Transforming Sand into Arable Substrate Using Biobased Microgels to Improve Land Productivity

Crop cultivation in coarse sand poses challenges due to its poor water-holding capacity, and as a consequence, such substrate is poor in holding nutrients necessary to support crop growth. The use of swellable microgel as a soil conditioner can enhance the hydraulic properties of sand, which may lead to better plant growth performance despite the inherent poor water-holding ability of sand. This study explores the use of a highly swellable microgel based on Ca²⁺-cross-linked carboxymethyl cellulose (CMC)/alginate for water retention and conditioning of the substrate-coarse sand. The microgel was spray-dried, resulting in spherical particles with an average diameter of ∼2 μm. The swelling ratio (SR) of the microgel was found to be dependent on the CMC:alginate mass ratio and displayed pH-responsive properties due to the ionizability of the −COOH groups. Displacement of Ca²⁺-alginate cross-link by nongelling ions (i.e., Na⁺, Mg²⁺) resulted in greater swelling but reduced the mechanical stability of the microgel. It was found that 0.1-0.5% (w/w) microgel addition in coarse sand greatly enhanced the water-holding and retention properties of the substrate. With this addition of microgels in sand, there is further enhancement in the survival and growth of Amaranthus tricolor seedlings during well-watered and drought conditions. These findings suggest the potential of Ca²⁺-cross-linked CMC/alginate microgels as a water retention agent and conditioner for coarse and dry substrates, hence providing the opportunity to expand the land available for agriculture.