A method for maintaining stable low phosphorus concentration in hydroponic solution and its application

Abstract

The present invention provides a method for maintaining a stable low phosphorus concentration in a hydroponic solution and its application, and the present invention belongs to the technical field of nutrient solution formulation. The present invention provides a method for maintaining a stable low phosphorus concentration in a hydroponic solution, wherein a granular phosphorus rock mineral (medium-grained structure, particle size 1-5 mm) is placed in a tea bag and put into a hydroponic nutrient solution, and the mass volume ratio of the granular phosphorus rock mineral to the hydroponic nutrient solution is 0.5-1.5 g:1 L. The present invention uses a granular phosphorus rock mineral wrapped in a tea bag and places it in a hydroponic nutrient solution, which can provide a continuous and stable low phosphorus concentration for plants cultured in a weakly acidic hydroponic solution within one hydroponic solution replacement cycle, that is, within at least 7 days.

Description

Technical Field

[0001] The present 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. While total phosphorus is quite abundant in most soil types, a significant portion is bound to various soil components, forming complexes with limited bioavailability. This results in phosphorus concentrations in the soil solution falling to 0.1–10 μM, 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, the phosphorus concentration will rapidly drop to near zero or the critical concentration for phosphorus absorption (CLmin). 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 unrestricted. 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 in real soil conditions.

[0004] In theory, 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 that may be produced during the cultivation process of the above method is close to the lower limit (CLmin<0.2μM) and 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 present invention provides a method for maintaining a stable low phosphorus concentration in a hydroponic solution. Granular phosphorus rock mineral is placed in a tea bag and added to a hydroponic nutrient solution. The mass volume ratio of the granular phosphorus rock mineral to the hydroponic nutrient solution is 0.5-1.5g:1L.

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

[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 the following concentrations: Ca(NO3)2·4H2O 2000-3000μM, KCl 800-1200μM, K2SO4800-1200μM, MgSO4·7H2O700-800μM, H3BO320-40μM, MnSO4·H2O2-3μM, 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 culture 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 tea bag-wrapped phosphorus rock 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 during one replacement cycle (7 days) for the 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 phosphorus rock 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 with reference to the embodiments, but they should not be construed as limiting the scope of protection 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 artificial climate chamber parameters were as follows: photoperiod from 6:00 am to 6:00 pm, temperature of 30 ± 3°C, night temperature of 25 ± 3°C, humidity of 60%, and light intensity of 400 μmol·m –2 ·s –1 . Transfer to half-strength Hoagland complete nutrient solution (the 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 diameter of 20 mm and a 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 per 1L hydroponic solution, which 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 purified 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 nutrient solution change (7 days after the start of treatment), the pH of the hydroponic solution was measured daily using a pH meter and the phosphorus concentration of the nutrient solution was measured. The plants were harvested 29 days after the start of treatment. The dry weight of the aboveground and underground parts was measured and recorded, and the phosphorus concentration in the plants was determined using the molybdate-vanadate method. The results were plotted. Figure 1 That is, the changes in phosphorus concentration (μM) in the nutrient solution under treatments of 500μM (high phosphorus), 2μM (traditional low phosphorus method) and tea bag phosphorus rock method were conducted 7-20 days after the start of treatment. The plant growth indicators were measured and the low phosphorus maintenance effect and plant growth status of the new method were analyzed.

[0023] like Figure 1As shown, in the high-phosphorus treatment (P500), the phosphorus concentration in the nutrient solution decreased from an initial 500 μM to a final concentration of approximately 200 μM over 7 days due to plant uptake. This concentration still ensures maximum plant uptake. The decrease in phosphorus concentration in the high-phosphorus treatment reflects the plant's demand for phosphorus. In the traditional low-phosphorus 2 μM treatment, the phosphorus concentration in the solution remained close to zero. Because solution samples were taken 1 hour after the nutrient solution was changed, this indicates that the plants absorbed all the phosphorus within the first hour after the solution change and received no phosphorus supply for the next 7 days until the next solution change. The rapid decrease in solution phosphorus concentration in the high-phosphorus treatment indicates that even an initial concentration higher than 2 μM cannot solve this problem.

[0024] Many previous studies on plant root responses to phosphorus deficiency have been conducted under extreme conditions, similar to traditional low-P methods. These conditions involve prolonged periods of deprivation of P-deficient plants, leading to a rapid on-off cycle of P supply. During the first and second rehydration cycles, the P concentration in the RP-treated solution remained within the range of 0.2-0.4 μM and 0.1-0.2 μM, respectively, indicating that P concentrations were not constant. The slightly elevated P concentration on the first day of the nutrient solution change may be due to the high concentration of soluble P compounds in the phosphate rock powder. To avoid this, tea bags were rinsed for one to two days before use. Another possible explanation is the decreased plant uptake rate under low P supply conditions. The lower P concentration in the second rehydration cycle than in the first may be due to an increased P demand as the plant grows, leading to an increased P uptake rate. Furthermore, changes in P concentration are influenced by the solution pH, which decreases from 6.2 to 5.6 due to plant activity. In summary, the RP-treated group has established a stable low-P state, characterized by phosphate rock dissolution and plant uptake.

[0025] Table 1 Dry weight and phosphorus content of aboveground and underground rice plants under high phosphorus (500 μM), tea bag phosphorus rock 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 can withstand 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 phosphorus sufficiency threshold (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] To determine the conditions for the tea bag phosphorite method, 5g of CaCO₃ was added to each tea bag containing phosphorite. The addition of CaCO₃ increased the pH of the solution to 7.5. However, the addition of CaCO₃ resulted in phosphorus levels in the solution falling below the detection limit. When rice plants were transferred to this solution, plant growth virtually ceased and the plants began to die (Table 2). This experiment demonstrates that the pH of the solution affects the steady-state phosphorus concentration in the method described herein.

[0031] Table 2 Dry weight and phosphorus content of aboveground and underground rice parts after CaCO3 addition 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 principles of the present invention. These improvements and modifications should also be regarded as within 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: Put the granular phosphorus rock mineral into a tea bag and put it into the hydroponic nutrient solution. The mass volume ratio of the granular phosphorus rock mineral to the hydroponic nutrient solution is 0.5-1.5g:1L. The tea bag is a disposable filter bag made of cotton or non-woven fabric with a length of 6-9 cm and a width of 4-8 cm. The granular phosphorite mineral has a medium-grained structure and a particle diameter of 1-5 mm.

2. The method according to claim 1, characterized in that The tea bag containing the granular phosphorite mineral is washed with water for 24-48 hours before use.

3. The method according to claim 2, characterized in that The hydroponic nutrient solution is a full-strength Hoagland nutrient solution lacking phosphorus, and is composed of the following components in the following concentrations: 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-EDDHA45-55μM.

4. The method according to claim 3, characterized in that The pH value of the solution during the hydroponic culture process is 5.6-6.

5.

5. Application of the method according to any one of claims 1 to 4 in plant nutrition research requiring control of low phosphorus concentrations.

6. The use according to claim 5, characterized in that The plant is rice.

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