Multifunctional Applications of Chitosan in Agriculture

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Characteristics and Mechanisms of Action of Chitosan​

The free amino groups in chitosan molecules exhibit strong affinity for various proteins, making it suitable as a carrier for physiologically active substances such as enzymes, antigens, and antibodies, thereby maintaining high activity in enzymes and cells. Simultaneously, chitosan possesses specific regulatory functions for plant short-term metabolism, effectively promoting the growth of roots, stems, and leaves, improving crop quality, and enhancing plant stress resistance. Furthermore, chitosan can form chelates with metal ions and adsorb negatively charged organic substances like proteins, amino acids, and nucleic acids, improving soil aggregate structure.

Chitosan also exhibits antibacterial properties. This is primarily due to the positively charged amino groups on its molecular chain, while bacterial cells are typically negatively charged. Chitosan can adsorb onto bacterial cell surfaces via its amino groups, forming a polymeric film that alters the permeability of the bacterial cell membrane, blocking nutrient entry and causing plasmolysis, thus killing the bacteria. Alternatively, chitosan can penetrate bacterial cells and bind with the negatively charged cytoplasm, causing coagulation and subsequent bacterial death. In practical applications, chitosan can function simultaneously as a plant growth regulator, soil conditioner, and preservative to regulate crop growth.

​​[1] Application Techniques​

​A. Regulating Crop Growth and Inducing Resistance​

• ​Wheat:​​ Seed coating with 125~165 mg chitosan per kg of seeds, or soaking seeds in a 0.1%~0.2% chitosan solution for 24 hours, activates proteases, promotes seed germination and seedling growth, improves seedling vigor, and enhances plant resistance.
• ​Rice:​​ Soaking seeds in a 0.1%~0.2% chitosan solution for 24~36 hours promotes seed germination and seedling growth; or spraying with a 0.3%~0.5% solution at the 2-leaf stage improves seedling vigor and enhances plant resistance.
• ​Corn:​​ Seed coating with 125~165 mg chitosan per kg of seeds, or soaking seeds in a 0.5% solution for 6 hours, increases seed germination rate and vigor, and improves kernel number per ear, kernel weight per ear, 100-kernel weight, and yield in later growth stages.
• ​Cotton:​​ Seed coating with 125~165 mg chitosan per kg of seeds enhances seed germination rate and vigor.
• ​Soybean:​​ Seed coating with 125~165 mg chitosan per kg of seeds, or soaking seeds in a 1.2% solution for 1 hour, increases seed germination rate and vigor.
• ​Peanut:​​ Soaking seeds in a 0.75% chitosan solution for 8 hours promotes rapid, sustained, and stable growth of roots, stems, and leaves, increases the number of total pods, filled pods, and pod weight per plant, and improves biological and economic yield.
• ​Tomato:​​ Soaking tomato seeds in a 0.075%~0.1% chitosan solution for 24 hours enhances germination potential and rate, prevents damping-off, and increases plant disease resistance.
• ​Cucumber:​​ Soaking cucumber seeds in a 0.01%~0.2% chitosan solution for 6 hours promotes seed germination and enhances seedling cold tolerance. Alternatively, whole-plant spraying with 20~30 mg/L chitosan solution before harvest increases yield.
• ​Bitter Gourd:​​ Soaking seeds in a 0.75%~1% chitosan solution for 3~6 hours promotes seed germination and seedling growth.
• ​Radish:​​ Soaking seeds in a 0.05% chitosan solution for 6 hours improves seed germination rate and seedling salt tolerance.
• ​Cowpea:​​ After the two true leaves unfold, irrigating with a 200~250 mg/L chitosan solution (relative molecular mass 20,000) promotes seedling growth, significantly increasing plant height and stem diameter, and facilitating morphological development. After chitosan induction, superoxide dismutase (SOD) and peroxidase (POD) activities are significantly higher than the control, while malondialdehyde (MDA) content and electrolyte leakage rate are significantly reduced, improving seedling salt tolerance.
• ​Kidney Bean:​​ Treating seeds with 1.5%~2% chitosan at a solution-to-seed ratio of 1:50 effectively promotes seed germination, increases germination rate, germination potential, and germination index, enhances seedling resistance, and effectively solves problems of difficult emergence and seedling survival.
• ​Chinese Cabbage:​​ Starting 7 days after transplanting, spraying 5 times with a 70 mg/L solution at 7-day intervals promotes heading and increases yield by 18.9%. Additionally, it provides some control against Chinese cabbage viral disease, anthracnose, and bacterial angular leaf spot.
• ​Broccoli:​​ Soaking seeds in a 100 mg/L solution for 30 minutes significantly increases chlorophyll content and enzyme activity, promotes strong seedlings, and improves salt tolerance. Spraying 3 times with 40~50 mg/L chitosan (relative molecular mass 6,000) at 10-day intervals during inflorescence differentiation significantly increases chlorophyll, flavonoids, chlorogenic acid, total phenols, soluble protein, and total soluble sugar content in the curd, markedly improving quality.
• ​Jujube (Chinese Date):​​ Spraying leaves 3 times with 500 mg/L chitosan (relative molecular mass 3,000) at 3~5-day intervals during the growth period induces the production of resistance substances, activates the immune system, and provides good control against jujube fruit shrinkage disease.
• ​Walnut:​​ Spraying walnut branches with a 0.1% chitosan solution significantly increases antioxidant enzyme activity and proline content under low-temperature stress, improving cold resistance.
• ​Highland Barley:​​ Soaking seeds in a 200 mg/L solution for 12 hours promotes seed germination and increases seedling chlorophyll and soluble protein content.

​B. Improving Soil​

• ​Enhancing Soil Aggregate Structure:​​ Irrigating nutrient soil or seedbeds with a 20~40 mg/L chitosan solution, or mixing soil with 7.5~15 mg chitosan per kg of soil, improves soil aggregate structure, reduces water evaporation, alleviates soil salinization, and benefits seedling growth of peppers, tomatoes, cucumbers, tobacco, etc.
• ​Remediation of Heavy Metal Contamination:​​ Applying chitosan solution to heavy metal-contaminated soil reduces the content of copper (Cu), lead (Pb), cadmium (Cd), etc., within 7 days as the chitosan application rate increases. Soil enzyme activity and microbial population increase with higher solution application rates. The recommended application rate is 450 mg per kg of soil.

​C. Promoting Preservation and Extending Shelf Life​

• ​Apple:​​ Spraying fruit surfaces evenly with a 1% chitosan solution after harvest and air-drying. After 5 months of storage at room temperature, the apples remain bright green and unwrinkled, with significantly higher moisture and vitamin C content than the control, achieving a sound fruit rate of 98%.
• ​Kiwifruit:​​ Spraying kiwifruit with a 0.3% chitosan solution at room temperature extends storage life to 70~80 days, compared to only 10~13 days for the control.
• ​Citrus:​​ Spraying fruit surfaces evenly with a 2% chitosan solution after harvest and air-drying. After 7 days of storage at 30°C, no significant blemishes appear.
• ​Strawberry:​​ Strawberries sprayed with a 1% chitosan solution maintain relatively high levels of superoxide dismutase (SOD) and vitamin C after storage.
• ​Potato:​​ Before storage, spray diluted solution (20 mg chitosan in water) onto potato surfaces, air-dry, then store. Effectively inhibits tuber sprouting.
• ​Grape:​​ Soaking harvested grapes in a 1% chitosan solution for 20 minutes helps maintain fruit energy levels and physiological quality, extending storage time.
• ​Pitaya (Dragon Fruit):​​ Spraying with 0.4% chitosan solution (relative molecular mass 5,000) at 5, 15, and 25 days after flowering. Post-harvest analysis shows it protects the fruit cell membrane to some extent, slows water loss, delays physiological processes like peel thinning, maintains postharvest quality during storage, and extends shelf life.
• ​Papaya:​​ After harvest, coating fruits with a 1.0% chitosan solution and storing at room temperature effectively reduces water loss, increases superoxide dismutase (SOD) activity, decreases malondialdehyde (MDA) accumulation, maintains fruit firmness, and delays senescence.
• ​Fresh-Cut Fruits and Vegetables:​​ Dipping fresh-cut produce in a 1%~2% chitosan solution for 1 minute, packaging with 0.11mm thick PE film, and storing at 4°C maintains sensory quality, delays nutrient decline, inhibits microbial growth, provides good color preservation, and effectively preserves the quality of fresh-cut apples, lychees, pumpkins, jackfruit, yams, potatoes, mangoes, grapes, etc., during storage.
• ​Cut Flowers:​​ Using a 0.1%~0.5% chitosan solution as a holding solution for cut flowers like gerbera and gladiolus provides good water retention and natural antibacterial ability, prevents water loss, scavenges active free radicals in biological tissues, induces the plant’s own disease resistance, and serves as a natural cut flower preservative.

​​[2] Precautions​

① Chitosan is a natural polysaccharide obtained by deacetylating chitin and is a natural biopolymer. Its quality is related to its degree of deacetylation.
② The application effect of chitosan is related to its molecular mass. Higher molecular mass results in stronger adsorption capacity but weaker plant absorption. Lower molecular mass results in stronger absorption capacity but weaker adsorption.
③ Chitosan is soluble in various dilute acids, with acetic acid solution being optimal. When diluting general chitosan solutions, vigorous stirring is required to ensure uniform concentration.
⑤ Low polymers obtained by degrading chitosan (degree of polymerization 2~20, also known as oligosaccharides or amino-oligosaccharins) are marketed in China as plant resistance inducers and are used in Japan as plant growth regulators.