Water unavailability and shortage are severe problems in agriculture, particularly in loamy sandy to sandy soil, since they inhibit plant growth, resulting in a low crop yield. Using biocompatible hydrogels with good water absorption and retention properties is essential to improve plant growth under unfavorable situations. This work aimed to investigate the influence of the carboxymethyl cellulose/nano-calcium carbonate (CMC/NCC) composite amended in the loamy sand soil on maize growth in a pot experiment. Two types of CMC hydrogels with 1 or 5% wv–1 of NCC, designated as CMC/NCC1 and CMC/NCC5 composite hydrogels, respectively, were selected in this study. Incorporating NCC nanoparticles into the physically crosslinked CMC hydrogel networks exhibited the ability to increase water absorption of the pristine and nanocomposite CMC hydrogels. We investigated the properties of hydrogels of different compositions and dosages added to cause increased water absorption capacity (WAC), water holding capacity (WHC), and carbon dioxide (CO2) evolution. The CMC/NCC hydrogels had better swelling capacity than those of the pristine CMC hydrogels at all pHs. The amendment of hydrogels in loamy sand soil enhanced the soil WHC. The CO2 evolution gradually increased with incubation time in the order of CMC > CMC/NCC1 > CMC/NCC5 > the control soil. The chlorophyll contents, the biomasses of the above- and below-ground parts, and root length were observed as the determining parameters of maize growth. Although the total chlorophyll contents of maize leaves did not significantly change with hydrogel supplementations, the root biomass and cumulative root length of the maize grown in the soil amended with hydrogels were significantly lower than that of untreated soil without changing the above-ground biomass. This suggests that the maize plant growing in the loamy sand soil amended with CMC/NCC hydrogels could affect the allocation of carbon without changing the overall crop yield. Thus, the CMC/NCC hydrogels can be used as an alternative soil amendment for agricultural applications in the loamy sand soil to maintain plant growth.