Environ. 613–614, 1339–1348.
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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv
Short Communication
Soil acidification in Chinese tea plantations Peng Yan a, Liangquan Wu b, Donghui Wang a, Jianyu Fu a, Chen Shen a, Xin Li a, Liping Zhang a, Lan Zhang a, Lichao Fan c, Han Wenyan a,⁎ a b c
Key Laboratory of Tea Quality and Safety Control, Ministry of Agriculture, Tea Research Institute, Chinese Academy of Agricultural Sciences, Hangzhou 310008, China College of Resources and the Environment, Fujian Agriculture & Forestry University, Fuzhou 350002, China University of Göttingen, Soil Science of Temperate Ecosystems, Büsgenweg 2, 37077, Göttingen DE 37077, Germany
H I G H L I G H T S • In China, the average soil pH of tea plantation was 4.68 nationally and ranged from 3.96 to 5.48 in different provinces. • Compared with cereal and cash crops systems, the greatest soil acidification occurred in the tea system. • Organic management is a way to prevent soil acidification in tea plantations.
a r t i c l e
i n f o
Article history: Received 21 December 2019 Received in revised form 18 January 2020 Accepted 25 January 2020 Available online 27 January 2020 Editor: Charlotte Poschenrieder Keywords: Soil acidification Tea Agricultural management Exchangeable acidity
G R A P H I C A L
Soil pH changes from 1980s to 2010s
A B S T R A C T
Soil pH with three crop systems
Soil pH with traditional and organic management
a b s t r a c t Soil acidification is a major problem in intensive agricultural systems and is becoming increasingly serious. Most research has reported the soil acidification of cereal crops, forests, and grasslands. However, there is no information about soil acidification under tea cultivation on a national scale. Therefore, we conducted a nationwide survey of soil acidification in the major tea-planting areas of China and used two nationwide surveys in three Chinese counties to evaluate changes in soil acidity over the past 20–30 years. Finally, the acidity of soil from forests and traditional and organic tea plantations was compared to evaluate the effects of agricultural management on soil acidification in tea plantations. Our results show that: (1) the average soil pH was 4.68 nationally and ranged from 3.96 to 5.48 in different provinces. Overall, 46.0% of the soil samples had a pH b4.5, which is too acidic for tea growth and only 43.9% had a soil pH of 4.5–5.5, which is optimal for tea growth. (2) In the past 20–30 years, the greatest soil acidification was observed in tea plantations; the pH decreased by 0.47 to 1.43, which is much greater than the decrease seen in fruit and vegetable systems (0.40 to 1.08) and cereals (0.30 to 0.89). (3) Compared with forests, tea cultivation with chemical fertilizer application caused serious soil acidification, while no significant acidification was observed at organic tea plantations. In conclusion, serious soil acidification occurs nationally in China, and organic management is an adaptive choice for sustainable tea growth. © 2020 Published by Elsevier B.V.
⁎ Corresponding author at: Tea Research Institute of the Chinese Academy of Agricultural Sciences, National Center for Tea Improvement, Key Laboratory of Tea Plant Biology and Resources Utilization, Ministry of Agriculture, Hangzhou, Zhejiang 310008, China. E-mail address: [email protected] (H. Wenyan).
https://doi.org/10.1016/j.scitotenv.2020.136963 0048-9697/© 2020 Published by Elsevier B.V.
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1. Introduction Soil acidification is a serious aspect of soil degradation worldwide and has been reported across a variety of ecosystems and regions (Guo et al., 2010; Kirk et al., 2010; Yang et al., 2012; Zhu et al., 2018). Soil acidification alters the biogeochemistry of ecosystems (De Vries et al., 2015; Caputo et al., 2016), causing diversity losses worldwide and increasing the leaching loss of cationic nutrients such as K, Na, Ca, and Mg, thereby reducing plant productivity and increasing greenhouse gas emissions (Bouwman et al., 2002; Zhang et al., 2016; Dai et al., 2017). Therefore, soil acidification has attracted increasing attention from both the scientific community and the public. One challenge to agricultural sustainability is land degradation resulting from agricultural management practices. Soil acidification in intensive agricultural systems is primarily due to the inappropriate use of fertilizers, especially N (Tian and Niu, 2015; Zeng et al., 2017), but also results from the removal of products and leaching of N, P, K, and Mg from the plant root zone (Duan et al., 2004; Yang et al., 2018). Compared with forest, greater soil acidification has been observed in tea plantations (Yan et al., 2018). In tea cultivation, a large amount of ammonium-N fertilizer is applied to increase the yield (Ruan et al., 2004). Moreover, tea plants can activate and take up large amounts of Al from soil, most of which accumulates in the leaves (Ruan and Wang, 2001). The biogeochemical cycle of Al in tea and soil further accelerates soil acidification in rainy environments (Wang et al., 2010). Tea is one of the top three non-alcoholic drinks worldwide and the major cash crop in developing countries such as China, India, Sri Lanka, and Kenya. Because of its high economic value, the area of tea cultivation has been expanding rapidly in China (Su et al., 2015). In 2017, tea cultivation covered about 3.05 million ha in China, accounting for 45.9% of the tea planting area worldwide. In China, there are tea plantations in 19 provinces, mainly in tropical and subtropical areas, with high temperatures and rainfall. Highly weathered soils are
sensitive to cation leaching and subsequent soil acidification (Yang et al., 2018). High rates of N fertilization, as high as 444 kg ha−1, further accelerate soil acidification in these areas (Ni et al., 2019). Understanding the scale of soil acidification can provide valuable information for guiding tea plantation development in China. Soil acidification is ascribed to the combination of high-N fertilization, plant uptake and the removal of base cations from soil, and acid deposition. The overuse of N fertilizer is the dominant factor in agricultural systems (Guo et al., 2010; Tian and Niu, 2015). Many studies have reported that the replacement of chemical N fertilizer by organic fertilizer can prevent soil acidification or even increase soil pH (Shi et al., 2019; Ye et al., 2019), which contributes to increasing the net base cation input (Cai et al., 2015) and producing Al-organic matter complexes (Iyamuremye and Dick, 1996; Hagvall et al., 2015). Therefore, we hypothesized the organic management of tea plantations is an effective way to avoid soil acidification in tea cultivation. The objective of this study was to: (1) evaluate soil acidification at tea plantation on a national scale in China; (2) compare soil pH changes with different cropping systems (i.e. cereal, vegetable or fruit, tea) in the past 20–30 years; (3) evaluate agricultural management (i.e. traditional and organic) on soil acidification in tea gardens. We believe that this work will be useful for us to guide tea development and management in future. 2. Materials and methods 2.1. Study area The study area included all of the tea-planting provinces in China (Fig. 1), extending between latitudes 18–36 N and longitudes 94–121E. The mean annual temperature and precipitation ranged from 12 to 22 °C and 700 to 2600 mm, respectively. The main soil types related to tea cultivation are Haplic, Humic, and Ferric Acrisols.
Fig. 1. The study area and sites where soil was sampled in each province. Blue points (n = 225) indicates soil sampling counties; green points (n = 25) is soil sampling sites with forest and tea plantations; and red points (n = 10) shows the soil sampling sites with forest and traditional and organic tea plantations. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Jiangsu, Shandong, Zhejiang, Henan, and Shaanxi, respectively. No province had a soil pH N5.5. The frequency distribution of soil pH in the intervals b4.5, 4.5–5.5, and N5.5 for each province varied from 4.8 to 100%, 0.0 to 88.5%, and 0.0 to 46.9%, respectively (Fig. 3). For the entire country, 46.0, 43.9, and 10.1% of the soil samples had a pH b4.5, 4.5–5.5, and N5.5, respectively. In nine provinces, N50% of the soil samples had a soil pH b4.5: 51.2, 53.2, 66.3, 77.0, 86.9, 87.3, 88.3, 89.1, and 100.0% for Guangdong, Yunnan, Hubei, Sichuan, Guangxi, Guizhou, Chongqing, Fujian, and Jiangxi, respectively. In only three provinces did N50% of the soil samples have a soil pH between 4.5 and 5.5: 66.1, 68.5, and 88.5% for Jiangsu, Zhejiang, and Henan, respectively. Six provinces had no soil with a pH N5.5, and the percentage of soil samples with a pH N5.5 was b15% for eight provinces. In Shanxi Province, N46.9% of the soil samples had a pH N5.5.
2.2. Data sources To evaluate the soil acidity at tea plantations on a national level, 2058 soil samples were collected at 0–20 cm depths from 225 teaplanting counties (the blue points in Fig. 1) in 19 provinces in China and the soil pH was measured (Fig. 1). In this study, soil pH datasets were obtained from two sources and used to evaluate the pH changes in major croplands over the past 20–30 years (Table 1). The first consisted of 61, 449, and 50 representative soil profiles obtained in Anxi, Songyang, and Wuyi Counties, respectively, from China's Second National Soil Inventory during the 1980s. The second soil pH dataset was derived from the National Soil Testing and Formulated Fertilization Project during the 2000s (2006–2009) and comprised 5062, 1423, and 719 samples from Anxi, Songyang, and Wuyi, respectively. Depending on the soil use types, the second soil dataset was subdivided into Cereal, Fruit and vegetable, and Tea groups (Table 1). To evaluate the changes in soil acidity resulting from tea cultivation, soil samples were collected at 25 sites (the green points in Fig. 1) in forests and tea plantations (Fig. 1). To understand the effect of different forms of agricultural management on soil acidity during tea cultivation, soil samples were collected at 10 sites (the red points in Fig. 1) within forests, traditional tea plantations, and organic tea plantations (Fig. 1). Soil samples were obtained at 0–10, 10–20, and 20–30 cm depths for each profile, and a suite of chemical properties, including soil pH and exchangeable acidity, was analyzed.
3.2. Topsoil pH changes in three counties with tea, cereal, and fruit and vegetable cultivation between the 1980s and 2000s There was significant topsoil acidification in three counties (average pH declines for the soil groups of 0.30 to 1.43) in the past 20–30 years (Table 1). In all soil groups, acidification was the greatest in tea systems; the pH decreased by 0.47, 1.37, and 1.43 for Songyang, Anxi, and Wuyi, respectively. Soil acidification was greater in fruit and vegetable systems (pH decrease of 0.40 to 1.08) than under cereals (pH decrease of 0.30 to 0.89).
2.3. Soil analysis and data processing
3.3. Soil pH, exchangeable acid, and its components change with tea cultivation
Soil pH was measured using a pH meter in soil water suspensions, with a soil-to-water ratio of 1:2.5 (Bao, 2005), which is the same approach used for the National Soil Inventory during the 1980s. The total exchangeable acidity (Al3+ and H+) was extracted with 1 M KCl and titrated with 0.02 M NaOH to the phenolphthalein endpoint to obtain the exchangeable H+. The exchangeable Al3+ was calculated from the difference between the exchangeable acidity and exchangeable H+ (Bertsch and Bloom, 1996). The averaged soil pH for all of China and the distribution of soil pH in the pH intervals b4.5, 4.5–5.5, and N 5.5 were analyzed using Sigmaplot 14.0. Data from the tea plantations and forests were analyzed using oneway ANOVAs at a 0.05 probability level, followed by a t-test using SPSS v. 16.0 (SPSS Inc., Chicago, IL, USA).
The difference in soil pH between tea plantations and adjacent forests was investigated (Fig. 4). Soil pH increased with soil depth in forest and tea plantations. Compared with forests, the soil pH at the tea plantations decreased 0.50, 0.66, and 0.58 at soil depths of 0–10, 10–20, and 20–30 cm, respectively (Fig. 4A). Tea cultivation significantly increased the soil exchangeable acidity, and the exchangeable H+ and Al3+ at the tea plantations were consistently higher than those in forest soil in the soil profile (Fig. 4B–D). Soil acidity was dominated by exchangeable Al3+ in both the forest and tea plantation soils, accounting for 51.0–57.8% and 63.2–70.5%, respectively. Compared with the forest soil, significantly higher soil exchangeable Ca2+, Mg2+ and K+ were observed in the forest soil (Fig. S1).
3. Results
3.4. Soil pH, exchangeable acidity, and its components change with different agricultural management systems
3.1. The averaged soil pH and distribution in three intervals for each province and the entire country
The soil pH of forests and organic tea plantations was significantly higher than that of traditional tea plantations at all three soil depths, while no significant differences were observed between the forests and organic tea plantations (Fig. 5A). The highest soil exchangeable acidity and exchangeable H+ and Al3+ were observed in traditional tea plantations. The exchangeable acidity and exchangeable H+ and Al3+ of organic tea plantations were higher than those of forest at 0–10 and 10–20 cm soil depths, while no differences were observed at
The averaged soil pH for each tea-cultivation province varied from 3.96 to 5.48 with a mean of 4.68 for China (Fig. 2). There were eight provinces with a pH b4.5: 3.96, 4.04, 4.11, 4.12, 4.23, 4.28, 4.36, and 4.37 for Jiangxi, Fujian, Chongqing, Guangxi, Guizhou, Sichuan, Hubei, and Guangdong, respectively. The other seven provinces had a pH N4.5: 4.50, 4.64, 4.67, 4.74, 4.85, 4.99, and 5.48 for Yunnan, Hunan,
Table 1 Topsoil pH changes in three countries with tea, cereal, fruit and vegetable cultivation between the 1980s and 2000s. 1980s County
Anxi Songyang Wuyi
Samples
61 449 40
2000s pH
5.59 5.56 5.83
Cereal
Fruit and vegetable
Tea
Samples
pH
pH change
Samples
pH
pH change
Samples
pH
pH change
57 759 173
5.29 (3.80–6.50) 5.43 (4.10–7.30) 4.94 (4.13–6.18)
−0.30 −0.33 −0.89
13 224 383
5.15 (4.00–7.10) 5.16 (3.74–7.23) 4.75 (3.43–6.68)
−0.44 −0.40 −1.08
4992 440 163
4.22 (3.00–6.90) 5.09 (3.24–6.23) 4.40 (3.55–5.99)
−1.37 −0.47 −1.43
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Fig. 2. The number of soil samples and average soil pH for each province and the whole of China. The white and black line in the box represent the mean and median of the data.
20–30 cm. What's more, the soil exchangeable Ca2+ and Mg2+ of forest and organic tea gardens were higher than that of traditional tea gardens (Fig. S2).
lower than the 5.74 of forest soil (Zhu, 2017), and 0.90 lower than the 5.58 of cash crop soil (Guo et al., 2010). The optimal soil pH for tea growth is 4.5–5.5 (Ruan et al., 2007). Tea growth is inhibited when the soil pH is lower than 4.0; both the quality and quantity of tea production are negatively affected (Fung et al., 2008). In our research, only 43.9% of the soil samples had a pH in the interval 4.5–5.5, while 46.0% of the soil samples had a pH b4.5. This constrains sustainable tea development in China.
4. Discussion There is serious soil acidification in tea plantations in China. The average soil pH of tea plantations for all of China was 4.68, which is 1.06
The size of circle represents The frequency (%) distribution of the averaged soil pH soil pH in the intervals <4.5, 4.5–5.5, and >5.5 pH 4.0
14
36
50
Shandong 47
49
Henan
74
Sichuan
84
22
31
Jiangxi
16 84
Fujian
Guizhou 6
Yunnan
Zhejiang
92
Hunan
6 24
pH 5.5
67
8 23 46
4
74
4847
9 23
Hubei
Chongqing
pH of 4.5–5.5
pH 5.0
pH >5.5
Anhui
60
14 2
Jiangsu
71
35
4
6
24
5 23
pH <4.5 34
63
86
Shaanxi
pH 4.5 3
104
4
5
10
44
46
Whole country
47
47
71
Guangdong
Guangxi
Fig. 3. The frequency (%) distribution of soil pH in the intervals pH b 4.5, 4.5–5.5, and N5.5 for each province and the whole country. The orange, green and blue colour represent the interval b4.5, 4.5–5.5, and N5.5, respectively. The number in each circle represents the percentage of soil samples in the intervals b4.5, 4.5–5.5, and N5.5. The size of the circle represents the averaged soil pH for each province. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
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Fig. 4. The soil pH (A), exchangeable acid (B), and exchangeable H+ (C) and exchangeable Al3+ (D) changes at soil depths of 0–10, 10–20, and 20–30 cm for the forests (n = 75) and tea plantations (n = 105). Different lowercase letters indicate significant differences at the p b 0.05 level. The lines and rectangles within the boxes represent the median and mean values of all data, the bottom and top edges of the boxes are the 25th and 75th percentiles of all data, and the bottom and top bars represent the 5th and 95th percentiles, respectively.
The topsoil pH changes in Anxi, Songyang, and Wuyi between the 1980s and 2000s revealed significant acidification of all crops (Table 1). This is consistent with reports of serious soil acidification in
China (Guo et al., 2010; Zhu et al., 2018), which is related to the high rate of N fertilization and low nitrogen use efficiency (NUE) (Tian and Niu, 2015; Mao et al., 2017) and the uptake and removal of base cations
Fig. 5. The soil pH (A), exchangeable acid (B), and exchangeable H+ (C) and exchangeable Al3+ (D) changes at soil depths of 0–10, 10–20, and 20–30 cm in the forests (n = 30) and traditional (n = 30) and organic (n = 30) tea plantations. Different lowercase letters indicate significant differences at the p b 0.05 level. The lines and rectangles within the boxes represent the median and mean values of all data, the bottom and top edges of the boxes represent the 25th and 75th percentiles of all data, respectively, and the bottom and top bars represent the 5th and 95th percentiles, respectively.
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by plants (Duan et al., 2004). Moreover, the acidification is greater in tea systems (pH decrease of 0.47 to 1.43) than under cash crop systems (0.40 to 1.08) or cereals (0.30 to 0.89). This could have the following two causes. First, the decrease in soil pH might be driven by the high rate of N fertilization and low NUE (Tian and Niu, 2015). The average rate of N fertilization was as high as 473 kg ha−1, while the NUE was only about 18.3% (Chen and Lin, 2016), and most of the N was lost via 2+ NO−1 and Mg2+ 3 leaching (Yan et al., 2018). Base cations such as Ca are leached with NO−1 based on the charge balance in soil solutions, 3 which further acidifies the soil (Gundersen et al., 2006; Rothwell et al., 2008). Second, the high pH decline in tea soil might be related to its physiology. The rhizosphere of tea plants can excrete organic acids, carbonic acid, and polyphenols, leading to acidification (Yang, 2005). Tea can take up large amounts of Al, most of which accumulates in the leaves (Ruan et al., 2004). The biogeochemical cycle of Al in tea litter is another factor that leads to soil acidification in tea plantations (Wang et al., 2010). The acidification of tea soil is regulated by agricultural management (Guo et al., 2010). Generally, soil acidity increased with the duration of tea cultivation and the rate of fertilization (Li et al., 2016; Yang et al., 2018; Yan et al., 2018). In our research, the pH of forest soils was consistently higher than that of the traditional tea plantations at all soil depths, while no significant differences were observed compared with organic tea plantations (Fig. 5). This is consistent with reports that soil acidification can be prevented by the application of manure (Noble et al., 1996; Zeng et al., 2017; Zhu et al., 2018; Shi et al., 2019). Tea is an NH+ 4 -fed plant, with a high cation/anion ratio, and it extrudes the net excess H+ (Ruan et al., 2004; Yang, 2005). The mechanisms involved in reducing soil acidity with manure include the specific adsorption of organic anions on hydrous Al surfaces and the corresponding release of hydroxyl ions (Wang et al., 2016), decarboxylation of organic anions (Xiao et al., 2013), return of basic cations to soil, increased soil exchangeable cations (e.g., Ca2+, Mg2+, and K+) (Cai et al., 2015), and ammonification of labile organic N in manure (Xu et al., 2006). In our research, the soil exchangeable Ca2+ and Mg2+ of the organic tea gardens were significantly higher than that of traditional tea gardens (Fig. S1, S2). The fundamental approach to alleviate soil acidification in tea plantations is to reduce N fertilizer inputs and increase the manure inputs to soil. 5. Conclusion This study assessed soil acidification in Chinese tea plantations at provincial and national levels. The average soil pH in each province varied from 3.96 to 5.48, with a mean value of 4.68 for the entire country. Only 43.9% of the soil samples had a pH in the range 4.5–5.5, which is optimal for tea growth, while 46.0% of the soil samples had a pH b4.5, indicating serious soil acidification at tea plantations. In the past 20–30 years, serious soil acidification has occurred across Chinese croplands, with the highest rate of acidification observed in soil under tea cultivation. Compared with forest soil, no significant decrease in soil pH was observed in organic tea plantations, indicating that organic management is a useful way to avoid soil acidification during tea cultivation. In conclusion, serious soil acidification occurs at tea plantations nationally in China, and organic management is necessary for the sustainable development of tea plantations. Author contributions Peng Yan and Wen-Yan Han conceived and designed the research; Liangquan Wu, Donghui Wang, Jianyu Fu, Chen Shen, Xin Li, Liping Zhang, Lan Zhang, Lichao Fan performed the experiments and analyzed the data; Peng Yan, Liangquan Wu and Wen-Yan Han discussed the data; Peng Yan wrote the manuscript with the contributions from the other authors.
Credit author statement Peng Yan: Conceptualization, Methodology, Formal Analysis, Investigation, Data curation, Validation, Writing- Reviewing and Editing. Liangquan Wu: Formal Analysis, Investigation, Data curation. Donghui Wang: Investigation, Validation, Data curation. Chen Shen: Investigation, Data curation. Jianyu Fu: Investigation, Data curation. Xin Li: Investigation, Data curation. Li-Ping Zhang: Investigation, Data curation. Lan Zhang: Formal Analysis. Wen-Yan Han: Conceptualization, Supervision, Resources, Project Administration, Funding Acquisition. Declaration of competing interest The authors declare no conflict of interest. Acknowledgements This work was financially supported by the National Key Research and Development of China (2017YFE0107500), the Science and Technology Innovation Project of the Chinese Academy of Agricultural Sciences (CAAS-ASTIP-2014-TRICAAS), the Funds for Science and Technology Innovation Project from the Chinese Academy of Agricultural Sciences (CAAS-XTCX2016015). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.scitotenv.2020.136963. References Bao, S.D., 2005. Agricultural and Chemistry Analysis of Soil. Agriculture Press, Beijing. Bertsch, P.M., Bloom, P.R., 1996. Soil pH and soil acidity. In: Sparks, D.L. (Ed.), Methods of Soil Analysis. Part 3. Chemical Methods, SSSA Book Series 5. ASA and SSSA, Madison, WI, pp. 517–576. Bouwman, A.F., Boumans, L.J.M., Batjes, N.H., 2002. Modeling global annual N2O and NO emissions from fertilized fields. Glob. Biogeochem. Cycles 2002 (16), 281–289. Cai, Z., Wang, B., Xu, M., Zhang, H., He, X., Zhang, L., Gao, S., 2015. Intensified soil acidification from chemical n fertilization and prevention by manure in an 18-year field experiment in the red soil of southern China. J. Soils Sediments 15, 260–270. Caputo, J., Beier, C.M., Sullivan, T.J., Lawrence, G.B., 2016. Modeled effects of soil acidification on long-term ecological and economic outcomes for managed forests in the Adirondack region (USA). Sci. Total Environ. 565, 401–411. Chen, C.F., Lin, J.Y., 2016. Estimating the gross budget of applied nitrogen and phosphorus in tea plantations. Sustainable Environment Research 26 (3), 124–130. https://doi. org/10.1016/j.serj.2016.04.007. Dai, Z., Zhang, X., Tang, C., Muhammad, N., Wu, J., Brookes, P.C., 2017. Potential role of biochar in decreasing soil acidification - a critical review. Sci. Total Environ. 581, 601–611. De Vries, W., Hettelingh, J.P., Posch, M., 2015. Critical Loads and Dynamic Risk Assessments: Nitrogen, Acidity and Metals in Terrestrial and Aquatic Ecosystems. 25. Springer, Dordrecht, Netherlands. Duan, L., Huang, Y., Hao, J., Xie, S., Hou, M., 2004. Vegetation uptake of nitrogen and base cations in China and its role in soil acidification. Sci. Total Environ. 330, 187–198. Fung, K.F., Carr, H.P., Zhang, J.H., Wong, M.H., 2008. Growth and nutrient uptake of tea under different aluminum concentrations. J. Sci. Food Agric. 88, 1582–1591. Gundersen, P., Schmidt, I.K., Raulund-Rasmussen, K., 2006. Leaching of nitrate from temperate forests-effects of air pollution and forest management. Environ. Rev. Lett. 14, 1–57. Guo, J.H., Liu, X.J., Zhang, Y., Shen, J.L., Han, W.X., Zhang, W.F., Christie, P., Goulding, K.W.T., Vitousek, P.M., Zhang, F.S., 2010. Significant acidification in major Chinese croplands. Science 327, 1008–1010. Hagvall, K., Persson, P., Karlsson, T., 2015. Speciation of aluminum in soils and stream waters: the importance of organic matter. Chem. Geol. 417, 32–43. Iyamuremye, F., Dick, R.P., 1996. Organic amendments and phosphorus sorption by soils. Adv. Agron. 56, 139–185. Kirk, G.J.D., Bellamy, P.H., Lark, R.M., 2010. Changes in soil pH across England and Wales in response to decreased acid deposition. Glob. Chang. Biol. 16, 3111–3119. Li, S.Y., Li, H., Yang, C.L., Wang, Y.D., Xue, H., Niu, Y.F., 2016. Rates of soil acidification in tea plantations and possible causes. Agric. Ecosyst. Environ. 233, 60–66. Mao, Q., Lu, X., Zhou, K., Chen, H., Zhu, X., Mori, T., Mo, J.M., 2017. Effects of long-term nitrogen and phosphorus additions on soil acidification in an N-rich tropical forest. Geoderma 285, 57–63. Ni, K., Liao, W.Y., Yi, X.Y., Niu, S.G., Ma, L.F., Shi, Y.Z., Zhang, Q.F., Liu, M.Y., Ruan, J.Y., 2019. Fertilization status and reduction potential in tea gardens of China. Journal of Plant Nutrition and Fertilizers. 25, 421–432 (in Chinese with English abstract). Noble, A.D., Zenneck, I., Randall, P.J., 1996. Leaf litter ash alkalinity and neutralisation of soil acidity. Plant Soil 179, 293–302.
P. Yan et al. / Science of the Total Environment 715 (2020) 136963 Rothwell, J.J., Futter, M.N., Dise, N.B., 2008. A classification and regression tree model of controls on dissolved inorganic nitrogen leaching from European forests. Environ. Pollut. 156, 544–552. Ruan, J.Y., Wang, M.H., 2001. Accumulation of fluoride and aluminum related to different varieties of tea plant. Environ. Geochem. Health 23, 53–63. Ruan, J.Y., Ma, L.F., Shi, Y.Z., Zhang, F.S., 2004. Effects of litter incorporation and nitrogen fertilization on the contents of extractable aluminum in the rhizosphere soil of tea plant (Camallia sinensis (L.) O. Kuntze). Plant Soil 263, 283–296. Ruan, J.Y., Gerendás, J., Härdter, R., Sattelmacher, B., 2007. Effect of nitrogen form and root-zone pH on growth and nitrogen uptake of tea (Camellia sinensis) plants. Ann. Bot. 99, 301–310. Shi, R.Y., Liu, Z.D., Li, Y., Jiang, T., Xu, M., Li, J.Y., Xu, R.K., 2019. Mechanisms for increasing soil resistance to acidification by long-term manure application. Soil Tillage Res. 185, 77–84. Su, S., Zhou, X., Wan, C., Li, Y., Kong, W., 2015. Land use changes to cash crop plantations: crop types: multilevel determinants and policy implications. Land Use Policy 50, 379–389. Tian, D., Niu, S., 2015. A global analysis of soil acidification caused by nitrogen addition. Environ. Res. Lett. 10, 024019. Wang, H., Xu, R.K., Wang, N., Li, X.H., 2010. Soil acidification of Alfisols as influenced by tea cultivation in eastern China. Pedosphere 20, 799–806. Wang, L., Butterly, C.R., Tian, W., Herath, H.M.S.K., Xi, Y., Zhang, J., Xiao, X., 2016. Effects of fertilization practices on aluminum fractions and species in a wheat soil. J. Soils Sediments 16, 1933–1943. Xiao, K., Xu, J., Tang, C., Zhang, J., Brookes, P.C., 2013. Differences in carbon and nitrogen mineralization in soils of differing initial pH induced by electrokinesis and receiving crop residue amendments. Soil Biol. Biochem. 67, 70–84.
7
Xu, J.M., Tang, C., Chen, Z.L., 2006. The role of plant residues in pH change of acid soils differing in initial pH. Soil Biol. Biochem. 38, 709–719. Yan, P., Shen, C., Fan, L.C., Li, X., Zhang, L.P., Zhang, L., Han, W.Y., 2018. Tea planting affects soil acidification and nitrogen and phosphorus distribution in soil. Agric. Ecosyst. Environ. 254, 20–25. Yang, X.D., Ni, K., Shi, Y.Z., Yi, X.Y., Zhang, Q.F., Fang, L., Ruan, J.Y., 2018. Effects of longterm nitrogen application on soil acidification and solution chemistry of a tea plantation in China. Agric. Ecosyst. Environ. 252, 74–82. Yang, Y.H., Ji, C.J., Ma, W.H., Wang, S.F., Wang, S.P., Han, W.X., Mohammat, A., Robinson, D., Smith, P., 2012. Significant soil acidification across northern china's grasslands during 1980s–2000s. Glob. Chang. Biol. 18, 2292–2300. Yang, Y.J., 2005. Tea Plant Cultivation in China. Shanghai Scientific and Technological Press, Shanghai (in Chinese with English abstract). Ye, G.P., Lin, Y.X., Liu, D.Y., Chen, Z.M., Luo, J.F., Bolan, N., Fan, J.B., Ding, W.X., 2019. Longterm application of manure over plant residues mitigates acidification, builds soil organic carbon and shifts prokaryotic diversity in acidic Ultisols. Appl. Soil Ecol. 133, 24–33. Zeng, M.F., De Vries, W., Bonten, L.T.C., Zhu, Q.C., Hao, T.X., Liu, X.J., Xu, M.G., Shi, X.J., Zhang, F.S., Shen, J.B., 2017. Model-based analysis of the long-term effects of fertilization management on cropland soil acidification. Environ. Sci. Technol. 51, 3843–3851. Zhang, Y., He, X., Liang, H., Zhao, J., Zhang, Y., Xu, C., 2016. Long-term tobacco plantation induces soil acidification and soil base cation loss. Environ. Sci. Pollut. R. 23, 5442–5450. Zhu, Q.C., 2017. Quantification and Modelling of Soil Acidification at Regional Scale of China[D] (in Chinese with English abstract). Zhu, Q.C., Liu, X.J., Hao, T.X., Zeng, M.F., Shen, J.B., Zhang, F.S., 2018. Modeling soil acidification in typical Chinese cropping systems. Sci. Total Environ. 613–614, 1339–1348.