This study aims to develop a novel hydrogel fertilizer containing humic acid and NPK to maintain soil moisture, enhance nutrient slow release, and improve plant growth and yield. A new PCHC-hydrogel was synthesized using polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), humic acid (HA), and citric acid (CA). This PCHC-hydrogel, after being loaded with NPK (nitrogen-phosphorus-potassium) fertilizer, is referred to as the PCHC-NPK hydrogel. The addition of the PCHC-NPK hydrogel significantly (p < 0.0001) increased soil water retention compared to the control. After 10 days, 0.5%, 1%, and 2% (w/w) hydrogel retained 15.66%, 18.70%, and 26.65% of water, respectively. After 15 days in the soil, the PCHC-NPK hydrogel leached 57.66% of nitrogen (N), 47.36% of phosphorus (P), and 38.18% of potassium (K). In pot tests using the PCHC-NPK hydrogel, plant growth and cabbage quality improved substantially (p < 0.05) compared to the control group. The inclusion of humic acid in the PCHC-NPK hydrogel not only enhanced nutrient retention and slow-release/leaching but also improved nutrient absorption by the cabbage roots, ultimately increasing plant growth and 10.25% higher yield compared to PCC–NPK (without humic acid). This hydrogel fertilizer offers a biodegradable and ecological alternative for effective fertilization and improved plant production.
Khatun et al. (Sun,) studied this question.