Table 1.
CS-based hydrogels in controlled release of active ingredients for agricultural applications (2010–2020).
| Entry | CS Source/Properties |
CS-Based Matrices | Method | Water Absorbency | Fertilizers/Active Ingredients | Ref. | ||
|---|---|---|---|---|---|---|---|---|
| [g/g] | Performances | Formulation | Performances | |||||
| Polyacrylic acid/polyacrylamide superabsorbent polymers containing CS | ||||||||
| 1 | CS (Jinxing Biochemical Co (Zhejiang, China): 600 kDa, DDA 90% |
CS/poly(AA-co-AM) three-layer hydrogel | Crosslinking (MBA) | 70 (H2O) | Water retention of soil 25% after 10 days, 16% after 20 days, and 8% after 30 days | NPK fertilizer granules as the core of the three-layer structures | The nutrients released in soil did not exceed 75% on the 30th day | [33] |
| 2 | CS (Seafresh CS): 100–200 kDa, DDA 95% | PVA/cross-CS/poly(AA-co-AM) three-layer hydrogel | Crosslinking (GA, MBA) | 233 (H2O) | n.d. | NPK fertilizer entrapped in the hydrogel during crosslinking | Release of 84% N, 63% P, and 36% K in water after 30 days | [34] |
| 3 | CS (Euromedex, France): DDA 85% | (CS/Cell)-g-PAA hydrogel | Crosslinking (thiourea formaldehyde resin, MBA) | 390 (H2O) 39.5 (0.9 wt.% NaCl) |
Evaporation of water in soil 42% and 76% on the 12th and 24th days, respectively | NPK fertilizer entrapped in the hydrogel by immersing dry hydrogel in fertilizer solution | Release of 75% N, 73% P, and 73% K on the 30th day. Release of nutrients after 3 days was below 15% and did not exceed 75% after 30 days | [35] |
| 4 | CS (Sigma-Aldrich): medium MW, DDA 75–85% | CS-g-P(AA-co-AM)/Basalt hydrogel | Crosslinking (MBA) | 75 (pH 2) 650 (pH 3) 525 (pH 6) 575 (pH 8) 200 (pH 10) |
Hydrogel composite retained available water for the plant up to 2 weeks after irrigation | n.d. | Hydrogel composite increased the yield of eggplant (Solanum melongena) | [36] |
| 5 | CS (Sigma-Aldrich, Germany): high MW, DDA 85% | PAM/CS hydrogel PAM/Alg/CS hydrogel |
Radiation-induced crosslinking |
ca. 380 (H2O) ca. 150 (1 mM NaCl) ca. 50 (1 M NaCl) |
Over 35% water retention after 4 days | n.d. | Growth promotion effect of Alg and CS observed based on quality and quantity of maize plants | [37] |
| CS-based hydrogels fabricated by chemical crosslinking | ||||||||
| 6 | CS (Sigma-Aldrich): High molecular weight 310-375 kDa | CS hydrogel PVA/CS hydrogel |
Crosslinking (GA) | CS: 0.7 (H2O) PVA/CS 1:1 (wt:wt): 2.25 (H2O) |
Water retention of soil 4% after 30 days Water retention of soil 10% after 30 days |
KNO3 entrapped in the hydrogel during crosslinking | Release of K in soil: CS: burst effect in soil, 35% after 2.5 days; prolonged release, 63% after 30 days PVA/CS: burst effect in soil, 22% after 2.5 days; prolonged release, 46% after 30 days |
[38] |
| 7 | CS (Merck) | PVA/CS hydrogel | Crosslinking (GA) | 0.58 (PBS) | Water retention of soil 48% after 15 days | NPK fertilizer entrapped in the hydrogel during crosslinking | Effect on Okra seed germination: better germination energy and growth of young plants |
[39] |
| 8 | CS (Marine Chemicals, Kerala, India): 200 kDa | CS-CuNP hydrogel | Crosslinking (GA) | 3 (H2O) | n.d. | Cu nanoparticles absorbed into CS hydrogels | Cu nanoparticles in CS hydrogels at a concentration of 0.06 g/L had positive effects on tomato growth, yield, and nutritional characteristics | [40] |
| 9 | CS (Marine Chemicals, Kerala, India): 200 kDa | CS/PVA-CuNP hydrogel | Crosslinking (GA) | n.d. | n.d. | Cu nanoparticles absorbed into CS-PVA hydrogels | Application of Cs-PVA-CuNP to grafted watermelon cultivar ‘Jubilee’ plants increased stoma width, primary stem length, and root length by 7%, 8%, and 14%, respectively | [41] |
| 10 | CS | CS hydrogel | Crosslinking (glyoxal) | n.d. | n.d. | DCD (nitrification inhibitor) encapsulation in CS hydrogel beads during CS gelling | Release of DCD in soil: 33% after 7 days under the high rainfall treatment | [42] |
| 11 | CS: 314 kDa, DDA 87% | CS hydrogel | Crosslinking (salicylaldehyde) | 68 (H2O) | Water holding capacity in soil up to 154% | Urea encapsulation during crosslinking | Burst effect ≅ 45% in first 5h; prolonged release ≅ 75% after 11 days, and release of the residual urea up to 35 day | [43] |
| 12 | CS (Sigma-Aldrich, USA): medium MW | CS microspheres | Emulsion crosslinking (genipin) | 1.64 (H2O) | n.d | Urea encapsulation during crosslinking | Urea release in water: about 90% after 7 days | [44] |
| 13 | CS (from seafood waste industry): 140 kDa, DDA 75% | CS-g-IA hydrogel | Graft copolymerization | 23 (H2O) 10 (NaCl, 0.9 w/v) <2.5 (pH 4), 3.5 (pH 2) |
n.d. | Urea loaded into CS films | Urea release in water 73% after 50 h | [45] |
| CS-based hydrogels fabricated by physical crosslinking | ||||||||
| 14 | CS: medium MW, DDA 81% | CS and CS/ST hydrogel macrospheres | Ionotropic gelation (TPP) | 1.21–1.63 (H2O) | n.d. | KNO3 entrapped in the hydrogel by immersing dry hydrogel in fertilizer solution | KNO3 release in water: 73% after 14 days | [46] |
| 15 | CS (Sigma-Aldrich, USA): medium MW, DDA 81% | CS/ST hydrogel macrospheres |
Ionotropic gelation (TPP) | 2.35 (sterilized H2O) 1.43 (H2O) |
n.d. | Plant growth-promoting bacteria were loaded into macrospheres | Bacteria release in soil: bacterial concentration increased progressively during the first 20 days, and then began to decrease after 24 days | [47] |
| 16 | CS (Sigma-Aldrich, USA): 190–310 kDa, DDA 81% | CS and CS/ST hydrogel macrospheres | Ionotropic gelation (TPP) | 1.21–1.63 (H2O) | n.d. | KNO3 entrapped in the hydrogel by immersing xerogel beads in fertilizer solution | KNO3 release in water: 72–95% after 16 days | [48] |
| 17 | CS (Polymar S/A): 180 kDa, DDA 85% | CS/MMt hydrogel microcapsules |
Ionotropic gelation (TPP) | 1.2 (H2O) | n.d. | KNO3 encapsulated in the core of microcapsules | Complete KNO3 release in water after 2 h | [49] |
| 18 | CS: DDA 80% | CS hydrogel | Ionotropic gelation (EDTA–urea adduct) | 570 (H2O) 100 (0.1% NaCl) 40 (1% NaCl) |
n.d. | Urea as an adduct with EDTA | Potential matrix for urea release | [50] |
| 19 | CS: 48.7 kDa, DDA 80% | CS hydrogel | Ionotropic gelation (citric acid–urea adduct) | 1250 (H2O) 210 (0.1% NaCl) |
Water retention of soil 25% after 1 h at 35 °C, while the control retained only 10% | Urea as an adduct with citric acid | n.d. | [51] |
| 20 | CS (Sinopharm Chemical Reagent Co., Ltd.) | CS/yeast hydrogel microspheres | Alkali gelation | 26–32 (H2O) | n.d. | Humic acid as a model fertilizer loaded into dry hydrogel microspheres | Slow-release efficiency of humic acid: 82.6% at pH 7 after 5 h. | [52] |
| 21 | CS: low MW, DDA 92% | Gelatin/CS/PVA hydrogel | Alkali gelation | 11 (H2O) | Water retention of soil ≅ 70% after 1 day | Inulin solution was injected into dried hydrogel | The hydrogels loaded with inulin were capable of inducing resistance against Phytophthora capsica in chili plants | [53] |
| 22 | CS (Aldrich): 480 kDa, DDA 85% | CS/high acetyl gellan gum (HAGG) hydrogel | Polyelectrolyte complexation | 71–219 (H2O) depending on composition of CS:HAGG (4:1 to 1:4) | Time for complete water loss in gels was 9 h, compared to 4 h for evaporation of pure water | MKP fertilizer entrapped in the hydrogel by immersing dry hydrogel in fertilizer solution | Complete MKP release into the water after 8 h | [54] |
| 23 | CS (Polymar Co., Brazil): DDA 74% | CS/humic spheres | Ionotropic gelation (TPP) | n.d. | n.d | Urea encapsulation during gelation | Release of urea in soil: 70% after 7 days | [55] |
| 24 | CS (Northern Chemicals and Glasswares Company, Thailand) | Silk Fibroin/Gelatin/CS hydrogel | Self-assembly by solvent casting | 3.0–4.2 (H2O) depending on CS content | Degree of swelling decreases with increasing CS content | Urea embedded in hydrogels | Urea release in water: about 80% after 13 days | [56] |