A combined cultivation method for improving soil and spraying leaves to improve quality of strawberries

Abstract

The application discloses a combined cultivation method for improving soil and synergistically spraying leaves to improve the quality of strawberries. The combined cultivation method comprises the following steps: S1, soil improvement: before planting strawberries, uniformly applying soil improver to the planting area; the soil improver comprises the following components in mass parts: 2-10 parts of hydroxypropyl methyl cellulose, 20-40 parts of calcium lignosulfonate and 50-80 parts of humic acid; S2, foliar spraying: 30 days to 3 days before picking strawberries, spraying a combined nutrient solution to the plants, wherein the combined nutrient solution comprises a magnesium sulfate solution and a citric acid solution. The application combines soil improvement and foliar spraying to achieve a synergistic effect: significantly improving the hardness, solid-to-acid ratio and soluble solids content of strawberries, and optimizing the flavor and storage performance.

Description

Technical Field

[0001] This invention relates to a combined cultivation method for improving strawberry quality through soil amendment and foliar spraying, belonging to the field of agricultural cultivation technology. Background Technology

[0002] Strawberry (Fragaria ananassa Duch.) is considered a natural hybrid of F. chiloensis and F. virginiana, native to South America. It is a perennial herbaceous plant with a history of approximately 300 years. Strawberries are widely loved by consumers for their sweetness, juiciness, and high content of vitamin C and fiber, which are beneficial to human health. However, strawberries are non-climacteric fruits, meaning their delicate and sensitive surface makes them prone to mechanical damage and moisture loss after harvesting. They are also susceptible to microbial invasion, leading to rot, and even under refrigeration, their shelf life is relatively short.

[0003] Strawberries require loose, well-drained soil with an organic matter content of 2%-5% being ideal. The soil can be neutral or slightly acidic. At the same time, since strawberries are intolerant of waterlogging and salinity, the planting site should be on high ground with good drainage.

[0004] Preservation technology refers to one or more measures taken during the growth process or after harvesting of agricultural products to intervene in the plants and fruits, thereby preserving their nutritional content and reducing their energy consumption. There are many types of fruit and vegetable preservation technologies, broadly categorized into pre-harvest and post-harvest treatments, and further subdivided into physical, chemical, and biological preservation methods. Past research on strawberry preservation technologies has largely focused on post-harvest methods, such as low-temperature storage, chemical reagent soaking, composite material coatings, and infrared / ultraviolet irradiation; however, pre-harvest preservation technologies have been less reported, hence this invention. Summary of the Invention

[0005] The purpose of this invention is to provide a combined cultivation method for improving strawberry quality through soil improvement and foliar spraying. This method addresses soil problems caused by excessive fertilization in greenhouse cultivation, such as soil compaction, salinization, and microbial imbalance, by restoring soil health through a formulated soil conditioner (containing hydroxypropyl methylcellulose, calcium lignosulfonate, etc.), creating a neutral environment suitable for strawberry growth. It also changes the passive approach of relying on post-harvest treatment by innovating pre-harvest intervention: spraying nutrient solution during key strawberry growth stages (30, 20, 10, and 3 days before harvest) to enhance fruit resistance and reduce storage decay and water loss. This invention combines soil improvement and foliar spraying to achieve a synergistic effect, significantly improving strawberry firmness, acid-solid ratio, and soluble solids content, while optimizing flavor and storage performance.

[0006] The co-cultivation method for improving the storage quality of strawberries provided by this invention includes the following steps: S1. Soil improvement: Before planting strawberries, apply soil conditioner evenly to the planting area; The soil conditioner has the following composition by mass fraction: Hydroxypropyl methylcellulose (HPMC) 2-10 parts, calcium lignosulfonate 20-40 parts, humic acid 50-80 parts; S2. Foliar spraying: Spray the plants with a combination of nutrients 30 days to 3 days before strawberry harvesting.

[0007] In step S1, the soil conditioner is spread on the soil surface, and the soil is rotary tilled to a depth of 0-20 cm. After being thoroughly mixed, the soil is then sealed in a greenhouse. The application rate of the soil conditioner is 100-200 kg / mu.

[0008] The combined nutrient solution includes a magnesium sulfate solution and a citric acid solution, wherein the concentration of the magnesium sulfate is 10-100 mg / L, preferably 50 mg / L, and the concentration of the citric acid is 10-100 mg / L, preferably 50 mg / L.

[0009] In step S2, the combined nutrient solution is sprayed 30 days, 20 days, 10 days and 3 days before strawberry harvesting. Preferably, the magnesium sulfate solution is sprayed at 30 days, 20 days and 10 days, and the citric acid solution is sprayed 3 days before harvesting.

[0010] Preferably, the soil conditioner has the following composition by weight: Five parts of hydroxypropyl methylcellulose improve soil structure and water retention; 35 parts of calcium lignosulfonate can reduce soil compaction and improve permeability. 60 parts of humic acid reduce soil alkalinity and activate trace elements in the soil.

[0011] The soil conditioner of this invention can reduce soil pH to neutral, reduce electrical conductivity, increase organic matter content, and alleviate compaction and salinization.

[0012] By spraying the combined nutrient solution, the SPAD value of chlorophyll can be increased, postharvest decay can be reduced, weight loss rate can be decreased (after 5 days of storage at room temperature), and the ratio of soluble solids to acid can be optimized.

[0013] Based on the aforementioned method, the present invention further provides a method for improving the storage quality of strawberries, comprising the following steps: The method described above is used for pre-harvest treatment, combined with post-harvest storage at ambient temperature (20-25℃, relative humidity 85%-90%) or refrigeration (4℃, relative humidity 90%-95%).

[0014] The strawberry storage quality includes the following indicators: Rot index, weight loss, hardness, soluble solids and solid-acid ratio; The method of this invention can reduce the decay index and weight loss rate of strawberries, increase the firmness, soluble solids and solid acid ratio of strawberries, improve the quality of strawberries and extend their shelf life.

[0015] This invention achieves synergistic optimization across four dimensions—soil health, plant growth, fruit quality, and storage performance—through a combined cultivation model of "soil improvement-foliar spraying" and post-harvest storage management. Specific beneficial effects are as follows: Soil improvement: Repairing continuous cropping obstacles and creating a high-quality growing environment.

[0016] For continuous cropping obstacles such as soil compaction, salinization, and microbial imbalance caused by excessive fertilization in greenhouse strawberry cultivation, specialized soil conditioners can rapidly improve soil physical and chemical properties, with the following specific effects: Adjusting soil pH to neutral: After improvement, the soil pH decreased from slightly alkaline (approximately 8.08 in CK1 group) to 7.18, which meets the suitable growth requirements of strawberries for "neutral / slightly acidic" conditions, with a pH reduction of 10.88%; thus solving the problem of poor strawberry growth caused by soil alkalization; Significantly reduced soil salinization: Soil electrical conductivity (reflecting salt content) was 76.52% lower than that of the unmodified group (CK1), which was far superior to the effect of simple irrigation and leaching, effectively reducing the damage of excessive salt in the soil to strawberry roots; Improve soil fertility and organic matter: The organic matter content of the improved soil reached 51.09 g / kg, which is 12.2% higher than that of the unimproved group. It is effective in a short period of time (6 weeks) and provides continuous nutrients for strawberry growth. At the same time, it promotes the formation of soil aggregates and enhances aeration and water retention.

[0017] Foliar spraying: enhances plant resistance to adverse conditions and improves the basic quality of fruits.

[0018] Spraying a magnesium sulfate + citric acid nutrient solution (concentration 50mg / L) 30 days, 20 days, 10 days, and 3 days before strawberry harvesting (critical growth stages) can improve both plant physiology and fruit quality. Enhanced plant photosynthesis: The chlorophyll SPAD value of leaves increased by 9.5% compared with the water control group (CK), promoting the accumulation of organic matter and providing sufficient nutrients for fruit development; Improved fruit physical properties: The fruit firmness at harvest was significantly higher than that of the control group. The firmness of the combined spraying group was 37% higher than that of CK, reducing the risk of post-harvest mechanical damage and laying the foundation for storage. Optimize fruit flavor and nutrition: At harvest, the soluble solids (sugar-related) content is 37.4% higher than the control, the solid-acid ratio (sweet and sour taste index) is 55.7% higher, and the titratable acid content is 11.3% lower, achieving a quality upgrade of "appropriate sweetness and sourness, and better taste".

[0019] Combined cultivation: synergistic effects and enhanced post-harvest storage performance. The combined model of "soil improvement + foliar spraying" is more effective than single measures (soil improvement only, foliar spraying only), especially in post-harvest storage, where it can significantly extend shelf life. The main effects are as follows: (a) Storage at room temperature (20-25℃): shelf life extended by more than 50%.

[0020] Indicator (Difference in efficacy between combined treatment group (T2) and blank control group (CK1): The decay index decreased by 54.95% compared to CK1 on the 7th day of storage, and was still not completely decayed on the 11th day (CK1 was completely decayed on the 9th day). The weight loss rate (moisture loss) was 18.9% lower than that of CK1 on the 6th day of storage, thus preventing fruit from shriveling and becoming dry and shriveled. The fruit firmness reaches 2.22N on the 6th day of storage, indicating stronger resistance to microbial invasion; Soluble solids were retained, and the content was consistently higher than that of CK1 during storage, reaching 32% higher than CK1 on day 6, while maintaining a sweet taste.

[0021] (ii) Cold storage (4℃): further extends shelf life Under refrigerated conditions, the advantages of the combined treatment group are further highlighted, and the indicators are more stable: Excellent appearance: No obvious rotten pieces were observed within 15 days of storage, only slight black spots, while black spots appeared in the CK1 group on the 6th day; Low decay index: On the 15th day of storage, the decay index of group T2 was only 1 / 3 of that of CK1, and the time of decay was delayed (decay occurred on day 15 in T2 and on day 6 in CK1). Slow quality loss: Soluble solids decrease by only 5.84% compared to when harvested (CK1 decreases by 8.94%), hardness is always more than 60% higher than CK1, and the solid-acid ratio remains stable, avoiding the problem of "flavor fading" caused by refrigeration.

[0022] Postharvest storage: adaptable to two scenarios to meet different needs.

[0023] Based on "pre-harvest treatment," this invention, combined with storage at room temperature (20-25℃) or refrigerated (4℃), can be flexibly adapted to different application scenarios: Room temperature storage: suitable for short-distance transportation and local sales. After joint processing, the shelf life is extended from 3-5 days for CK1 to 7-9 days, reducing retail losses. Refrigerated storage: Suitable for long-distance transportation and cross-seasonal supply. After 18 days of storage, the weight loss rate is only 3.77% and the decay index is less than 20%, which is far superior to the untreated group (CK1 weight loss rate 4.24%, decay index over 50%), achieving quality assurance for "off-peak sales".

[0024] Breaking away from the passive preservation model of "emphasizing post-harvest and neglecting pre-harvest": Traditional preservation methods rely heavily on post-harvest chemical soaking and coating, while this invention starts with "source optimization" (soil + growth period), reducing post-harvest processing costs and better meeting the needs of green agriculture; Low cost and easy to operate: Soil conditioner and nutrient solution raw materials are readily available, and the rotary tillage depth (0-20cm) and spraying time (critical growth period) are adapted to the existing strawberry planting process, without the need for additional complicated equipment; The effects are quantifiable and highly stable: all indicators (rot index, hardness, soluble solids, etc.) have been verified by standardized testing (such as hardness tester and sugar-acid meter), and multiple repeated experiments (150 fruits per group, 3 replicates) show that the effects are stable and suitable for large-scale promotion.

[0025] In summary, this invention, through the technical solution of "soil remediation - plant strengthening - storage adaptation", not only solves the pain point of continuous cropping obstacles in greenhouse strawberries, but also achieves the dual goals of "quality improvement + shelf life extension", thus possessing both agricultural practicality and economic value. Attached Figure Description

[0026] Figure 1 This is the distribution of the pre-harvest water-soluble nutrient solution spraying test in Example 1 of the present invention.

[0027] Figure 2 This is the distribution of the greenhouse soil improvement experiment in Embodiment 2 of the present invention.

[0028] Figure 3 This is the distribution of the combined fertilization experiment in Embodiment 3 of the present invention.

[0029] Figure 4 This describes the surface rot of strawberries in the treatment group and control group after 5 days of storage at room temperature in Example 1 of this invention.

[0030] Figure 5 This refers to the change in the decay index of strawberries in the treatment group and the control group after 9 days of storage at room temperature in Example 1 of this invention.

[0031] Figure 6 In Example 1 of this invention, the weight loss rate of strawberries in both the treatment group and the control group showed an increasing trend during storage at room temperature.

[0032] Figure 7 This refers to the change in hardness of strawberries in the treatment group and the control group during storage in Example 1 of this invention.

[0033] Figure 8 This refers to the change in soluble solids content of strawberries in the treatment group and the control group during storage in Example 1 of this invention.

[0034] Figure 9This refers to the change in titratable acid content of strawberries in the treatment group and the control group during storage in Example 1 of this invention.

[0035] Figure 10 This refers to the change in the soluble solids-acid ratio of strawberries in the treated and control groups during storage in Example 1 of this invention.

[0036] Figure 11 This describes the effect of the soil conditioner on the pH of greenhouse soil in Example 2 of this invention.

[0037] Figure 12 This describes the effect of the soil conditioner on the electrical conductivity of greenhouse soil in Example 2 of the present invention.

[0038] Figure 13 This describes the effect of the soil conditioner on the organic matter in greenhouse soil in Example 2 of the present invention.

[0039] Figure 14 This illustrates the effect of room temperature (top image) and refrigeration (bottom image) conditions on the appearance of strawberries in the treatment and control groups in Example 3 of this invention.

[0040] Figure 15 This shows the changes in the strawberry decay index during storage in Example 3 of the present invention (Figure A shows storage at room temperature, and Figure B shows storage at 4 ℃).

[0041] Figure 16 This shows the change in the weight loss rate of strawberries during storage in Example 3 of the present invention (Figure A shows storage at room temperature, and Figure B shows storage at 4°C).

[0042] Figure 17 This shows the change in strawberry firmness during storage in Example 3 of the present invention (Figure A shows storage at room temperature, and Figure B shows storage at 4°C).

[0043] Figure 18 This shows the changes in soluble solids in strawberries during storage in Example 3 of the present invention (Figure A shows storage at room temperature, and Figure B shows storage at 4 ℃).

[0044] Figure 19 This shows the change in titratable acidity of strawberries during storage in Example 3 of the present invention (Figure A shows storage at room temperature, and Figure B shows storage at 4 ℃).

[0045] Figure 20 This shows the change in the sterol-acid ratio of strawberries during storage in Example 3 of the present invention (Figure A shows storage at room temperature, and Figure B shows storage at 4 ℃). Detailed Implementation

[0046] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0047] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0048] Sample processing and index determination are described in the following examples: 1. Sample processing Soil samples: Collect background, control, and improved soil samples for testing at a depth of 0-20 cm. Use the five-point method to randomly collect five soil samples and mix them. Allow a portion of the soil samples to air dry naturally. Remove any stones and plant roots remaining in the soil by sieving. Grind the soil using a soil grinder. Pass one portion of the soil samples through a 1 mm sieve and another portion through a 0.25 mm sieve. These samples will be used when determining the soil's physicochemical properties.

[0049] Strawberry Samples: Collect strawberry samples for testing. Harvest strawberries when they are 90% ripe, selecting fruits that are generally uniform in size and color, without mechanical damage, obvious disease spots, or insect bites. Individually wrap the freshly picked strawberries in foam netting and place them in breathable cardboard boxes, transporting them back to the laboratory on the same day. Set up 8 treatment groups and 1 control group, with 150 fruits in each group. Pack them into 5 open cardboard boxes, stacking them 3 layers deep in each box, with 10 strawberries per layer. Each strawberry is individually wrapped and separated by foam netting to avoid mechanical damage from compression, which is detrimental to storage. Storage temperatures are 20-25°C at room temperature and 4°C under refrigeration.

[0050] 2. Soil index determination (1) pH: Weigh 10 g of air-dried soil sample and mix with water at a ratio of 1:5. Shake for 30 min and let stand for 10 min. Centrifuge and filter to obtain the supernatant. Measure the pH using a pH meter. Perform three replicates for each sample.

[0051] (2) Conductivity: Weigh 10 g of air-dried soil sample and mix it with water at a ratio of 1:5. Shake for 30 min and let stand for 10 min. After centrifugation and filtration, take the supernatant and measure it with a conductivity meter. Three replicates were performed for each sample.

[0052] (3) Soil organic matter: Potassium dichromate titration method. First, accurately weigh 0.2 g of sieved soil and place it into a clean, dry test tube. Note that the sample should not remain on the test tube wall during the slow pouring process. Use a burette to add 5 mL of 0.8 mol K2Cr2O7 to the test tube, shake thoroughly to mix and disperse the sample, and be careful not to let the sample stick to the upper part of the test tube wall. Then add 5 mL of H2SO4 along the wall.

[0053] Heat the oil bath to 190°C, then maintain a stable temperature of approximately 180°C. Insert the test tube into the wire cage and start timing from the moment the sample boils, keeping the sample boiling for 5 minutes. Note that the oil bath temperature and boiling time have a significant impact on the measurement results; accurate operation is essential. After removing the test tube, allow it to cool and wipe the outside of the tube clean.

[0054] Rinse the mixture in the test tube with deionized water into an Erlenmeyer flask, ensuring the liquid volume in the flask is less than two-thirds full. Add 3 drops of o-phenanthroline indicator and titrate with 0.2 mol FeSO4. The titration endpoint is reached when the solution changes from orange-yellow to green and then abruptly turns brownish-red. Perform a blank experiment simultaneously.

[0055]

[0056] Where: V0—volume of FeSO4 consumed during blank titration; V—Volume of FeSO4 consumed during sample titration; Equivalent concentration of N-FeSO4; 0.003-1 mg equivalent of carbon in grams.

[0057] (4) Exchangeable calcium and magnesium: Using atomic absorption spectrophotometry, 0.4 g of sieved soil sample was weighed through a 2 mm sieve and placed into a 50 mL centrifuge tube. 12 mL of ammonium acetate solution was added along the wall of the centrifuge tube and stirred thoroughly with a glass rod to form a homogeneous slurry. Then, ammonium acetate solution was added until the total volume was about 30 mL. The glass rod was washed with ammonium acetate solution, and the washing solution was also added to the centrifuge tube.

[0058] Centrifuge tubes were placed in pairs on the two disks of a coarse balance, and ammonium acetate solution was added for equilibration. The equilibrated tubes were then symmetrically placed into a centrifuge, set to 3000 r / min, and centrifuged for 3 min. The supernatant was collected in a 250 mL volumetric flask. This process was repeated three times to ensure no calcium ion reaction occurred in the leachate. Finally, the solution was brought to volume with ammonium acetate, and then filtered through a 0.45 μm filter membrane. A blank experiment was also performed.

[0059] 3. Strawberry index determination (1) Plant height: The stem height was measured with a ruler. Each treatment group and the control group were divided into three groups, with 10 plants randomly selected from each row. The average value was taken.

[0060] (2) Leaf area: The length and width of the leaves were measured with a ruler. For each treatment group and the control group, 10 leaves were randomly selected from each row and three groups were repeated. The average value was taken.

[0061] (3) Leaf chlorophyll: Before picking strawberries, 10 strawberry plants with 3 leaves were randomly selected from the treatment group and the control group. The chlorophyll content of each plant was measured using a SPAD-502 Plus chlorophyll meter.

[0062] (4) Appearance of strawberries: Several strawberries of similar size and quantity were selected for the treatment group and the control group, and images of representative fruits were taken to facilitate direct observation of the rot on the surface of the strawberries.

[0063] (5) Record the rot status of strawberries in the treatment and control groups on days 1, 3, 5, 7, and 9 of room temperature storage. Fruits were classified into four grades based on the size of the rotten area. The grading criteria were: Grade 0 (no lesions), Grade 1 (less than one-tenth of the fruit's surface area), Grade 2 (between one-tenth and one-quarter of the fruit's surface area), Grade 3 (between one-quarter and one-half of the fruit's surface area), and Grade 1 (more than one-half of the fruit's surface area). The rot index was calculated using the following formula:

[0064] (6) Total color difference: For strawberries stored at room temperature, the color difference was measured for 5 consecutive days, and for strawberries stored in cold storage, the color difference was measured for 2 days at intervals, for a total of 6 times. Three strawberries of similar size were selected from the treatment group and the control group, and the color difference of the fruit was measured using a CR-400 fully automatic colorimeter. * a * b * Value. Where L * The value represents brightness; a positive value indicates white. * The value represents red and green, with a positive value being red; b * The value represents yellow or blue, with a positive value being yellow; E represents the total color difference. Calibration using a standard white board is required before using the instrument. Five random sampling points are taken from each strawberry fruit, and the average value is calculated. The formula for calculating the total color difference is:

[0065] Where: L0 * —Brightness of the sample immediately after harvesting; L * —Brightness of the sample after storage for several days; a0 * —The redness of the sample immediately after picking; a * —Redness of the sample after storage for [number] days; b0 * —The yellowness of the sample immediately after harvesting; b * —The yellowness of the sample after storage for a certain number of days.

[0066] (7) Weight loss rate: Strawberry fruits of similar size and quantity were selected from both the treatment and control groups. The weight of the strawberries was measured using an electronic balance (0.01g), and the weight loss rate was calculated. The formula for calculating the weight loss rate is:

[0067] (8) Hardness: Three strawberry fruits were taken from each treatment group and control group for each measurement, and the hardness was measured using an 8mm diameter probe of a GY-4 fruit hardness tester. The measurement was performed once on each side of the equator, and the measurement was repeated three times. The average value was taken.

[0068] (9) Soluble solids and titratable acid: The soluble solids (TSS) and titratable acid (TA) of the fruit were determined using an Atago PAL-1 handheld sugar-acid analyzer. Three strawberry fruits were selected from the treatment and control groups, and the fruits were mashed into a pulp and then filtered through gauze. 0.2 mL of the filtrate was then pipetted onto a microscope to determine the TSS content. 0.2 mL of the filtrate was pipetted into a small measuring cup, diluted 50 times with deionized water, stirred evenly with a glass rod, and then the TA was determined using the instrument. Each treatment was repeated three times, and the solid-acid ratio was calculated.

[0069] The test site conditions for the following embodiments are as follows: The experimental site, located in a strawberry plantation in the suburbs of Beijing, covers 200 mu (approximately 33 acres) and consists of greenhouses, orchards, and farmland. The temperature inside the greenhouses can be controlled at 19-25°C year-round. The soil in the greenhouses is loam, also known as mixed loam, a loose soil with moderately sized particles. Its texture is between clay and sand, possessing good aeration, water permeability, water retention, and heat retention. It is also widely adaptable to various crops and is considered a relatively ideal agricultural soil. When artificially preparing loam, clay, silt, and fine sand can be thoroughly mixed.

[0070] The experimental strawberry variety was Christmas Red, grown in a greenhouse. Christmas Red plants exhibited thicker stems, greater height, and wider leaves compared to other varieties, such as Red Face strawberries. The strawberries were predominantly orange-red, with most fruits being conical in shape, and a smaller number being wedge-shaped or oval. The first and second inflorescences produced particularly high-quality fruit, with an average single fruit weight of 40g and a maximum weight of 60g. In a normal year in the Beijing area, this variety was planted in early September, entered the budding stage in late October, and began flowering in November. The first crop was almost ripe by mid-to-late December and could be harvested in bulk. The harvest period for marketable fruit typically lasted until mid-May of the following year, a long period of nearly six months.

[0071] Example 1: Foliar nutrient solution spraying In this embodiment, spraying was performed 30, 20, 10, and 3 days before strawberry harvest, during which time the strawberry plants showed good growth. Five nutrient solutions were used: calcium chloride, aluminum chloride, calcium sulfate, magnesium sulfate, and citric acid, labeled A, B, C, D, and E, with a concentration of 50 mg / L. The experiment included eight treatment groups (A, B, C, D, A+E, B+E, C+E, D+E), each with six rows of strawberries. Treatment groups were spaced two rows apart to eliminate interference from different water-soluble nutrient solutions. Additionally, water was used as a control group (CK), also with six rows of strawberries. The spraying experiment distribution design is as follows: Figure 1 As shown.

[0072] The effects of preharvest foliar spraying on strawberry quality in this embodiment are as follows: (1) Leaf chlorophyll Chlorophyll, as the main pigment in plant photosynthesis, plays a crucial role in promoting light absorption during photosynthesis. Table 1 shows that, compared to the control group, strawberry plants treated with either single or combined nutrient solutions exhibited varying degrees of increased chlorophyll SPAD values ​​in their leaves. The combined nutrient solution treatment showed a more significant increase in SPAD values. The D+E treatment group showed the best effect, with a SPAD value 9.5% higher than the control group. These results indicate that trace elements in the nutrient solution can increase the chlorophyll content of strawberry plants, promote the accumulation of organic matter, and benefit plant growth.

[0073] Table 1. chlorophyll SPAD values ​​of strawberry leaves at harvest time

[0074] Note: The above data are the mean ± standard deviation of three measurements in the experiment. Different letters above the data indicate significant differences between treatments. p <0.05).

[0075] (2) Appearance of strawberries like Figure 4 The graph shows the surface rot of strawberries in the treatment and control groups after 5 days of storage at room temperature. It can be seen from the graph that the strawberries treated with nutrient solution showed significantly less rot than the control group. Starting from day 3, black rot spots appeared on the control group strawberries, and by day 5, large areas of rot and maggots had appeared. In contrast, the strawberries in the treatment groups showed less rot than the control group, with treatments D, C+E, and D+E showing the best results, showing no rot by day 5. Therefore, nutrient solution spraying can effectively delay the post-harvest rot process of strawberries.

[0076] (3) Decay Index Figure 5This study shows the changes in the decay index of strawberries in the treatment and control groups after 9 days of storage at room temperature. During the first 7 days, the decay index of strawberries in both the treatment and control groups increased with storage time, but the decay index of the treatment group was consistently lower than that of the control group. The difference in decay index between the two groups was more pronounced on days 3 and 5. Compared to the control group, the C+E treatment group showed the best results, maintaining the lowest decay index throughout. By day 9, due to the prolonged storage time, almost all strawberries in both the treatment and control groups had decayed. The trend in the decay index indicates that pre-harvest nutrient spraying can effectively reduce the post-harvest decay rate of strawberries, a result consistent with strawberry decay imaging.

[0077] (4) Weight loss rate like Figure 6 As shown, the weight loss rate of strawberries in both the treatment and control groups increased during storage at room temperature. On day 1, there was no significant difference in weight loss rate. With increasing storage time, the weight loss rate of strawberries in the treatment group gradually decreased compared to the control group, and the difference widened. This phenomenon indicates that pre-harvest nutrient solution spraying can effectively delay post-harvest water loss in strawberries and maintain fruit weight. Among them, the D+E treatment group showed the best effect, maintaining the lowest weight loss rate throughout, reaching 18% lower than the control group on day 5.

[0078] (5) Hardness Firmness is often used as an important indicator for evaluating the storage quality of strawberries. When strawberries maintain firmness during storage, they can effectively prevent microbial contamination to a certain extent. The changes in firmness of strawberries in the treatment and control groups are shown below. Figure 7 As shown, at harvest time, the firmness of strawberries treated with nutrient solution was significantly higher than that of the control group, indicating that nutrient solution can effectively enhance strawberry firmness and improve strawberry quality during the strawberry plant's growth period. With increasing storage time, the firmness of both the treated and control groups showed a decreasing trend, but the treated strawberries still maintained a firmness value higher than the control group during storage. On day 5, the strawberries treated with the combined nutrient solution had the highest firmness; compared to the control group, the firmness of strawberries in the B+E, C+E, and D+E treatment groups was 35%, 33%, and 37% higher, respectively.

[0079] (6) Soluble solids Soluble solids, as the main decomposition products during strawberry metabolism, directly affect the quality and taste of strawberries. For example... Figure 8As shown, the soluble solids content of strawberries in the treated group was significantly higher than that in the control group immediately after harvesting. Furthermore, during storage, due to strawberry metabolism, the soluble solids content of strawberries in both the treated and control groups decreased, but the soluble solids content of strawberries in the treated group remained higher than that in the control group. Among them, the D+E treatment group showed the most significant effect in delaying the decline in soluble solids content, reaching its highest level on day 5. These results indicate that pre-harvest nutrient spraying can effectively increase and maintain the solids content of strawberry fruits after harvest, thus resulting in better strawberry taste.

[0080] (7) Titratable acid Titratable acidity, like soluble solids, is also an important factor affecting the taste and quality of strawberries. For example... Figure 9 As shown, during storage, the titratable acid content of strawberries in both the treatment and control groups decreased due to the decomposition of organic acids. There was no significant difference in titratable acid content between the treatment groups and the control group. The D+E treatment group showed the smallest change in titratable acid content during storage, indicating that the combined nutrient solution treatment can, to some extent, slow down the consumption of titratable acids and inhibit the metabolism of organic acids.

[0081] (8) Solid-acid ratio The soluble solids-acid ratio of strawberries is calculated by measuring their soluble solids and titratable acidity. A higher soluble solids-acid ratio indicates a sweeter, more balanced sweetness and better taste. Figure 10 As shown, the glutamate-to-acid ratio of strawberries in the treated groups was higher than that in the control group when freshly picked, indicating that the nutrient solution can provide nutrients during the strawberry growth period, thereby improving the taste and quality of the strawberries. In addition, the glutamate-to-acid ratio of strawberries in the treated groups was still significantly higher than that in the control group during the storage period, with the D+E treatment group showing the best effect, and the glutamate-to-acid ratio was 32% higher than that in the control group on the 5th day.

[0082] Example 2: Application of soil conditioner This embodiment included two treatments: CK1 (unmodified soil) and T1 (modified soil), with two replicates for each treatment. Based on the actual conditions of the greenhouse, it was divided longitudinally into four equal areas, each 166.67 square meters. The soil conditioner formulation (by weight) was as follows: 5 parts hydroxypropyl methylcellulose (HPMC) powder, 35 parts calcium lignosulfonate, and 60 parts humic acid. The soil conditioner experimental distribution design was as follows: Figure 2 As shown. During the high-temperature fumigation of the greenhouse in summer, the soil conditioner is evenly spread in both areas, followed by mechanical rotary tillage to a depth of 0-20 cm. The tillage depth is determined based on the root depth of the strawberries at the time of planting. After thoroughly mixing the soil conditioner, the greenhouse is fumigated again before planting the strawberries.

[0083] The effect of applying soil conditioner on soil quality in this embodiment: (1) Soil pH Depend on Figure 11 It was found that there was a significant difference in soil pH before and after the application of soil conditioner. In the 0-20 cm soil layer, the soil pH values ​​were in the order of BLK > CK1 > T1. There was a significant difference between the T1 treatment and the control CK1 and the blank background BLK treatment; however, there was no significant difference between the blank background BLK treatment and the control CK treatment. This indicates that normal irrigation and leaching in the greenhouse cannot significantly reduce soil pH, and the greenhouse soil remains weakly alkaline. After the application of soil conditioner, the soil pH dropped to 7.18, changing from weakly alkaline to neutral soil, which meets the normal growth conditions for strawberry plants. Compared with the CK1 control group, the pH value decreased by 10.88%.

[0084] (2) Soil electrical conductivity from Figure 12 It can be seen that the electrical conductivity in the soil follows the same pattern as the pH value. The electrical conductivity of the greenhouse soil changed significantly before and after the application of soil amendments. In the 0-20 cm soil layer, the electrical conductivity was in the order: BLK > CK1 > T1; there were significant differences among the T1 treatment, the control CK1 treatment, and the blank background BLK treatment. Although the significant difference between the control CK1 treatment and the blank background BLK treatment indicates that normal irrigation and leaching in the greenhouse can effectively remove salt ions from the soil, its effect is far less pronounced than that of applying soil amendments. Furthermore, compared to the control CK1, the electrical conductivity of the soil in the T1 treatment group decreased by 76.52%.

[0085] (3) Soil organic matter Depend on Figure 13 It was found that there was a significant difference in soil organic matter content before and after the application of the soil amendment. In the 0-20cm soil layer, the soil organic matter content among the treatments was: T1 > CK1 > BLK. The T1 treatment was significantly higher than the control CK1 and the blank background BLK treatment. Although there was no significant difference between the blank background BLK treatment and the control CK1 treatment, soluble substances in soil organic matter do migrate with water, resulting in a slightly lower soil organic matter content in the control CK1 treatment than in the blank background BLK treatment. After the soil amendment was applied, the T1 treatment achieved a soil organic matter content of 51.09 g / kg, which was 12.20% higher than the control CK1. The improvement effect was remarkable in a short period of only 6 weeks after the application of the amendment.

[0086] Example 3: Application of soil conditioner combined with foliar nutrient solution Strawberries were planted in the greenhouse according to the previously prepared soil setup. Three treatments were established: CK1 (no treatment), T1 (soil improvement), and T2 (soil improvement combined with nutrient solution spraying). The strawberry seedlings were planted with roots at a depth of 10 cm. Based on the results of the foliar spraying experiment, the most effective nutrient solution was selected at a concentration of 50 mg / L. Spraying was conducted 30, 20, 10, and 3 days before strawberry harvest. The strawberry plants showed good growth at all time points. Strawberries not treated with foliar spraying served as a control group (water). The combined fertilization experiment distribution is shown below. Figure 3 As shown.

[0087] The effect of combined fertilization on strawberry varieties in this embodiment: (1) Appearance of strawberries Figure 14 This describes the effect of room temperature and refrigeration conditions on the appearance of strawberries in the treatment and control groups. Figure 14 As shown in the upper and lower figures, the strawberry CK1, grown without any cultivation measures, exhibited the most obvious rot under normal temperature storage. Faint black spots appeared on the second day of storage, and by the third day, some individual strawberries showed localized rot, until all strawberries developed rot by the sixth day. In contrast, the strawberry T1, grown with the improver, showed significantly better rot than the control group CK1. Black spots appeared on the third day, gradually expanding in area, but no rot developed until a few individual strawberries showed localized rot on the sixth day. The strawberry T2, cultivated using integrated cultivation measures, performed best during normal temperature storage, gradually showing black spots from the fourth day and showing no rot within six days. Figure 14 The lower figure shows that refrigeration storage has a significant advantage over room temperature storage in maintaining the appearance of strawberries; neither the control group nor the treatment group developed rotten patches during refrigeration. The differences are as follows: strawberries CK1, grown without any cultivation measures, began to show faint black spots from day 6, which gradually increased in size; strawberries T1, grown with the improver, showed slightly less black spot symptoms than the control group CK1; while strawberries T2, cultivated with integrated cultivation measures, maintained their bright color and showed little black spot symptoms throughout the entire storage period, demonstrating a significant improvement in integrated cultivation.

[0088] (2) Decay Index Figure 16Figure A shows the changes in the decay index of strawberries under normal temperature conditions. The figure shows significant differences between strawberries grown without any cultivation measures (CK1), strawberries grown with the improver (T1), and strawberries cultivated with integrated cultivation measures (T2) starting from day 3, with the differences reaching their peak on day 7 of storage. The decay index of strawberries in the T1 and T2 treatment groups was reduced by 24.57% and 54.95% respectively compared to the control group (CK1). Furthermore, due to storage at normal temperature, by day 9, the strawberries in the control group were completely decayed, while the decay indices of the T1 and T2 treatment groups were 90.3% and 76.3% respectively; by day 11, the strawberries in the T2 treatment group were not completely decayed. Figure 16 Figure B shows the changes in the decay index of strawberries under refrigeration conditions. The figure shows that the decay index of all groups of strawberries decreased significantly under refrigeration. In the first 6 days of storage, although the decay index of strawberries grown without any cultivation measures (CK1) increased, there was no significant difference compared to strawberries grown with the improver (T1) and strawberries cultivated with comprehensive cultivation measures (T2). From the 9th day of storage, the differences changed and gradually increased. The decay index of the treatment group (T1) decreased from 3% initially to 5% later compared to the control group (CK1). The treatment group (T2) showed the best results among the three groups, with the decay index appearing only on the 15th day of storage and at a low value. This is consistent with the results obtained from the appearance of the strawberries, indicating the highest freshness and longest storage life.

[0089] (3) Weight loss rate Figure 15 Figure A shows the weight loss rates of strawberries in each treatment group and the control group under normal temperature conditions. The figure shows that in the first 3 days of storage, there was no significant difference in weight loss rate among strawberries (CK1, grown without any cultivation measures), strawberries (T1, grown with the improver), and strawberries (T2, cultivated with integrated cultivation measures). From the 4th day onwards, the differences became significant and gradually widened. By the 6th day, the weight loss rates of the T1 and T2 treatment groups were reduced by 6.5% and 18.9% respectively compared to the control. This reduction in strawberry weight loss rate is consistent with the results obtained from the wrinkling of the strawberry surface and the reduction in volume. Figure 15 Figure B shows the weight loss rates of strawberries in each treatment group and the control group under cold storage conditions. Similar to the appearance of strawberries, cold storage also showed a significant advantage in weight loss rate compared to room temperature storage. The overall weight loss rate range of cold storage was 85% lower than that of room temperature storage. After 18 days of cold storage at 4 ℃, the weight loss rates of strawberries CK1 (grown without any cultivation measures), T1 (grown with a plant growth regulator), and T2 (grown with integrated cultivation measures) were 4.24%, 4.02%, and 3.77%, respectively. T2 was 11.3% lower than CK1, but there was no significant difference among the three groups. The smaller overall weight loss rate range also corresponds to the fact that the strawberry volume did not shrink significantly.

[0090] (4) Hardness Depend on Figure 17 It was found that there were significant differences in fruit firmness among strawberry groups CK1 (grown without any cultivation measures after harvest and without storage), T1 (grown with soil conditioner), and T2 (grown with integrated cultivation measures). Treatment with soil conditioner and water-soluble nutrient solution enhanced fruit firmness and improved fruit quality, laying a more solid foundation for subsequent storage. Before storage after harvest, the fruit firmness of treatment groups T1 and T2 was increased by 34.7% and 45.3% respectively compared to the control group CK1. Figure 17 Figure A shows the changes in strawberry firmness under normal temperature conditions. During storage at room temperature, the firmness of strawberries (CK1, grown without any cultivation measures), (T1, grown with a grower, and T2, cultivated using integrated cultivation methods) remained significantly different, and the difference increased with prolonged storage. By day 6, the firmness of the control group (T1) and the treatment groups (T2) were 1.01, 2.03, and 2.22, respectively. The firmness of the treatment groups (T1 and T2) was 82.4% and 99.9% higher than that of the control group (CK1), respectively, demonstrating a highly significant effect. Figure 17 Figure B shows the changes in strawberry firmness under refrigeration conditions. Although the firmness of strawberries under refrigeration conditions remained significantly different throughout the storage period, the changes themselves were relatively small. Therefore, the difference was not as large as that of strawberries stored at room temperature. The firmness of the treatment groups T1 and T2 was consistently about 60% higher than that of the control group CK1.

[0091] (5) Soluble solids Depend on Figure 18 It was found that there were significant differences in the soluble solids content of strawberry fruits grown without any cultivation measures after harvesting and without storage (CK1), strawberry grown with soil conditioner (T1), and strawberry grown with integrated cultivation measures (T2). Treatment with soil conditioner and water-soluble nutrient solution effectively promoted strawberry plant growth, enabling them to store more soluble substances after photosynthesis, thus improving the quality of the strawberry fruit. Before storage after harvesting, the soluble solids content of fruits in treatment groups T1 and T2 increased by 16.7% and 37.4% respectively compared to the control group CK1. Figure 18Figure A shows the changes in soluble solids in strawberries under normal temperature conditions. During storage at normal temperature, the firmness of strawberries (CK1) grown without any cultivation measures, strawberries (T1) grown with soil conditioner, and strawberries (T2) cultivated with integrated cultivation measures maintained significant differences. The soluble solids content of strawberries in the control group and treatment group decreased with storage time because the soluble solids in mature fruits gradually decompose. However, the figure shows that soil conditioner and water-soluble nutrient solution can effectively delay the decrease in soluble solids in strawberries in treatment groups T1 and T2. Figure 18 Figure B shows the changes in soluble solids content in strawberries under refrigeration conditions. Although the soluble solids content of strawberries in the control and treatment groups remained significantly different under refrigeration, the trend was smaller and less pronounced than under room temperature conditions. Compared to strawberries harvested without storage, the soluble solids content of the control group (CK1), and the treatment groups (T1 and T2) decreased by 8.94%, 6.85%, and 5.84%, respectively.

[0092] (6) Titratable acid from Figure 19 It can be seen that the titratable acid content of strawberry fruit itself is low. The titratable acid content of strawberry CK1 grown without any cultivation measures after harvesting and without storage, strawberry T1 grown with the improvement agent, and strawberry T2 cultivated with comprehensive cultivation measures are 0.62%, 0.56%, and 0.55%, respectively. Figure 19 Figure A shows the changes in titratable acid content of strawberries under normal temperature conditions. As can be seen from the figure, with increasing storage time, the decomposition of organic acids led to a gradual decrease in the titratable acid content of the control group CK1 and the treatment groups T1 and T2, with no significant differences among the three groups. However, the soil conditioner and water-soluble nutrient solution effectively delayed the decrease in titratable acid content of strawberries in treatment groups T1 and T2 until the 6th day of storage at room temperature. The titratable acid content of the three groups was reduced by 23.8%, 19.8%, and 18.8% respectively compared to when harvested and not stored. Figure 19 Figure B shows the changes in titratable acid content of strawberries under refrigeration conditions. Due to the low titratable acid content and the minimal variation in strawberry content under refrigeration, the regularity of titratable acid content in strawberries under refrigeration conditions is not obvious. This phenomenon may be due to individual differences in strawberries during the measurement process, and there were no significant differences in titratable acid content between the control group CK1 and the treatment groups T1 and T2 during the overall storage period.

[0093] (7) Solid-acid ratio Figure 20It was found that, before harvesting and storage, there were significant differences in the soluble acid ratio of strawberries (CK1, grown without any cultivation measures), strawberries (T1, grown with soil conditioner), and strawberries (T2, cultivated with integrated cultivation measures). Soil conditioner and water-soluble nutrient solution have a significant impact on the taste and quality of strawberries. Compared with the control group (CK1), the soluble acid ratios of the treatment groups (T1 and T2) were 29.3% and 55.7% higher, respectively. Figure 20 Figure A shows the changes in the glutamate-to-acid ratio of strawberries under normal temperature conditions. As can be seen from the figure, with increasing storage time, the glutamate-to-acid ratio of the control group CK1 and the treatment groups T1 and T2 increased slightly, with significant differences consistently observed among the three groups. These differences are attributed to the improvement in strawberry quality caused by soil conditioner and water-soluble nutrient solution during the growth period. Figure 20 Figure B shows the changes in the solid-acid ratio of strawberries under refrigeration conditions. Under refrigeration conditions, the change pattern of the solid-acid ratio is similar to that of titratable acid, and the trend is not obvious. It can be seen that when the decrease in soluble solids is not significant, titratable acid has a greater impact on the solid-acid ratio. During the overall storage period, the solid-acid ratios of the control group CK1 and the treatment groups T1 and T2 are relatively stable with little change.

Claims

1. A method for combined cultivation to improve the storage quality of strawberries, comprising the following steps: S1. Soil improvement: Before planting strawberries, apply soil conditioner evenly to the planting area; The soil conditioner has the following composition by mass fraction: Hydroxypropyl methylcellulose 2-10 parts, calcium lignosulfonate 20-40 parts, humic acid 50-80 parts; S2. Foliar spraying: Spray the plants with a combination of nutrients 30 days to 3 days before strawberry harvesting. The combined nutrient solution includes a magnesium sulfate solution and a citric acid solution, wherein the concentration of the magnesium sulfate is 10-100 mg / L and the concentration of the citric acid is 10-100 mg / L. Spray the magnesium sulfate solution 30, 20 and 10 days before strawberry picking, and spray the citric acid solution 3 days before picking; The strawberry storage quality includes the following indicators: Rot index, weight loss rate, hardness, soluble solids and solid-acid ratio.

2. The method according to claim 1, characterized in that: In step S1, the soil conditioner is spread on the soil surface, and the soil is rotary tilled to a depth of 0-20 cm. After being thoroughly mixed, the soil is then sealed in a greenhouse. The application rate of the soil conditioner is 100-200 kg / mu.

3. A method for improving the storage quality of strawberries, comprising the following steps: Pre-harvest treatment is performed using the method described in claim 1 or 2, combined with post-harvest storage at room temperature or refrigeration. The strawberry storage quality includes the following indicators: Rot index, weight loss rate, hardness, soluble solids and solid-acid ratio.

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