Method for maintaining stable low-phosphorus concentration in hydroponic solution and application thereof

Abstract

The invention provides a method for maintaining stable low-phosphorus concentration in a water culture solution and application of the method, and belongs to the technical field of nutrient solution formulas. According to the method for maintaining the stable low phosphorus concentration in the hydroponic solution, granular phosphorite minerals (with a medium grain structure and the grain size of 1-5 mm) are placed in a tea bag and put into a hydroponic nutrient solution, and the mass-volume ratio of the granular phosphorite minerals to the hydroponic nutrient solution is (0.5-1.5) g: 1 L. According to the method, the granular phosphorite minerals wrapped by the tea bags are placed in the hydroponic nutrient solution, and continuous and stable low-phosphorus concentration can be provided for cultivation of plants in the weakly acidic hydroponic solution in one hydroponic solution replacement period, namely within at least 7 days.

Description

Technical Field

[0001] The invention relates to the technical field of nutrient solution formulation, and in particular to a method for maintaining a stable low phosphorus concentration in a hydroponic solution and an application thereof. Background Art

[0002] The low mobility of phosphorus in soil is a major limiting factor for plant growth. In most types of soil, the total amount of phosphorus is quite abundant, but a large part is bound to different soil components, forming a complex with limited bioavailability, resulting in phosphorus concentrations in soil solution falling to 0.1-10 μM, which is insufficient to meet plant needs.

[0003] For hydroponic experiments that require controlled low phosphorus concentrations, the main disadvantage of traditional methods is the lack of buffering capacity for phosphorus nutrients in the solution. As plants grow and absorb nutrients, phosphorus concentrations drop rapidly to near zero or the critical concentration for phosphorus absorption (CLmin), and this rhythm of change causes a sharp on-off switch in phosphorus supply. However, in phosphorus-deficient soils, plants are usually faced with very low but stable phosphorus concentrations, and the total amount of phosphorus in the soil is often not limited. Low phosphorus stress under natural conditions refers to a reduced absorption rate at stable and low concentrations. Plants may show different physiological responses to these different phosphorus deficiency conditions, so the results obtained in hydroponic experiments cannot well restore the low phosphorus concentrations of real soil conditions.

[0004] Theoretically, this problem can be solved by frequently changing the nutrient solution or automatically adding a small amount of corresponding nutrients through computer control. However, these methods will cause plant stress and are laborious and time-consuming on the one hand, and require accurate prior knowledge of plant growth rate and nutrient absorption rate on the other hand. In particular, the lowest concentration of phosphorus (CLmin<0.2μM) that may be produced during the cultivation process of the above method is difficult to detect. In response to the problem of lack of nutrient buffering capacity of the solution in traditional hydroponic experiments, the present invention proposes a simple method to better simulate the phosphorus concentration in the soil by using stable and low-concentration phosphorus rock (granules) in the nutrient solution. Summary of the invention

[0005] The object of the present invention is to provide a simple method for maintaining a stable low phosphorus concentration in a hydroponic solution.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The invention provides a method for maintaining a stable low phosphorus concentration in a hydroponic solution. Granular phosphorus rock minerals are placed in a tea bag and put into a hydroponic nutrient solution. The mass volume ratio of the granular phosphorus rock minerals to the hydroponic nutrient solution is 0.5-1.5 g:1 L.

[0008] Preferably, the tea bag is a cotton or non-woven disposable filter bag with a length of 6-9 cm and a width of 4-8 cm.

[0009] Preferably, the phosphorite is a granular phosphorite mineral with a medium-grained structure (particle size 1-5 mm).

[0010] Preferably, the tea bag containing the granular phosphorite mineral is washed with water for 24-48 hours before use.

[0011] Preferably, the hydroponic nutrient solution is a full-strength Hoagland nutrient solution lacking phosphorus, and is composed of the following components in concentration: Ca(NO3)2·4H2O 2000-3000μM, KCl 800-1200μM, K2SO4 800-1200μM, MgSO4·7H2O 700-800μM, H3BO3 20-40μM, MnSO4·H2O 2-3μM, ZnSO4·7H2O 0.8-1.2μM, CuSO4·5H2O 0.8-1.2μM, (NH4)6Mo7O 24 ·4H2O 0.2-0.4μM, Fe-EDDHA45-55μM.

[0012] Preferably, the pH value of the solution during the hydroponic process is 5.6-6.5.

[0013] The invention also provides application of the method in plant nutrition research requiring control of low phosphorus concentration.

[0014] Preferably, the plant is rice.

[0015] The present invention uses phosphorus rock wrapped in tea bags and placed in a hydroponic nutrient solution, which can provide a continuous and stable low phosphorus concentration for plants cultured in a weakly acidic hydroponic solution for at least 7 days. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The phosphorus concentration changes in the nutrient solution within one replacement cycle (7 days) for different low-phosphorus control methods in Example 1;

[0017] Figure 2 These are photos of rice growing in nutrient solutions at day 29 (harvest) after the start of treatment with 500 μM high phosphorus (right), tea bag phosphorite method (middle) and 2 μM traditional low phosphorus method (left) in Example 1. DETAILED DESCRIPTION

[0018] The technical solutions provided by the present invention are described in detail below in conjunction with the embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0019] Example 1

[0020] The method of the present invention is used to cultivate rice seedlings, and compared with other existing methods:

[0021] Rice seeds were germinated in 96-well black hydroponic boxes (500 mL per box) with a pore size of 5 mm and cultured in an artificial climate chamber. The parameters of the artificial climate chamber were as follows: light duration 6:00 am-18:00 pm, temperature 30 ± 3 °C, night temperature 25 ± 3 °C, humidity 60%, light intensity 400 μmol·m –2 ·s –1 . Transfer to half-strength Hoagland complete nutrient solution (concentration is 50% of the concentration of each component of Hoagland complete nutrient solution) 4 days after germination. After another 7 days of cultivation, select seedlings with uniform growth and transplant them into a 6-hole plant hydroponic box with a pore size of 20 mm and complete nutrient solution (12 seedlings per pot). Nutrient solution composition (μM): Ca(NO3)2·4H2O (2500), KCl (1000), K2SO4 (1000), MgSO4·7H2O (750), H3BO3 (30), MnSO4·H2O (2.5), ZnSO4·7H2O (1), CuSO4·5H2O (1), (NH4)6Mo7O 24 ·4H2O (0.3), Fe-EDDHA (50). After transplanting into a 6-well plant hydroponic box, three phosphorus treatments were performed: (i) high phosphorus - 500μM P (NaH2PO4·2H2O) as a sufficient control; (ii) traditional low-phosphorus method - 2μM P (NaH2PO4·2H2O); (iii) tea bag phosphate rock method RP (Rock Phosphorus) - add 1g of phosphate rock to each 1L hydroponic solution, that is, the method of the present invention. The phosphate rock powder was stored in a tea bag (8cm long × 6cm wide) to avoid direct contact and adhesion to the rice roots. Before use, the filled tea bag was washed with pure water for 1 day to remove soluble impurities. Each tea bag was placed in a plant hydroponic box for cultivation. The solution was changed every 7 days. Each treatment was repeated 6 times.

[0022] After the first change of the nutrient solution (7 days after the start of the treatment), the pH value of the hydroponic solution was measured every day using a pH meter and the phosphorus concentration of the nutrient solution was measured. The plants were harvested 29 days after the start of the treatment. The dry weight of the aboveground and underground parts was measured and recorded, and the phosphorus concentration in the plants was determined by the molybdate-vanadate method. The results were plotted Figure 1 That is, the changes in phosphorus concentration (μM) in the nutrient solution under the treatments of 500μM (high phosphorus), 2μM (traditional low phosphorus method) and tea bag phosphorus rock method were measured 7-20 days after the start of treatment, and the plant growth indicators were measured to analyze the low-phosphorus maintenance effect and plant growth status of the new method.

[0023] like Figure 1As shown in the figure, in the high phosphorus treatment (P500), due to plant absorption, the phosphorus concentration in the nutrient solution dropped from the initial 500 μM to a final concentration of about 200 μM within 7 days, and this concentration can still ensure the maximum uptake rate of the plant. The decrease in phosphorus concentration in the high phosphorus treatment reflects the plant's demand for phosphorus. The phosphorus concentration of the solution treated with the traditional low phosphorus 2 μM method is always close to zero. Because the solution samples were sampled 1 hour after the nutrient solution was replaced, it shows that the plants have absorbed all the phosphorus within the first hour after the solution was replaced, and there is no phosphorus supply in the next 7 days until the next solution change. It can be seen from the rapid decrease in the solution phosphorus concentration in the high phosphorus treatment that even an initial concentration higher than 2 μM cannot solve this problem.

[0024] Many previous studies on the response of plant roots to phosphorus deficiency were conducted under extreme conditions similar to the traditional low-phosphorus method, that is, phosphorus-deficient plants were deprived of any phosphorus supply for a long time, resulting in a sharp opening and closing of phosphorus supply. In the first and second liquid replacement cycles, the phosphorus concentration of the RP-treated solution remained in the range of 0.2-0.4μM and 0.1-0.2μM, respectively, and the phosphorus concentration was not constant. The slightly higher phosphorus concentration on the first day of changing the nutrient solution may be due to the fact that the phosphorus rock powder contains more soluble phosphorus compounds. Therefore, in order to avoid this, the tea bags were washed for 1-2 days before use. Another reason may be that the plant absorption rate decreases under low phosphorus supply conditions. The phosphorus concentration in the second liquid replacement cycle was lower than that in the first cycle, which may be due to the increase in phosphorus absorption rate as the plant grows and the increase in phosphorus supply demand. In addition, the change in phosphorus concentration is affected by the pH of the solution. Due to plant activity, the solution pH dropped from 6.2 to 5.6. In summary, the RP treatment group has formed a stable low-phosphorus state of phosphate rock dissolution-plant absorption.

[0025] Table 1 Dry weight and phosphorus content of aboveground and underground rice parts under high phosphorus (500 μM), tea bag phosphorite method (RP) and traditional low phosphorus method (2 μM) treatments

[0026]

[0027] Different lowercase letters indicate significant differences among treatments (p<0.05).

[0028] The total phosphorus content in soil is quite high, but the soil solution phosphorus concentration is usually low (0.1-10 μM). The tea bag phosphate rock method (RP) can simulate the almost unlimited phosphorus source in the soil. The phosphorus concentration in the tea bag phosphate rock method solution is low enough to ensure that plants are subjected to low phosphorus stress (Table 1, Figure 1 , Figure 2). When harvested on the 29th day after the start of the phosphorus treatment, rice plants treated with both the tea bag phosphate rock method and the traditional low phosphorus 2μM treatment showed obvious symptoms of phosphorus deficiency. However, the symptoms of phosphorus deficiency were more intense in the traditional low phosphorus 2μM treatment. The aboveground dry weight of rice plants treated with the tea bag phosphate rock method was significantly higher than that treated with the traditional low phosphorus 2μM treatment, but the biomass of both low phosphorus treatments was significantly lower than that of the high phosphorus 500μM treatment. The changes in the underground dry weight of rice also showed a similar trend. The aboveground phosphorus concentration of plants treated with the tea bag phosphate rock method was significantly higher than that treated with the traditional low phosphorus 2μM treatment, but both treatments were below the threshold of phosphorus sufficiency (0.35-1.1%). Although the tea bag phosphate rock method and the traditional low phosphorus treatment had the same phosphorus deficiency level, it was more similar to the situation in the soil.

[0029] Example 2

[0030] In order to determine the conditions for the use of the tea bag phosphorite method, 5g of CaCO3 was added to each tea bag containing phosphorite. The pH value of the solution rose to 7.5 after the addition of CaCO3. However, the phosphorus in the solution dropped below the detection limit after the addition of CaCO3. After the rice plants were transferred to the solution, plant growth almost stopped and the plants began to die (Table 2). This experiment shows that the pH value of the solution will affect the steady-state concentration of phosphorus in the method described in the present claim.

[0031] Table 2 Dry weight and phosphorus content of aboveground and underground rice parts after adding CaCO3 in the tea bag phosphorite method (RP)

[0032]

[0033] Different lowercase letters indicate significant differences among treatments (p<0.05).

[0034] In summary, in the phosphorus deficiency study, the tea bag phosphorus rock method was able to provide a continuous and stable low phosphorus concentration for plants cultured in a weakly acidic hydroponic solution for at least 7 days.

[0035] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for maintaining a stable low phosphorus concentration in a hydroponic solution, characterized in that: The granular phosphorus rock mineral is placed in a tea bag and put into a hydroponic nutrient solution, wherein the mass volume ratio of the granular phosphorus rock mineral to the hydroponic nutrient solution is 0.5-1.5 g:1 L.

2. The method according to claim 1, characterized in that The tea bag is a disposable residue filter bag made of cotton or non-woven fabric and has a specification of 6-9 cm in length and 4-8 cm in width.

3. The method according to claim 1, characterized in that The granular phosphorite mineral has a medium-grained structure and a particle diameter of 1-5 mm.

4. The method according to claim 2, characterized in that: The tea bag containing the granular phosphorite mineral is washed with water for 24-48 hours before use.

5. The method according to claim 4, characterized in that The hydroponic nutrient solution is a full-strength Hoagland nutrient solution lacking phosphorus, and is composed of the following components in concentration: Ca(NO3)2·4H2O 2000-3000 μM, KCl 800-1200 μM, K2SO4 800-1200 μM, MgSO4·7H2O 700-800 μM, H3BO3 20-40 μM, MnSO4·H2O 2-3 μM, ZnSO4·7H2O 0.8-1.2 μM, CuSO4·5H2O 0.8-1.2 μM, (NH4)6Mo7O 24 ·4H2O 0.2-0.4μM, Fe-EDDHA 45-55μM.

6. The method according to claim 5, characterized in that During the hydroponic culture process, the pH value of the solution is 5.6-6.

5.

7. Use of the method described in any one of claims 1 to 6 in plant nutrition research requiring control of low phosphorus concentration.

8. The use according to claim 7, characterized in that The plant is rice.

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