Method for improving saline-alkali soil by planting sweet sorghum at low investment

Abstract

The invention provides a method for improving saline-alkali soil through low-investment planting of sweet sorghum. The method is characterized in that a circulating planting method with one period of three years is adopted; in each period, in the first year and the second year, the sweet sorghum is planted under the condition of zero fertilization, high-sugar-content sweet sorghum stalks and sweet sorghum grains with balanced nutrition are harvested, and more salt ions are taken away through the strong absorption effect of the sweet sorghum, so that the salt content in the saline-alkali soil is reduced. In the third year, balanced fertilization is conducted on the saline-alkali soil, and other salt-tolerant crops are subjected to crop rotation. The sweet sorghum is planted through zero fertilization in the first two years, more salt ions Na < + > in the saline-alkali soil are taken away while the requirements for normal growth, the stem sugar content and the grain nutrient content of the sweet sorghum are met, and biological improvement of the saline-alkali soil is achieved; in the third year, after nutrients are comprehensively and quantitatively supplemented, cotton or oil sunflowers are planted in an alternate cropping mode, the biodiversity microenvironment of the saline-alkali soil is further improved, the nutrients are balanced, the salinity and alkalinity are reduced, and therefore the purposes of saline-alkali soil nutrient conservation, biodiversity planting and soil-borne disease prevention are achieved.

Description

Technical Field

[0001] The invention relates to the technical field of saline-alkali land treatment, in particular to a method for improving saline-alkali land by planting sweet sorghum with low investment. Background Art

[0002] The area of ​​saline-alkali land in my country is 990,000 km 2 , of which nearly 1 / 10 (about 123,000 km 2 ) has agricultural utilization potential, but 4 / 5 of it has not been developed and utilized. The reduction of cultivated land area and the waste of resources are serious challenges facing my country's agriculture and economy. In most salinized soils, the organic matter content is low, the mineral nutrients are unbalanced, and trace elements are deficient. The high pH value of salinized soils causes the mineral elements necessary for crops to precipitate and are difficult to be absorbed and utilized by crops, thus leading to nutrient deficiency of crops and difficulty in planting. The commonly used method to improve saline-alkali land is to use a large amount of bio-organic fertilizers. Bio-organic fertilizers can quickly reduce soil salinity and alkalinity, destroy soil capillary action, block further accumulation of salt to the surface, increase organic matter and available phosphorus and ammonium nitrogen content, and improve the defects of poor soil aggregate structure, poor soil fertility, and decreased soil permeability. However, the large-scale application of organic fertilizers cannot improve the alkalinity of saline-alkali land. It only treats the symptoms and not the root cause. Long-term application will also lead to further compaction of the land. In order to completely improve the compaction problem of saline-alkali soil, in recent years, researchers have mostly used salt- and alkali-tolerant microbial agents to improve the soil, lowering the soil pH and reducing salinization by using acidic substances produced by microbial decomposition of organic matter. However, due to the existence of soil compaction, the penetration of microbial agents into the soil has become a limiting factor in the improvement effect. Moreover, the high cost of microbial agents has also affected their large-scale promotion.

[0003] Therefore, simple, low-cost and easy-to-promote saline-alkali land improvement methods have become the research focus of current scientific researchers.

[0004] Sweet sorghum is an important biomass energy crop, hailed as "the strongest contender in the bioenergy system." A C4 plant, it boasts high photosynthetic efficiency and tolerance to drought, waterlogging, salinity, and infertility. It is well-suited for cultivation in areas with abundant sunlight but nutrient deficiencies, particularly in low- and medium-yield saline-alkali regions. Sweet sorghum grows quickly, produces a large biomass, and its sugar-rich stems are used for ethanol production. Its grains are used for food, feed, and winemaking, making it a high-yield, high-efficiency, and low-cost biomass energy crop. Numerous patents have been filed using sweet sorghum to improve saline-alkali land.

[0005] Chinese Patent No. 201310189425.7 discloses a method for intercropping sweet sorghum and sesbania suitable for saline-alkali land. This invention utilizes the complementary advantages of the two salt-tolerant crops to promote balanced yield increases of sweet sorghum and sesbania, reduce fertilizer input, and compensate for the defect of sweet sorghum due to its high fertilizer requirement, which causes rapid depletion of soil nutrients. At the same time, it avoids the threat of secondary salinization of the soil caused by the large amount of fertilizer applied during the process of monoculture of sweet sorghum or monoculture of sesbania, and effectively alleviates the obstacle of nutrient deficiency in saline-alkali land, reduces secondary salinization of the soil, and improves the composite utilization rate of the land. In addition, the plants accumulate a large amount of salt during growth, and as the plants are harvested, they can remove the soil salt, thereby reducing the soil salinity and achieving the effect of plant restoration of saline-alkali land. However, this solution focuses on the cultivation of the symbiotic system of intercropping sweet sorghum and sesbania. The patent does not involve the planting benefits of monoculture of sweet sorghum and its soil improvement effect. Moreover, chemical fertilizers still need to be applied during the planting process of this symbiotic system, which not only increases fertilizer expenses but also has the risk of increasing soil salinity.

[0006] Chinese patent 201810028654.3 discloses an effective method for improving saline-alkali land by combining physical and biological methods, which includes the following steps: S1, deep plowing and loosening of saline-alkali land; S2, land leveling, damming, water storage, and salt washing in the alkali land; S3, replacing the soil in the alkali land with a special artificially prepared soil matrix; S4, applying biological organic fertilizer to the saline-alkali land; S5, improving the saline-alkali land with biotechnology; S6, planting salt-tolerant sweet sorghum in the saline-alkali land; S7, water and fertilizer management for sweet sorghum in the improved saline-alkali land; S8, repeating the above procedures for two consecutive years, and completing the saline-alkali land improvement after planting sweet sorghum in the third year. After two years of sweet sorghum cultivation on saline-alkali land, the invention shows that soil salinity can be reduced from 0.3% to 0.6% to approximately 0.125%, and organic matter content can be increased from 0.7% to approximately 2.23%. Three years after sweet sorghum cultivation, the saline-alkali soil salinity can be reduced to the level of normal arable land, becoming desalinated soil, indicating successful saline-alkali land improvement. However, this solution primarily uses physical methods of washing salt and replacing soil, and chemical methods of increasing fertilization to improve saline-alkali land. Regardless of the expected improvement effect, saline-alkali areas are already scarce in freshwater, leading to soil salinization. Large-scale freshwater washing and subsequent soil replacement are essentially importing soil, a massive and costly undertaking. Field operations are extremely difficult and impractical, making large-scale saline-alkali land improvement difficult to implement. Funding and labor shortages will hinder its widespread adoption.

[0007] Chinese patent 202211658900.6 discloses a method for improving coastal saline-alkali land by planting sweet sorghum. This patent is based on the water and salt migration laws of coastal saline-alkali soil and the growth and development characteristics of sweet sorghum. First, the soil is covered with whole corn stalks in mid-to-late October to control soil salt return. At the end of April of the following year, the corn stalks are crushed and returned to the field for fertilization, providing an excellent planting, germination and growth environment for sweet sorghum. Then the sweet sorghum is covered with film and sown early. From late July to early August, the sweet sorghum is mowed and the mowed plants are used as silage. In early to mid-November, the sweet sorghum stalks are harvested and the whole plants are covered on the ground to reduce soil salt return in winter and spring, providing low-salt and high-humidity soil conditions for sweet sorghum planting the following year. In April of the following year, the sweet sorghum stalks are returned to the field to improve soil fertility. Then the sweet sorghum is covered with film and sown early to achieve a cyclic planting and harvesting of sweet sorghum, ensuring the continuous and efficient production of sweet sorghum in coastal saline-alkali land. The essence of this invention is to increase soil nutrients through straw return technology while controlling the return of soil salt to the soil surface with water transport. Our experimental results show that, like most crops, sweet sorghum is highly selective in nutrient and even salt content in the soil, preferring to absorb N, P, and K while rejecting salt. In particular, the salt content of the grain is relatively low. Therefore, the patent focuses on nutrient recycling through straw return. However, salt also returns to the soil with the straw return. Whether mowing or harvesting the grain, the amount of salt removed from the soil is limited, so the effectiveness of reducing soil salinity is questionable. In addition, the patent focuses on harvesting sweet sorghum grains rather than stalks. However, as an economic crop, sweet sorghum's large biomass, especially the stalks with high sugar content, are the important target organs worthy of harvesting. Sweet sorghum stalks are thick and have large biomass. If they are directly returned to the fields, they will encounter the cold winter season. The straw is difficult to decompose during the low temperature period from November to April of the following year. Regardless of whether returning the straw to the fields can reduce the migration of soil salt to the surface with water, the difficult-to-decompose straw returned to the fields not only fails to improve soil fertility in a short period of time, but also affects the spring farming of the following year. Secondly, the most valuable part of sweet sorghum is its high sugar content straw, which can be used to produce bioethanol. If the sweet sorghum stalks are returned to the fields and only its grains with low nutritional value are retained, it is like picking up sesame seeds and losing watermelons, and the value of sweet sorghum cannot be maximized. Summary of the Invention

[0008] The purpose of the present invention is to address the shortcomings of the existing technology and the phenomenon that saline-alkali areas are generally deficient in phosphorus, nitrogen and potassium, and to provide a method for improving saline-alkali land by planting sweet sorghum with low investment. The method is simple and practical, and can ensure the sugar content and grain nutrition of sweet sorghum under extremely low investment conditions, while being able to reduce the salt content in the soil and improve saline-alkali land.

[0009] The technical solution adopted by the present invention to solve its technical problem is:

[0010] A low-input method for improving saline-alkali land by planting sweet sorghum is to adopt a three-year cycle of cyclic planting. In each cycle, sweet sorghum is planted under zero fertilization conditions in the first and second years. While harvesting the high-sugar sweet sorghum stalks and nutritionally balanced sorghum grains, the salt in the saline-alkali land is removed through the strong absorption effect of the sweet sorghum. In the third year, after balanced fertilization and soil adjustment of the saline-alkali land, other salt-tolerant crops are rotated to achieve the goals of conserving soil nutrients in the saline-alkali land, cultivating biodiversity, and preventing the occurrence of soil-borne diseases.

[0011] The cyclic planting method is applied to the soil with a pH of 8.0-8.4 and a salt content of 2.98 g·kg -1 ~3.2g·kg -1 The saline-alkali land that meets the conditions can be improved by this method.

[0012] The cycle planting method specifically comprises the following steps:

[0013] a. Soil desalination: When the temperature in the north drops below -4°C in January in winter, carry out winter saline-alkali land irrigation with frozen salt water; in March in spring, carry out mulching to prevent the soil from returning to salt;

[0014] b. Sowing and mulching: Sow sweet sorghum in late April or early May. Apply no fertilizer before sowing. After sowing, level and compact the soil, then immediately mulch and compact the soil.

[0015] c. Field management: Thin out or replant the sweet sorghum when it has 3 to 4 leaves, planting one seedling per hole;

[0016] d. Harvest: Harvest sweet sorghum 135-138 days after sowing. Remove the ears promptly and store the stalks immediately.

[0017] e. Repeated planting: In the second year, repeat the planting of sweet sorghum according to methods a to d;

[0018] f. Cropping: After sowing sweet sorghum with zero fertilizer for two years, adjust the nutrients of the saline-alkali land through balanced fertilization in the third year and change the crop to other salt-tolerant crops.

[0019] In the step a, the water volume of the salt water freezing irrigation is 52-58 mm.

[0020] In the step b, the sowing depth of the sweet sorghum is 3 to 4 cm, 2 to 3 seeds are sown in each hole, and the row spacing is 55 to 58 cm.

[0021] In step f, during balanced fertilization in the third year, the effective amount of fertilizer applied per hectare of soil is: 91.5-97.5 kg, preferably 93-95 kg, of pure nitrogen; 105-135 kg, preferably 112-125 kg, of PO; 37.5-51 kg, preferably 42-48 kg, of K; and 600-675 kg, preferably 620-650 kg, of organic fertilizer with an organic matter content greater than 30%. To improve nutrient absorption, a fertilizer containing attapulgite is preferably used.

[0022] The balanced fertilization method is specifically as follows: nitrogen fertilizer, phosphorus fertilizer and organic fertilizer are applied as base fertilizer before sowing, and potassium fertilizer is applied as topdressing during the jointing stage.

[0023] In this method, balanced fertilizer application and crop rotation with cotton or oil sunflower are carried out in the third year.

[0024] Through the above technical solution, the beneficial effects obtained by the present invention are:

[0025] The present invention provides a method for improving saline-alkali land by planting sweet sorghum as an energy crop. Based on the pH and salinity of saline-alkali land in North China, the method adopts the method of planting sweet sorghum without fertilizer application in the first two years, giving full play to the strong nutrient absorption capacity, tall stalks and large biomass characteristics of sweet sorghum. While meeting the normal growth and sugar content of sweet sorghum and stalks, it removes more salt ions Na from the saline-alkali land. + , reduce soil salinity, maintain soil fertility, and achieve biological improvement of saline-alkali land; after two years of salinity reduction, fully and quantitatively supplement nutrients in the third year and then plant cotton or oil sunflower instead to balance the nutrients in the saline-alkali soil and reduce salinity. In the fourth year, repeat the planting of sweet sorghum, and rotate in sequence to achieve sustainable planting of sweet sorghum and cotton / oil sunflower. After long-term rotation planting, the salinity and alkalinity of the saline-alkali land can be steadily reduced, and the soil quality of the saline-alkali land can be completely improved.

[0026] The present invention uses sweet sorghum planted with zero fertilization and sweet sorghum planted after fertilization as control groups. Testing after 115 days revealed that the sugar brix of the sweet sorghum in the zero-fertilization group was lower than that of the fertilized group. However, when the planting period was extended to 138 days, sugar content in each stem node of the sweet sorghum treated with zero fertilization rapidly accumulated, and the sugar brix significantly increased. The average sugar brix of each stem node increased by 6.6 percentage points, an increase of 55.5%. Testing showed that the average sugar brix of each stem node of the sweet sorghum treated with zero fertilization was 0.8% and 1.1% higher than the average sugar brix of each stem node of the sweet sorghum treated with the comparative patent method (CN103222387A) and the traditional fertilization method used by farmers, respectively. Within 23 days before harvest, the sugar content of the stems surpassed that of the sweet sorghum treated with the traditional fertilization method.

[0027] Data collected over many years of cultivation shows that using the present invention to treat saline-alkali land results in an average sodium ion content of 0.70 g / kg per node in the sweet sorghum stalks. This compares to only 0.56 g / kg and 0.42 g / kg, respectively, in sweet sorghum stalks grown using the patented method (CN103222387A) and traditional farmer fertilization methods. The high sodium content in the sweet sorghum nodes means they remove more salt ions from the soil. Without fertilization, the sodium in the sweet sorghum nodes is absorbed from the soil, effectively reducing the salinity of the saline-alkali land and achieving the goal of improving it.

[0028] In the present invention, soil salinity is desalinated by irrigating the land in winter to freeze it, or by diverting water from the Yellow River for irrigation in spring. Ploughing, sowing, and fertilizing are integrated into farming, and the emphasis is on reducing the application of chemical fertilizers, thus avoiding secondary salinization of the soil caused by the large-scale application of chemical fertilizers. No fertilization is required in the first two years of planting, which reduces field farming operations and alleviates the labor intensity of farmers. At the same time, it avoids frequent disturbance of the soil, plays a role in water storage and moisture conservation, and increases the soil's storage rate and utilization rate of limited water resources. In addition, since the sweet sorghum planted by the present invention is a large-biomass salt-tolerant energy plant, it can take away soil salt as the crop is harvested, thereby reducing the soil salt content, achieving a win-win effect of planting suitable crops and harvesting target products while repairing saline-alkali land. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Comparison chart of sugar brix at each stem node at the maturity stage (125 days) of sweet sorghum in the first year under three different planting methods;

[0030] Figure 2 This is a comparison chart of sugar brix of each stem node of sweet sorghum 115 days after sowing in the second year under three different planting methods;

[0031] Figure 3 This is a comparison chart of sugar brix of each stem node of sweet sorghum 138 days after sowing in the second year under three different planting methods;

[0032] Figure 4 This is a comparison chart of the growth rate of sugar brix of sweet sorghum stem nodes within 23 days before maturity in the second year under three different planting methods;

[0033] Figure 5 Comparative line graph of Na content in sweet sorghum stems grown using three different planting methods;

[0034] Figure 6 This is a photo of the growth of sweet sorghum at maturity according to an embodiment of the present invention;

[0035] Figure 7 A photo of the actual operation of sowing sweet sorghum according to an embodiment of the present invention.

[0036] In the figure, * indicates that there are significant differences among the three methods (P<0.05). DETAILED DESCRIPTION

[0037] The technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0038] A low-input sweet sorghum cultivation method for improving saline-alkali soils employs a three-year rotational planting method. In the first and second years of each cycle, sweet sorghum is cultivated with zero fertilizer. Low-input sweet sorghum's exceptional salt tolerance and robust nutrient absorption ensure high sugar content in the stalks and nutrient-rich grains, resulting in high-sugar stalks and nutritionally balanced grains. This method also absorbs and removes more soil salt, reducing the salinity of saline-alkali soils. In the third year, balanced fertilization and rotation with other salt-tolerant crops are implemented to conserve soil nutrients, cultivate biodiversity, and prevent soil-borne diseases.

[0039] The cyclic planting method is applied to the soil with a pH of 8.0-8.4 and a salt content of 2.98 g·kg -1 ~3.2g·kg -1 The saline-alkali land that meets the conditions can be improved by this method. Sweet sorghum planted under zero fertilizer conditions for two years has a high stalk sugar content, nutritionally balanced grains and effective soil Na + This method is based on the results of experiments in coastal saline-alkali land and saline-alkali areas around Bohai Sea, and is worthy of promotion in this area.

[0040] The cycle planting method specifically comprises the following steps:

[0041] a. Soil desalination: When the temperature in the north drops below -4°C in January in winter, carry out winter saline-alkali land irrigation with frozen salt water; in March in spring, carry out mulching to prevent the soil from returning to salt;

[0042] b. Sowing and mulching: Sow sweet sorghum in late April or early May. Apply no fertilizer before sowing. After sowing, cover the soil with flattened soil and tamp it down, then immediately mulch and compact the soil.

[0043] c. Field management: Thin out or replant the sweet sorghum when it has 3 to 4 leaves, planting one seedling per hole;

[0044] d. Harvesting: Sweet sorghum is harvested 135-138 days after sowing. The ears are promptly removed and the stalks are immediately stored for bioethanol production.

[0045] e. Repeated planting: In the second year, repeat the planting of sweet sorghum according to methods a to d;

[0046] f. Cropping: After sowing sweet sorghum with zero fertilizer for two years, adjust the nutrients of the saline-alkali land through balanced fertilization in the third year, and change the crop to salt-tolerant crops such as oil sunflower or cotton.

[0047] In step a, a strip field model is adopted for saltwater freezing irrigation, that is, water storage ridges are built around the strip field, and saltwater is poured into the land after the land is leveled and plowed.

[0048] Before sowing, during the winter of the previous year, when temperatures remained below -4°C, local groundwater was pumped for surface flooding at a rate of 52-58 mm. The low-temperature freezing of the saltwater quickly froze. The following spring, as temperatures rose, the high-concentration saltwater melted first and seeped into the soil, followed by brackish water and then freshwater, leaching, desalinating, and desalinating the surface soil. When the salt ice began to melt in early March, a film was applied to the soil to prevent evaporation and soil salinization, thus ensuring a suitable growing environment for sweet sorghum.

[0049] In the Yellow River Delta, water can also be diverted for irrigation before spring sowing, also achieving the same effect of desalinating the soil and creating moisture for seedlings. Specifically, water is diverted from the Yellow River in late March, using a flood irrigation method of 50-55 mm.

[0050] In the step b, the sowing depth of the sweet sorghum is 3 to 4 cm, 2 to 3 seeds are sown in each hole, and the row spacing is 55 to 58 cm.

[0051] In step d, the delayed harvesting of the sweet sorghum of the present invention can achieve rapid accumulation of sugar in the mature stage of the sweet sorghum. Compared with 115 days after sowing, the sugar brix of the sweet sorghum stalks increased by an average of 6.6% 138 days after sowing, an increase of up to 55.5%.

[0052] In step f, during balanced fertilization in the third year, the effective amount of fertilizer applied per hectare of soil is: 91.5-97.5 kg, preferably 93-95 kg, of pure nitrogen; 105-135 kg, preferably 112-125 kg, of PO; 37.5-51 kg, preferably 42-48 kg, of K; and 600-675 kg, preferably 620-650 kg, of organic fertilizer with an organic matter content greater than 30%. To improve nutrient absorption, a fertilizer containing attapulgite is preferably used.

[0053] The balanced fertilization method is specifically as follows: nitrogen fertilizer, phosphorus fertilizer and organic fertilizer are applied as base fertilizer before sowing, and potassium fertilizer is applied as topdressing during the jointing stage.

[0054] In this method, the salt-tolerant crop that is rotated in the third year is preferably cotton or oil sunflower. Rotation can prevent the damage caused by soil infectious diseases caused by continuous planting of the same crop. Secondly, by rotating other salt-tolerant crops, the soil microecological environment is improved, and a good soil environment is cultivated for biodiversity planting.

[0055] In this method, balanced fertilization is based on the replenishment of nutrients consumed by the soil after two consecutive years of sweet sorghum cultivation on saline-alkali land. The cultivation method of other salt-tolerant crops in the third year is not the key point of this invention and is not explicitly defined or elaborated here.

[0056] In order to better illustrate the present invention, further examples are given below.

[0057] The present invention was tested in the core experimental area of ​​heavy saline-alkali land in Haixing County, Hebei Province. The soil type in this area is mainly coastal saline soil, the ion composition is mainly NaCl, the soil pH is 8.0-8.4, and the salt content is 2.98g·kg -1 ~3.2g·kg -1 .

[0058] The steps of the rotation planting method are as follows:

[0059] a. Soil desalination: When the temperature in the north drops below -4°C in January in winter, carry out winter saline-alkali land irrigation with frozen salt water; in March in spring, carry out mulching to prevent the soil from returning to salt;

[0060] Specifically, before sowing, during the winter of the previous year, when temperatures remained below -4°C, local groundwater was pumped for surface flooding at a rate of 52-58 mm. The low-temperature freezing of the saltwater quickly caused it to freeze. The following spring, as temperatures rose, the high-concentration saltwater melted first and seeped into the soil, followed by the dilute saltwater, and finally the freshwater, achieving the goal of leaching and desalinating the surface soil. When the salt ice began to melt in early March, a film was applied to the soil to prevent evaporation and the return of salt to the soil.

[0061] b. Sowing and Film Covering: Remove the film from the ground in late April or early May. After briefly drying the ground, prepare the soil immediately and sow sweet sorghum without applying fertilizer. Sow 2 to 3 seeds per hole at a depth of 3 to 4 cm, with row spacing of 55 to 58 cm. After sowing, cover the soil with a flat surface, tamp it down, and then immediately cover with film and compact the soil.

[0062] To ensure the seed germination rate, sweet sorghum seeds are soaked for 6 to 12 hours before sowing. When sowing, a manual seeder is used to open furrows, and the seeds are sown manually along the furrows or in holes.

[0063] c. Field Management: After seedlings emerge, promptly puncture the film around the seedlings to allow them to ventilate. Thin or replant the sweet sorghum when they have 3-4 leaves, planting one seedling per hole to ensure the desired planting density. Manually remove weeds and control pests and diseases when the sweet sorghum has 5-6 leaves to ensure normal growth.

[0064] d. Harvesting: Harvest sweet sorghum on the 138th day after sowing. First, cut the plant 2-3 cm close to the ground with a sickle. Keep the stems as needed, remove the leaves, and cut off the ears. The stems are immediately stored for bioethanol production.

[0065] e. Repeated planting: In the second year, repeat the planting of sweet sorghum according to methods a to d;

[0066] f. Cropping: After sowing sweet sorghum with zero fertilizer for two years, adjust the nutrients of the saline-alkali land through balanced fertilization in the third year and rotate to plant other salt-tolerant crops such as oil sunflower or cotton.

[0067] To verify the effectiveness of this method, two control fields were treated using the method disclosed in patent CN103222387A and traditional farmer planting methods. These two fields served as control groups for a comparative experiment with this method. Both the control and experimental fields were located in the core experimental area of ​​heavily saline-alkali land in Haixing County, Hebei Province.

[0068] The method of patent CN103222387A will not be described in detail. The traditional planting method described is essentially the same as steps a through d of the present invention, with the following differences: Before sowing, basal fertilizers of N, P, and K are applied, with the amount of fertilizer applied per hectare of soil equivalent to 100-180 kg of pure N, 75-80 kg of P2O5, and 10-15 kg of K2O; and sweet sorghum is harvested 125 days after sowing.

[0069] Two years after sowing, the nutrient and salt contents of the grains, leaves and stalks of sweet sorghum in the experimental fields of this method, the patented control fields and the farmers' traditional control fields were tested. The test results are shown in Table 1.

[0070] Table 1 Nutrient content of different parts of sweet sorghum (g·kg -1 )

[0071]

[0072] Note: Different lowercase letters in the same column of the table indicate significant differences between different methods at the P<0.05 statistical level. The data marked with a are significantly higher than the data marked with b. Data marked with ab are not significantly different from the data marked with a or b. The confidence interval of such differences is 95%.

[0073] As can be seen from the data in Table 1, the N, P, and K contents in the sweet sorghum grains and ear nodes using this method did not decrease significantly, proving that zero fertilization does not reduce the content of nutrients in the sweet sorghum grains, does not affect the normal germination and growth of the grains as seeds, and does not affect their nutritional value as food.

[0074] The P content in the leaves of sweet sorghum grown using this method was similar to that in the control group, indicating that the P in the leaves primarily supplies the grain to maintain genetic material. The K content in the leaves was lower than that in sweet sorghum grown using traditional methods. This is because more potassium in the sweet sorghum plants is allocated to the stems in the later stages of growth, resulting in a decrease in the potassium content in the leaves. This increased potassium allocation to the stems facilitates the conversion and accumulation of sugars in the stems, leading to a rapid increase in sugar content in the stems during the later stages of production.

[0075] See Figure 1 The following chart compares the sugar brix of each sweet sorghum node at maturity (125 days) in the first year of cultivation using three different planting methods. The data in the figure show that the sugar brix of sweet sorghum nodes under the 10th node was significantly higher using this method than using the other two methods, demonstrating that zero fertilization does not affect the conversion and accumulation of sugars within the sweet sorghum nodes.

[0076] See Figure 2 The following is a comparison of the sugar brix of each sweet sorghum node 115 days after sowing in the second year using three different planting methods. The data in the figure show that the sugar brix of each node using this method is significantly lower than that using the patented method and the traditional farmer method.

[0077] See Figure 3 This chart compares the sugar brix of each sweet sorghum node 138 days after sowing in the second year using three different planting methods. The data in the chart shows that in the late maturity stage, the sugar brix of all nodes of sweet sorghum grown using this method increases significantly, showing significant differences compared to the patented method and traditional farmers' methods.

[0078] See Figure 4, which is a comparison chart of the growth rate of sugar brix of sweet sorghum stem nodes within 23 days before maturity under three different planting methods. The data in the figure show that compared with the comparative patent method, the average sugar brix of the sweet sorghum stem nodes treated by this method increased rapidly 23 days before harvest. The average sugar brix of the stem nodes increased by 6.6 percentage points, an increase of 55.5%, and the sugar content of all stem nodes increased significantly; followed by the traditional farmer method, the sugar brix of the stem nodes increased by 5.5 percentage points, an increase of 44.0%, and the accumulation of sugar brix of 4 to 12 stem nodes of this method contributed the most; the sugar brix of the stem nodes of the comparative patent method (CN103222387A) increased by 4.4 percentage points, an increase of 35.2%, mainly increasing the sugar brix of the 10th to 13th nodes in the middle and upper stems. This proves that zero fertilization not only does not affect the accumulation of sugar in the stem, but is beneficial to the increase of sugar in all stem nodes. Under comprehensive comparison, the sugar brix of each stem node of this method is better than the other two control methods.

[0079] Figure 5 A comparative line graph of the Na content in sweet sorghum stalks using three different planting methods is given. The data in the figure show that the Na content in the sweet sorghum stalks treated with this method is significantly higher than that in the comparative document (CN103222387A) and the traditional method of farmers, and is significantly different from the other two planting methods in multiple stem nodes. Since this method requires no fertilizer, the Na in the sweet sorghum stalks can only come from saline-alkali soil, indicating that this method is significantly more effective in removing salt from saline-alkali soil than the other two methods. By removing a large amount of salt from saline-alkali soil with sweet sorghum, rapid improvement of saline-alkali soil can be achieved.

[0080] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for improving saline-alkali land by planting sweet sorghum with low investment, characterized by: A three-year cycle of cropping is adopted; in each cycle, sweet sorghum is planted without fertilizer in the first and second years, and high-sugar stalks and nutritionally balanced grains are harvested, which removes soil salt and reduces the salt content of saline-alkali soil; in the third year, balanced fertilization is implemented on the saline-alkali land, and other salt-tolerant crops are rotated.

2. The method for improving saline-alkali land by planting sweet sorghum with low investment according to claim 1, characterized in that: The cyclic planting method is applied to the soil with a pH of 8.0-8.4 and a salt content of 2.98 g·kg -1 ~3.2 g·kg -1 of saline-alkali land.

3. The method for improving saline-alkali land by planting sweet sorghum with low investment according to claim 2, characterized in that: The cycle planting method specifically comprises the following steps: a. Soil desalination: When the temperature in the north drops below -4°C in January in winter, carry out winter saline-alkali land irrigation with frozen salt water; in March in spring, carry out mulching to prevent the soil from returning to salt; b. Sowing and mulching: Sow sweet sorghum in late April or early May. Apply no fertilizer before sowing. After sowing, level and compact the soil, then immediately mulch and compact the soil. c. Field management: Thin out or replant the sweet sorghum when it has 3 to 4 leaves, planting one seedling per hole; d. Harvest: Harvest sweet sorghum 135-138 days after sowing. Remove the ears promptly and store the stalks immediately. e. Repeated planting: In the second year, repeat the planting of sweet sorghum according to the method a to d; f. Cropping: After planting sweet sorghum with zero fertilizer for two years, adjust the nutrients of the saline-alkali land through balanced fertilization in the third year and change to other salt-tolerant crops.

4. The method for improving saline-alkali land by planting sweet sorghum with low investment according to claim 3, characterized in that: In step a, the water volume of the salt water freezing irrigation is 52-58 mm.

5. The method for improving saline-alkali land by planting sweet sorghum with low investment according to claim 4, characterized in that: In the step b, the sowing depth of the sweet sorghum is 3-4 cm, 2-3 seeds are sown in each hole, and the row spacing is 55-58 cm.

6. The method for improving saline-alkali land by planting sweet sorghum with low investment according to claim 3, characterized in that: In step f, during the balanced fertilization in the third year, the effective amount of fertilizer applied per hectare of soil is: 91.5-97.5 kg of pure N, 105-135 kg of P2O5, 37.5-51 kg of K2O, and 600-675 kg of organic fertilizer with an organic matter content greater than 30%.

7. The method for improving saline-alkali land by planting sweet sorghum with low investment according to claim 6, characterized in that: In the step f, during the balanced fertilization in the third year, the effective amount of fertilizer applied per hectare of soil is: 93-95 kg of pure N, 112-125 kg of P2O5, 42-48 kg of K2O, and 620-650 kg of organic fertilizer with an organic matter content greater than 30%.

8. The method for improving saline-alkali land by planting sweet sorghum with low investment according to any one of claims 6 or 7, characterized in that: When applying balanced fertilization, use fertilizer containing attapulgite soil.

9. The method for improving saline-alkali land by planting sweet sorghum with low investment according to any one of claims 6 or 7, characterized in that: The balanced fertilization method is that nitrogen fertilizer, phosphorus fertilizer and organic fertilizer are applied as base fertilizer before sowing, and potassium fertilizer is applied as topdressing during the jointing stage.

10. The method for improving saline-alkali land by planting sweet sorghum with low investment according to claim 1, characterized in that: In the third year, apply balanced fertilizer and rotate to cotton or oil sunflower.

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