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

Abstract

The application provides a method for improving saline-alkali land by low-input planting of sweet sorghum, which adopts a three-year cycle planting method; in each cycle, sweet sorghum is planted in the first year and the second year under the condition of zero fertilization, high-sugar sweet sorghum stalks and nutrition-balanced sweet sorghum grains are harvested, and more salt ions are taken away by the strong absorption of sweet sorghum, so as to reduce the salt content in the saline-alkali land. In the third year, balanced fertilization is carried out on the saline-alkali land, and other salt-tolerant crops are planted by rotation. By planting sweet sorghum with zero fertilization in the first two years, the normal growth of sweet sorghum, the sugar content of the stalks and the nutritional content of the grains are met, and more salt ions Na + are taken away from the saline-alkali land, so that the biological improvement of the saline-alkali land is realized; after the nutrients are fully and quantitatively supplemented in the third year, cotton or oil sunflower is planted by rotation, the biodiversity microenvironment of the saline-alkali land soil is further improved, the nutrients are balanced, and the salinity is reduced, so that the purposes of soil nutrient conservation, biodiversity planting and prevention of soil-borne disease are achieved.

Description

Technical Field

[0001] This invention relates to the field of saline-alkali land management technology, and in particular to a method for improving saline-alkali land by planting sweet sorghum with low input. Background Technology

[0002] my country's saline-alkali land area is 990,000 km² 2 Of these, nearly 1 / 10 (approximately 123,000 km) 2 While arable land possesses agricultural potential, four-fifths of it remains undeveloped. The shrinking arable land area and resource waste pose serious challenges to my country's agriculture and economy. Most saline-alkali soils are characterized by low organic matter content, unbalanced mineral nutrients, and a lack of micronutrients. The high pH value of saline-alkali soils causes essential mineral elements for crops to precipitate, making them difficult for crops to absorb and utilize, thus leading to nutrient deficiencies and planting difficulties. A common method for improving saline-alkali land is the extensive use of bio-organic fertilizers. These fertilizers rapidly reduce soil salinity, disrupt soil capillary action, prevent further salt accumulation on the surface, and increase organic matter, available phosphorus, and ammonium nitrogen content, thus improving poor soil structure, fertility, and permeability. However, applying large amounts of organic fertilizer cannot improve the alkalinity of saline-alkali land; it only treats the symptoms, not the root cause, and long-term application can lead to further soil compaction. In recent years, researchers have increasingly used salt- and alkali-tolerant microbial agents to improve soil conditions and reduce soil pH by decomposing organic matter into acidic substances. However, due to the soil compaction problem, the penetration of microbial agents into the soil has become a limiting factor for 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 methods for improving saline-alkali land have become the focus of current research.

[0004] Sweet sorghum is an important biomass energy crop, hailed as "the most powerful competitor in bioenergy systems." Belonging to the C4 plant family, it possesses high photosynthetic efficiency and is resistant to drought, flooding, salinity, and poor soil conditions. It is suitable for planting in areas with abundant sunlight but nutrient-deficient soils, particularly low- to medium-yield saline-alkali regions. Sweet sorghum grows rapidly, has a large biomass, and its stems are rich in sugar, which can be used to produce ethanol. The grains are edible, used as feed, and for brewing. It is a high-yield, high-efficiency, and low-cost biomass energy crop, and several patents have already been published on its use in improving saline-alkali land.

[0005] Chinese Patent 201310189425.7 discloses a method for intercropping sweet sorghum and sesbania in saline-alkali land. This invention utilizes the complementary advantages of the two salt-tolerant crops in a symbiotic system to promote balanced yield increases for both sweet sorghum and sesbania, reduce fertilizer input, and compensate for the rapid depletion of soil nutrients caused by the high fertilizer requirements of sweet sorghum. Simultaneously, it avoids the threat of secondary soil salinization caused by excessive fertilizer application during monoculture of sweet sorghum or sesbania, effectively alleviating nutrient deficiency in saline-alkali land, reducing secondary soil salinization, and improving the comprehensive utilization rate of land. Furthermore, the plants accumulate a large amount of salt during their growth, which can be removed from the soil upon harvest, thereby reducing soil salinity and achieving the effect of phytoremediation of saline-alkali land. However, this solution focuses on the cultivation of the sweet sorghum and sesbania intercropping symbiotic system; the patent does not address the planting benefits of monoculture of sweet sorghum or its soil-improving effects. Moreover, the symbiotic system still requires fertilizer application, increasing fertilizer costs and posing a 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, leveling the land, building dams to store water and soaking the fields, and washing away salt with fresh water; S3, replacing the soil in the saline-alkali land with artificially prepared special soil matrix; S4, applying biological organic fertilizer to the saline-alkali land; S5, improving the saline-alkali land using biotechnology; S6, planting salt-tolerant sweet sorghum in the saline-alkali land; S7, water and fertilizer management for planting sweet sorghum in the improved saline-alkali land; S8, repeating the above procedures for two consecutive years, and completing the improvement of saline-alkali land after planting sweet sorghum in the third year. After planting sweet sorghum on saline-alkali land for two years, the soil salinity decreased from 0.3%–0.6% to approximately 0.125%, while organic matter increased from 0.7% to approximately 2.23%. After three years of planting sweet sorghum, the soil salinity decreased to the level of normal arable land, becoming desalinated soil, meaning the saline-alkali land improvement was successful. However, this method mainly relies on physical methods such as salt leaching and soil replacement, as well as chemical methods such as increased fertilization to improve saline-alkali land. Regardless of the expected improvement effect, saline-alkali areas are already short of fresh water and have salinized soil. Large-scale freshwater leaching and soil replacement through external freshwater transport is essentially a soil import process, which is massive, extremely expensive, and very difficult and impractical to implement in the field. Its feasibility for large-scale saline-alkali land improvement is poor, and the shortage of funds and labor will restrict its large-scale promotion.

[0007] Chinese Patent 202211658900.6 discloses a method for improving coastal saline-alkali land by planting sweet sorghum. Based on the soil water and salt transport patterns in coastal saline-alkali land and the growth and development characteristics of sweet sorghum, this patent first controls soil salinization by covering the entire soil with corn stalks in mid-to-late October. The corn stalks are then crushed and returned to the field at the end of April of the following year to enrich the soil, providing an excellent planting, emergence, and growth environment for sweet sorghum. Sweet sorghum is then sown early under mulch, and harvested from late July to early August. The harvested plants are used for silage. In early to mid-November, the sweet sorghum stalks are harvested and the entire plant is used as a ground cover to reduce soil salinization in winter and spring, providing low-salt, high-moisture soil conditions for the following year's sweet sorghum planting. In April of the following year, the sweet sorghum stalks are returned to the field to improve soil fertility, and sweet sorghum is sown early under mulch again. This achieves a cyclical planting and harvesting system for sweet sorghum, ensuring continuous and efficient production 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 salts to the soil surface via water transport. Our experimental results show that, like most crops, sweet sorghum exhibits highly selective absorption when soil nutrient and even salt content is high, choosing to absorb N, P, and K while rejecting salt, especially since the grains have a relatively low salt content. Therefore, this patent focuses on achieving nutrient recycling through straw return. However, salt also returns to the soil with the straw, and the amount of salt removed from the soil during harvesting or grain removal is limited. Consequently, the effectiveness in reducing soil salinity is questionable. Furthermore, this patent focuses on harvesting sweet sorghum grains rather than stalks. However, as an economic crop, the high biomass of sweet sorghum, especially its high-sugar stalks, is the important target organ for harvesting. Sweet sorghum stalks are thick and have a large biomass. If they are directly returned to the field, they will encounter the cold winter season. During the low-temperature period from November to April of the following year, the straw is difficult to decompose. Regardless of whether returning the straw to the field can reduce the transport of soil salts to the surface with water, the straw that is difficult to decompose will not only fail to improve soil fertility in the short term, but also affect the planting in the following spring. Secondly, the most valuable part of sweet sorghum is the high-sugar stalks, which can be used to produce bioethanol. If the sweet sorghum stalks are returned to the field and only the grains with lower nutritional value are retained, it is like picking up sesame seeds and losing watermelons, which fails to maximize the value of sweet sorghum. Summary of the Invention

[0008] The purpose of this invention is to address the shortcomings of existing technologies and the phenomenon of phosphorus and nitrogen deficiency and potassium abundance in saline-alkali areas by providing a low-input method for planting sweet sorghum to improve saline-alkali land. This method is simple and practical, ensuring the sugar content and grain nutrition of sweet sorghum under extremely low input conditions, while reducing soil salinity and improving saline-alkali land.

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

[0010] A low-input method for improving saline-alkali land by planting sweet sorghum involves a three-year cyclical planting method. In each cycle, sweet sorghum is planted in the first and second years under zero-fertilizer conditions. While harvesting the high-sugar sweet sorghum stalks and nutritionally balanced sorghum grains, the strong absorption capacity of sweet sorghum removes salt from the saline-alkali land. In the third year, the saline-alkali land is fertilized in a balanced manner and the soil quality is adjusted before rotating with other salt-tolerant crops. This achieves the goals of soil nutrient conservation, biodiversity cultivation, and prevention of soil-borne diseases.

[0011] The aforementioned cyclic planting method is applied to soil with a pH of 8.0–8.4 and a salt content of 2.98 g·kg⁻¹. -1 ~3.2g·kg -1 This method can be used to improve saline-alkali land that meets the above conditions.

[0012] The cyclic planting method specifically includes the following steps:

[0013] a. Soil desalination: When the temperature in northern winters drops below -4℃ in January, irrigate the saline-alkali land with saline water that has frozen in winter; cover the soil with plastic film in March to prevent soil salinization.

[0014] b. Sowing and mulching: Sow sweet sorghum at the end of April to the beginning of May, with no fertilizer applied before sowing; after sowing, cover the soil with soil, level it, tamp it down, and then immediately cover it with mulch and press the soil down.

[0015] c. Field management: When the sweet sorghum has 3-4 leaves, thin out or replant seedlings, with 1 seedling per hole;

[0016] d. Harvesting: Harvest sweet sorghum 135-138 days after sowing. After harvesting, cut off the ears of sorghum promptly and store the stalks immediately.

[0017] e. Repeat planting: In the second year, sweet sorghum is repeatedly planted according to methods a to d.

[0018] f. Crop rotation: After two years of planting sweet sorghum with zero fertilizer, the nutrients in the saline-alkali land are adjusted by balanced fertilization in the third year, and other salt-tolerant crops are rotated.

[0019] In step a, the irrigation volume for saltwater freezing irrigation is 52-58 mm.

[0020] In step b, the sowing depth of sweet sorghum is 3-4 cm, with 2-3 seeds sown per hole and a row spacing of 55-58 cm.

[0021] In step f, during the third year of balanced fertilization, the effective amount of fertilizer applied per hectare of soil is as follows: pure N 91.5–97.5 kg, preferably 93–95 kg; P2O5 105–135 kg, preferably 112–125 kg; K2O 37.5–51 kg, preferably 42–48 kg; and organic fertilizer with an organic matter content >30% 600–675 kg, preferably 620–650 kg. To improve nutrient absorption, fertilizer containing attapulgite is preferred.

[0022] The specific method of balanced fertilization is as follows: nitrogen fertilizer, phosphorus fertilizer and organic fertilizer are applied as basal fertilizer before sowing, and potassium fertilizer is applied as top dressing during the jointing stage.

[0023] In this method, balanced fertilization is applied in the third year, and crop rotation is carried out with cotton or sunflower.

[0024] The beneficial effects obtained by the present invention through the above technical solution are as follows:

[0025] This invention provides a method for improving saline-alkali land by planting sweet sorghum, an energy crop. Based on the pH and salinity of saline-alkali land in North China, the method involves planting sweet sorghum with zero fertilizer for the first two years. This leverages the strong nutrient absorption capacity and the characteristics of tall stems and large biomass of sweet sorghum. While meeting the needs for normal growth and stem sugar content of sweet sorghum, it also removes more sodium ions from the saline-alkali land. + This process reduces soil salinity, maintains soil fertility, and achieves biological improvement of saline-alkali land. After two years of salinity reduction, in the third year, nutrients are fully and quantitatively replenished before cotton or sunflowers are planted to balance the nutrients in the saline-alkali soil and reduce salinity. In the fourth year, sweet sorghum is planted again, and this rotation is repeated to achieve sustainable planting of sweet sorghum and cotton / sunflowers. Long-term rotation can achieve a steady reduction in salinity and alkalinity in saline-alkali land, thoroughly improving the soil quality of saline-alkali land.

[0026] This invention uses sweet sorghum planted with zero fertilization and sweet sorghum planted with fertilization as control groups. After 115 days, the sugar content of the sorghum planted with zero fertilization was found to be lower than that of the fertilized group. However, when the planting period was extended to 138 days, sugar content accumulated rapidly in each stem node of the sorghum planted with zero fertilization, and the sugar content increased significantly, with an average increase of 6.6 percentage points, representing a 55.5% increase. Tests showed that the average sugar content of each stem node of the sorghum planted with zero fertilization was 0.8% and 1.1% higher than that of the method described in the comparative patent (CN103222387A) and the traditional fertilization method used by farmers, respectively, achieving a reversal in stem sugar content within 23 days before harvest.

[0027] Data collected over many years of planting experience shows that when sweet sorghum is treated using the method of this invention, the average sodium ion content in each node of the stalk reaches as high as 0.70 g / kg. In contrast, the average sodium ion content in the stalks of sweet sorghum grown using the patented method (CN103222387A) and traditional fertilization methods is only 0.56 g / kg and 0.42 g / kg, respectively. The high sodium content in the sweet sorghum stalks means that it removes more salt ions from the soil. Under the premise of zero fertilization, the sodium in the sweet sorghum stalks is absorbed entirely from the soil, thereby effectively reducing the salinity of the saline-alkali land and achieving the goal of improving saline-alkali land.

[0028] This invention desalinates soil salinity by irrigating frozen soil in winter or by diverting water from the Yellow River in spring. The integrated tillage process of plowing, sowing, and fertilization, with a focus on reducing fertilizer application, avoids secondary soil salinization caused by excessive fertilizer use. No fertilization is required for the first two years after planting, reducing fieldwork and labor intensity for farmers. It also avoids frequent soil disturbance, helping the soil retain moisture and increasing its capacity to store and utilize limited water resources. Furthermore, since the sweet sorghum planted in this invention is a high-biomass, salt-tolerant energy plant, harvesting it removes soil salts, thus reducing soil salinity. This achieves a win-win situation: planting suitable crops, harvesting the target product, and simultaneously restoring saline-alkali land. Attached Figure Description

[0029] Figure 1 Comparison of sugar content at different stem nodes during the first year of sweet sorghum cultivation (at 125 days) under three different planting methods;

[0030] Figure 2 A comparison chart of sugar content at different stem nodes of sweet sorghum 115 days after sowing in the second year for three different planting methods;

[0031] Figure 3 A comparison chart of sugar content at different stem nodes of sweet sorghum 138 days after sowing in the second year for three different planting methods;

[0032] Figure 4 A comparison chart showing the growth rate of sugar content in sweet sorghum stem nodes within 23 days before maturity in the second year for three different planting methods;

[0033] Figure 5 Line graph comparing the Na content in sweet sorghum stalks under three different planting methods;

[0034] Figure 6 This is a photograph of the growth of sweet sorghum at maturity, as described in an embodiment of the present invention.

[0035] Figure 7 Photos 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 Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] A low-input method for improving saline-alkali land by planting sweet sorghum involves a three-year cyclical planting system. In the first and second years of each cycle, sweet sorghum is planted without fertilizer. The high salt tolerance and strong nutrient absorption capacity of sweet sorghum ensure high sugar content in the stalks and nutrients in the grains, resulting in a harvest of high-sugar sorghum stalks and nutritionally balanced grains. Simultaneously, it absorbs and removes more soil salt, reducing the salinity of the saline-alkali soil. In the third year, balanced fertilization and crop rotation with other salt-tolerant crops are implemented to achieve the goals of soil nutrient conservation, biodiversity cultivation, and prevention of soil-borne diseases.

[0039] The aforementioned cyclic planting method is applied to soil with a pH of 8.0–8.4 and a salt content of 2.98 g·kg⁻¹. -1 ~3.2g·kg -1 This method can be used to improve saline-alkali land that meets the above conditions. Sweet sorghum grown under zero-fertilizer conditions for two years consistently yielded high stalk sugar content, nutritionally balanced grains, and effective soil Na+. + The amount of waste removed. This method is based on experiments in coastal saline-alkali land and the saline-alkali land around the Bohai Sea, and it is worth promoting in this area.

[0040] The cyclic planting method specifically includes the following steps:

[0041] a. Soil desalination: When the temperature in northern winters drops below -4℃ in January, irrigate the saline-alkali land with saline water that has frozen in winter; cover the soil with plastic film in March to prevent soil salinization.

[0042] b. Sowing and mulching: Sow sweet sorghum at the end of April to the beginning of May, with no fertilizer applied before sowing; after sowing, cover the soil with soil, level it, tamp it down, and then immediately cover it with mulch and press the soil down.

[0043] c. Field management: When the sweet sorghum has 3-4 leaves, thin out or replant seedlings, with 1 seedling per hole;

[0044] d. Harvesting: Harvest sweet sorghum 135-138 days after sowing. After harvesting, cut off the ears in time and store the stalks immediately for bioethanol production.

[0045] e. Repeat planting: In the second year, sweet sorghum is repeatedly planted according to methods a to d.

[0046] f. Crop rotation: After two years of planting sweet sorghum with zero fertilizer, the nutrients in the saline-alkali land are adjusted by balanced fertilization in the third year, and the crop is rotated to salt-tolerant crops such as sunflower or cotton.

[0047] In step a, the strip field model is used for saltwater freezing irrigation, that is, water storage dikes are built around the strip field, and saltwater is poured in after the plot is leveled.

[0048] Before sowing, during the winter when the temperature stabilizes below -4℃, local brackish groundwater is extracted for surface irrigation, with a water volume of 52-58 mm. The brackish water freezes rapidly due to the low temperature. The following spring, as temperatures rise, the high-concentration brackish water melts and seeps into the soil first due to the different melting points of different salt concentrations. Then, the slightly brackish water and fresh water seep into the soil in sequence, achieving leaching, desalination, and desalination of the topsoil. In early March, when the salt ice begins to melt, a thin film is used to cover the soil to prevent water evaporation and soil salinization, thus ensuring a suitable growing environment for sweet sorghum.

[0049] In the Yellow River Delta region, irrigation with Yellow River water can be carried out once before spring sowing to achieve the same effect of desalinating the soil, creating moisture, and protecting seedlings. Specifically, Yellow River water is used for irrigation in late March, with the irrigation method being flood irrigation and the water volume being 50-55 mm.

[0050] In step b, the sowing depth of sweet sorghum is 3-4 cm, with 2-3 seeds sown per hole and a row spacing of 55-58 cm.

[0051] In step d, the sweet sorghum of this invention is harvested late, which allows for rapid accumulation of sugar content during the ripening period. Compared to 115 days after sowing, the sugar content of sweet sorghum stalks increased by an average of 6.6% 138 days after sowing, representing an increase of up to 55.5%.

[0052] In step f, during the third year of balanced fertilization, the effective amount of fertilizer applied per hectare of soil is as follows: pure N 91.5–97.5 kg, preferably 93–95 kg; P2O5 105–135 kg, preferably 112–125 kg; K2O 37.5–51 kg, preferably 42–48 kg; and organic fertilizer with an organic matter content >30% 600–675 kg, preferably 620–650 kg. To improve nutrient absorption, fertilizer containing attapulgite is preferred.

[0053] The specific method of balanced fertilization is as follows: nitrogen fertilizer, phosphorus fertilizer and organic fertilizer are applied as basal fertilizer before sowing, and potassium fertilizer is applied as top dressing during the jointing stage.

[0054] In this method, the preferred salt-tolerant crop for the third year is cotton or sunflower. Crop rotation can prevent soil-borne infectious diseases caused by continuous planting of the same crop. Secondly, rotating other salt-tolerant crops can improve the soil's micro-ecological environment and cultivate a good soil environment for biodiversity planting.

[0055] In this method, the balanced fertilization is based on replenishing the nutrients consumed by the soil after two consecutive years of planting sweet sorghum in saline-alkali land. The method for planting other salt-tolerant crops in the third year is not the focus of this invention and will not be explicitly limited or elaborated upon here.

[0056] To better illustrate the present invention, further examples are provided below.

[0057] This invention was verified through planting in the core experimental area of ​​heavily saline-alkali land in Haixing County, Hebei Province. This area is located in the Bohai Rim Plain, with soil type mainly consisting of coastal saline soil, dominated by NaCl ions, a soil pH of 8.0–8.4, and a salt content of 2.98 g·kg⁻¹. -1 ~3.2g·kg -1 .

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

[0059] a. Soil desalination: When the temperature in northern winters drops below -4℃ in January, irrigate the saline-alkali land with saline water that has frozen in winter; cover the soil with plastic film in March to prevent soil salinization.

[0060] The specific method involves extracting local saline groundwater during the winter of the year preceding sowing, when the temperature remains below -4℃, and then flooding the surface with 52-58 mm of water. The saline water freezes rapidly due to the low temperature. The following spring, as temperatures rise, the higher concentration of saline water melts and seeps into the soil first, followed by the lower concentration, and finally the fresh water, thus leaching and desalinizing the topsoil. In early March, when the salt ice begins to melt, a thin film is used to cover the soil to prevent moisture evaporation and soil salinization.

[0061] b. Sowing and Mulching: Remove the mulch film in late April to early May, allow the soil surface to dry slightly, and immediately prepare the land. Sow sweet sorghum under zero-fertilizer conditions. The sowing depth is 3-4 cm, with 2-3 seeds per hole and a row spacing of 55-58 cm. After sowing, cover the soil with a leveling and firming motion, then immediately cover with mulch film and press down the soil.

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

[0063] c. Field Management: After emergence, promptly puncture the plastic film around the seedlings to allow ventilation. When the sweet sorghum has 3-4 leaves, thin or replant seedlings, ensuring one seedling per hill to achieve the required planting density. When the seedlings have 5-6 leaves, manually remove weeds and control pests and diseases to ensure normal growth of the sweet sorghum.

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

[0065] e. Repeat planting: In the second year, sweet sorghum is repeatedly planted according to methods a to d.

[0066] f. Crop rotation: After two years of planting sweet sorghum with zero fertilizer, in the third year, adjust the nutrients in the saline-alkali land by applying balanced fertilizer and then plant sunflowers or other salt-tolerant crops such as cotton.

[0067] To verify the planting effect of this method, two control fields were treated with the method disclosed in patent CN103222387A and the traditional planting method of farmers, serving as a control group and a comparative experiment with this method. Both the control field and the experimental field are located in the core experimental area of ​​heavily saline-alkali land in Haixing County, Hebei Province.

[0068] The method described in patent CN103222387A will not be elaborated further. The traditional planting method used by farmers is basically the same as steps a to d of the method of this invention, except that: N, P, and K fertilizers are applied as basal fertilizers before sowing, 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; the sweet sorghum is harvested 125 days after sowing.

[0069] Two years after sowing, the nutrient and salt content of sweet sorghum grains, leaves, and stalks were tested in the experimental field of this method, the control field of the patent, and the traditional control field of farmers. 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 that the differences between the different methods are significant at the P<0.05 statistical level. Data labeled a are significantly higher than data labeled b. Data labeled ab are not significantly different from data labeled a or b. The confidence interval for 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 spikelets obtained using this method were not significantly reduced, proving that zero fertilization does not reduce the nutrient content in 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 phosphorus (P) content in the leaves of sweet sorghum obtained using this method was not significantly different from that of the control group, indicating that the P in the leaves is mainly supplied to the grains to ensure the supply of genetic material. However, the potassium (K) content in the leaves was lower than that of sweet sorghum leaves obtained using the traditional method. This is because, in the later stages of growth, more potassium in the sweet sorghum plant is allocated to the stems, resulting in a decrease in potassium content in the leaves. The increased allocation of potassium to the stems helps in the conversion and accumulation of sugars in the stems, thus enabling a rapid increase in stem sugar content in the later stages of production.

[0075] See Figure 1 This figure shows a comparison of sugar content at different stem nodes during the first year of sweet sorghum cultivation (125 days) using three different planting methods. The data in the figure indicates that the sugar content at stem nodes below the 10th node of the sweet sorghum grown using this method is significantly higher than that of the other two methods, proving that zero fertilization does not affect the conversion and accumulation of sugar in the stem nodes of sweet sorghum.

[0076] See Figure 2 This is a comparison chart of sugar content at various stem nodes of sweet sorghum planted using three different planting methods 115 days after sowing in the second year. The data in the chart shows that the sugar content at each stem node using this method is significantly lower than that of the patented method and the traditional farmer's method.

[0077] See Figure 3 This is a comparison chart of sugar content at various stem nodes of sweet sorghum planted 138 days after sowing in the second year using three different planting methods. The data in the chart shows that, entering the late maturity stage, the sugar content of all stem nodes of sweet sorghum planted using this method is significantly improved, showing a marked difference compared to the patented method and the traditional farmer's method.

[0078] See Figure 4This chart compares the growth rate of sugar content in sweet sorghum stem nodes during the 23 days before harvest using three different planting methods. The data shows that, compared to the patented method, the average sugar content in stem nodes treated with this method increased rapidly during the 23 days before harvest. The average sugar content in stem nodes increased by 6.6 percentage points, a significant increase of 55.5%, with a substantial increase in sugar content in all stem nodes. The traditional farmer method followed, with a 5.5 percentage point increase in sugar content in stem nodes, a 44.0% increase, primarily due to the accumulation of sugar content in stem nodes 4-12. The patented method (CN103222387A) showed a 4.4 percentage point increase in sugar content in stem nodes, a 35.2% increase, mainly due to an increase in sugar content in the upper and middle stem nodes (10-13). This demonstrates that zero fertilization not only does not affect the accumulation of sugar content in the stems but also promotes the increase of sugar content in all stem nodes. In summary, the sugar content in all stem nodes treated with this method is superior to the other two control methods.

[0079] Figure 5 A line graph comparing the Na content in sweet sorghum stalks under three different planting methods is presented. The data clearly shows that the Na content in the sorghum stalks treated by this method is significantly higher than that of the method in the comparative document (CN103222387A) and the traditional farmer method, with significant differences observed at several stem nodes compared to the other two planting methods. Since this method involves zero fertilization, the Na in the sweet sorghum stalks can only originate from the saline-alkali soil, indicating that this method is significantly more effective at removing salt from saline-alkali soil than the other two methods. By significantly removing salt from saline-alkali soil through sweet sorghum, rapid improvement of saline-alkali land can be achieved.

[0080] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made within the scope of the claims of the present invention should be included in the scope of the present invention.

Claims

1. A method for improving saline-alkali land by planting sweet sorghum with low input, characterized in that: A three-year cycle planting method is adopted. In each cycle, sweet sorghum is planted with zero fertilizer in the first and second years to harvest high-sugar stalks and nutritionally balanced grains, and to remove soil salt and reduce the salinity of saline-alkali soil. In the third year, balanced fertilization is implemented in saline-alkali land, and other salt-tolerant crops are rotated. The cyclic planting method specifically includes the following steps: a. Soil desalination: When the temperature in northern winters drops below -4℃ in January, irrigate the saline-alkali land with saline water that has frozen in winter; cover the soil with plastic film in March to prevent soil salinization. b. Sowing and mulching: Sow sweet sorghum at the end of April to the beginning of May, with no fertilizer applied before sowing; after sowing, cover the soil with soil, level it, tamp it down, and then immediately cover it with mulch and press the soil down. c. Field management: When the sweet sorghum has 3-4 leaves, thin out or replant seedlings, with 1 seedling per hole; d. Harvesting: Harvest sweet sorghum 135-138 days after sowing. After harvesting, cut off the ears of sorghum promptly and store the stalks immediately. e. Repeat planting: In the second year, sweet sorghum is repeatedly planted according to methods a~d. f. Crop rotation: After planting sweet sorghum with zero fertilizer for 2 years, the nutrients in the saline-alkali land are adjusted by balanced fertilization in the third year, and other salt-tolerant crops are rotated in. The described cyclic planting method is applied to soil with a pH of 8.0–8.4 and a salinity of 2.98 g·kg⁻¹. -1 ~3.2 g·kg -1 The saline-alkali land.

2. The method for improving saline-alkali land by planting sweet sorghum with low input according to claim 1, characterized in that: In step a, the irrigation volume for saltwater freezing irrigation is 52-58 mm.

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

4. The method for improving saline-alkali land by planting sweet sorghum with low input according to claim 1, characterized in that: In step f, during the third year of balanced fertilization, 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 >30%.

5. The method for improving saline-alkali land by planting sweet sorghum with low input according to claim 4, characterized in that: In step f, during the third year of balanced fertilization, 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 >30%.

6. A method for improving saline-alkali land by planting sweet sorghum with low input according to any one of claims 4 or 5, characterized in that: When applying balanced fertilizer, use fertilizers containing attapulgite soil.

7. A method for improving saline-alkali land by planting sweet sorghum with low input according to any one of claims 4 or 5, characterized in that: The balanced fertilization method involves applying nitrogen, phosphorus, and organic fertilizers as basal fertilizers before sowing, and applying potassium fertilizer as top dressing during the jointing stage.

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

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