Saline-alkali soil multi-stage circulation agricultural system and method based on saline-alkali water multi-stage resource utilization

Abstract

The invention belongs to the technical field of saline-alkali soil comprehensive treatment and circular agriculture, and particularly relates to a saline-alkali soil multi-stage circular agriculture system and method based on saline-alkali water multi-stage resource utilization. And efficient cyclic utilization of natural resources in saline-alkali areas is realized. The method mainly comprises the following steps: detecting saline-alkali water in a saline-alkali area, extracting the saline-alkali water for seawater-like regulation to obtain regulated saline-alkali water, desalting the regulated saline-alkali water through a reverse osmosis system to obtain fresh water and seawater-like water which are respectively used for crop planting and aquatic product culture, and recycling culture tail water after solid-liquid separation. By the adoption of the system and method, fresh water does not need to be supplied externally, the system is formed by itself, the win-win effect of ecological benefits, social benefits and economic benefits is achieved, green and sustainable development is achieved, and the system and method have universal popularization value for comprehensive development and utilization of saline-alkali soil.

Description

Technical Field

[0001] The present invention relates to the technical field of comprehensive management of saline-alkali land and circular agriculture, and in particular to a saline-alkali land multi-stage circular agriculture system and method based on multi-stage resource utilization of saline-alkali water. Background Art

[0002] Saline-alkali land is where excessive saline-alkali components accumulate in the surface layer of the soil due to the influence of natural and human factors, resulting in a continuous increase in the saline-alkali concentration and osmotic pressure of the surface soil, causing a "physiological drought" phenomenon in which crops have difficulty absorbing water, thus affecting the growth of agricultural crops.

[0003] The existing saline-alkali land management uses physical measures, chemical measures, biological measures and a combination of the above three measures to reduce the salinity and alkali content in the soil, thereby converting saline-alkali land into arable land.

[0004] Physical engineering improvement methods include open ditch drainage, vertical shaft drainage, and concealed pipe drainage. Open ditch drainage results in high evaporation and occupies surface area, reducing effective arable land. Concealed pipe drainage is expensive to lay, prone to clogging, and requires high maintenance. Vertical shaft drainage merely transfers salinity from underground to the surface, which then seeps back into the groundwater through the surface, causing secondary salinization. Alternatively, the salinity of underground water can be discharged into rivers, increasing the salinity of downstream soils and even turning them into saline-alkali land.

[0005] Agronomic improvement method: refers to the use of agronomic measures such as soil application, straw interlayer, and sand spreading in saline-alkali land, especially in saline-alkali land in areas with strong evaporation, to create a loose isolation layer in the soil, cut off soil capillaries, reduce the upward migration of water and salt, break up soil compaction, reduce the salinization degree of the soil surface, and improve soil structure. However, this method is only intended for the current season and has a short time effect. It fails to solve the problem at the root cause of groundwater level. The effect of saline-alkali land improvement varies depending on different natural conditions.

[0006] Chemical amendment methods primarily rely on the principle of ion exchange, replacing ions in the soil with those of the amendment. Once the soil's physical and chemical properties reach their ideal state, water is used to rinse it to remove the saline and alkaline components. Chemical amendments offer the advantages of rapid results, flexible formulations, a wide range of materials, and targeted effectiveness. However, their effects are limited, short-lived, and costly. They can also easily cause secondary contamination of saline-alkali land, and leaching requires significant amounts of water.

[0007] Bioremediation: By planting new salt- and alkali-tolerant varieties or microorganisms that can directly utilize saline-alkali soil, they can remove some of the salt from the root system or alter the diversity of the soil microbial community, thereby improving soil quality and achieving ecological balance and long-term stability in saline-alkali soil. Essentially, this involves selecting salt- and alkali-tolerant varieties suitable for saline-alkali soil and planting them appropriately. In the short term, it will be difficult to grow staple crops such as rice, wheat, soybeans, and corn on moderately and severely saline-alkali soil.

[0008] Comprehensive improvement method: The current view is that engineering improvement methods are mostly used for the improvement of medium and heavy saline-alkali land, biological and chemical improvement methods are mostly used for the improvement of light and moderate saline-alkali land, and agronomic improvement methods are particularly effective in areas with large evaporation. None of the above measures can completely control saline-alkali land when used alone, so the comprehensive use of various improvement measures is gradually gaining attention. For example, the "terraced field-shallow pond" type comprehensive land use model suitable for coastal areas is a combination of engineering improvement measures such as digging soil to form ponds and building soil to form terraces, as well as biological improvement measures such as terraced field planting and shallow pond aquaculture. This method of raising the land and digging ponds to lower the groundwater level is suitable for areas with heavy rainfall or external freshwater replenishment, but is not suitable for areas with high evaporation, low precipitation, and no external freshwater replenishment. In other words, the suitability of saline-alkali land improvement methods needs to be evaluated based on local hydrological conditions.

[0009] Furthermore, because many saline-alkali land improvements primarily rely on freshwater flooding to wash away salt, water-soluble salts migrate with the water from high to low areas, accumulating in low-lying areas. This creates a significant amount of newly generated saline-alkali water. Low-lying saline-alkali soils are prone to waterlogging, high salt content, and surface crusting, making water infiltration difficult and seriously hindering crop growth.

[0010] In summary, resources such as saline-alkali land and surface saline-alkali water collected by drainage channels are not being effectively utilized. Given the limitations of the aforementioned methods for effectively utilizing saline-alkali land and saline-alkali water, there is an urgent need for a novel saline-alkali land and / or saline-alkali water recycling agricultural system and method to achieve efficient utilization of natural resources in saline-alkali areas and improve the comprehensive production capacity of saline-alkali land / water, fisheries, and agriculture. Summary of the Invention

[0011] The purpose of the present invention is to provide a saline-alkali land multi-stage circular agriculture system and method based on the multi-stage resource utilization of saline-alkali water. The entire system is self-contained and does not require external fresh water supply. Based on the multi-stage resource utilization of saline-alkali water, a saline-alkali land multi-stage circular agriculture system with good economic benefits is formed, achieving a win-win situation in ecological benefits, social benefits, and economic benefits, realizing green and sustainable development, and having universal promotion value for the comprehensive development and utilization of saline-alkali land.

[0012] To achieve the above-mentioned object, the present invention provides a saline-alkali land multi-stage circulation agriculture method based on multi-stage resource utilization of saline-alkali water, comprising the following steps:

[0013] Step S1, after testing saline-alkali water in saline-alkali areas, extracting saline-alkali water and regulating it to be seawater-like, that is, adjusting the ion composition and ratio of the saline-alkali water according to the water demand for aquaculture to obtain regulated saline-alkali water;

[0014] Step S2, desalinating the regulated saline water through a primary reverse osmosis system to obtain fresh water and seawater-like water;

[0015] Quasi-seawater is the associated concentrated saline-alkali water produced after the regulated saline-alkali water is desalinated. It refers to saline-alkali water with a main ion composition and content similar to that of seawater of the same salinity, and can be used for aquaculture of aquatic products.

[0016] Step S3: the obtained fresh water is used for planting and freshwater aquaculture, and the obtained seawater-like water is used for aquaculture;

[0017] Step S4: After the aquatic products are caught, the aquaculture tail water is subjected to solid-liquid separation, and the residue obtained by filtration is used as fertilizer for crop planting. The filtered tail water is discharged into an external pond or recycled for aquaculture.

[0018] Preferably, before carrying out seawater-like regulation, terraced land reclamation is carried out in saline-alkali areas.

[0019] Preferably, the distance between the surface soil and the groundwater level after terraced field construction is 2.5 to 5 m, which can block the formation of soil capillaries and avoid repeated salinization.

[0020] Preferably, in step S1, the outer ponds generated after terraced fields are reclaimed are used as ponds / greenhouses for aquatic product farming, reservoirs for storing water or for storing aquaculture tail water.

[0021] Preferably, in step S1, the saline-alkali water is regulated by the seawater-like regulation method to obtain regulated saline-alkali water, including the following two situations:

[0022] Case 1: When the calcium hardness of the extracted saline water is greater than that of the water used for aquaculture, the calcium ion concentration that needs to be removed is calculated based on the original calcium ion concentration of the saline water and the calcium ion, potassium ion, and magnesium ion concentrations in the water to be used for aquaculture after adjustment. Then, the calcium ions are removed and potassium and magnesium ions are added.

[0023] The method to remove calcium ion concentration is to add potassium oxalate or sodium oxalate to the water to precipitate calcium ions;

[0024] Case 2: When the calcium hardness of the extracted saline water is lower than that of the water used for aquaculture, calcium ions, potassium ions and magnesium ions are added to the saline water according to the adjusted concentrations of calcium ions, potassium ions and magnesium ions in the water to be used for aquaculture.

[0025] Preferably, in step S2, the yield of fresh water obtained by the reverse osmosis system is 45-50%.

[0026] Preferably, in step S2, the salinity of the water for aquaculture obtained by the reverse osmosis system is not higher than 35‰.

[0027] Preferably, in step S3, when the amount of seawater-like water meets the needs of aquaculture, the remaining saline-alkali water is directly desalinated without being regulated by seawater-like water, and the generated concentrated saline-alkali water is directly recharged to the bottom of the saline-alkali water layer.

[0028] The present invention also provides a system for realizing the above-mentioned saline-alkali land multi-stage circular agriculture method based on multi-stage resource utilization of saline-alkali water, and a seawater-like regulation module for regulating saline-alkali water to saline-alkali water with an ion composition and content similar to or consistent with that of aquaculture water and seawater of the same salinity;

[0029] The saline-alkali water desalination module is used to desalinate the regulated saline-alkali water through a reverse osmosis system to obtain fresh water and seawater-like water at the same time;

[0030] Planting module, equipped with sub-film drip irrigation system;

[0031] Aquaculture module, used for aquaculture of aquatic products;

[0032] Terraced field module, used to increase the distance between the surface soil and the groundwater level, while obtaining external ponds and / or reservoirs;

[0033] The photovoltaic power generation module is used to supply power to the seawater control module, saline-alkali water desalination module, planting module, and aquaculture module.

[0034] Therefore, the present invention adopts the above-mentioned saline-alkali land multi-stage circular agriculture system and method based on multi-stage resource utilization of saline-alkali water, and the beneficial technical effects are as follows:

[0035] (1) Terraced land reclamation achieves multiple goals at once. On the one hand, by raising the ground surface to control the relative height between the surface layer and the groundwater level, the problem of land salinization can be solved from the root, avoiding repeated salinization. On the other hand, the earthwork supply area can provide a place for aquatic product breeding, without the need to dig ponds separately. Thirdly, the dug ponds can also be used as reservoirs to store water. When a large amount of fresh water is generated, the fresh water can be collected in the freshwater reservoir, which can be used as a reserve for subsequent applications.

[0036] (2) By using seawater-like control technology, the calculated calcium salt remover or the required ions in the water are added in advance, thereby regulating the concentration of calcium ions in the water, and ultimately accurately adjusting the water hardness. It can also avoid the problem of reverse osmosis system fouling caused by the precipitation of high concentrations of calcium salts in the water during the desalination of saline water;

[0037] (3) The fresh water yield of the reverse osmosis system can be 45% to 50%, avoiding the fouling of the reverse osmosis membrane due to salt precipitation, and converting the regulated saline water into seawater. This is different from the fresh water yield of 65% to 85% in industrial wastewater desalination. The water body of the method used in the present invention does not suffer from the fouling of the reverse osmosis membrane due to saturated precipitation of salts. In addition, the traditional reverse osmosis system for desalination of saline water / seawater often requires a secondary reverse osmosis system (i.e., the first reverse osmosis water is subjected to reverse osmosis treatment again) to obtain high-purity fresh water. Similarly, in order to improve the total fresh water yield, it is necessary to utilize the reverse osmosis concentrated water reflux process and perform a secondary reverse osmosis treatment on the concentrated saline water to obtain fresh water and saline water with a higher concentration. Therefore, the method used in the present invention has low cost and few requirements or restrictions on equipment.

[0038] (4) Multi-level resource utilization of saline-alkali water: ① The regulated saline-alkali water obtained after seawater-like regulation can be directly used for aquaculture, converting idle saline-alkali water resources into aquaculture water, generating economic benefits. ② The regulated saline-alkali water obtained after seawater-like regulation is desalinated using a reverse osmosis system, and the obtained fresh water is used for crop planting or used for crop planting after freshwater aquaculture. ③ The regulated saline-alkali water is treated by a reverse osmosis system to obtain seawater-like water for high-value aquaculture, which has good economic benefits (compared with traditional planting, the per-acre output value of seawater-like aquaculture seafood can be increased by more than 100 times), making the entire circular agriculture sustainable. ④ Aquaculture uses factory-scale recirculating aquaculture, using far less water than concentrated saline water. Once the amount of seawater meets aquaculture needs, the remaining saline water undergoes desalination without seawater regulation. The resulting concentrated saline water is then directly recharged to the bottom of the saline water layer, preventing contamination of the existing saline water (concentrated saline water is simply concentrated saline water and has the same composition as the original saline water). Furthermore, this recharge stabilizes groundwater and surface water levels, preventing geological disasters such as ground collapse caused by excessive extraction of underground saline water. ⑤ The resulting seawater is used for aquaculture. Conventional solid-liquid separation techniques are used to remove organic matter such as feces and leftover bait from the aquaculture water, which can be used as fertilizer for crops. The filtered aquaculture tailwater, saline water, can be recycled for aquaculture or discharged into external ponds. The original saline water level is stabilized by balancing surface evaporation, saline water recharge, external pond evaporation, and external pond groundwater replenishment.

[0039] (5) The desalination of saline-alkali water consumes a lot of energy, and the cost of preparing fresh water is high. When used for open-air planting of crops, the planting income is often lower than the cost, and the economic benefit is in a loss-making state. This is the key factor that the idea of ​​using saline-alkali water for planting after desalination has not been promoted. Secondly, the discharge of concentrated saline-alkali water associated with saline-alkali water desalination will cause environmental pollution. The above two objective disadvantages hinder the promotion and application of a single saline-alkali water desalination technology in saline-alkali areas. Directly using saline-alkali water for aquaculture, on the one hand, is affected by the large deviation between the main ions of saline-alkali water and seawater, and saline-alkali water is not suitable for direct use in aquaculture of high-value seafood and aquatic products. On the other hand, saline-alkali water aquaculture and saline-alkali land crop planting cannot be coupled, and saline-alkali land cannot be developed into arable land. The method used in the present invention creatively integrates seawater-like regulation, saline-alkali water desalination, terraced fields, planting, aquaculture, photovoltaics and other modules to form a circular agricultural system with good economic benefits, achieving unexpected results. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is a flow chart of a saline-alkali land multi-stage circular agriculture method based on multi-stage resource utilization of saline-alkali water according to the present invention;

[0041] Figure 2 The present invention is a structural schematic diagram of a saline-alkali land multi-stage circulation agricultural system based on multi-stage resource utilization of saline-alkali water. DETAILED DESCRIPTION

[0042] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0043] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0044] Example 1

[0045] like Figure 1 FIG. 1 is a flow chart of a circular agricultural method based on saline-alkali water desalination according to the present invention, which specifically includes the following steps:

[0046] Step S1: Terraced fields.

[0047] Specifically, when the evaporation in the saline-alkali land area is not large, consider digging ponds in terraced fields and lowering the groundwater level through vertical drainage. When the evaporation is large, only terraced fields should be considered, and open-air aquaculture ponds should not be considered. Increasing the distance between the surface soil and the groundwater level can effectively block the formation of soil capillaries and avoid soil salinization. It is best to control the distance between the surface soil and the groundwater level at 2.5 to 5 meters.

[0048] Earthwork can be supplied by digging ponds, which can be carried out locally, thus avoiding or reducing transportation costs. The earthwork generated by digging ponds can be used for terraced fields, and the excavated foundations or pond entrances can be used as factory aquaculture bases, reservoirs, or external ponds for storing aquaculture tailwater.

[0049] The terraced land creation method of this invention achieves multiple goals at once. First, by widening and regulating the distance between the surface and groundwater levels, it addresses the root cause of land salinization. Second, it provides a flat surface for aquaculture. Third, the excavated ponds can be used to construct freshwater reservoirs for storing freshwater. When excess freshwater is generated by desalination of saline-alkali water, it can be discharged into the reservoirs for storage, preparing for subsequent freshwater applications.

[0050] The groundwater level is controlled by vertical well drainage. If the groundwater level is too high, saline water is extracted and a reverse osmosis system (step S3 below) is used to produce more fresh water, thereby accelerating the transformation of saline-alkali land.

[0051] Step S2: seawater-like regulation.

[0052] Before seawater-like regulation is performed, the saline water is first tested, and the test indicators are mainly the main ions in the saline water. The saline water in the present invention can be surface saline water or underground saline water.

[0053] The present invention regulates saline-alkali water and detects its salinity in order to determine suitable aquaculture species based on the actual salinity of the saline-alkali water. According to actual testing results, field tests conducted in a certain area of ​​Xinjiang showed that the salinity of saline-alkali water generally ranges from 3‰ to 18‰.

[0054] The purpose of detecting the ion situation in saline-alkali water is to adjust the ion composition and proportion of saline-alkali water according to the ion situation, and then compare it with seawater of the same salinity based on the existing ion situation to supplement or remove ions.

[0055] Specifically, seawater-like regulation includes the following two situations:

[0056] 1) When the calcium hardness of the extracted saline water is greater than that of the water used for aquaculture, the calcium ion concentration that needs to be removed and the potassium ion and magnesium ion added are calculated based on the original calcium ion concentration in the water and the calcium ion, potassium ion and magnesium ion concentrations in the water to be used for aquaculture after adjustment;

[0057] The method to remove calcium ion concentration is to add potassium oxalate or sodium oxalate to the water to precipitate calcium ions;

[0058] 2) When the calcium hardness of the extracted saline water is lower than that of the water used for aquaculture, the concentrations of calcium ions, magnesium ions and potassium ions that need to be added are calculated based on the concentrations of calcium ions, magnesium ions and potassium ions in the water to be used for aquaculture after adjustment.

[0059] After the above-mentioned control steps, seawater-like properties are obtained, which have an ion profile similar to that of seawater with the same salinity. In addition, the hardness of the water body is adjusted, which reduces the precipitation of calcium salts during subsequent reverse osmosis membrane desalination, thereby preventing the occurrence of reverse osmosis membrane fouling.

[0060] Some specific control examples are given below.

[0061] 1) Oxalate precipitation of calcium ions in high-hardness saline-alkali water

[0062] 1. Prepare oxalic acid, sodium oxalate, and potassium oxalate solutions separately: (1) Dissolve 19.80 g of H2C2O4 in 900 ml of water, dilute to 1000 ml, and mix thoroughly to obtain an oxalic acid solution with a concentration of 19.80 g / L (220 mmol / L). (2) Dissolve 29.48 g of Na2C2O4 in 900 ml of water, dilute to 1000 ml, and mix thoroughly to obtain a sodium oxalate solution with a concentration of 29.48 g / L (220 mmol / L). (3) Dissolve 22.10 g of K2C2O4·H2O in 900 ml of water, dilute to 1000 ml, and mix thoroughly to obtain a potassium oxalate solution with a concentration of 120 mmol / L.

[0063] 2. The salinity of underground saline water in a certain area B is about 9‰, and the Na + , K + , Ca 2+ Mg 2+ 、Cl - 、SO4 2- The ion concentrations are 2277.0mg / L, 43.6mg / L, 441.2mg / L, 212.6mg / L, 2963.8mg / L, and 2211.6mg / L, respectively. + , K + , Ca 2+ Mg 2+ 、Cl - 、SO4 2- The ion concentrations are 2771.5mg / L, 99.5mg / L, 108.3mg / L, 332.5mg / L, 4990.0mg / L, and 696.8mg / L, respectively. It can be seen that, in terms of the four main cations, compared with seawater of the same salinity, the 9‰ saline-alkali water lacks K. + Mg 2+ ions, and Ca 2+However, it is 4 times that of seawater with the same salinity, and the ion composition and proportion are very different from those of seawater. In order to use saline water to realize seawater aquaculture, it is necessary to regulate the saline water into seawater-like water.

[0064] 3. Take three 2L beakers and add 1000mL of underground saline water from a certain area B to each beaker. Then add 10mL of oxalic acid, sodium oxalate and potassium oxalate solution to the saline water. It was found that sodium oxalate and potassium oxalate groups immediately produced white suspended matter as the solution was added. After mixing, white suspended matter was present in the entire water body. After standing overnight, white precipitates were found to accumulate at the bottom of the tube, and the water body changed from white turbidity to transparent. After inductively coupled plasma mass spectrometry (ICP-MS) detection, it was found that oxalate treatment could precipitate an equimolar amount of Ca 2+ Ions: After treatment with sodium oxalate, Ca 2+ ions decreased by nearly 88.0 mg / L (2.2 mmol / L), Mg 2+ and K + The ion concentration remains unchanged; after potassium oxalate treatment, the Ca 2+ ions decreased by nearly 48.0 mg / L (1.2 mmol / L), Mg 2+ The ion concentration remains constant, while K + The ion concentration increased by nearly 93.6 mg / L (2.4 mmol / L). This shows that sodium oxalate can accurately reduce the calcium hardness in saline-alkali water without affecting the magnesium hardness; potassium oxalate can not only accurately reduce the calcium hardness in saline-alkali water without affecting the magnesium hardness, but also accurately increase K + The situation of the oxalic acid group is completely different. With the addition of oxalic acid solution, no white suspended matter appears in the saline water. Even if the amount of oxalic acid is increased by 10 times, no white suspended matter will form. This shows that oxalates (sodium oxalate and potassium oxalate) can accurately precipitate Ca in water. 2+ ions, but oxalic acid does not have this function.

[0065] 2) Potassium oxalate and sodium oxalate solutions regulate calcium hardness and potassium ion concentration in high-hardness saline-alkali water

[0066] 1. Prepare sodium oxalate and potassium oxalate solutions: (1) Dissolve 30.55 g of Na2C2O4 in 900 mL of water, then dilute to 1000 mL, and mix thoroughly to obtain a sodium oxalate solution with a concentration of 30.55 g / L (228 mmol / L). (2) Dissolve 53.05 g of K2C2O4·H2O in 900 mL of water, then dilute to 1000 mL, and mix thoroughly to obtain a potassium oxalate solution with a concentration of 288 mmol / L. (3) Take 334 mL of the sodium oxalate solution prepared above, add 25 mL of the potassium oxalate solution prepared above, and mix thoroughly to obtain a potassium oxalate / sodium oxalate mixed solution.

[0067] 2. Take three 2L beakers and add 1000mL of underground saline-alkali water from a certain area B to each beaker, numbering them #1, #2, and #3. First add 2.5mL of potassium oxalate solution to sample #1. It was found that with the addition of the solution, white suspended matter immediately appeared in the water body. After mixing, white suspended matter existed in the entire water body. Then add 33.4mL of sodium oxalate solution, and it was found that more white precipitates were generated in the saline-alkali water. After standing overnight or filtering the precipitation, saline-alkali water with reduced calcium and increased potassium was obtained. First add 33.4mL of sodium oxalate solution to sample #2. It was found that with the addition of the solution, a large amount of white suspended matter immediately appeared in the water body. After mixing, white suspended matter existed in the entire water body. Then add 2.5mL of potassium oxalate solution, and white precipitates continued to form in the saline-alkali water. After standing overnight or filtering the precipitation, saline-alkali water with reduced calcium and increased potassium was obtained. 35.9 mL of potassium oxalate / sodium oxalate mixed solution was added to #3. As the solution was added, a large amount of white suspended matter immediately appeared in the water. After mixing, the solution was allowed to stand overnight or filtered to precipitate to obtain saline water with reduced calcium and increased potassium. After inductively coupled plasma mass spectrometry (ICP-MS) detection, it was found that the Na content of the saline water with reduced calcium and increased potassium obtained after treatment with #1, #2, and #3 was 2.34 mmol / l. + , K + , Ca 2+ Mg 2+ The ion concentrations are 2536.2 mg / L, 96.3 mg / L, 104.1 mg / L, and 205.2 mg / L. This indicates that the potassium oxalate solution and the sodium oxalate solution are used to treat saline-alkali water in sequence or at the same time, which does not affect the final result of water quality regulation, and both can accurately reduce the Ca 2+ Ion concentration, precise increase of K + ion concentration, without affecting Mg 2+ Ion concentration. Adding a potassium oxalate / sodium oxalate mixture to saline-alkaline water achieves precise calcium reduction and potassium increase in a single operation, achieving two goals with one stone and simple operation. Furthermore, ion chromatography testing of oxalate ions revealed an oxalate ion concentration of <10 mg / L, less than 1.5% of the original added concentration, indicating sufficient calcium oxalate precipitation and minimal residual oxalate ions.

[0068] 3) Based on K + , Ca 2+ Mg 2+ Method for regulating ion-based saline-alkaline seawater

[0069] 1. Prepare sodium oxalate, potassium oxalate, and magnesium chloride solutions: (1) Dissolve 30.55 g of Na2C2O4 in 900 mL of water, dilute to 1000 mL, and mix thoroughly to obtain a sodium oxalate solution with a concentration of 30.55 g / L (228 mmol / L). (2) Dissolve 53.05 g of K2C2O4·H2O in 900 mL of water, dilute to 1000 mL, and mix thoroughly to obtain a potassium oxalate solution with a concentration of 288 mmol / L. (3) Take 334 mL of the sodium oxalate solution prepared above, add 25 mL of the potassium oxalate solution prepared above, and mix thoroughly to obtain a potassium oxalate / sodium oxalate mixed solution. (4) Dissolve 304.95 g of MgCl2·6H2O in 900 mL of water, dilute to 1000 mL, and mix thoroughly to obtain a magnesium chloride solution with a concentration of 1500 mmol / L.

[0070] 2. Take three 2L beakers and add 1000mL of underground saline-alkali water from a certain area, B, to each beaker. Number them #1, #2, and #3. First, add 2.5mL of potassium oxalate solution to #1. White suspended matter immediately appears in the water as the solution is added. After mixing, the white suspended matter is present throughout the water. Then, add 33.4mL of sodium oxalate solution. More white precipitate forms. After allowing the solution to stand overnight or filtering the precipitate, add 3.5mL of magnesium chloride solution to the clear solution to obtain saline-alkali water with reduced calcium, increased potassium, and increased magnesium. First, add 33.4mL of sodium oxalate solution to #2. A large amount of white suspended matter immediately appears in the water as the solution is added. After mixing, the white suspended matter is present throughout the water. Then, add 2.5mL of potassium oxalate solution. White precipitate continues to form. After allowing the solution to stand overnight or filtering the precipitate, add 3.5mL of magnesium chloride solution to the clear solution to obtain saline-alkali water with reduced calcium, increased potassium, and increased magnesium. 35.9 mL of potassium oxalate / sodium oxalate mixed solution was added to #3. As the solution was added, a large amount of white suspended matter immediately appeared in the water. After mixing, the solution was allowed to stand overnight or filtered for precipitation. Then, 3.5 mL of magnesium chloride solution was added to the clear solution to obtain saline water with reduced calcium, increased potassium and increased magnesium. After inductively coupled plasma mass spectrometry (ICP-MS) detection, it was found that the Na content of the saline water with reduced calcium, increased potassium and increased magnesium obtained after treatment with #1, #2 and #3 was 2.34 mmol / l. + , K + , Ca 2+ Mg 2+ The ion concentrations are approximately 2527.7 mg / L, 96.0 mg / L, 103.7 mg / L, and 325.8 mg / L. + ions, the concentrations of the other three cations are basically consistent with the ion concentration corresponding to 9‰ seawater, achieving the goal of regulating saline water into K + , Ca 2+ Mg 2+ Seawater-like at the ionic level.

[0071] 3. Amplify the system, prepare and utilize the aforementioned K + , Ca 2+ Mg 2+ The ion concentration of the saline-alkali water was adjusted to be consistent with that of the seawater with a salinity of 9‰, and the white shrimp in southern Xinjiang was cultured. Except that the water used for culture was the adjusted saline-alkali water, the rest of the operation was consistent with the "Factory Culture Technology of White Shrimp" (Shi Chaobin, Sun Yanhui. Henan Fisheries, 2023, No. 2: 14-15, 20). The results showed that although the adjusted saline-alkali water Na + The ion concentration is not related to the salinity of 9‰ seawater Na + The ion concentration is exactly the same, and the Na + The ion concentration is 91.5% of that of seawater with the same salinity, but the normal culture of whiteleg shrimp can still be achieved, which shows that the Na + , K + , Ca 2+ Mg 2+ When the plasma concentration is roughly equivalent to that of seawater of the same salinity, successful cultivation of whiteleg shrimp is achieved. This adjusted saline-alkaline water can be used for shrimp farming. After 60 days of breeding and management, the shrimp reached a size of 70-80 per kg, with a yield of 3,000 kg per mu, and a per-mu output value exceeding 180,000 yuan per mu.

[0072] 4. Amplify the system, prepare and utilize the aforementioned K + , Ca 2+ Mg 2+ The ion concentration of the regulated saline water was consistent with that of the seawater with a salinity of 9‰, and the pearl grouper of southern Xinjiang was cultured. Except that the culture water was regulated saline water with a depth of 1.2m and the fry stocking size was 100g, the rest of the operation was consistent with the "Experimental Study on Factory Culture and Breeding Technology of Gentian Grouper" (Tian Lili et al. Fishery Guide to Getting Rich, 2023(11): 50-52). The results showed that the regulated saline water can be used as the culture water for pearl grouper. After 5 months of breeding and management, the size of the pearl grouper reached 500-900g / tail, and the per-mu output value reached 500,000 yuan.

[0073] 4) Based on Na + , K + , Ca 2+ Mg 2+ Method for regulating ion-rich saline-alkaline seawater

[0074] 1. Prepare sodium oxalate, potassium oxalate, magnesium chloride, and sodium chloride solutions: (1) Dissolve 30.55 g of Na2C2O4 in 900 mL of water, dilute to 1000 mL, and mix to obtain a sodium oxalate solution with a concentration of 30.55 g / L (228 mmol / L). (2) Dissolve 53.05 g of K2C2O4·H2O in 900 mL of water, dilute to 1000 mL, and mix to obtain a potassium oxalate solution with a concentration of 288 mmol / L. (3) Take 334 mL of the sodium oxalate solution prepared above, add 25 mL of the potassium oxalate solution prepared above, and mix to obtain a potassium oxalate / sodium oxalate mixed solution. (4) Dissolve 304.95 g of MgCl2·6H2O in 900 mL of water, dilute to 1000 mL, and mix to obtain a magnesium chloride solution with a concentration of 1500 mmol / L. (5) Dissolve 360 ​​g of NaCl in 900 mL of water, then dilute to 1000 mL. Mix thoroughly to obtain a sodium chloride solution with a concentration of 360 g / L (6160 mmol / L). (6) Take 350 mL of the magnesium chloride solution prepared above and add 130 mL of the sodium chloride solution prepared above. Mix thoroughly to obtain a magnesium chloride / sodium chloride mixed solution.

[0075] 2. Take three 2L beakers and add 1000mL of underground saline-alkali water from a certain area B, numbered #1, #2, and #3. Add 35.9mL of potassium oxalate / sodium oxalate mixed solution to sample #1. As the solution is added, a large amount of white suspended matter immediately appears in the water. After mixing, let the solution stand overnight or filter and precipitate. Then add 3.5mL of magnesium chloride solution, mix well, and then add 1.3mL of sodium chloride solution. Mix well to obtain Na + , K + , Ca 2+ Mg 2+ The composition and ratio of the four ions are consistent with those of seawater with the same salinity. 35.9 mL of potassium oxalate / sodium oxalate mixed solution was added to the #2 sample. As the solution was added, a large amount of white suspended matter immediately appeared in the water. After mixing, the solution was allowed to stand overnight or filtered for precipitation. 1.3 mL of sodium chloride solution was added first, mixed, and then 3.5 mL of magnesium chloride solution was added. Mix well to obtain Na + , K + , Ca 2+ Mg 2+ The composition and ratio of the four ions are consistent with those of seawater with the same salinity. 35.9 mL of potassium oxalate / sodium oxalate mixed solution was added to the #3 sample. As the solution was added, a large amount of white suspended matter immediately appeared in the water. After mixing, the solution was allowed to stand overnight or filtered for precipitation. Then 4.8 mL of magnesium chloride / sodium chloride mixed solution was added and mixed to obtain Na + , K + , Ca 2+ Mg2+ The composition and ratio of the four ions are consistent with those of seawater with the same salinity. After inductively coupled plasma mass spectrometry (ICP-MS) detection, it was found that the Na + , K + , Ca 2+ Mg 2+ The ion concentrations are approximately 2701.5 mg / L, 96.0 mg / L, 103.6 mg / L, and 325.4 mg / L. The concentrations of the four cations are basically consistent with the ion concentrations corresponding to 9‰ seawater, achieving the goal of regulating saline water into Na + , K + , Ca 2+ Mg 2+ Seawater-like structure with ion concentrations and ratios consistent with seawater of the same salinity.

[0076] 3. Amplify the system, prepare and utilize the aforementioned Na + , K + , Ca 2+ Mg 2+ The saline-alkali water with the same ion concentration as that of seawater with a salinity of 9‰ was used to culture white shrimp in southern Xinjiang. Except for the regulated saline-alkali water used for aquaculture, the rest of the operations were consistent with the "Factory-scale Culture Technology of White Shrimp" (Shi Chaobin, Sun Yanhui. Henan Fisheries, 2023, No. 2: 14-15, 20). The results showed that the saline-alkali water was precisely regulated to Na + , K + , Ca 2+ Mg 2+ Regulated saline water, with ion concentrations consistent with those in seawater of the same salinity, enables the normal cultivation of whiteleg shrimp. This regulated saline water can be used for the cultivation of whiteleg shrimp. After 60 days of breeding and management, no disease was found throughout the entire cultivation process. The shrimp reached a size of 70-80 per kilogram, with a yield of 3,200 kilograms per mu, and a per-acre output value exceeding 190,000 yuan per mu.

[0077] Step S3: Desalinate saline water using a reverse osmosis system.

[0078] The saline water desalinated by the reverse osmosis system in the present invention is the regulated saline water obtained by the regulation in step S2. The purpose is to simultaneously obtain fresh water for crop cultivation and seawater-like water for seafood aquaculture, without considering a high freshwater yield. The freshwater yield in the present invention is controlled at 45% to 50%, which differs from conventional industrial saline water purification, which has a freshwater yield of 65% to 85%.

[0079] Furthermore, traditional reverse osmosis systems often require a secondary reverse osmosis system (i.e., re-treatment of the primary reverse osmosis product) to produce high-purity fresh water. Similarly, to increase the overall freshwater yield, a reverse osmosis concentrate recirculation process is used to reprocess the concentrated saline water to produce fresh water and higher concentrations of saline water.

[0080] In the present invention, only one reverse osmosis system is used, and the freshwater yield is controlled at 45% to 50%. The resulting concentrated salinity is between 6‰ and 35‰, which is suitable for marine aquaculture. Furthermore, when the freshwater yield is controlled at 45% to 50%, the salinity does not precipitate salt from the salinized water, which could foul the reverse osmosis membrane.

[0081] Therefore, by combining the seawater-like regulation in step S2 and the novel reverse osmosis strategy in step S3, the problem of reverse osmosis membrane fouling and clogging during reverse osmosis desalination of saline water is solved.

[0082] The test was conducted in two areas of the First Division of the Xinjiang Production and Construction Corps. The main ions in the water of Area A and Area B are shown in Table 1.

[0083] Table 1 Main ion composition and concentration index of saline-alkali water in two regions (concentration unit: mg / L)

[0084] <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> salinity‰ Region A 4612.6 52.2 409.9 274.7 5647.1 3334.8 15.3 Region B 2198.5 43 418.3 213.2 2906.8 2105.3 8.9

[0085] The salinity of underground saline water in Region A was 15.3‰, and the main ions are shown in Table 1. When the saline water was concentrated to twice its original concentration, to a salinity of 30.6‰, no salt precipitation occurred. When the saline water was concentrated to 2.5 times its original concentration, to a salinity of 38.3‰, no salt precipitation occurred. When the saline water was concentrated to 3.3 times its original concentration, to a salinity of 50.9‰, fine crystals precipitated.

[0086] The salinity of underground saline water in Region B was 8.9‰, and the main ions are shown in Table 1. When the saline water was concentrated to twice its original concentration, reaching a salinity of 17.8‰, no salt precipitation occurred. When the saline water was concentrated to three times its original concentration, reaching a salinity of 26.7‰, no salt precipitation occurred. When the saline water was concentrated to four times its original concentration, reaching a salinity of 35.6‰, no salt precipitation occurred. When the saline water was concentrated to five times its original concentration, reaching a salinity of 44.5‰, elongated crystals precipitated.

[0087] The main ion composition and concentration indicators of the desalinated saline-alkali water in area B are shown in Table 2.

[0088] Table 2 Main ion composition and concentration index of saline-alkali water in region B before and after desalination (concentration unit: mg / L)

[0089]

[0090] Step S4: Planting crops and raising aquatic products.

[0091] In the present invention, the fresh water obtained by the reverse osmosis system is used for crop planting or domestic water. When in the non-irrigation period, crops require less water, and the excess fresh water generated can be poured into the reservoir obtained in step S1 to store fresh water. When irrigation is needed, water can be pumped for irrigation. The seawater-like water obtained by the reverse osmosis system is used for factory-scale recirculating aquaculture of aquatic products. Since the amount of water required for recirculating aquaculture is small, the concentrated saline-alkali water obtained over a long period of time will far exceed the seawater-like water demand for aquaculture. At this time, when the amount of seawater-like water meets the needs of aquaculture, the remaining saline-alkali water is directly desalinated without being regulated by seawater-like water. The concentrated saline-alkali water generated is directly re-injected into the bottom of the saline-alkali water layer, which will not pollute the original saline-alkali water and is also beneficial to the relative stability of underground or surface water levels, preventing geological disasters such as ground collapse.

[0092] The aforementioned seawater-like water was prepared and used to culture whiteleg shrimp in southern Xinjiang. Except that the aquaculture water was seawater-like, the rest of the operations were consistent with the "Factory-Scale Aquaculture Technology of Whiteleg Shrimp" (Shi Chaobin, Sun Yanhui. Henan Fisheries, 2023, Issue 2: 14-15, 20). The results showed that seawater-like water can achieve normal aquaculture of whiteleg shrimp, indicating that this type of seawater can be used as aquaculture water for whiteleg shrimp. After 60 days of feeding and management, no disease occurred during the entire aquaculture process. The shrimp size reached 60-70 tails / kg, the yield per mu was 3,700kg, and the output value per mu of a single-crop aquaculture exceeded 220,000 yuan.

[0093] The aforementioned seawater-like system was prepared and used to culture pearl grouper in southern Xinjiang. Except for the use of 1.2m deep seawater-like system and the stocking size of fry being 100g, the remaining operations were consistent with the "Experimental Study on Factory-Scale Culture and Aquaculture Technology of Gentian Grouper" (Tian Lili et al. Fisheries Guide to Getting Rich, 2023(11): 50-52). The results showed that after 5 months of breeding and management, the pearl grouper reached a size of 550-950g per tail, with an output value of over 530,000 yuan per mu.

[0094] The reason why excess concentrated saline water can be directly re-injected is that it has not been cultivated. It is only the concentration of the original saline water. It will not add extra bacteria and other exogenous substances. Direct re-injection is safe and reliable.

[0095] When the saline-alkali water is extracted from underground, the concentrated saline-alkali water is recharged at the bottom of the subsurface water layer. When the saline-alkali water is extracted from the surface, the concentrated saline-alkali water is recharged at the bottom of the surface water layer. Different recharge locations for concentrated saline-alkali water have different effects on the salinity of saline-alkali water at different depths. For example, the main water ion indicators of the original surface saline-alkali water sample from Aral City are shown in Table 3.

[0096] Table 3 Main water ion indicators after surface saline-alkali water desalination and salt redistribution (concentration unit: mg / L)

[0097] <![CDATA[Na + ]]> <![CDATA[K + ]]> <![CDATA[Ca 2+ ]]> <![CDATA[Mg 2+ ]]> <![CDATA[Cl - ]]> <![CDATA[SO4 2- ]]> Saline water 50cm below the surface 4777.1 27.1 784.5 558.4 6833.2 3943.1 Saline water reverse osmosis water production 63.2 0.0 0.0 0.0 97.6 0.0 Reverse osmosis associated concentrated saline water 6736.2 38.7 1121.1 798.0 9625.2 5634.7 Bottom saline water before bottom recharge 4779.8 27.5 786.4 557.7 6835.4 3946.7 Bottom saline water after bottom recharge 5948.0 34.2 980.4 696.3 8521.7 4953.5 After the bottom layer is recharged, 50cm of saline water is 4776.3 27.2 784.8 559.1 6834.4 3942.7 50cm saline water below the water surface after water surface recharge 5364.6 30.8 884.6 631.2 7672.2 4451.2 Bottom saline water after surface recharge 6007.8 34.7 990.3 703.4 8606.5 5003.4

[0098] Saline-alkali water was extracted from 50 cm below the surface water surface. After microfiltration to remove particles, the water was desalinated using a reverse osmosis membrane system. This yielded reverse osmosis product water with a recovery rate of approximately 30% (product quality meeting GB / T 14848-2017 Class III standards) and associated concentrated saline-alkali water. The water quality indicators were stable, as shown in Table 3. The concentrated saline-alkali water generated during the desalination process was transported to the bottom of the water body for recharge. 200 tons of concentrated saline-alkali water were recharged daily. After 30 days of recharge, the main water ion indicators of the saline-alkali water at 50 cm below the bottom recharge pipe and 50 cm below the water surface are shown in Table 3. The concentrated saline-alkali water was then recharged at the surface, 30 m south of the pumping point, with the recharge pipe facing downward. After 5 days of surface recharge, the main water ion indicators of the saline-alkali water at 50 cm below the recharge pipe and at the bottom of the water body are shown in Table 3.

[0099] During crop cultivation, water-saving measures such as sub-mulch drip irrigation are employed. In arid regions, where annual evaporation averages 2-3 m³, using film mulching can save 1,250-1,950 tons of fresh water per mu (approximately 1,000-2,000 ft) of land. Combined with drip irrigation, this provides personalized freshwater supply to crops, addressing freshwater resource shortages and potentially alleviating or even resolving declining groundwater levels.

[0100] The traditional approach to film covering is to maintain the temperature inside the film and reduce evaporation, thereby reducing water consumption. This invention differs from the traditional approach in that the purpose of reducing water consumption is to maintain a stable groundwater level without disrupting the existing hydrogeological conditions. Unlike traditional methods that cause groundwater levels to drop or even collapse, this method is a green and sustainable way to create farmland.

[0101] The drainage or tail water (the aquaculture water remaining after the seafood is caught) produced by aquaculture is subjected to solid-liquid separation, and solid organic matter such as excrement and leftover bait is used for crop growth as organic fertilizer. The aquaculture water or tail water after filtration can be used for circulation aquaculture or enter the outer pond dug in step S1. The evaporation of the outer pond can also increase the water vapor content in the local air, and salt-tolerant plants and animals can also be raised in the outer pond. The tail water in the present invention is not directly recharged with groundwater because the tail water contains foreign substances such as bacteria, which is different from the original groundwater. Direct recharge may cause groundwater pollution. The outer pond water can be supplemented with groundwater level after sand and gravel filtration or separated by a waterproof layer as the salinity continues to increase and precipitate salt, which is then used to prepare and sell industrial salt.

[0102] Step S5: photovoltaic power generation.

[0103] The present invention also includes a photovoltaic power generation module, which is used for desalination of saline-alkali water, crop cultivation, and aquaculture. By configuring the photovoltaic power generation module, the entire system can be self-sufficient in electricity without the need for external power supply.

[0104] In addition, the energy in the entire system is basically circulated, and the saline water and fresh water in the system are also circulated, which is beneficial to the stability of the local ecology and regional development.

[0105] Example 2

[0106] like Figure 2 As shown, the present invention also provides a saline-alkali land multi-stage circulation agricultural system based on multi-stage resource utilization of saline-alkali water, including a seawater-like regulation module, a saline-alkali water desalination module, a planting module, a breeding module, a terraced field module and a photovoltaic power generation module;

[0107] Among them, the seawater-like regulation module is used to adjust underground saline-alkali water to saline-alkali water with ion composition and content similar to or consistent with that of aquaculture water and seawater of the same salinity;

[0108] The saline water desalination module is used to desalinate the regulated saline water through a reverse osmosis system to obtain fresh water and seawater-like water at the same time;

[0109] The planting module is used to grow local crops and can be equipped with corresponding sub-film drip irrigation technology or water evaporation prevention technology;

[0110] The aquaculture module is used to cultivate aquatic products that are compatible with seawater. Fresh water can be used in the planting module or can be used to cultivate freshwater aquatic products, or first used to cultivate freshwater aquatic products, and then the tail water of the aquaculture is used in the planting module.

[0111] The terraced field module is used to increase the distance between the surface soil and the groundwater level, while obtaining external ponds and / or reservoirs;

[0112] Photovoltaic power generation modules are used to provide power for seawater regulation, saline-alkali water desalination, crop planting, and aquaculture.

[0113] Example 3

[0114] At the base located at the northern edge of the Taklimakan Desert, four kilometers away from K104 of the No. 1 Highway in Tazhong, the 14th Regiment of Aral City, its typical desert saline-alkali land characteristics are high underground saline-alkali water level (the salinity of underground saline-alkali water is 9‰), white saline-alkali crystals covering the surface, and extremely sparse vegetation. On April 7, 2025, an excavator was used to level out 1.2 acres of experimental field. Since April 8, the fresh water prepared in Example 1 was used for flooding and washing salt, with a total irrigation of 166m 3After the saltwater had fully infiltrated, comprehensive renovations were implemented on the experimental field on April 14, including the application of base fertilizer, rotary tillage to loosen the soil, land leveling, the laying of drip irrigation tape, and covering with plastic film. At the same time, sowing and transplanting were completed: a portable seed drill was used to sow the Heilongjiang soybean variety "Heihe 35" as well as local peanut, cotton, and corn seeds. Local sweet potato seedlings were also transplanted, and conventional planting and management were carried out.

[0115] The planting results showed that:

[0116] May 4: The overall germination rate of all types of seeds reached 70%.

[0117] May 26: Observations showed that soybean plants were about 20 cm tall and had entered the flowering and podding stage. Some soybean plants that had emerged and grown earlier had already formed pods. Peanut plants were about 10 cm tall (some were flowering), cotton plants were about 15 cm tall, corn plants were about 50 cm tall, and sweet potato plants were about 10 cm tall.

[0118] June 4: The soybean plant height increased to about 40cm, and the pods that had formed began to enter the grain-filling stage. The beans gradually became full, and many flowers had formed pods. The overall plant was in full bloom. The peanut plant height was about 12cm, and the flowering ratio increased. The cotton plant height was about 20cm. The corn plant height was about 80cm. The sweet potato plant height was about 15cm. All crops grew well overall.

[0119] June 9: The soybean plant height increased to about 55cm, and the beans became increasingly full (the fuller beans can be seen when the pods are peeled off). All the early flowering plants have formed pods, and the subsequent ones have also begun to enter the flowering and pod-forming period; the peanut plant height is about 14cm, and the flowering ratio has increased; the cotton plant height is about 30cm; the corn plant height is about 120cm; the sweet potato plant height is about 20cm; all crops are growing well overall.

[0120] The above results fully prove that:

[0121] Actively improve saline-alkali land: Using the fresh water generated by the present invention to flood and wash away salt can effectively improve severely saline-alkali land into arable land suitable for the growth of conventional crops.

[0122] Crop growth performance is normal: the test crops (including non-salt-alkali tolerant varieties such as Heihe 35 soybean) not only successfully emerged, but also completed the normal growth and development cycle, including growth, flowering and fruiting.

[0123] The technology is highly universal: This technology does not rely on the screening and creation of specific salt- and alkali-tolerant germplasm and is universally applicable to conventional crops.

[0124] The improvement timeliness is good: after using the fresh water salt washing method of the present invention, crops can be planted and harvested in the same year, which significantly shortens the saline-alkali land improvement cycle.

[0125] It is worth noting that any details not elaborated in this invention are prior art and are well known to those skilled in the art. Before reverse osmosis treatment, if the potassium and / or magnesium ion concentrations are higher than those of seawater of equivalent salinity, there is no need to reduce them. During reverse osmosis treatment, as long as the reverse osmosis membrane is not clogged with fouling, the method of this invention can be used even if the seawater salinity is greater than 35‰ or the freshwater yield is greater than 50%. If the groundwater level or surface evaporation can be controlled, saline-alkali land can be reclaimed without terraced fields. Freshwater aquaculture can also be used before irrigation, with the aquaculture tailwater used for planting, not only increasing economic benefits but also fertilizing the fields and reducing alkali. Since photovoltaic power generation can not only power modules such as desalination, but also generate profits through photovoltaic grid connection, a minimalist model consisting of only photovoltaic modules, desalination and recharging modules, and planting modules can be selected. This "energy-assisted agriculture" approach can achieve sustainable development of saline-alkali land or desert land reclamation, achieving the goal of rapid, large-scale utilization and transformation of saline-alkali land or deserts.

[0126] Therefore, the present invention adopts the above-mentioned saline-alkali land multi-stage circular agriculture system and method based on the multi-stage resource utilization of saline-alkali water, that is, a saline-alkali land multi-stage circular agriculture system is constructed based on the multi-stage resource utilization of saline-alkali water. The entire system does not require external supply of fresh water and external power supply, and is a self-contained system that achieves a win-win situation in ecological benefits, social benefits, and economic benefits, realizes green and sustainable development, and has universal promotion value for the comprehensive development and utilization of saline-alkali land.

[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A saline-alkali land multi-stage circulation agricultural method based on multi-stage resource utilization of saline-alkali water, characterized in that: The following steps are involved: Step S1, after testing saline-alkali water in saline-alkali areas, extracting saline-alkali water and regulating it to be seawater-like, that is, adjusting the ion composition and ratio of the saline-alkali water according to the water demand for aquaculture to obtain regulated saline-alkali water; Step S2: desalinating the regulated saline water through a primary reverse osmosis system to obtain fresh water and seawater-like water; Step S3: the obtained fresh water is used for growing crops, and the obtained seawater-like water is used for aquaculture; Step S4: After the aquatic products are caught, the aquaculture tail water is subjected to solid-liquid separation, and the residue obtained by filtration is used as fertilizer for crop planting. The filtered tail water is discharged into an external pond or recycled for aquaculture.

2. The saline-alkali land multi-stage circulation agriculture method based on multi-stage resource utilization of saline-alkali water according to claim 1, characterized in that: In step S1, the saline-alkali water is regulated by the seawater-like regulation method to obtain regulated saline-alkali water, including the following two situations: Case 1: When the calcium hardness of the extracted saline water is greater than that of the water used for aquaculture, the calcium ion concentration that needs to be removed is calculated based on the original calcium ion concentration of the saline water and the calcium ion, potassium ion, and magnesium ion concentrations in the water to be used for aquaculture after adjustment. Then, the calcium ions are removed and potassium and magnesium ions are added. The method to remove calcium ion concentration is to add potassium oxalate or sodium oxalate to the water to precipitate calcium ions; Case 2: When the calcium hardness of the extracted saline water is lower than that of the water used for aquaculture, calcium ions, potassium ions and magnesium ions are added to the saline water according to the adjusted concentrations of calcium ions, potassium ions and magnesium ions in the water to be used for aquaculture.

3. The saline-alkali land multi-stage circulation agriculture method based on multi-stage resource utilization of saline-alkali water according to claim 1, characterized in that: In step S2, the fresh water yield of the reverse osmosis system is 45-50%.

4. The saline-alkali land multi-stage circulation agriculture method based on multi-stage resource utilization of saline-alkali water according to claim 1, characterized in that: In step S2, the salinity of the seawater obtained by the reverse osmosis system is not higher than 35‰.

5. The saline-alkali land multi-stage circulation agriculture method based on multi-stage resource utilization of saline-alkali water according to claim 1, characterized in that: In step S3, when the amount of seawater-like water meets the needs of aquaculture, the remaining saline-alkali water is directly desalinated without being regulated by seawater-like water, and the generated concentrated saline-alkali water is directly recharged to the bottom of the saline-alkali water layer.

6. A saline-alkali land multi-stage circulation agricultural system based on multi-stage resource utilization of saline-alkali water, characterized in that: include: A seawater-like control module is used to adjust saline water to have an ion composition and content similar to or consistent with that of aquaculture water and seawater of the same salinity; The saline-alkali water desalination module is used to desalinate the regulated saline-alkali water through a reverse osmosis system to obtain fresh water and seawater-like water at the same time; Planting module, equipped with sub-film drip irrigation system; Aquaculture module, used for aquaculture of aquatic products; Terraced field module, used to increase the distance between the surface soil and the groundwater level, while obtaining external ponds and / or reservoirs; Photovoltaic power generation module is used to supply power to seawater control module, saline-alkali water desalination module, planting module and breeding module.

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