Global water scarcity and soil desertification underscore the critical need for efficient, cost-effective water-retentive materials in sustainable agriculture. To address this, graphene oxide (GO), carbon nanotubes (CNT), and rice husk biochar (RBC) were incorporated into an acrylic acid/2-acrylamido-2-methylpropanesulfonic acid/sodium alginate copolymer network, fabricating three carbon-composite superabsorbent polymers (GO-SAP, CNT-SAP, RBC-SAP). Systematic evaluation revealed that carbon materials dispersed uniformly within the polymer matrix via hydrogen bonding and van der Waals forces, with surface oxygen-containing groups significantly enhancing hydrophilicity. XRD and SEM analyses confirmed amorphous porous structures, with GO-SAP and RBC-SAP exhibiting superior pore distribution. Maximum swelling ratios occurred at loadings of 0.08 g (GO), 0.12 g (CNT), and 0.12 g (RBC). At equivalent loadings, GO-SAP demonstrated the highest absorption capacity, attributable to GO's strong hydrophilicity, 2D lamellar structure, and exceptional dispersibility. All composites maintained high swelling ratios between pH 5-10 and 20-50 degrees C but showed sensitivity to multivalent ions. Swelling kinetics followed a pseudo-second-order model (R-2 > 0.99), indicating chemically controlled absorption governed by hydrophilic groups. Remarkably, the composites retained water for > 4.5 h at 50 degrees C and preserved > 97% water retention after centrifugation (12,000 rpm). Cyclic stability exceeded 80% of initial swelling capacity after 6 absorption-desorption cycles. This work provides a robust foundation for developing high-performance, sustainable superabsorbents.