A novel nanosuperabsorbent composite (NSAPC) was prepared by in situ grafting polymerization and cross-linking on to a novel biopolymer of plant origin (complex heteropolysaccharide in nature) in the presence of a clay mineral using a green chemistry technique. The optimization studies of various synthesis parameters, namely, type of clay, backbone/clay ratio, monomer concentration, cross-linker concentration, initiator concentration, quantity of water per unit reaction mass, particle size of backbone, etc., were done. The NSAPC was characterized by X-ray diffraction and scanning electron microscopy. Swelling behavior of NSAPC in response to external stimuli namely salt solutions, fertilizer solutions, temperature, and pH was studied and compared with the performance of P-gel, a commercial superabsorbent material developed earlier in our laboratory. The NSAPC exhibited significant swelling in various environments. Effect of NSAPC on water absorption and retention characteristics of sandy loam soil and soil-less medium was also studied as a function of temperature and tensions. Addition of NSAPC significantly improved the moisture characteristics of plant growth media (both soil and soil-less), showing that it has tremendous potential for diverse applications in moisture stress agriculture. 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1448-1458, 2011