Vertical Distribution of pH and Nutrients in Forest Soil on Water-eroded Area of Southern China
- 1. College of Biology and the Environment, Nanjing Forestry University
- 2. Pearl River Water Resources Research Institute, Pearl River Water Resources Commission
- 3. Changting Bureau of Soil and Water Conservation
- 4. School of Environmental Science, Nanjing Xiaozhuang University
- 5. Pearl River Water Resources Research Institute, Pearl River Water Resources Commission
- 6. Pearl River Water Resources Research Institute, Pearl River Water Resources Commission
The analysis of soil physical and chemical properties in typical water erosion area is helpful to understand the mechanism of soil and water conservation. Vertical soil samples were collected from topsoil to 50cm depth in southern China under coniferous forests, coniferous and broad-leaved mixed forests, and broad-leaved forests. The distribution characteristics of soil pH and nutrients were then analyzed. The nutrients include organic matter (OM), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP) available phosphorus (AP) total potassium (TK), and available potassium (AK). Results showed that, with the increase of soil depth, the average pH increased, OM, TN, an, AK decreased, while TK, TP, AP changed not significantly. The soil nutrients were mostly the greatest in broad leaved forests, and the least in the coniferous forests. All the soil nutrients were the greatest in the Light soil erosion grade, the least in the Moderate grade, and the middle in the Intense grade. These results indicated that ground litter contributed mainly to the vertical change of soil properties, broad leaved forests had a stronger capacity to gather nutrients and could increase the contents of soil nutrients in vertical profiles, and the soil erosion resulted in the loss of soil nutrients, but the degree of the loss was affected by the forest communities. This study provided valuable references for vegetation restoration and ecological reconstruction in water-eroded areas.
Water-eroded areas, Forests, Soil depth, Soil nutrients
Damin L, Zhujun G, Hui Y, Xiaoxia W, Xiaogang W, et al. (2021) Vertical Distribution of pH and Nutrients in Forest Soil on Water-eroded Area of Southern China. JSM Biol 4(1): 1018.
Soil degradation caused by water erosion has been a key factor plagued regional or national development . The red soil area in southern China, with the special soil parent materials, vegetation and climatic environments, had become one of the areas with the most severe soil erosion (2,3). Soil pH and nutrients are the main factors affecting vegetation reconstruction, and play an important role in the ecological restoration of watereroded areas in southern China (4). The research on the spatial distribution pattern of soil pH and nutrients in the areas will help understand the mechanism of water and soil conservation and provide scientific basis for water and soil conservation.
In recent years, many researchers have studied the vertical distribution characteristics of soil properties. Literatures reported that as soil depth increased, soil pH showed a slowly increasing trend (5,6) , while soil organic matter (OM), total nitrogen (TN), available nitrogen (AN), total phosphorus (TP) and available potassium (AP) were affected by litter and showed a decreasing trend (7, 8). There was no significant change in the content of total potassium (TK) (9), and the content was mainly affected by the soil parent material. Some studies have shown that the content of TK decreased gradually with the increase of soil depth (10). The content of TP reduced slightly (11 ; 12) while other studies showed no obvious change in the content of TP (13, 14). The content of AP generally decreased gradually (15, 16). It was also found that soil nutrients varied under different vegetation types (17)During the process of vegetation growth, vegetation absorbs soil nutrients, and litter returns to soil, thereby affecting the accumulation of soil nutrients. Besides, soil erosion led to the loss of soil nutrients and a decrease in the contents (18) obvious reduction of soil OM and TN (19), and a decrease in AP (20, 21).
Studies on the soil physical and chemical properties had achieved fruitful results, but there were few reports on the integrated analysis of the soil properties on water-eroded forest area, which restricts understanding of the mechanism and the effect of soil and water conservation. In this paper, soil pH and contents of main nutrients in different soil depths were measured, and their characteristics were analyzed with the variation of soil depth, forest type, and soil erosion grade, so as to provide scientific basis for vegetation restoration in the watereroded area.
MATERIALS AND METHODS
The study area is situated in Changting County (25.18’40”-26.02’05”N, 116.00’45”- 116.39’20” E) in the southwest of Fujian Province, China, with a total land area of 3 099 km2 (Figure 1). It is located in the mid-subtropical monsoon region, with the annual average temperature of 17.5- 18.8 ?. The annual average precipitation is about 1 700 mm, which from March to June accounts for 60%. It is dominated by secondary vegetation such as Pinus massoniana Lamb. and shrubs. The humic Planosols (FAO-WRB) is distributed most widely, accounting for 79.8% of the total area, and the soil parent material is mainly the early Yanshanian biotite granite with strong weathering, and poor resistance to erosion (22). Because of its special lithology and characteristics of subtropical monsoon climate, it has become one of the most typical areas of soil erosion in southern China, and the loss of soil nutrients is serious (23).(Figure 1)
Figure 1 Geographic location of the study area
Collection and measurement of soil samples
According to the distribution of typical forest stands, 14 field plots (10 m × 10 m) were selected for different soil erosion grade, which was in situ evaluated according to soil bareness, slope, and vegetation coverage. In the plots, there were different types of vegetation, such as coniferous forests (CF) (Pinus. massoniana Lamb., Dicranopteris dichotoma (Thunb.) Berhn. and Baeckea frutescens L.), coniferous and broad-leaved mixed forests (CB) (P. massoniana Lamb., Cunninghamia lanceolata (Lamb.) Hook. and broad-leaved trees), and broad-leaved forests (BF) (Castanopsis nigrescens). The general situation of the plots is shown in (Table 1). Two quadrats (1m × 1m) were set as repetitions in each plot, and soil profiles were cut in each plot, to collect soil samples at a depth of 0-10, 10-20, 20-30, 30-40 and 40-50 cm respectively. A total of 128 soil samples collected from each sampling point in each quadrat were dried by air in a ventilated, dry and dark room, from which plant roots and residue and stones were removed. The samples were then sieved through a sieve with 60 meshes. The measurement methods of soil pH and nutrients are shown in (Table 2).
Figure 2 Distribution of soil pH and nutrients in vertical profiles
Data processing and analysis
The two values of the same soil depth of two measurement points were averaged as the pH or nutrient content value of the sample in each soil depth. In the analysis of soil pH and nutrient content with the change of soil depth, forest type and soil erosion grade, the other two factors were ignored, and the mean and standard deviation of soil pH and nutrient content with each of the factors were calculated. For example, when analyzing the soil pH and nutrient content with the change of the soil depth, the mean and standard deviation of pH and nutrient content of all soil samples in each soil depth were calculated respectively, while the differences of forest type and soil erosion grade were not considered. When the soil pH and nutrient content with the change of forest type (or soil erosion grade) were analyzed, the soil depth and soil erosion grade (or soil depth and forest type) were not concerned. All analyses were conducted using SPSS 19.0 statistical analysis software (SPSS Inc., USA).
RESULTS AND DISCUSSIONS
Changes of soil pH and nutrients with soil depth
With the increasing of soil depth (for all forest type and soil erosion grade), the average value of pH increased, OM, TN, an, AK decreased, while TK, TP, AP changed not significantly (Figure 2). That is to say, the topsoil in the study area was acid, the deeper the soil layer was, the weaker the acid was, and most of the nutrients tended to decrease with the soil depth. This is consistent with the conclusions of other studies (24, 17). Because the topsoil is rich in dry branches, leaves, litter, plant roots and various biological humus, which will release various organic acids under the decomposition of microorganisms. The air subsidence will also input more H+ to the topsoil to replace alkali metal ions, and then enter the deeper soil, which further enlarge the vertical distribution of the pH value (25). Nutrients first accumulate in the topsoil and then infiltrate down through water or other media. With the increase of soil depth, the bulk density of soil increases, the permeability of soil becomes poor, and the decomposition activity of microorganisms also weakens (26), which leads to the decrease of nutrients in the soil from surface to the bottom. The TK content had no significant change with the increase of soil depth, indicating that TK content was mainly related to soil parent material (27, 28) TP is mainly affected by soil parent material and litter, where the litter decomposition is the source of rapid phosphorus supplement in the soil (29, 30).
Compared with the mean value, the standard deviation of soil pH and nutrients in each vertical layer was greater in TP and AP (except for AP in 10-20cm), which showed that the content of P in the soil vertical layer was affected by multiple factors. OM, TN, AN, and AK decreased with the soil depth, while pH and TK were close to each other, showing the different attenuation characteristics of the soil nutrients in the vertical distribution.
Changes of soil pH and nutrients with forest type
From CF, CB to BF, the average pH value (for all soil depth and soil erosion grade) gradually decreased, while the other nutrients increased (except AK first decreased and then increased). In other words, from CF, CB to BF, the soil acidity gradually increased, while the soil nutrients were mostly the greatest in BF, followed by CB and CF. These are mainly related to the differences of litter quantity and nature, vegetation absorption and accumulation of soil nutrients, and vegetation community structure among the three forests (31), especially the key role of the litter in the forest nutrient cycling process. Forest litters, including dead branches and leaves, fruits and animal excrement and debris living in the canopy layer, is generally positively correlated with the return of soil nutrients. The Pinus massoniana of the CF type are dominantly but sparsely distributed in the study area, with small leaf area and small litter biomass, which has non-degradable tannins, waxes, and resins, etc., resulting in the least soil nutrients among the three forests (31, 32).The ground litter of BF is relatively rich, and there are more acid substances, leading the pH value of soil slightly lower than that of other forests. In contrast, the BF litter has a high nutrient content and is easy to be decomposed and absorbed by the soil. Besides, higher canopy density of BF can effectively reduce soil nutrient loss and leaching, causing the greatest nutrient content among the three forests. The standard deviation of soil pH and nutrients corresponding to each vegetation type was smaller in CF and CB, but greater in BF type, which further showed the complex coupling of soil-rainvegetation in the BF type. The standard deviation of TP and TK was very small, which indicated that these two soil nutrients were slightly affected by vegetation types.
The impact of soil erosion on Soil pH and nutrients
The average pH value (for all soil depth and forest type) was the least in the Light soil erosion grade, the greatest in the Moderate grade, and the middle in the Intense grade. All the soil nutrients are on the contrary: the greatest in the Light soil erosion grade, the least in the Moderate grade, and the middle in the Intense grade (Figure.3). As for the standard deviation, among all soil erosion grades, TP, TK were very low, followed by pH. All other soil nutrients were low in Moderate soil erosion grade, and of the Slight grade a little bit higher than those of the Intense grade. Compared with other soil erosion grades, the standard deviation of soil pH and nutrients of the Moderate grade were all very low.
Figure 3 Comparison of contents of soil nutrients in the slightly eroded plots and strongly eroded plots with the broad-leaved forests
It is generally believed that there is a significant positive correlation between nutrient loss and soil loss (33, 34, 35).Soil erosion leads to the decrease of N, P, K and other soil available nutrients and organic matter. The decrease of organic matter will weaken the soil erosion resistance, which in turn favor the occurrence of soil erosion. In this study, the soil nutrient content of Moderate soil erosion grade was the lowest, not the Intense grade, mainly thanks to only the CF forest land of the Moderate grade, while the Intense grade was of the CB type (Table 1). Therefore, soil erosion leads to the loss of soil nutrients, thus reducing the productivity of soil and the ability to maintain life (36), but the degree of the loss is affected by the vegetation. Soil and water conservation measure like forestation is of great significance in the controlling of soil nutrient loss (37)
Table 1: General situation of the plots.
|1||Pinus. massoniana Lamb.,
dichotoma (Thunb.) Berhn Baeckea
|2||broad-leaved trees Pinus.
|3||broad-leaved trees Cunninghamia
|4||Pinus. massoniana Lamb.,
dichotoma (Thunb.) Berhn
|5||Pinus. massoniana Lamb.,
dichotoma (Thunb.) Berhn
|6||Pinus. massoniana Lamb.,
dichotoma (Thunb.) Berhn
|7||Pinus. massoniana Lamb.,
dichotoma (Thunb.) Berhn
|9||Castanopsis nigrescens Chun et C.
|10||Castanopsis nigrescens Chun et C.
|11||Castanopsis nigrescens Chun et C.
|12||Castanopsis nigrescens Chun et C.
|13||Castanopsis nigrescens Chun et C.
|14||Castanopsis nigrescens Chun et C.
CF: coniferous forests. CB: coniferous and broad-leaved mixed forests.
Table 2: Determination meathod of soil pH and nutrients.
|pH and nutrients||Determination method||Literature cited|
|pH||potentiometry||Allen et al.,1986|
|OM||potassium dichromate-sulfuric acid digestion method||Nelson et al., 1996|
|TN||semimicro-kjeldahl method||Bremner et al., 1996|
|AN||alkaline hydrolysis diffusion method||Bremner et al., 1996|
|TP||sodium hydroxide alkali fusion-molybdenum antimony colorimetric method||Olson et al.,1990|
|AP||ammonia fluoride and hydrochloric acid extraction-molybdic acid colorimetric method||Olson et al.,1990|
|TK||sodium hydroxide alkali fusion-flame photometry||Page et al.,1982|
|AK||ammonium acetate extraction-flame photometry||Page et al.,1982|
|OM:organic matter, TN:total nitrogen, AN:available nitrogen, TP:total phosphorus, AP:available phosphorus, TK:total potassium, AK:available
In this study, soil pH and contents of main nutrients in different soil depths under the forests were measured in a watereroded area in southern China, and their change characteristics with soil depth, forest type, and soil erosion grade were analyzed. Some conclusions were drawn as follows.
(1)With the increasing of soil depth, the average value of pH increased, OM, TN, and AK decreased, TK, TP, AP changed not significantly. The standard deviations of TP and AP in each soil depth were greater, showing that the content of P in the soil vertical layer was affected by multiple factors.
(2)From CF, CB to BF, the soil acidity gradually increased, while the soil nutrients were mostly the greatest in BF, followed by CB and CF. The standard deviation of soil pH and nutrients corresponding to each forest type were smaller in CF and CB, but greater in BF.
(3)All the soil nutrient contents were the greatest in the Light soil erosion grade, the least in the Moderate grade, and the middle in the Intense grade, the soil pH was on the contrary. The standard deviations of most soil nutrients were low in the Moderate grade, and of the Slight grade a little bit higher than those of the Intense grade.
(4)Ground litter contributed mainly to the changes of soil properties. Broad leaved forests had a stronger capacity to gather nutrients in the topsoil and could increase the contents of soil nutrients in vertical profiles. Soil erosion resulted in the loss of soil nutrients, but the degree of the loss was affected by the forest communities.
This study was supported by the National Natural Science Foundation of China (No.41571415, 41071281), and the Natural Science Foundation of Jiangsu Province (No. BK20131078).
1. Pournader M, Ahmadi H, Feiznia S, Karimi H, Peirovan HR. 2018. Spatial prediction of soil erosion susceptibility: an evaluation of the maximum entropy model. Earth Sci Inform. 2018; 11: 389-401.
2. Gao Y, Zhong BL, Yue H, Wu B, Cao SX. A degradation threshold for irreversible loss of soil productivity: a long-term case study in China. J Appl Ecol. 2011; 48: 1145-1154.
3. Ma HY, Wang, Yue H, Zhong BL. The threshold between natural recovery and the need for artificial restoration in degraded lands in Fujian Province, China. Environ Monit Assess 2013; 185: 8639–8648.
4. Chen B, Lu SW, Li SN, Pan QH, Zhang YP. Study on Soil Nutrient of Seven Artificial forests in Mountain of Beijing. J Anhui Agric Univ. 2014; 35: 46-48.
5. Dorji T, Inakwu OA, Odeh IOA, Field DJ. Vertical Distribution of Soil Organic Carbon Density in Relation to Land Use/Cover, Altitude and Slope Aspect in the Eastern Himalayas. Land. 2014; 3: 1232-1250.
6. Mishra A ,Pattnaik TM, Das D, Das M. Vertical Distribution of Available Plant Nutrients in Soils of Mid Central Valley at Odisha Zone, India. Am J Exp Agric. 2015; 7: 214-221
7. GUAN GC, Wei XH. Analysis on Soil Nutrient Characteristics and Their Correlation in Three Finds of Forest in Dinghushan (In Chinese). Envi Sci Manag. 2017; 42: 139-144
8. Deng XJ, Cao JZ, Song XC, Tang J, Chen FF. 2014.Vertical distribution characteristics of three forest types soil properties on Mao’er Mountain Biosphere Reserve. Ecological Science. 2014; 33: 1129-1134.
9. Zheng JB, ZF Wang, XL Tan, A L Li, M GAO. Effects of Land Use Patterns on the Physico-chemical Properties of the Soil Profile in Purple Hilly Areas (In Chinese). Journal of Southwest University. 2008; 30: 101- 106.
10. ZHANG YJ, YE XJ, YANG Y. Analysis on soil nutrients of different land utilization type in Guizhou Anshun Area (In Chinese). GASS. 2015; 42: 56-62.
11. Lu C, WY Zhanu, L Shi, CH Lin, TB Tengbing. Difference of Soil Nutrients under Different Vegetation Type in Fanjing Mountain Nature Reserve (In Chinese). Guizhou Agricultural Sciences 44(2): 177-181
12. XU B, ZHU ZF, LI JY, WU Y, DENG GP, et al. Leaf decomposition and nutrient release of dominant species in the forest and lake in the Jiuzhaigou National Nature Reserve, China (In Chinese). Chin J Plant Ecol. 2016; 40: 883-892
13. Lin MZ, SY Xie, YS Lin. Characteristics of Soil Nutrient under Different Land Use Types in Karst Mountain Area (In Chinese). Acta Prataculturae Sinica. 2009; 9: 8-11.
14. QIU LP, XC ZHANG, et al. Vegetation Types Effects on Soil Properties in Small Watershed of the Loess Plateau (In Chinese). Res Soil Water Conserv. 2010; 17: 64-68.
15. Gou LH, Sun ZD, Nie LS, Luo PP, Wu JG, Xu W. Vertical distribution patterns of nitrogen phosphorus and potassium in Chinese pine forest soils developed from different parent materials in Songshan Mountain Nature Reserve Beijing of China.Ying Yong Sheng Tai Xue Bao. 2013; 24: 961-966.
16. liu ZX, Jiang CS, Hu TZ. Effects of Different Land Use Patterns on Soil Total Phosphorus and Available Phosphorus in Jinyun Mountain (In Chinese). Journal of Southwest University(Natural Science Edition). 2013; 35: 140-145.
17. Guan GC, Wei XH. Analysis on Soil Nutrient Characteristics and Their Correlation in Three Finds of Forest in Dinghushan (In Chinese). Environmental Science and Management. 2017; 42: 139-144.
18. YANG RQ Lu CL, Li SP. A STUDY ON SOIL EROSION IN HETIAN CHANGTING, FUJIAN. J Anhui Agric Univ. 1981.
19. Li ZP, Zhang TL, Yang YS, Wang XX, He YQ, Zeng XB. Process and Comprehensively Harnessing Techniques of Soil and Water Loss in Hilly Red Soil Regions. Bulletin of Soil and Water Conservation. 2001; 21: 12-17.
20. Huang CM, Liu SZ. Effects of Soil Erosion on Soil Fertility io Yuanmou Dry and Hot Valley,Yunnan. Trop Subtrop Soil Sci. 1996; 5: 102-107.
21. Feng H, YB Guo, XH Wei, Zhang Zhi-hong, LI Hua-xing. Study on Variation of Soil Nutrient and Microbe on Different Erosion Position of Hilly Slope in Latosolic Red Soil Region (In Chinese). Journal of Soil and Water Conservation. 2008; 22: 149-201.
22. Lin JL, Jiang FS, Lin JS, Chen WX. Assessment of Soil Qualities under Different Management Measures in the Severe Red Soil Hilly Erosion Areas of South China. Subtropical Soil and Water Conservation. 2015; 27: 11-16.
23. LUI QIYJ, ZHANG LM, ZHOU BQ-ZHANG JB, XING SH. Regionalization of the Abundance and Deficiency of the Farmland Soil Nutrients in Soil and Water Loss Region of Southern China Based on GIS (In Chinese). Acta Agriculturae Universitatis Jiangxiensis. 2014; 36: 684-691.
24. ZHANG Z, HE HZ, ZHANG YW. Soil Fertility and Carbon Content of Different Vegetation Types in Leigong Mountain Natural eserve Area. Southwest Chin J Agri Sci. 2014; 27:1202-1206.
25. Lu C, Zhanu WY, Shi L, Lin CH, Tengbing TB. Difference of Soil Nutrients under Different Vegetation Type in Fanjing Mountain Nature Reserve (In Chinese). Guizhou Agricultural Sciences; 2016; 44: 177-181.
26. Ding FJ, Pan ZS, Zhou FJ, Wu P. Organic Carbon Contents and Vertical of the Karst Distribution Characteristics the Soil in Three Forest Types Regions in Central Guizhou of Province (In Chinese). J Soil Water Conserv. 2012; 26: 161-169.
27. ZHENG JB, WANG ZF, TAN XL, Li AL, GAO M. Effects of Land Use Patterns on the Physico-chemical Properties of the Soil Profile in Purple Hilly Areas (In Chinese). J Southwest Univ. 2008; 30: 101-106.
28. Lin MZ, Xie SY, Lin YS. Characteristics of Soil Nutrient under Different Land Use Types in Karst Mountain Area (In Chinese). Conservation in China, 2009; 9: 8-11.
29. Feng H, Guo YB, Wei XH, Zhi-hong Z, Hua-xing LI. Study on Variation of Soil Nutrient and Microbe on Different Erosion Position of Hilly Slope in Latosolic Red Soil Region (In Chinese). J Soil Water Conserv. 2008; 22: 149-201.
30. XU B, ZHU ZF, LI JY, WU Y, DENG GP, et al. Leaf decomposition and nutrient release of dominant species in the forest and lake in the Jiuzhaigou National Nature Reserve, China (In Chinese). Chin J Plant Ecol. 2016; 40: 883-892
31. Xu B, Z F Zhu, JY Li, Y Wu, GP Deng, et al. Soil nutrient characteristics in different forest types at the Jiuzhaigou National Nature Reserve, China (In Chinese). Chin J. Appl Environ Biol. 2016; 22: 0767-0772.
32. ZHANG J, CHANG QR. Effects on Soil Fertility in Different Types of Forest on Loess Plateau (In Chinese). Bull tin Soil Water Conserv. 2006; 26: 26-28.
33. Robert Zougmoré & Abdoulaye Mando,Leo Stroosnijder. Soil Nutrient and Sediment Loss as Affected By Erosion Barriers and Nutrient Source in Semi-Arid Burkina Faso. Arid Land Research and Management. 2009; 23:85-101.
34. Berhane Lemma1, Fassil Kebede, Shimbahri Mesfin, Ibrahim Fitiwy, Zenebe Abraha, Lindsey Norgrove. Quantifying annual soil and nutrient lost by rill erosion in continuously used semiarid farmlands, North Ethiopia. Environ Earth Sci. 2017; 76:1-8.
35. Yibo Wang, Yan Sun, Fujun Niu, Qingbai Wu. Using 137Cs measurements to investigate the impact of soil erosion on soil nutrients in alpine meadows within the Yangtze River region, China. Cold Regions Science and Technology. 2017; 135:28–33.
36. Alemsha G Bogale, Dessalew W Aynalem, Anwar A Adem, Wolde Mekuria, Seifu A Tilahun. Evaluating the Role of Runoff and Soil Erosion on Nutrient Loss in the Chenetale Watershed, Upper Blue Nile Basin,Ethiopia. Advances of Science and Technology. 2019; 274: 274- 287.
37. M.Martínez-Mena, E.Carrillo-López, C.Boix-Fayos, M.Almagro, N.García Franco. Long-term effectiveness of sustainable land management practices to control runoff, soil erosion, and nutrient loss and the role of rainfall intensity in Mediterranean rainfed agroecosystems. Catena. 2020; 187:104352