Method for safely planting navel oranges in rare earth tailings based on Zeta potential

Abstract

The invention relates to the technical field of agricultural planting, in particular to a method for safely planting navel oranges in rare earth tailings based on Zeta potential. The method comprises the following steps that planting pits with the row spacing and the column spacing being 1-2 m are dug in soil of the rare earth tailings, the radius of each planting pit is 60-80 cm, and the depth of each planting pit is 50-70 cm; the soil dug out is evenly mixed with a modifier to form planting soil, the modifier comprises, by weight, 10-20 parts of biochar and 75-85 parts of humus, and the pH value of the planting soil is adjusted to be neutral so that the Zeta potential of the biochar and the humus can be negative; 2-3-year navel orange seedlings with nutrition plates are placed in the planting pits; the planting pits are backfilled with planting soil, and root systems are covered with 3-6 cm of covering soil. The Zeta potential of the biochar and the humus is adjusted to be negative potential, so that the biochar and the humus adsorb positively charged rare earth elements, and the effective state content of the rare earth element plant is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of agricultural planting, and in particular to a method for safely planting navel oranges in rare earth tailings based on zeta potential. Background Art

[0002] Gannan navel oranges are highly valued for promotion due to their unique aroma, superior quality, good commercial appeal, high fruit set rate, early production, and exceptional storage durability. A moderate concentration of rare earth elements in the soil can increase the soluble solids, titratable acid, and vitamin C content of navel oranges, improving their quality. However, because rare earth tailings contain significant amounts of these elements, navel oranges grown within these tailings will absorb significant amounts, potentially impacting their safety. Summary of the Invention

[0003] The present invention addresses the problem of how to reduce the rare earth content of navel oranges planted in rare earth tailings and proposes a method for safely planting navel oranges in rare earth tailings based on zeta potential. The method adjusts the zeta potential of biochar and humus to a negative potential, thereby adsorbing positively charged rare earth elements, and simultaneously increases the pH value of the soil, passivates the rare earth elements, and reduces the plant-available content of the rare earth elements (EDTA-extracted state).

[0004] The technical solution adopted by the present invention to solve the technical problem is:

[0005] A method for safely planting navel oranges in rare earth tailings based on zeta potential, comprising the following steps:

[0006] Step 1: digging planting pits in the soil of the rare earth tailings with a row spacing and a column spacing of 1 to 2 meters, a radius of 60 to 80 cm, and a depth of 50 to 70 cm;

[0007] Step 2: taking the soil dug out from the planting pit and mixing it with an amendment in a mass ratio of 1:0.02 to 1:0.03 to form planting soil, wherein the amendment includes 10 to 20 parts by weight of biochar and 75 to 85 parts by weight of humus, and adjusting the pH value of the planting soil to neutral, the pH value of the planting soil is the optimal survival condition for plants, and the Zeta potential of the biochar and the humus is negative, that is, the Zeta potential of the biochar and the humus is negative under the optimal survival conditions for vegetation;

[0008] Step 3, placing 2-3 year old navel orange seedlings with nutrient trays in the planting pit;

[0009] Step 4: backfill the planting soil with adjusted pH value into the planting pit, and cover the roots of the navel orange seedlings with 3 to 6 cm of soil.

[0010] In the above-mentioned method for safely planting navel oranges in rare earth tailings, the pH value of the planting soil is 6 to 8, and the Zeta potential of the biochar and the humus is between -20 and -35 mV.

[0011] In the above-mentioned method for safely growing navel oranges in rare earth tailings, the biochar is charcoal or bamboo charcoal.

[0012] In the above-mentioned method for safely planting navel oranges in rare earth tailings, the modifier also includes 5 to 8 parts by weight of calcium magnesium phosphate fertilizer.

[0013] In the above-mentioned method for safely planting navel oranges in rare earth tailings, the type of navel orange seedlings is Newhall navel orange, and the average seedling height of the navel orange seedlings is 80 to 90 cm.

[0014] In the above-mentioned method for safely planting navel oranges in rare earth tailings, the organic matter content of the planting soil is above 3%.

[0015] By means of the above technical solution, the present invention has at least the following advantages:

[0016] (1) The present invention adjusts the Zeta potential of biochar and humus to a negative potential, thereby enabling the adsorption of positively charged rare earth elements by biochar and humus, passivating the rare earth elements, and reducing the plant-available content of rare earth elements (EDTA extraction state);

[0017] (2) The amendment improved the physical structure of the soil, reduced the soil bulk density, increased the soil field water holding capacity, significantly increased the chemical pH value, and greatly improved the soil nutrients;

[0018] (3) Compared with the control, the amendment significantly reduced the total amount of available rare earth elements (EDTA extractable) in the soil. Compared with the CK, the T1 and T2 treatments decreased by 41.15% and 40.23%, respectively, which was a significant effect. At the same time, the amendment significantly reduced the total amount of rare earth elements in navel orange pulp. Compared with the CK, the total amount of rare earth elements in the T1 and T2 navel orange fruits decreased by 42.83% and 48.31%, respectively.

[0019] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention. DETAILED DESCRIPTION

[0020] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with preferred embodiments.

[0021] This embodiment provides a method for safely growing navel oranges in rare earth tailings based on zeta potential, comprising the following steps:

[0022] Step 1: digging planting pits in the soil of the rare earth tailings with a row spacing and a column spacing of 1 to 2 meters, a radius of 60 to 80 cm, and a depth of 50 to 70 cm;

[0023] Step 2: Take about 800 kg of soil dug out from the planting pit (radius 60 cm, depth 50 cm, soil bulk density 1.4-1.5 g / cm 3 Calculated), mixed with 20-30 kg of an improver at a mass ratio of 1:0.025 to form planting soil, wherein the improver includes 10-20 parts by weight of biochar and 75-85 parts by weight of humus, and the pH value of the planting soil is adjusted to neutral and the soil organic matter content reaches more than 3%, so that the zeta potential of the biochar and the humus is negative under the optimal living conditions for vegetation;

[0024] Step 3, placing 2-3 year old navel orange seedlings with nutrient trays in the planting pit;

[0025] Step 4: backfill the planting soil with adjusted pH value into the planting pit, and cover the roots of the navel orange seedlings with 3 to 6 cm of soil.

[0026] Since the chemical properties of a substance are the fundamental factors that determine its potential, the nature of the substance (such as redox ability) determines its standard potential; external conditions (concentration / activity, temperature, gas partial pressure, pH, precipitation / complex formation, surface state) affect the actual measured potential by changing the thermodynamic driving force of the reaction.

[0027] The present invention specifically selects the specific components of the biochar and humus modifiers, and by adjusting the pH value of the planting soil to 6-8, the Zeta potential of the biochar and the humus can be adjusted to between -20 and -35 mV.

[0028] The chemical properties of a substance are the fundamental factors that determine its potential. Therefore, biochar and humus have a fixed negative potential under neutral conditions. Factors that influence the magnitude of this fixed negative value include: 1. The electron affinity / ionization energy of the oxidized and reduced states. The lower the ionization energy of the reduced state (the easier it is to lose electrons), the more likely the oxidation reaction (electron loss) occurs, and the corresponding electrode potential is lower. 2. Molecular stability. 3. The strength and type of chemical bonds. For complex molecules (such as oxygen-containing acid radicals and complexes), the strength of their internal chemical bonds can affect the stability of the oxidized state, thereby changing the potential. 4. The charge and radius of the atom or ion. 5. The valence electron configuration of the substance. 6. The chemical polarity of the substance. Therefore, we use modified materials with a larger negative potential under neutral pH conditions. Biochar and humus have stable molecular structures.

[0029] The alkaline substances and functional groups in the amendment adjust the pH to neutral. The organic matter in the amendment improves the physical properties of the soil, enhancing aeration and redox conditions, further affecting the soil potential. High organic matter content in the amendment can form precipitates or complexes in the soil, affecting the potential. The biochar and humus in the amendment have a large specific surface area, enhancing adsorption and further affecting the potential.

[0030] Furthermore, the amendment also includes 5-8 parts by weight of calcium magnesium phosphate. The calcium magnesium phosphate fertilizer contains: P2O5 ≥ 12.0%, available calcium (Ca) ≥ 20.0%, available magnesium ≥ 4.0%, and soluble silicon (SiO2) ≥ 20.0%. The phosphorus in the calcium magnesium phosphate fertilizer increases soil phosphorus content, improving fertility. The calcium and magnesium further increase the pH of the rare earth tailings soil, increasing the negative potential of the amendment in the soil and enhancing its ability to absorb rare earth elements using this potential.

[0031] Furthermore, the type of navel orange seedlings is Newhall navel orange, and the average seedling height of the navel orange seedlings is 80 to 90 cm.

[0032] The specific implementation location of this implementation is an abandoned ionic rare earth mine in southern Jiangxi. Due to the special mining process, the abandoned ionic rare earth mine in southern Jiangxi has caused serious damage to the environment and is in urgent need of ecological restoration. Through laboratory analysis of the soil degradation characteristics of the abandoned mining area, soil conditioners were developed to repair the abandoned mining area based on the degradation characteristics of the soil in the abandoned mining area, and Gannan navel oranges were planted, in order to build an ecological restoration model of "soil cultivation-greening-resumption of production" in the abandoned rare earth mining area, increase economic benefits, and achieve a win-win situation of ecological restoration and economic benefits in the abandoned rare earth mining area. A total of 3 treatments were formed: CK (no use of conditioners, planting navel oranges), T1 (conditioner 1 + planting navel oranges), and T2 (conditioner 2 + planting navel oranges). The effects of different restoration measures on soil properties and navel orange fruit safety were analyzed, and restoration measures suitable for abandoned mining areas were screened out.

[0033] The biochar in this embodiment is charcoal or bamboo charcoal, wherein the improver component is charcoal improver 1 (T1), which has the following specific components: charcoal 15%, humus 85%. The main component charcoal: synthesized at 300 ° C, pH 8.50, C content 58.76%, N content 0.56%, specific surface area 189.49m 2 / g, Zeta potential is shown in Table 1.1; humus: organic matter ≥45%, total nutrients N, P2O5, K2O ≥5%, Zeta potential is shown in Table 1.2, rare earth element and heavy metal content is shown in Table 2.

[0034] The improver component of the improver is improver 2 (T2), and the specific components are as follows: bio-bamboo charcoal 15%, humus 85%. The main component bio-bamboo charcoal: synthesized at 400℃, with a pH of 8.13, a carbon content of 75.84%, a nitrogen content of 0.82%, and a specific surface area of ​​19.75m 2 / g, Zeta potential is shown in Table 1.1; humus: organic matter ≥45%, total nutrients N, P2O5, K2O ≥5%, Zeta potential is shown in Table 1.2, rare earth element and heavy metal content is shown in Table 2.

[0035] The navel orange seedlings are Newhall navel oranges, all of which are 2.5-year-old navel orange seedlings with an average seedling height of about 85 cm and come with nutrient trays.

[0036] Table 1.1 Zeta potential (mV) of biochar at different pH values

[0037]

[0038] Table 1.2 Zeta potential (mV) of humic substances at different pH values

[0039]

[0040] Table 2 Total amount of humic elements (mg / kg)

[0041]

[0042] A total of three treatments were formed: CK, T1, and T2. When planting navel oranges, dig a pit with a radius of about 70 cm and a depth of 60 cm, mix the loose soil and amendment (25 kg / plant) thoroughly and put them into the pit, and leave 4 cm of topsoil to cover the roots of the plants. After the plants are planted, they are fertilized and no fertilizer is applied later. The experimental area is located in Yangmei Village, west of Dingnan County, Ganzhou City, Jiangxi Province, with coordinates: 24°59.2′N, 115°2.0′E, and a total land area of ​​2959.39 acres. Each treatment has 3 replicates, and 5 navel oranges are planted in each replicate. Each plot is 10 meters long and 4 meters wide, with a row spacing of 1 meter and a plant spacing of 1 meter.

[0043] After the test site was turned over, the S-type sampling method was used, and five points were mixed into one sample. A total of 9 surface soils from 0 to 20 cm were collected from the test site, representing the background value of the test site. The soil pH was 4.40, the organic matter content was 2.52 g / kg, the available phosphorus content was 0.87 mg / kg, the total rare earth content and the available rare earth content were 981.33 mg / kg and 453.51 mg / kg, respectively. The specific basic properties are shown in Table 3.

[0044] Table 3 Foundation properties of the test site

[0045]

[0046]

[0047] Among them, for the collection of soil samples, this embodiment adopts the following method: soil samples are collected at about 40 cm near the plant, with one sampling point being due north, and then two more points being taken 120° to the left and right, that is, three points are taken for each navel orange tree, and 15 points are combined into one soil sample, each sample weighing about 1.0 kg. Stones, branches, roots and other debris in the soil sample are picked out, the soil is naturally air-dried, passed through 10 mesh (2 mm) and 100 mesh (0.149 mm) nylon sieves, bagged, labeled, and taken back for measurement.

[0048] With regard to the collection of plant samples, this embodiment adopts the following method: After the navel oranges are planted and mature, the leaves and fruits of the navel oranges are collected. 20 leaves are taken from each navel orange, and the leaves of the five navel orange seedlings in each treatment are mixed into one sample, for a total of 12 leaf samples. The sampling method of navel orange fruits is as follows: 2 navel orange fruits are randomly taken from the east, south, west and north directions of each navel orange seedling, and a total of 10 fruits are collected from the five navel orange seedlings in each treatment and mixed into one sample. The collected leaves and fruits are washed with ultrapure water and dried. At the same time, the peel and pulp of the navel orange fruits are separated. After the leaves, peel and pulp are blanched at 105°C in an oven for 25 minutes, the temperature is adjusted to 70°C and dried to constant weight. The dried samples are crushed in a grinder, all passed through a 60-mesh nylon sieve, and bagged. A total of 36 samples are used for the determination of rare earth and non-rare earth heavy metal elements.

[0049] Among them, for the analysis of soil samples, this embodiment adopts the following methods: the soil pH value is determined by potentiometric method (soil: water = 1:2.5); the soil organic matter (SOM) is determined by concentrated sulfuric acid-potassium dichromate oxidation method; the soil available nitrogen (AN) is determined by alkaline diffusion method; the soil available phosphorus (AP) is determined by sodium bicarbonate extraction method; the soil available potassium (AK) is determined by ammonium acetate extraction method; the total amount of non-rare earth heavy metals (Cd, As, Cu, Zn, Ni, Cr, Pb) and rare earth elements (16 rare earth elements except Pm) is subjected to microwave digestion and determined by inductively coupled plasma mass spectrometry (ICP-MS); the biologically available content of non-rare earth heavy metals (Cd, As, Cu, Zn, Ni, Cr, Pb) and rare earth elements (16 rare earth elements except Pm) is determined by acidic ammonium acetate-EDTA leaching method. Weigh 2.50 g of soil sample, add 25 mL of ammonium acetate-EDTA extract (0.5 M CH3COONH4, 0.5 M CH3COOH, 0.02 M Na2EDTA, pH 4.65), shake at 27 rpm in an oscillating box for 1 h, centrifuge at 3500 rpm for 25 min, filter using a syringe (0.45 μm water filter membrane), take 5 mL of the filtrate into a 25 mL volumetric flask, add deionized water to the volume, and determine using inductively coupled plasma mass spectrometry (ICP-MS).

[0050] For the analysis of navel orange samples, this example adopts the following method: the moisture content of navel orange pulp is determined by drying method; navel orange leaves, peel and pulp are subjected to microwave digestion and ICP-MS determination, referring to GB 5009.268-2016 and GB5009.94-2012. The specific steps are: weigh about 0.3g of the dried sample using a 1 / 10,000 balance and place it in a digestion tank, add 6mL of concentrated nitric acid, tighten the tank lid, let it stand for 1 hour, and then transfer it to a microwave digester for sample digestion. The heating program is shown in Table 4. After digestion is completed, the acid is removed in an acid removal instrument at 140°C for about 1 hour. After cooling, the digestion solution in the digestion tank is transferred to a 25mL volumetric flask, made up to volume with ultrapure water, and then tested. Each sample is repeated twice, and GBW10020 (GSB-11 citrus leaves) is used as a quality control sample. A customized mixed standard (solubility of 100 ppm, including 16 rare earth elements and 7 common heavy metals) was used as the calibration line, and 10 PPb of Rh was used as the internal standard. The determination was carried out by inductively coupled plasma mass spectrometry (ICP-MS).

[0051] Table 4 Microwave digestion reference conditions

[0052]

[0053] In this example, Microsoft Excel software was used for data pre-processing, and SPSS 22.0 software was used for principal component analysis and analysis of significance of differences between treatments (LSD method, significance level was 0.05).

[0054] The soil bulk density of the different treatments is shown in Table 5. The results show that compared with CK, the soil bulk density of T1 and T2 decreased slightly, by 9.00% and 4.75% respectively, but there was no significant difference (p>0.05). There was no significant difference in soil bulk density between T1 and T2 (p>0.05).

[0055] The field water holding capacity of the different treatments is shown in Table 5. The results show that compared with CK, the bulk density of soil field water holding capacity of T1 and T2 increased slightly, by 10.16% and 5.62%, respectively. There was no significant difference in soil field water holding capacity between T1 and T2 (p>0.05).

[0056] High soil bulk density can lead to reduced soil porosity, poor air permeability, and decreased water holding capacity, which can seriously hinder plant root development and microbial activity. The biochar and humus in the amendment can increase soil porosity, maintain a good soil structure, and reduce soil bulk density to varying degrees. Mining under the heap leaching process often leads to soil structural degradation and a significant reduction in field water holding capacity, which is manifested as a reduction in soil effective water capacity and an imbalance in water infiltration and evaporation, exacerbating drought stress and the difficulty of vegetation recovery. The biochar and humus in the amendment have a loose, porous structure and a large specific surface area, which can reduce soil bulk density and increase field water holding capacity. By adding amendments, the soil pore distribution can be optimized, and the field water holding capacity can be restored to 25%-35%.

[0057] Table 5 shows the sand content of soils from different treatments. The results show that compared to CK, soils T1 and T2 had significantly lower sand content (p < 0.05), with reductions of 21.28% and 20.02%, respectively. Sand dominates the macropores of soil, affecting permeability and drainage capacity. Mining operations increase the proportion of sand abnormally, leading to loose soils and poor water and nutrient retention. The biochar and humus in the amendments embed themselves in the interstices between sand particles, absorbing free sand particles to form a "skeleton-filler" structure, reducing the dispersion of coarse particles.

[0058] Table 5 shows the silt content of the different soil treatments. The results show that compared with CK, soil silt content in T1 and T2 was significantly higher (p < 0.05), increasing by 21.49% and 19.23%, respectively. Silt serves as the "binding medium" between sand and clay, and an imbalance in its proportion can disrupt soil structural coherence.

[0059] Table 5 shows the clay content of the soils under different treatments. The results show that clay content in T1 and T2 soils was slightly higher than that in CK (p>0.05), with T1 and T2 showing increases of 35.74% and 35.94%, respectively. When the clay content is too low, the soil's ability to retain water and fertilizer is weakened.

[0060] Based on the mechanical composition of the soil, the soil texture was classified according to the American system. The CK soil texture was sandy loam, while the T1 and T2 treatments were loam. This showed that the addition of amendments affected the soil texture by reducing the sand content and increasing the silt and clay content, thus changing the sandy loam into loam.

[0061] Table 5 Effects of different treatments on soil physical properties

[0062]

[0063]

[0064] Note: Different letters indicate significant differences (p<0.05)

[0065] Table 6 shows the soil pH values ​​for the different treatments. The results show that compared with CK, soil pH in treatments T1 and T2 increased significantly (p < 0.05), by 2.69 and 2.75 units, respectively. There was no significant difference in soil pH between T1 and T2 (p > 0.05). Compared to the pH classification of the Second National Soil Survey, CK (4.38) is classified as strongly acidic, while treatments T1 and T2 are classified as neutral. Because the humus, biochar, and wood charcoal in the amendments are alkaline, their application to the soil can rapidly increase soil pH. Rare earth mines are mostly exposed, lacking vegetation, resulting in poor soil structure and rapid water infiltration. Planting vegetation in abandoned rare earth mines can alleviate soil acidification.

[0066] Table 6 Effects of different treatments on soil pH

[0067]

[0068] Note: Different letters indicate significant differences (p<0.05)

[0069] Table 7 shows the SOM content of soils treated differently. The results show that compared to the CK, soil SOM in treatments T1 and T2 increased significantly (p < 0.05), by 93.34% and 93.86%, respectively. Compared to the nutrient classification of the Second National Soil Survey, CK (3.91) was classified as extremely poor, while treatments T1 and T2 were classified as extremely rich. The humus in the amendments directly replenished organic matter, while the charcoal and biochar stabilized the carbon pool and promoted microbial activity, accelerating organic matter accumulation. These improvements synergistically increased soil organic matter content.

[0070] Table 7 shows the soil AN content of the different treatments. The results show that compared with the CK, soil AN content in T1 and T2 increased significantly (p < 0.05), by 45.29% and 52.02%, respectively. There were no significant differences in soil AN values ​​between T1 and T2 (p > 0.05). Compared with the nutrient classification of the Second National Soil Survey, the CK (45.25) was classified as poor, while the T1 and T2 treatments were classified as relatively rich. The humus in the amendment directly supplemented the available nitrogen source, while the biochar adsorbed and inactivated ammonium nitrogen, reducing leaching. Furthermore, the amendment neutralized soil acidity and activated microbial activity, promoting organic nitrogen mineralization and nitrification, synergistically increasing the soil's available nitrogen content and retention capacity.

[0071] Table 7 shows the soil AP values ​​for the different treatments. The results show that compared with the CK, soil AP in T1 and T2 significantly increased (p < 0.05), by 94.13% and 92.22%, respectively. There were no significant differences in soil AP values ​​between T1 and T2 (p > 0.05). Compared with the nutrient classification of the Second National Soil Survey, the CK (4.99) was classified as nutrient-poor, while the T1 and T2 treatments were classified as extremely nutrient-rich. Biochar neutralized acidity, inhibiting phosphorus fixation. Humic matter in the amendment released organic acids that complexed iron and aluminum ions, activating stored phosphorus. Enhanced microbial activity promoted organic phosphorus mineralization, synergistically increasing both available phosphorus content and bioavailability in the soil.

[0072] Table 7 shows the AK content of soils treated differently. The results show that compared with the CK, soil AK in T1 and T2 significantly increased (p < 0.05), by 69.75% and 71.22%, respectively. Compared with the nutrient classification of the Second National Soil Survey, the CK (134.09) was classified as relatively nutrient-rich, while the T1 and T2 treatments were classified as extremely nutrient-rich. This change is attributed to the high humus content in the amendment, which directly replenished soluble potassium. The biochar and wood charcoal, by increasing their cation exchange capacity, absorbed potassium ions, reducing leaching. They also neutralized the acidic soil, inhibiting potassium fixation, and synergistically promoted the activation of mineral potassium and its release by microorganisms, significantly increasing the content and effectiveness of available potassium.

[0073] Table 7 Effects of different treatments on soil available nutrients

[0074]

[0075] Note: Different letters indicate significant differences (p<0.05)

[0076] Table 8 shows the TN content of soils from different treatments. The results show that compared with the CK, soil TN content in T1 and T2 increased significantly (p < 0.05), reaching 68.23% and 71.76% higher than the CK, respectively. There was no significant difference in TN content between T1 and T2 (p > 0.05). Compared with the nutrient classification of the Second National Soil Survey, the CK (338.93) was classified as extremely poor, while the T1 and T2 treatments were classified as relatively rich. This change is attributed to the direct input of organic nitrogen from the humus in the amendment, the adsorption and fixation of ammonium nitrogen by the biochar, and the promotion of microbial nitrogen fixation. This neutralization of acidity inhibited nitrogen volatilization, synergistically improving the efficiency of organic nitrogen mineralization and nitrogen pool stability.

[0077] Table 8 shows the TP content of soils from different treatments. The results show that compared with CK, soil TP content in T1 and T2 increased significantly (p < 0.05), by 89.10% and 88.92%, respectively. There were no significant differences in soil TP content between T1 and T2 (p < 0.05). Compared with the pH classification of the Second National Soil Survey, CK (203.52) was classified as poor, while T1 and T2 treatments were classified as extremely rich. This change is attributed to the direct supplementation of exogenous phosphorus by the humus in the amendment, the adsorption and fixation of phosphorus by biochar, and the reduction of iron and aluminum oxide fixation. This, in turn, neutralizes acidic activation of mineral phosphorus, synergistically promoting the mineralization of organic phosphorus and the release of inorganic phosphorus, significantly increasing the total phosphorus storage capacity and stability of the soil.

[0078] Table 8 shows the TK content of soils treated differently. The results show that compared with CK, soil TK content in T1 and T2 decreased significantly (p>0.05), by 15.49% and 13.51%, respectively. Compared with the total potassium nutrient classification of the Second National Soil Survey, CK (38.19), T1, and T2 treatments were classified as moderate. Amendments can promote the decomposition of potassium-containing minerals and microbial-mediated potassium activation, synergistically increasing soil total potassium reserves and bioavailability.

[0079] Table 8 Effects of different treatments on total soil nutrients

[0080]

[0081] Note: Different letters indicate significant differences (p<0.05)

[0082] Table 9 shows the plant-available rare earth element content (EDTA-extractable) in soils from different treatments. The results show that the total REE content (EDTA-extractable) in soils from T1 and T2 decreased significantly compared to the CK, with T1 and T2 treatments showing decreases of 41.15% and 40.23%, respectively. Y, La, and Nd were the highest in CK, T1, and T2, accounting for 65.62%, 60.86%, and 60.76%, respectively. After the addition of amendments, Y in soils from T1 and T2 decreased by 35.86% and 36.70%, respectively; La in soils from T1 and T2 decreased by 53.31% and 41.91%, respectively; and Nd in soils from T1 and T2 decreased by 43.24% and 41.91%, respectively. The reason may be that the charcoal and bio-bamboo charcoal in the T1 and T2 treatments have a negative potential under the modified pH, which can adsorb positively charged rare earth elements and simultaneously increase the soil pH, passivate the rare earth elements, and reduce the plant-available content of rare earth elements (EDTA-extractable state).

[0083] Table 9 Plant available content of rare earth elements in soils with different treatments (EDTA extraction)

[0084]

[0085]

[0086] Table 10 shows the rare earth element content in navel orange fruits from different treatments. The results show that the distribution patterns of rare earth elements were consistent across all treatments, with the highest concentrations found in Y, La, Ce, and Nd. Compared to CK, the total rare earth content in navel orange fruits from T1 and T2 decreased significantly, by 42.83% and 48.31%, respectively. The changes in Y element in navel orange fruits under different treatments are as follows: compared with CK, Y in soil T1 and T2 was significantly reduced, down by 48.66% and 50.01% respectively; the changes in La element in navel orange fruits under different treatments are as follows: compared with CK, La in soil T1 and T2 was significantly reduced, down by 47.45% and 48.81% respectively; the changes in Ce element in navel orange fruits under different treatments are as follows: compared with CK, Ce in soil T1 and T2 was significantly reduced, down by 21.07% and 43.49% respectively; the changes in Nd element in navel orange fruits under different treatments are as follows: compared with CK, Nd in soil T1 and T2 was significantly reduced, down by 48.05% and 54.69% respectively. The reason for this change is that the charcoal, bamboo biochar, and humus in the amendments can reduce the bioavailability of rare earth elements in the soil by increasing soil pH, while increasing the organic matter content in the soil. Furthermore, biochar and humus have multiple functional groups and a large specific surface area, which can adsorb rare earth elements in the soil. Their negative charge can also adsorb cations in the soil, reducing the absorption of rare earth elements by navel orange roots, thereby reducing the total amount of rare earth elements in the fruit. At the same time, they enhance soil aggregate fixation and plant competition for absorption, synergistically reducing the accumulation of rare earth elements by roots and their transport to the fruit.

[0087] Table 10 Rare earth element content in navel orange pulp with different treatments (dry weight)

[0088]

[0089] Note: ——refers to the detection limit not being reached

[0090] The quality of navel oranges from the different treatments is shown in Table 11. The results show that compared to the CK, the vitamin C content of the T1 and T2 navel oranges increased, by 11.06% and 19.21%, respectively. The titratable acidity of the T1 and T2 treatments was slightly higher than that of the CK by 0.6 and 0.1 units, respectively. Both the longitudinal and transverse diameters of the T1 and T2 treatments were higher than those of the CK, while the fruit shape index and edible rate of the T1 and T2 treatments were similar to those of the CK. Furthermore, the soluble solids content of the T1 and T2 treatments increased significantly, by 16.32% and 16.02%, respectively, compared to the CK. This indicates that the use of the amendment to improve rare earth tailings in navel orange cultivation can significantly increase the vitamin C and soluble solids content, enhance the sweetness, and significantly improve the quality of navel oranges.

[0091] Table 11 Effects of different treatments on navel orange fruit quality

[0092]

[0093] In this embodiment, the ionic rare earth mines in southern Jiangxi have undergone long-term mining activities, and the ecological and environmental problems caused by the heap leaching process have become increasingly prominent, and treatment is urgently needed. This study takes the abandoned rare earth mining area in Yangmei Village, Dingnan County as the research object, collects surface soil samples for laboratory testing, and studies the key limiting factors for soil ecological restoration in the mining area. Based on the diagnostic results, the study uses bio-bamboo charcoal, charcoal and humus as soil improvement materials to construct a navel orange economic forest restoration system. The research results show that:

[0094] (1) Amendments improve the physical structure of the soil, reduce soil bulk density, and increase soil field water holding capacity.

[0095] (2) The chemical pH value increased significantly and the soil nutrients increased significantly.

[0096] (3) Compared with the control, the amendment significantly reduced the total amount of available rare earth elements (EDTA extractable) in the soil. Compared with the CK, the T1 and T2 treatments decreased by 41.15% and 40.23%, respectively, which was a significant effect. At the same time, the amendment significantly reduced the total amount of rare earth elements in navel orange pulp. Compared with the CK, the total amount of rare earth elements in the T1 and T2 navel orange fruits decreased by 42.83% and 48.31%, respectively.

[0097] (4) Compared with the control, the modifier further improved the quality of navel oranges by increasing the vitamin C content and soluble solids content in the navel orange pulp. Compared with CK, the vitamin C content of treatments T1 and T2 increased by 11.06% and 19.21%, respectively, and the soluble solids content increased by 16.32% and 16.02%, respectively.

[0098] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiment based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A method for safely planting navel oranges in rare earth tailings based on zeta potential, characterized in that: The steps include: Step 1: digging planting pits in the soil of the rare earth tailings with a row spacing and a column spacing of 1 to 2 meters, a radius of 60 to 80 cm, and a depth of 50 to 70 cm; Step 2: taking the soil dug out from the planting pit and mixing it with an amendment in a mass ratio of 1:0.02 to 1:0.03 to form planting soil, wherein the amendment includes 10 to 20 parts by weight of biochar and 75 to 85 parts by weight of humus, and adjusting the pH value of the planting soil to neutral, the pH value of the planting soil is the optimal condition for plant survival, and the zeta potential of the biochar and the humus is negative; Step 3, placing 2-3 year old navel orange seedlings with nutrient trays in the planting pit; Step 4: backfill the planting soil with adjusted pH value into the planting pit, and cover the roots of the navel orange seedlings with 3 to 6 cm of soil.

2. The method for safely planting navel oranges in rare earth tailings according to claim 1, wherein: The pH value of the planting soil is 6 to 8, and the Zeta potential of the biochar and the humus is between -20 and -35 mV.

3. The method for safely planting navel oranges in rare earth tailings according to claim 1, wherein: The biochar is charcoal or bamboo charcoal.

4. The method for safely planting navel oranges in rare earth tailings according to claim 1, wherein: The improver also includes 5 to 8 parts by weight of calcium magnesium phosphate fertilizer.

5. The method for safely planting navel oranges in rare earth tailings according to claim 1, characterized in that: The type of the navel orange seedlings is Newhall navel orange, and the average seedling height of the navel orange seedlings is 80 to 90 cm.

6. The method for safely planting navel oranges in rare earth tailings according to claim 1, characterized in that: The organic matter content of the planting soil is more than 3%.

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