CN117617101A - Method for covering phosphogypsum storage yard with ophiopogon japonicus vegetation - Google Patents

Abstract

The invention discloses a method for covering a phosphogypsum stockyard with Ophiopogon japonicus vegetation. It is characterized in that rice husk is selected as a modifier. According to the ratio of phosphogypsum: rice husk, they are 20:1, 30:1, 40:1, and 50 respectively. :1, 60:1 ratio, get different proportions of mixed substrate, sow Ophiopogon japonicus on it, and manage the rest according to the conventional methods of Ophiopogon japonicus cultivation, and measure its chlorophyll, propylene glycol, total phosphorus indicators, and the survival rate of Ophiopogon japonicus. , the average plant height and root length were significantly greater than the pure phosphogypsum group; among them, the best growth occurred under the ratio of phosphogypsum:rice husk of 30:1. After planting Ophiopogon japonicus, the plant of the present invention improves the pH of the substrate, absorbs a certain amount of total phosphorus in the substrate, and Ophiopogon japonicus has the potential to enrich cadmium.

Description

A method of covering the phosphogypsum stockyard with Ophiopogon japonicus vegetation

Technical field

The invention belongs to the technical field of phosphogypsum improvers, and specifically relates to a method of improving phosphogypsum using rice husks and covering the phosphogypsum stockpile with Ophiopogon japonicus vegetation.

Background technique

Phosphogypsum is one of the by-products released from the production of phosphoric acid. The main component is CaSO ₄ ·2H ₂ O ^[1] , and there is also a certain amount of F ^- , Fe ³⁺ , Al ³⁺ , Cd, Cu, Pb, etc. and undecomposed phosphorus. Mineral powder and acid-insoluble matter, etc. The production of 1 ton of phosphoric acid produces approximately 5 tons of phosphogypsum. Further development of the phosphate industry will add more phosphogypsum. Currently, the main disposal method of phosphogypsum is open-air stacking, where it is blown by wind and wipers into surrounding rivers, farmland, forests and other ecosystems, causing potential pollution risks to the environment.

Although people have conducted a lot of research on the treatment and resource utilization of phosphogypsum, due to the large phosphogypsum production, concentrated production capacity distribution and complex impurity composition in my country, it is difficult to fundamentally solve the problem of excessive phosphogypsum production using several treatment methods. Therefore, many domestic companies still use the stacking and storage method. It is expected that my country's phosphogypsum treatment will still be in a "coexistence of stacking and storage" situation for a long time to come.

How to deal with accumulated phosphogypsum? The use of vegetation restoration technology to treat phosphogypsum stockpiles is a potential solution to this problem. This method plant plants in the phosphogypsum stockyards and cover the stockyards with vegetation to reduce harmful substances in phosphogypsum from entering the surrounding environment and polluting water bodies and Soil, improve the air quality in the stacking area, and the phosphogypsum planted with plants may be used to produce flower substrates or plant other economic crops, realizing the resource utilization of phosphogypsum.

Ophiopogon japonicus is a perennial evergreen herbaceous plant of the Liliaceae family. It has the advantages of cold tolerance, shade tolerance, drought tolerance, barren tolerance, few pests and diseases, and almost no need for pruning. It can be used to build evergreen buildings in green spaces and on both sides of roads in summer. Flower landscapes, when planted in garden green spaces, can significantly reduce maintenance and management costs, improve greening effects, and have promotion value for the success of subsequent plantings. The inventors conducted experiments to explore suitable modifying agents to improve the phosphogypsum matrix and to use suitable plants to repair the phosphogypsum matrix.

Contents of the invention

The object of the present invention is to provide a method for covering a phosphogypsum storage area with Ophiopogon japonicus vegetation. This method first investigates the stress-resistant plants growing in the phosphogypsum storage area and collects phosphogypsum samples, and then consults the data to select plants growing in the phosphogypsum storage area. Ophiopogon japonicus, the same plant in the phosphogypsum dump site, was cultivated and planted in modified phosphogypsum. Through experiments, the growth of Ophiopogon japonicus was observed, and the effect of the amendment modified phosphogypsum on the growth of Ophiopogon japonicus and the different addition ratios of the amendment were explored. To influence the growth of Ophiopogon japonicus, find the appropriate proportion of added amendments for growing Ophiopogon japonicus on phosphogypsum.

The purpose of the present invention and solving its main technical problems are achieved by adopting the following technical solutions:

A method of covering the phosphogypsum stockyard with Ophiopogon japonicus vegetation. Rice husk is selected as the amendment agent. According to the ratio of phosphogypsum: rice husk is 20:1, 30:1, 40:1, 50:1 and 60:1 respectively. Ratio, obtain a mixed substrate with different proportions, sow Ophiopogon japonicus on it, and manage the rest according to the conventional methods of Ophiopogon japonicus cultivation, and measure its chlorophyll, propylene glycol, and total phosphorus indicators, as well as the survival rate, average plant height, and root length of Ophiopogon japonicus. Significantly greater than the pure phosphogypsum group.

Furthermore, adding rice husk to pure phosphogypsum is beneficial to growing Ophiopogon japonicus. Among them, the best growth occurs when the ratio of phosphogypsum: rice husk is 30:1. After planting Ophiopogon japonicus, the pH of the substrate is improved, and the pH of the substrate is improved. A certain amount of total phosphorus in the matrix is absorbed.

Description of drawings

Figure 1 is a technical roadmap of the present invention.

Figure 2 is a standard curve for phosphorus concentration.

Figure 3 is the standard curve of cadmium concentration.

Detailed ways

Specific implementations, features and effects of the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments.

A method of covering the phosphogypsum stockyard with Ophiopogon japonicus vegetation. Rice husk is selected as the amendment agent. According to the ratio of phosphogypsum: rice husk is 20:1, 30:1, 40:1, 50:1 and 60:1 respectively. Ratio, obtain a mixed substrate with different proportions, sow Ophiopogon japonicus on it, and manage the rest according to the conventional methods of Ophiopogon japonicus cultivation, and measure its chlorophyll, propylene glycol, and total phosphorus indicators, as well as the survival rate, average plant height, and root length of Ophiopogon japonicus. Significantly greater than the pure phosphogypsum group. Among them, the best growth occurred when the ratio of phosphogypsum: rice husk was 30:1. Planting Ophiopogon japonicus improved the pH of the substrate and absorbed a certain amount of total phosphorus in the substrate.

The present invention is obtained through the following experiments:

This experiment plans to use phosphogypsum in the stockyard as the main cultivation substrate to grow Ophiopogon japonicus. The cultivation test will be completed after 60 days of cultivation and various indicators will be tested. The specific process can be roughly divided into the following aspects.

1. Technical route, see Figure 1.

1. Preliminary experiment:

Select a variety of plants (artemisia annua, mint, white radish, ryegrass, tall wool, Ophiopogon japonicus) and plant them on phosphogypsum. By observing their growth conditions, you can find out which plants are suitable for growing on phosphogypsum. Based on this, proceed to the next formal experiment.

2. Formal trial of Ophiopogon japonicus cultivation:

Effects of adding different proportions of rice husk on the growth of Ophiopogon japonicus.

A planting experiment was conducted on Ophiopogon japonicus at the greenhouse base of Guiyang University. Different proportions of rice husk were added to phosphogypsum to improve phosphogypsum for planting. The nutrient soil purchased from the market was used as the control group. Each group had three pots. Each pot was sown with 100 Ophiopogon japonicus and managed according to conventional methods. Each pot was watered at 6pm every day. The seed germination and seedling growth were observed and photographed every day. Record the number of germinated seeds every 5 days, and record the germination rate on the 30th day. It is expected that the cultivation test will be completed after 60 days of cultivation and various indicators will be tested. The specific planting plan is as follows:

Table 2.1. Rice husk addition ratio and sowing number of each group

3. Materials and methods

3.1 Materials and sources used in the study

The phosphogypsum used in this experiment came from Guizhou Xiyang Fertilizer Co., Ltd., the flower pots and nutrient soil were purchased from the Flower and Bird Market on Youzha Street, Nanming District, Guiyang City, the improver and experimental seeds: Ophiopogon japonicus were purchased online, among which, rice husk The particle size is 5mm.

3.2 Instruments and equipment used in research

Table 3.1 Experimental instruments and equipment

3.3 Reagents used in research

Table 3.2 Experimental reagents

3.4 Experimental methods

This experiment sets different ratios, and each ratio is run in 6 parallels. The ratios of phosphogypsum and modifier are all mass ratios. When the words "mixed XX" appear in the text, it is the abbreviation of the mixed matrix of phosphogypsum and modifier. The data of each experimental result are analyzed graphically.

3.4.1 Select plants suitable for planting on phosphogypsum

The study selected a variety of plants (artemisia annua, mint, white radish, ryegrass, tall wool, Ophiopogon japonicus) to be planted on phosphogypsum. The germination rate, survival rate, etc. of the planted plants were recorded to find out whether they were suitable for growing on phosphogypsum. plants, and use this as a basis for the next formal experiment.

Post-planting maintenance: Manage according to conventional methods of crop cultivation. Check the growth of Ophiopogon japonicus at 6 p.m. every day. Water appropriately depending on the moisture content of the substrate. Observe the seed germination and seedling growth. Record the number of germinated seeds every 5 days.

3.4.2 Study on the growth of Ophiopogon japonicus on phosphogypsum substrates with different amendments added

Add five kinds of amendments such as rice husk, rapeseed powder, fine white sand, corn dry powder, and fly ash in different proportions to phosphogypsum to plant Ophiopogon japonicus. The daily maintenance during the planting process is the same as 3.4.1. Observe the growth of Ophiopogon japonicus. , select the amendment with the best growth of Ophiopogon japonicus for the next experiment.

3.4.3 Effects of different proportions of amendments on the growth of Ophiopogon japonicus

A planting experiment was carried out on Ophiopogon japonicus in the greenhouse base of Guiyang University. Different proportions were added to phosphogypsum (the mixing ratios of phosphogypsum and improver were 20:1, 30:1, 40:1, 50:1, and 60:1 respectively. Planted) rice husk, modified phosphogypsum for planting. Use nutrient soil purchased from the market as the control group. Each group has three pots. Each pot is sown with 100 grains of Ophiopogon japonicus and managed according to conventional methods. Each flower pot is watered at 6pm every day. The daily maintenance during the planting process is the same as 3.4.1, and daily observation is carried out. Seed germination and seedling growth were recorded with photos. The number of germinated seeds was recorded every 5 days, and the germination rate was recorded on the 30th day. It was expected that the cultivation test would be completed after 60 days of cultivation and various indicators would be tested. Based on the germination rate and survival rate of Ophiopogon japonicus, the best mixing ratio suitable for the growth of Ophiopogon japonicus was determined.

Harvest of Ophiopogon japonicus and sample storage: Harvest after 60 days of cultivation, uproot the Ophiopogon japonicus and wash the roots, and then measure chlorophyll, malondialdehyde, root length and plant height immediately. The remaining samples are dried with a vacuum freeze dryer and stored in a dry place to facilitate the subsequent measurement of corresponding indicators. Use a small shovel to scrape off the surface matrix in the flowerpot, take the middle layer sample, put it in a sampling bag, and store it in a 4°C refrigerator for later measurement of corresponding indicators.

3.4.4 Main indicator detection methods

3.4.4.1 Plant height and root length of Ophiopogon japonicus

Use a tape measure to measure the plant height and root length of Ophiopogon japonicus.

3.4.4.2 Measuring biomass

At the end of the cultivation test, cut the plants close to the soil surface, collect all the plants in the pots, dry them at 105°C to constant weight and then weigh them (accurate to 0.0001g). Plants in each pot are measured individually.

3.4.4.3 Germination rate of Ophiopogon japonicus

Germination rate (%) = (number of seeds emerging/number of seeds sown) × 100%

3.4.4.4 Plant survival rate

Survival rate (%) = (number of surviving plants on a certain day/total number of seedlings emerging on that day) × 100%

3.4.4.5 Determination of cadmium in Ophiopogon japonicus

Cd (cadmium) determination: TAS-990F flame atomic absorption spectrophotometry

1. Preparation of test solution:

Weigh about 0.5000g soil sample into 25mL polytetrafluoroethylene base, moisten it with a little water, add 10mL hydrochloric acid, heat and dissolve at low temperature on an electric hot plate for 2 hours, then add 15mL nitric acid and continue heating until about 5rmL of dissolved material remains When adding 5ml of hydrofluoric acid and heating to decompose silica and colloidal silicate, finally add 5ml of perchloric acid (HCIO,) and heat to evaporate to almost dryness, add 1ml of (1+5) nitric acid, and heat to dissolve the residue , add 0.25g of lanthanum nitrate [La(NO ₃ ) ₃ ·6H,O] to dissolve and adjust the volume to 25mL, and make a reagent blank for the entire procedure.

2. Drawing of calibration curve:

Take the mixed standard operating solution 0, 0.2, 0.80, 1.60, 3.20.6.40ml and put it into six 25ml volumetric flasks respectively. Add 0.25g La(NO,), ·6H, O to each. After dissolving, use 0.2% Dilute nitric acid to volume. The standard solution contains lead 0, 1.60, 6.40, 12.80, 25.60, 51.20 μg/L, and cadmium 0, 0.16, 0.64, 1.28, 2.56, 5.12 μg/L: measure the absorbance of each standard solution according to the working conditions of the instrument.

3. Sample measurement

4. Calibration curve method:

Measure the absorbance of the test solution according to the conditions for drawing the calibration curve, subtract the absorbance of the reagent blank, and check the lead and cadmium content from the calibration curve.

5.Standard addition method:

Divide 5.0 mL of the sample solution into four 10 mL volumetric flasks, add mixed standard operating solution 0, 0.50, 1.00, 1.50 mL respectively, dilute to 10 mL with 0.2% nitric acid, and use the curve extrapolation method to obtain the sample Contents of lead and cadmium.

6. Result calculation:

The content of lead and cadmium is calculated according to formula (1)

Lead/cadmium (mg/g)=c·V/m(1)

In the formula: c is the content of cadmium and lead found from the calibration curve, μg/L;

V is the constant volume of the sample, mL;

m is the mass of the weighed sample, g.

3.4.4.6. Determination of chlorophyll, chlorophyll a, chlorophyll b and carotene content

Spectrophotometry (GB/T22182-2008) ^[23]

The main steps are as follows:

(1) Take fresh Ophiopogon japonicus leaves, wash, dry and cut into pieces.

(2) Weigh 3 samples of chopped Ophiopogon japonicus leaves, each 0.2g, place them repeatedly into pre-cooled mortars, add 3 to 4 mL of 95% ethanol to each, grind quickly into a homogenate, and let stand for 3 to 5 minutes. The entire process takes place in the dark.

(3) Take a piece of filter paper, place it in a funnel, moisten it with ethanol, pour the extraction solution into the funnel along the glass rod, filter it into a 25mL volumetric flask, rinse the bowl body with a small amount of ethanol, pour all of it into the funnel, and pour the liquid on the filter paper into the funnel. Wash all the pigment into the volumetric flask, and finally adjust the volume to 25ml.

(4) Pour the chloroplast pigment extract into a cuvette with a light path of 1cm, use 95% ethanol as the blank, and measure the absorbance at wavelengths of 470nm, 649nm, and 665nm.

(5) Calculation

When using 95% ethanol as the extraction agent, the wavelengths of the maximum absorption peaks of chlorophyll a, chlorophyll b, and carotene are 665nm, 649nm, and 470nm respectively, so the concentration of each pigment obtained by 95% ethanol extraction is

The formula is as follows:

Ca＝13.95A665-6.88A649

(3.1)

Cb=24.96A649-7.32A665

(3.2)

Ct＝Ca+Cb＝18.08A649+6.63A665

(3.3)

C x·c＝(1000A470-2.05Ca-114.8C _b )/245 (3.4)

Chlorophyll a content (mg·g ^-1 )=Ca*Vt*n/FW (3.5)

Chlorophyll b content (mg·g ^-1 )=Cb*Vt*n/FW (3.6)

Carotenoid content (mg·g ^-1 )=Cx·c*Vt*n/FW (3.7)

According to formulas (3.1), (3.2), (3.3), and (3.4), use the above wavelengths to calculate the concentrations of chlorophyll a, chlorophyll b, and carotenoids Ca, Cb, and C x·c. The units are mg·L ^-1 ; and then calculate the content of each pigment (mg·g ^-1 ) according to formulas (3.5), (3.6), and (3.7).

In the formula: Ca is the concentration of chlorophyll a (mg·L ^-1 );

Cb is the concentration of chlorophyll b (mg·L ^-1 );

Ct is total chlorophyll (mg·L ^-1 );

C x·c is the concentration of carotenoids (mg·L ^-1 );

FW is fresh weight (g);

Vt is the total volume of the extraction solution (mL);;

n is the dilution ratio;

3.4.4.7 Determination of malondialdehyde content of Ophiopogon japonicus:

thiobarbituric acid method

The main steps are as follows:

(1) Extraction of MDA: Weigh 1g of Ophiopogon japonicus leaves and cut them into pieces, add 2mL of 100g·L ^-1 trichloroacetic acid (TCA) and a small amount of quartz sand, and grind; further add 8mL of TCA and grind thoroughly, and the homogenate is heated at 4000r· Centrifuge for 100 min at min ^-1 , and the supernatant is the sample extraction solution.

(2) Color development reaction and measurement: Take 2 mL of the extraction solution, add 2 mL of 6 g·L ^-1 TBA solution, mix evenly, react on a boiling water bath for 15 min, cool quickly and then centrifuge. Take the supernatant and measure the absorbance at wavelengths of 450nm, 532nm and 600nm. For the control, 2 mL of distilled water was used instead of the extraction solution.

(3) Result calculation

C _MDA =6.45(A ₅₃₂ -A ₆₀₀ )-0.56A ₄₅₀ (3.8)

MDA content in the sample (μmol·g ^-1 )=C _MDA (μmol·L ^-1 )*V _t (L)/FW (3.9)

Calculate the concentration of MDA in the sample according to formula (3.8), and calculate the MAD content in the extraction solution according to formula (3.9).

In the formula:

CMDA is the concentration of MDA (μmol·L ^-1 );

A450, A532, and A600 represent the absorbance at wavelengths of 450nm, 532nm, and 600nm (non-specific absorption) respectively.

V _t is the volume of extraction liquid

FW is the fresh weight of plant tissue (g)

3.4.4.8 Determination of matrix TP

Alkali fusion - molybdenum antimony spectrophotometry (GB11893-1989)

The main steps are as follows:

(1) Preparation of samples

Weigh 0.25g of the sample at the bottom of the nickel crucible, moisten the sample with absolute ethanol, then add 2g of sodium hydroxide to cover the sample, cover the crucible lid, and put the crucible into a muffle furnace to heat up. When it is about 400°C, Keep it for 15 minutes, then when the temperature rises to about 640°C, keep it for 15 minutes and take it out to cool. Then add 10ml of water to the crucible and heat it to 80°C. After the frit in the crucible is dissolved, transfer it all to a 50ml centrifuge cup. Wash the crucible three times with 10ml of sulfuric acid solution, and then wash it with an appropriate amount of water three times. Transfer all the washing liquid to 50ml. In the centrifuge cup, use a centrifuge to separate for 10 minutes at a speed of 2500-3500r/min. After letting it stand, transfer all the supernatant to a 100ml volumetric flask, dilute to volume with water, and wait for measurement.

(2) Drawing of calibration curve

Measure 0, 0.5, 1, 2, 4, and 5 mL of phosphorus standard working solutions into six 50 mL colorimetric tubes with stoppers, and add water to the mark. The phosphorus contents in the standard series are 0, 2.50, 5.00, 10.00, and 20.00 respectively. ,25.00μg. Add 2-3 drops of 2,4-dinitrophenol to the colorimetric tube respectively, then adjust the pH value to about 4.4 with sulfuric acid solution and sodium hydroxide solution to make the solution look slightly yellow, then add 1.0ml of ascorbic acid solution. Mix well. After 30 seconds, add 2.0 mL of molybdate solution, mix thoroughly, and place at 20-30°C for 15 minutes. Use a 30mm cuvette to measure the absorbance at a wavelength of 700nm, using water as a reference. Draw a calibration curve with the reagent blank-corrected absorbance as the ordinate and the corresponding phosphorus content as the abscissa.

(3) Determination

Measure 10.0 mL of sample into a 50 mL stoppered colorimetric tube, and add water to the mark. Then follow the same steps as drawing the calibration curve for color development and measurement.

(4) Blank test

Without adding a soil sample, follow the same steps as the preparation and measurement of the sample for color development and measurement.

(5) Result calculation

ω＝[(AA ₀ )-a]xV ₁ /bxmxW _dm xV ₂ (3.10)

In the formula:

ω is the total phosphorus content in the soil, mg/kg

A is the absorbance value of the sample;

A ₀ is the absorbance value of the blank test;

a is the interception of the calibration curve;

V ₁ is the constant volume of the sample, ml;

b is the slope of the calibration curve;

m is the sample size, g;

V ₂ is the sample volume, ml;

W _dm is the dry matter content of the soil, %;

3.4.4.8 Measurement of water holding capacity before and after substrate planting

The main steps are as follows:

(1) Pass the air-dried phosphogypsum matrix through a 1mm sieve;

(2) Weigh the weight of the plastic cup W ₁ ; place 50.0 of the air-dried phosphogypsum matrix sample into the plastic cup (with holes evenly punched in the bottom of the cup) and weigh W ₂ . (Three parallel samples were made for each)

(3) Use 6 burettes to drip water evenly into the cup at the same time.

(4) When water seeps out from the bottom of the cup, stop adding water and weigh W ₃ ; when water no longer seeps from the bottom of the cup, calculate the moisture content of the sample = (W ₃ -W ₂ )/50×100%.

3.4.5 Data processing

The charts and data analysis in this experiment were mainly processed with SPSS and Excel2016. The germination rate, survival rate, fresh weight and other data should be kept to two decimal places, and the data of TP, malondialdehyde, chlorophyll and other data should be kept to two decimal places. Data are average values.

4. Results and analysis

4.1 Growth of Ophiopogon japonicus on pure phosphogypsum and nutrient soil

Table 4.1 Growth conditions of Ophiopogon japonicus on substrate

It can be seen from Table 4.1 that Ophiopogon japonicus can grow normally on nutrient soil and has high germination and survival rates. However, under the same growth conditions, although the germination rate of Ophiopogon japonicus is high when planted with pure phosphogypsum, its survival rate is very low after planting for a period of time. Low, so in order to successfully grow Ophiopogon japonicus on pure phosphogypsum, pure phosphogypsum needs to be improved. The experiment started in November, and it is suitable for planting Ophiopogon japonicus. However, during the experiment, in the pots planted with Ophiopogon japonicus using pure phosphogypsum, the leaves of the plants appeared yellow and withered, and there were no signs of insects crawling on the plants. Among them, the pots with serial numbers ② and ③ Mold appears on the phosphogypsum substrate and there are signs of decay. The germination rate and survival rate of Ophiopogon japonicus on nutrient soil are very high, the growth condition is good, and there are no abnormalities in plant growth during the entire planting process. Through reviewing relevant data and analysis, it was found that Ophiopogon japonicus cannot grow normally on phosphogypsum due to its own characteristics such as insufficient porosity that prevents air from entering and weak water-holding properties. Therefore, the porosity and water-holding capacity of phosphogypsum are increased by adding the modifier: rice husk, and are improved through different proportions of modifiers.

4.2 Growth results and analysis of Ophiopogon japonicus on phosphogypsum matrix mixed with different amendments

Table 4.2 Various growth indicators of Ophiopogon japonicus at different mixing ratios (%)

It can be seen from the difference statistics in Table 4.2 that Ophiopogon japonicus began to emerge 8 to 9 days after planting under various proportions of substrates. The plant height was 34 to 36cm, the root length was between 16 and 17cm, and the germination rate was as high as 100%. , there is a difference in survival rates. Among them, ① the mixing ratio of 30:1 (phosphogypsum: rice husk) has the highest survival rate. ②With a mixing ratio of 30:1 (phosphogypsum:rice husk), the root length of the plant will be higher and the root length of the plant will be longer than that of other ratios. ③ In the mixing ratios of 40:1, 50:1, and 60:1 (phosphogypsum: rice husk), the fresh weight is less than that of 20:1 and 30:1. ④The mixing ratio of 30:1 (phosphogypsum:rice husk) also has the largest biomass. Therefore, based on various growth indicators, a mixing ratio of 30:1 (phosphogypsum:rice husk) is most suitable for the growth of Ophiopogon japonicus.

4.3 Results and analysis of malondialdehyde (MDA) content in mixed matrices with different proportions

Table 4.3 Content of malondialdehyde (MDA) in mixed matrix at different proportions (μmol·g-1)

Malondialdehyde (MDA) is produced due to peroxidation of lipids in tissue or organ membranes due to aging of plant organs or damage under adverse conditions. Propylene glycol content is closely related to plant aging and stress damage. Using Waller-Dunce statistical analysis, it can be seen from Table 4.3 that the content of propylene glycol is different under each mixing ratio. Among them, the MDA content of Ophiopogon japonicus grown in a mixed matrix of 30:1 (phosphogypsum: rice husk) was the lowest. It can be seen that the antioxidant capacity of Ophiopogon japonicus grown under the mixed matrix 30:1 (phosphogypsum:rice husk) is higher than that of the other four ratios.

4.4 Results and analysis of pH changes before and after planting with mixed matrix in different proportions

Table 4.4 pH before and after planting of mixed matrix with different proportions

Soil pH is an important chemical property that affects the interaction between nutrients in soil and crops. Using Waller-Dunce statistical analysis, it can be seen from Table 4.4: ① The pH of adding rice husk substrate at different mixing ratios before and after planting did not change much, but it increased. ②The pH of pure phosphogypsum is 4.31. After adding mixed matrix, the pH increases in every ratio. To a certain extent, it makes Ophiopogon japonicus plants grow better. 4.5 Results and analysis of chlorophyll, chlorophyll a, chlorophyll b and carotenoids content in Ophiopogon japonicus

Table 4.5 Chlorophyll content of Ophiopogon japonicus (mg/g)

Chlorophyll content is the material basis that affects photosynthesis. Within a certain range, there is a positive correlation between chlorophyll content and photosynthesis. The higher the chlorophyll content, the stronger the photosynthesis; but when the chlorophyll content exceeds a certain limit, it has no effect on photosynthesis. Its function is to strengthen roots and add green, lay a good material foundation for yield, and delay leaf aging. Using Waller-Dunce statistical analysis, it can be seen from Tables 4.6 to 4.9 that the chlorophyll indicators are different under each mixing ratio. Among them, the total chlorophyll, chlorophyll b, and carotenoid content under the mixing ratio of 30:1 (phosphogypsum: rice husk) The content is significantly different from other mixing ratio groups, and is higher than that of other mixing ratio groups. It can be seen that the photosynthesis of Ophiopogon japonicus under the mixing ratio of 30:1 (phosphogypsum:rice husk) is stronger than that of the other four groups, which is more conducive to the growth of Ophiopogon japonicus.

4.6 Results and analysis of changes in total phosphorus (TP) content of phosphogypsum with different mixing ratios before and after planting (see Figure 2 for the standard curve of phosphorus concentration)

4.6 TP content (mg/kg) of phosphogypsum with different mixing ratios before planting

Phosphorus is one of the three essential elements for plants. It plays a very important and indispensable role in cell membrane structure, enzyme activity regulation, material metabolism, and signal transduction. Phosphorus plays an important role in photosynthesis and respiration of plants. The dry matter production of plants treated with low phosphorus will be reduced. Using WallerDunce statistical analysis, it can be seen from Table 4.6: ① The TP content decreased after planting in the mixed matrix ② The change in total phosphorus was the largest under the mixing ratio of 30:1 (phosphogypsum: rice husk), and the differences before and after planting were greater than the other four groups. It can be seen that Ophiopogon japonicus is best planted in a mixed substrate of 30:1 (phosphogypsum:rice husk).

4.7 Results and analysis of water holding capacity of phosphogypsum with different mixing ratios

Table 4.7 Water holding capacity (%) of phosphogypsum with different mixing ratios

The water holding capacity of pure phosphogypsum is 30.2%. Using Waller-Dunce statistical analysis, it can be seen from Table 4.7 that there is a significant difference in water holding capacity between the improved mixed matrix and pure phosphogypsum groups, and the water holding capacity of the matrix increased significantly after being improved by the modifier. Among them, the water holding rate of the mixed matrix at 30:1 (phosphogypsum: rice husk) is the highest, and the improvement effect is the most obvious. It can be seen that in rice husk-improved Ophiopogon japonicus, the optimal ratio is 30:1 (phosphogypsum:rice husk).

4.8 Results and analysis of cadmium in Ophiopogon japonicus (see Figure 3 for the standard curve of cadmium concentration)

Table 4.8 Cadmium content in Ophiopogon japonicus (mg/kg)

As shown in Table 4.8, it can be seen that: ① The cadmium content in all planted Ophiopogon japonicus does not exceed the limit value of 0.1mg/kg for cadmium in the "National Food Safety Standard Limits of Contaminants in Food" (GB2762-2017). ②After mixing different proportions of phosphogypsum and rice husk, the cadmium content in Ophiopogon japonicus increased as the amount of phosphogypsum added increased. ③ The cadmium content in Ophiopogon japonicus is the highest when grown in the mixed matrix at 60:1 (phosphogypsum: rice husk), but the mixed matrix at 20:1 (phosphogypsum: rice husk) and 30:1 (phosphogypsum: rice husk) Cadmium could not be detected. It can be seen that Ophiopogon japonicus has the potential to repair cadmium enrichment and is a plant with potential cadmium enrichment ability. This characteristic of Ophiopogon japonicus can be used to repair cadmium enriched soil.

[Results] The germination rate of Ophiopogon japonicus on pure phosphogypsum is as high as 99%, but the survival rate is very low, only 7%. The average plant height and root length are 32.33cm and 15.67cm respectively, while the groups mixed with a certain proportion of rice husk , the survival rate, average plant height, and root length of Ophiopogon japonicus were significantly greater than those of the pure phosphogypsum group. Comparing the groups added with rice husk, Ophiopogon japonicus grew best in the 30:1 (phosphogypsum:rice husk) experimental group, and its survival rate, plant height, root length, fresh weight, and total chlorophyll content were 99% and 99%, respectively. 35.50cm, 16.33cm, 55.17g, 0.82mg·g ^-1 , which were significantly higher than those of other groups. The water holding rate (63.5%) of the matrix of this group was also significantly higher than that of other groups; the pH of the matrix of each group before planting was the same. It was significantly lower than after planting, and the TP content of each group of substrates after planting was significantly lower than before planting. The malondialdehyde content, total phosphorus content in the substrate before planting, and total phosphorus content in the substrate after planting were: 4.96 μmol·g ^-1 , 896.17.84 mg/kg, and 550.00 mg/kg respectively. [Conclusion] Adding a certain proportion of rice husk to pure phosphogypsum is beneficial to growing Ophiopogon japonicus. Among them, the best growth occurs at the ratio of 30:1 (phosphogypsum: rice husk). Planting Ophiopogon japonicus will improve the pH of the substrate. , and all absorbed a certain amount of total phosphorus in the matrix.

Claims (3)

1. A method for covering a phosphogypsum storage yard with ophiopogon japonicus vegetation is characterized by comprising the following steps: selecting rice hulls as an improver, and respectively obtaining mixed matrixes with different proportions according to the proportions of phosphogypsum to rice hulls of 20:1, 30:1, 40:1,50:1 and 60:1, sowing ophiopogon japonicus on the mixed matrixes, and measuring various indexes of chlorophyll, propylene glycol and total phosphorus of the ophiopogon japonicus according to the conventional ophiopogon japonicus cultivation method, wherein the survival rate, average plant height and root length of the ophiopogon japonicus are obviously larger than those of a pure phosphogypsum group, so that a phosphogypsum storage yard is covered by ophiopogon japonicus vegetation; the phosphogypsum is a oversize product with the particle size of 100 meshes.

2. A method of covering an phosphogypsum yard with ophiopogon japonicus vegetation as claimed in claim 1, wherein: the addition of rice hulls to pure phosphogypsum is beneficial to planting ophiopogon japonicus, wherein the growth is best under the condition that the ratio of phosphogypsum to rice hulls is 30:1.

3. A method of covering an phosphogypsum yard with ophiopogon japonicus vegetation as claimed in claim 2, wherein: repairing phosphogypsum matrix with radix Ophiopogonis, improving pH of matrix after planting radix Ophiopogonis, and absorbing a certain amount of total phosphorus in matrix; and the ophiopogon japonicus has the capability of covering the phosphogypsum storage yard by vegetation, so that the phosphogypsum storage yard and the surrounding environment are improved.