Agriculture in drylands is intensifying in response to the global deficit of food; however, long-term land cultivation in semi-arid and arid regions requires soil-protection measures. Failure to protect from erosion the thin and loose arable soils leads to their swift and irreversible loss. Additionally, productivity of dryland mineral soils depends on intensive irrigation and heavy fertilization, whereas low content of moisture-retaining organics warrants significant loss of the applied resources to evaporation and infiltration beyond the root zone. We examined how polysaccharide-rich cyanobacterial biomass affects the retention of water and nutrients within the root zone. Large quantities of negatively charged polysaccharides are exuded by some cyanobacteria exposed to excess availability of inorganic carbon. Their negative charge, conferred by sulfate moieties and carboxyl groups of uronic acids, increases the capacity of saccharides to form electrostatic interactions with water dipoles and mineral cations, such as K+, Ca2+ and Mg2+. In turn, the saccharide-associated divalent cations can bind loose clay particles into stable aggregates. Furthermore, the immobilized cations can bridge between the saccharides and NO3– and H2PO4– fertilizer anions, averting their loss to infiltration. Here I present the initial results of small-scale studies testing this carbon-neutral approach for increasing sustainability of agricultural practices in the drylands.
