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Journal of Resources and Ecology >

2023 , Vol. 14 >Issue 4: 847 - 855

DOI: https://doi.org/10.5814/j.issn.1674-764x.2023.04.017

Revegetation and Management of Mines

Study on the Effect of Topsoil Storage Mode on Topsoil Availability

  • LIN Yachao , 1 ,
  • FENG Changdong 2 ,
  • GUO Xiaoping , 1, * ,
  • LUO Chao 3 ,
  • LI Wenye 1 ,
  • XUE Guolian 1 ,
  • ZHANG Wei 1 ,
  • YANG Fan 1
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  • 1. School of Soil and Water Conservation, Beijing Forestry University, Beijing 100083, China
  • 2. Taihu Basin Administration of Ministry of Water Resources, Shanghai 200434, China
  • 3. Research Institute of Subtropical Forestry, Chinese Academy of Forestry, Hangzhou 311400, China
*GUO Xiaoping, E-mail:

LIN Yachao, E-mail:

Received date: 2022-10-20

  Accepted date: 2023-02-20

  Online published: 2023-07-14

Supported by

Key Research and Development Program of China(2017YFC0504406)

The Inner Mongolia Autonomous Region Science and Technology Major Projects(2020ZD0021-03)

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Abstract

Topsoil resources are important resources for ecological restoration in mining areas, although the topsoil stripped in practical projects can not be used for ecological restoration immediately. The changes that occur in topsoil after a certain period of storage in arid areas are not clear, so we have no insight on how to make the best use topsoil for ecological restoration after storage in the mining areas. Therefore, this study investigated the effects of topsoil accumulation on seed density and topsoil nutrient content in seed banks, which could provide a technical basis for vegetation reconstruction of coal mine damaged land in desert areas and theoretical support for ecological restoration practices. In this study, two storage methods of round table piles (hereafter referred to as YT) and cube ton bags (hereafter referred to as DD) were used to preserve uniformly mixed topsoil samples, and the loss of the soil seed bank and nutrient depletion under different topsoil storage methods were analyzed. In the two storage modes, the soil seed density loss on the surface of the pile was the largest, and the loss rate was 79.30%-83.65%. At a given sampling location, soil seed density increased significantly with soil depth (P<0.05). Compared with the change in seed density, soil nutrient loss was less pronounced, and the loss rate was between 8.92% and 16.62%. The seed density loss of the topsoil was the highest in both stacking modes. With the increase in the soil layer, soil seed density was significantly increased (P<0.05). At the same time, there was no significant difference in seed loss between the two storage modes. In the process of preservation, shrub seeds were the most seriously lost in the pile. The nutrient preservation effect of the ton bag storage mode (DD) was better than that of the round table storage mode (YT), and the soil nutrient loss of the top layer of the pile was the greatest, while the soil nutrient losses of other soil layers were lower.

Key words： soil seed bank; opencast coal mine; topsoil stockpile; seed bank density

Cite this article

LIN Yachao , FENG Changdong , GUO Xiaoping , LUO Chao , LI Wenye , XUE Guolian , ZHANG Wei , YANG Fan . Study on the Effect of Topsoil Storage Mode on Topsoil Availability[J]. Journal of Resources and Ecology, 2023 , 14(4) : 847 -855 . DOI: 10.5814/j.issn.1674-764x.2023.04.017

1 Introduction

The soil seed bank refers to the sum of viable seeds on the soil surface and in the substrate (Amiaud and Touzard, 2004). It plays an essential role in buffering species extinction and is a survival strategy formed by seed plants in the long-term evolutionary process. When vegetation is disturbed or damaged by the external environment, the seeds with recovery potential that are buried in soil can provide vegetation provisions for restoration and population continuation, and they are especially critical in areas with very harsh living conditions (O’Meara et al., 2015; Li et al., 2019). Therefore, in the past 20 years, the soil seed bank has gradually become one of the hot issues in both restoration ecology and population ecology research (Lin et al., 2012).
In ecological restoration, compared with other restoration methods, soil seed banks contain many genetic characteristics and variations of the native ecosystems, which can prevent genetic interference and realize resource recycling. The seed bank is a potential plant community, that is especially important for restoring degraded ecosystems (Yu et al., 2020; Zhang et al., 2021). In the process of topsoil storage, the physical and chemical properties of the soil will change, and these changes will affect the lives of the seeds and may lead to the decomposition of seeds in the soil (Heida and Jones, 1988; Rocha et al., 2021). Some studies have shown that seed vigor loss was reduced under low temperature, low humidity and low oxygen conditions (Jiang, 2018), and that topsoil storage will reduce soil seed bank density compared with undisturbed soil seed bank storage (Buss and Pinno, 2019). Therefore, this study addresses two main questions regarding the changes during topsoil storage: 1) How does the soil seed bank change under the two topsoil preservation methods of cube ton bag and round table stacking? and 2) How does the soil nutrient content change under the two topsoil preservation methods of cubic ton bag and round table stacking?
Wuhai City, Inner Mongolia, is located in the arid region of northwestern China and it is a typical city for open-pit coal mining in China. The soil layer in this area is thin, the soil resources are precious, the regional vegetation is distinctive, the combination of wind and hydraulic forces erode the soil, and the ecological protection pressure is high. Therefore, systematically studying the availability of local topsoil resources and how to scientifically apply them to ecological restoration projects of dumps is of great significance. The Xinxing Coal Mining area of Wuhai City was selected as the research area for this study. Statistical methods were used to analyze the characteristics of the soil seed bank, soil fertility quality and the availability of local topsoil resource production was clarified. Two preservation methods of seed topsoil were investigated to explore the changes in soil quality and seed bank vitality after short-term storage and to provide a technical basis for ecological restoration and the reconstruction of coal bases in arid areas.

2 Study area and methods

2.1 Study area

Wuhai City is located in the upper reaches of the Yellow River, adjacent to Table Mountain in the east, Helen Mountain in the west, Ningxia Plain in the south, and Hetao Plain in the north. With an average evaporation of 3289 mm, it belongs to a typical continental climate (Wang et al., 2010). The annual average wind speed in the study area is 3.1-4.7 m s-1, and the maximum wind speed is 28 m s-1. At the same time, the soil in this area has a high degree of salinization and poor water retention, and the zonal soil is desert calcareous soil. Therefore, it is suitable for the growth of relatively few plants, and the vegetation is heavily thickened. The vegetation type belongs to the grassland-desert transition vegetation type, mainly including the desert vegetation type, arid grassland vegetation type, and sandy vegetation type. The plant types found in the survey included a total of 565 species in 72 families, and 267 genera, and they represent rich plant resources, including national second-class, endangered, rare, and protected plants such as Tetraena mongolica, Helianthemum songaricum, and others.
Xinxing Open-pit Coal Mine is located at the northern edge of Wuhai City, about 10 km away from Haibowan District, covering an area of 2.06 km2. The main surface engineering facilities include an open pit mining area, external dump, inner dump, mining roads, industrial sites, and others, which are representative of a typical open-pit coal mine in Wuhai City, and the thickness of the topsoil in the original landform area is about 15 cm (Guo, 2020).

2.2 Methods

For the two different storage methods in this study, the mixed topsoil resources were piled into a 1 m high round table pile (hereafter referred to as YT) and into a 1 m×1 m× 1 m cubic ton bag (hereafter referred to as DD). For DD (Table 1), after 9 months of preservation, excavation and sampling were carried out in the divided area of the heap to explore the depletion of topsoil resources in the short-period preservation of the topsoil.
Table 1 Stacking modes and specifications
Item Round table storage mode (YT) Big bag storage mode (DD)
Size H=1 m
R=1.67 m
r=0.3 m
Slope 35°		 The specification is 1 m × 1 m× 1 m
Coverage measures Fiber mesh thatch cover None
Volume About 3.54 m³ About 1 m³
The soil environment may vary among different spatial positions in a heap, especially since the surface of the heap in contact with the outside world is more obviously affected by the natural environment. Therefore, in order to further explore the changes in topsoil quality during the storage process, it is necessary to sample the topsoil piles in layers at different times. As shown in Fig. 1, DD was divided into four soil layers of A (0-10 cm), B (10-40 cm), C (40-70 cm), and D (70-100 cm). The planes were cut along the diagonals of the top of the ton bag, with side lengths of 12 cm and 36 cm, respectively, three straight lines at 60 cm were perpendicular to the ground to form L1, L2, L3, and other areas, and then the soil samples were taken from the center of the soil layer where each area is located. YT was divided into the same four soil layers A, B, C and D, two straight lines were drawn from the bottom of the section to divide the hypotenuse into three equal parts to form areas P1, P2, and P3, and then soil samples were taken from the center of the soil layer where each area is located.
(1) Sampling of the heap seed bank and the outdoor germination test
Each soil sample was transferred to a germination pot (37 cm × 20 cm × 15 cm), and then the germination test was carried out. Ensuring that the thickness of the surface soil of the germination basin was 2-3 cm, each test was replicated three times. The subsoil of the germination basin was seedless coarse fine sand with a thickness of about 5-7 cm, and the subsoil and topsoil were separated by peat. Watering was conducted once every morning and evening, and the soil volume moisture content after watering was about 30%. At the same time, the seed germination was assessed and recorded, and seedlings were removed after identification. When no new seedlings had germinated for one week, the soil sample was turned over and sprayed with gibberellin, so as to reduce the influence of plant seeds that had entered dormancy during burial. After that step, the experiment ended when no new seedlings germinated for 3 consecutive weeks. At the same time, three high temperature treated soil sample flower pots were placed in the test site to eliminate the interference of foreign seeds. The germination test site was located in the project department of the Xinxing Mining Area in Wuhai City, and the testing was conducted from June 2020 to October 2020.
Fig. 1 Locations of sampling points inside the soil pile
(2) Determination of soil nutrients. After taking the soil samples at various points in the topsoil, the five indicators of soil organic matter, total nitrogen, total phosphorus, total potassium, and pH, were measured in the laboratory.

2.3 Data analysis

Because the dependent variable (seed germination rate) does not follow a normal distribution, a nonparametric test (Mann-Whitney U test) was used to analyze the differences in the germination rates of buried seeds under the different covering methods. The seed germination rate was analyzed for significance (P = 0.05), and all of the above data analyses were done by SPSS 24.0 (IBM, USA), and graphed by Sigmplot software.
Table 2 Assay methods
Index pH Organic matter Total nitrogen Total phosphorus Total potassium
Method Potentiometric method Potassium dichromate method Sulfuric acid-hydrogen peroxide digestion, diffusion absorption method Sulfuric acid-hydrogen peroxide digestion, vanadium molybdenum yellow colorimetry Sulfuric acid-hydrogen peroxide digestion, flame photometry
Standard NY/T 1121.2-2006 NY/T 1121.6-2006 NY/T 53-1987 HJ 632-2011 NY/T 87-1988

3 Results

3.1 Influence of the ton bag (DD) storage method on the characteristics of the soil seed bank

The data in Fig. 2 show that except for the C soil layer, the seed densities at each site have no significant difference in the same soil layer (P>0.05). For the seed density of the C soil layer, the seed density of the L1 position is significantly lower than those of the L2 and L3 positions. (P<0.05). At the same sampling point, there was a significant difference in seed density among the same layers (P<0.05), among which the seed density in soil layer D at the L1 position was the highest, at 183.67 grain m-2, and the seed density in soil layer C at the L2 and L3 positions was the highest, with values of 197.33 and 195.00 grain m-2, respectively.
Fig. 2 Seed density inside the DD pile

Note: A, B, C and D are the sampling depths of the stacked topsoil, which are 0-10 cm, 10-40 cm, 40-70 cm and 70-100 cm respectively. Different capital letters represent significant differences in seed densities between sampling points in the same soil layer (P<0.05), and different lowercase letters represent significant differences in seed densities between different soil depths in the same sampling point (P<0.05); and L1, L2 and L3 are sampling areas. The same annotations apply to subsequent figures.

The data in Table 3 show that after nine months of stacking tons of bags, the seed densities in the soil decreased to varying degrees, and the average seed loss rate was 62.95%. Among the layers, the seed loss in soil layer A was the most pronounced, reaching 79.30%. With the increase in the soil depth, the seed loss rate showed a downward trend. The seed loss rates in the C and D soil layers were relatively similar at 53.44% and 54.14%, respectively.
Table 3 Variation characteristics of seed density levels inside the DD pile
Soil layer Volume of each soil layer (m3) Average seed density before stockpiling (grain m-2) Average seed density of germination test (grain m-2) Average loss rate (%)
A 0.1 398.33 82.45 79.30
B 0.3 139.78 64.91
C 0.3 185.44 53.44
D 0.3 182.67 54.14
Total 62.95

Note: A, B, C and D are the sampling depths of the stacked topsoil, which are 0-10 cm, 10-40 cm, 40-70 cm and 70-100 cm respectively, and the same annotations are used in subsequent tables.

The data in Table 4 show that in the DD storage mode, the loss rates of 10 plant seeds in the pile surface (layer A) exceeded 90%. Among them, the loss rates of five kinds of plants (Agriophyllum squarrosum (L.) Moq., Salsola ruthenica Iljin, Chenopodium strictum Roth, Salsola collina Pall. and Oxytropis aciphylla Ledeb.), were as high as 100.00%. In the B layer, the most severe seed losses are Bassia dasyphylla (Fisch. et Mey.) O. Kuntze, Salsola ruthenica Iljin, Salsola collina Pall. and Oxytropis aciphylla Ledeb., and their loss rates reached 100.00%. In layer C, Agriophyllum squarrosum (L.) Moq., Salsola ruthenica Iljin, Chenopodium strictum Roth, Salsola collina Pall. and Oxytropis aciphylla Ledeb. had the highest seed loss rates, reaching 100.00%. In layer D, Agriophyllum squarrosum (L.) Moq., Salsola ruthenica Iljin, Allium tenuissimum Linn., Chenopodium strictum Roth, Salsola collina Pall. and Oxytropis aciphylla Ledeb. had the largest seed loss rates, also reaching 100.00%.
Table 4 Average losses of plant seeds in each soil layer of the DD pile
Latin name Seed loss rate of each soil layer (%)
A B C D
Eragrostis minor 65.93 29.90 11.52 16.42
Bassia dasyphylla 90.48 100.00 42.86 76.19
Tribulus terrestris 83.87 79.57 12.90 17.74
Halogeton glomeratus 76.97 78.79 12.12 3.03
Agriophyllum squarrosum 100.00 85.72 100.00 100.00
Salsola ruthenica 100.00 100.00 100.00 100.00
Stipa krylovii 49.01 27.44 60.78 60.78
Achnatherum splendens 88.76 74.91 60.67 52.81
Stipa glareosa 74.56 53.50 39.90 40.34
Cleistogenes 68.83 41.99 18.61 31.17
Allium tenuissimum 90.24 77.23 98.37 100.00
Artemisia desertorum 91.61 85.17 83.83 84.03
Artemisia frigida 41.49 19.38 12.24 19.72
Agropyron cristatum 67.95 46.16 62.82 21.80
Melilotus officinalis 76.19 59.52 88.09 85.71
Chenopodium strictum 100.00 97.44 100.00 100.00
Salsola collina 100.00 100.00 100.00 100.00
Leymus secalinus 98.72 94.87 96.15 97.43
Reaumuria songarica 93.33 93.33 96.67 96.67
Oxytropis aciphylla 100.00 100.00 100.00 100.00

3.2 The influence of the round table (YT) storage method on the characteristics of the soil seed bank

The data in Fig. 3 show that in a given sampling location, soil seed density increased significantly with the increase in soil layer depth (P<0.05). In the same soil layer, there was no significant difference in soil seed density at the different sampling locations. In soil layer A, the seed density at P2 was significantly lower than those of P1 and P3 (P<0.05), but there was no significant difference between P1 and P3 (P>0.05). In soil layer B, P1 was significantly lower than P3 (P<0.05). In soil layer C, the seed density of P3 was significantly higher than those of P1 and P2 (P<0.05), and the seed density was 170.00 grain m-2. In soil layer D, the seed density of the P3 location was significantly lower than that of the P2 location (P<0.05), but there was no significant difference between the P1 and P2 locations (P>0.05).
Fig. 3 Seed density inside the YT pile
The data in Table 5 show that the average seed loss rate of topsoil was 61.07% after nine months of piling, which was similar to the average loss in DD. The seed density in the soil showed a downward trend with an increase in soil depth. The average loss rate of soil seeds in layer A was the highest, reaching 83.65%, and the average loss rate of soil seeds in layer D was the lowest, at 49.87%.
Table 5 Changes in the seed characteristics inside the YT pile
Soil layer Volume of each soil
layer (m3)		 Average seed density before
stockpiling (grain m-2)		 Average seed density of
germination test (grain m-2)		 Average loss rate (%)
A 0.35 398.33 66.22 83.65
B 1.06 135.89 65.89
C 1.06 159.33 60.00
D 1.06 199.67 49.87
Total 61.07
For the different species under the YT storage mode (Table 6), the seed loss rates of 10 species in the A layer soil reached more than 90%, including four plants which reached 100.00%. The seed loss rate of Artemisia frigida Willd. was the lowest, but even it reached 55.10%. The loss rates were higher than those in the DD stockpiling model. In soil layer B, only Allium tenuissimum Linn. and Reaumuria songarica (Pall.) Maxim. had seed loss rates of more than 90%. The seed loss rates were generally below 90%, and the rates for all 20 plants in the seed bank decreased with the increase of burial depth inside the heap. Among them, the loss rate of Bassia dasyphylla (Fisch. et Mey.) O. Kuntze decreased the most with the increase in burial depth, from 100.00% in layer A to 23.81% in layer D, which is a difference of 76.19%.
Table 6 Average loss rates of plant seeds in each soil layer of the YT pile
Latin name Seed loss rate of each soil layer (%)
A B C D
Eragrostis minor 67.40 38.48 37.99 30.64
Bassia dasyphylla 100.00 71.43 71.43 23.81
Tribulus terrestris 87.63 64.52 67.20 66.67
Halogeton glomeratus 89.09 78.79 70.30 62.42
Agriophyllum squarrosum 71.43 71.43 28.57 23.81
Salsola ruthenica 100.00 20.00 13.33 40.00
Stipa krylovii 80.39 54.90 37.25 11.76
Achnatherum splendens 91.76 84.27 81.27 76.78
Stipa glareosa 86.84 62.72 54.82 60.53
Cleistogenes 89.18 54.55 60.17 64.50
Allium tenuissimum 90.24 90.24 79.67 77.23
Artemisia desertorum 91.21 80.00 69.07 51.76
Artemisia frigida 55.10 33.67 37.41 36.39
Agropyron cristatum 61.54 69.23 66.67 41.03
Melilotus officinalis 83.33 76.19 73.80 59.52
Chenopodium strictum 100.00 64.10 64.10 38.46
Salsola collina 93.75 75.00 77.08 70.83
Leymus secalinus 96.15 73.08 73.08 61.50
Reaumuria songarica 100.00 93.33 90.00 73.32
Oxytropis aciphylla 96.16 84.62 84.62 80.78

3.3 Effects of different stockpiling methods on soil fertility and quality

Through the one-way analysis of variance on the nutrient contents of different soil layers in a pile, the results showed that under the mode of stacking the ton bags (Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8), there was no significant difference in either soil pH or soil organic matter between the soil layers (P>0.05), while the soil layer A had no significant difference (P>0.05). The contents of total nitrogen, phosphorus, and potassium in layer A were significantly lower than those of soil layers B, C, and D (P<0.05). The contents of total nitrogen, total phosphorus, and total potassium of soil layer A were 0.42 g kg-1, 0.35 g kg-1, and 14.28 g kg-1, respectively.
Fig. 4 Soil pH inside the DD pile
Fig. 5 Soil SOC inside the DD pile
Fig. 6 Soil TN inside the DD pile
Fig. 7 Soil TP inside the DD pile
Fig. 8 Soil TK inside the DD pile
Through the one-way analysis of variance on the nutrient contents of different soil layers in the heap (Fig. 9,Fig. 10,Fig. 11,Fig. 12,Fig. 13), the results show that there is no significant difference in soil pH among the soil layers under the YT piling mode (P>0.05), and the contents of soil organic matter and total nitrogen varied with soil layers. The increase in layer depth showed an upward trend for the content of soil organic matter, and it was significantly lower in soil layer A than that in soil layers C and D (P<0.05). The total soil nitrogen content in soil layer A was 0.34 g kg-1, which was significantly lower compared with the other soil layers (P<0.05). The contents of total phosphorus and total potassium increased at first and then decreased with the increase in soil layer depth. They were the lowest in soil layer A, at 0.36 g kg-1 and 13.40 g kg-1, respectively, which were significantly lower than their contents in soil layers C and D (P<0.05).
Fig. 9 Soil pH inside the YT pile
Fig. 10 Soil SOC inside the YT pile
Fig. 11 Soil TN inside the YT pile
Fig. 12 Soil TP inside the YT pile
Fig. 13 Soil TK inside the YT pile
When the changes in soil nutrient contents under the two stacking modes of topsoil are compared with those before stacking (CK), there are different degrees of loss. The soil nutrient loss degree of topsoil under these two stacking modes is 8.92%-16.62% (Table 7). The soil nutrient loss rates in the DD stacking mode are lower than those in the YT stacking mode. The losses of organic matter and total potassium are significantly different, and the losses in DD are 5.58% and 7.05% less than those in the YT mode, respectively; followed by the total nitrogen and total phosphorus content, which showed 2.65% and 2.19% less loss in DD than in YT, respectively.
Table 7 Depletion of soil nutrient structure under the two storage modes
Type Percentage decrease in soil nutrient contents
SOC TN TP TK
DD 8.92 9.93 10.43 9.57
YT 14.50 12.58 12.63 16.62
YT-DD 5.58 2.65 2.19 7.05

4 Discussion

4.1 Variations in the characteristics of soil seed banks in the two stockpiling modes

The results of this study show that the topsoil in the two storage modes of YT and DD both have significant losses of seed density in the soil. In the two storage modes, seed loss was greatest in the surface soil depth of 0-10 cm, which may be because most of the seeds on the soil surface are short-term seeds (Zhang et al., 2017a; Zhang et al., 2017b; Li et al., 2018) that will seize favorable conditions in time to complete germination, while seeds buried in deep soil are generally considered to be produced earlier and are mostly persistent seed banks (Yan et al., 2005). Therefore, the deeper seeds will remain dormant, to avoid the risk of one-time precipitation and ensure subsequent survival (Rivera et al., 2012; Bie et al., 2016), thus resulting in fewer dormant seeds in the topsoil; but as the depth of burial increases, the seeds are less likely to be deposited during storage. It is easy to induce germination, and it will form a low oxygen, low temperature and stable temperature environment, which is more likely to cause the seeds to enter a dormant state, so the seeds can be better preserved. Therefore, the density of seeds in the position with a deep burial depth is higher than that of the surface soil of the heap (Bowen et al., 2005; Hall et al., 2010). However, some studies have also found that seed death will occur in the deep soil when the soil is stored for more than six months (Rivera et al., 2012), which may be due to the heavy precipitation in the study area in winter. The increases in depth and humidity are not conducive to the long-term dormancy of seeds, and the dead seeds will pollute the soil, increasing the population of pathogenic bacteria in the soil and the spread of death (Feng, 2021).
In the burial process, the survival rates of seeds may also be different due to different seed characteristics, and there will be differences with the increase in burial depth. Currently, most research on soil seed banks in the arid regions of Northwest China investigate shallow depths of 0-10 cm. There are few studies on the burial of different plant seeds and burial depths (Zhang et al., 2011; Wang et al., 2012), so there is a lack of research on the response relationship between different plant seeds and environmental factors under deep burial conditions. The average loss of shrub seeds, such as red sand and cat's head thorn, in this study was up to more than 80% during the storage process. The herbal seeds were lost at a rate of only about 60%, which may be because the seeds of herbs increased with the depth of burial and the internal environment. They are relatively stable, so it is easier for them to enter a dormant state. In contrast, the dormancy ability and stress resistance of shrub seeds are lower than those of herb seeds. In addition, as the burial depth inside the pile increases, the number of pathogenic bacteria in the soil increases, which will also lead to seed death (Feng, 2021).

4.2 Characteristics of soil nutrient changes in the two stockpiling models

Appropriate soil conditions are the basis for the average growth and development of vegetation. Soil nutrient content is an integral part of the availability of topsoil. The most commonly used indicators include soil texture, pH value, total nitrogen, total phosphorus, total potassium, and organic matter (Lin et al., 2017; Ma et al., 2020). The results of this study show that under the two stockpiling modes, the nutrient losses of the topsoil of the piles are apparent. With the increase of the burial depth, the losses of soil pH, total nitrogen, total phosphorus, total potassium, and organic matter are diminished. This may be because the microbial activity in the topsoil is higher than that in the soil inside the heap (Visser et al., 1984), which leads to the rapid nutrient transformation in the surface soil of the heap; and it may also be due to a small amount of rainfall in the study area in spring leading to decomposition of organic matter in topsoil and leaching of some nutrients from the soil (Quintela et al., 2018). Some studies have shown that the soil organic matter inside the heap increases after a long-term stacking of topsoil (Williamson and Johnson, 1990). This is contrary to the results of this study, which may be because the stacking time of this study was relatively short, and the accumulation of organic matter under anaerobic conditions is not formed in the pile body (Williamson and Johnson, 1990).

5 Conclusions

(1) The loss of the soil seed bank was greater in the two different kinds of storage processes, and the loss rate of soil seed density was 79.30%-83.65% in the surface layer of the pile. At the same sampling position, soil seed density increased significantly with an increase in soil depth (P<0.05). There was no significant difference in seed loss between the two storage modes. In the process of preservation, shrub seed loss in the pile is the most serious, with loss rates of more than 80%.
(2) The nutrient preservation effect of the ton bag storage mode is better than that of the round table storage mode, but the soil nutrient indexes decrease less than the change of seed density, and the nutrient change rates are between 8.92% and 16.62%. In addition to the significant loss at the surface 0-10 cm, the nutrient changes in other soil layers are small, and the impact on subsequent topsoil utilization is low.
In summary, the changes in the availability of topsoil resources in the Xinxing Mining Area after stockpiling mainly come from the loss of the soil seed bank. Therefore, when utilizing the stockpiled topsoil, seed storage and the expected restoration of vegetation should be considered first.

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