Super absorbent polymers mitigate drought stress in corn (Zea mays L.) grown under rainfed conditions

Under climate change, the rainfall is predicted to become more intense and less frequent, causing summer drought events and rainwater loss by deep percolation, resulting in both inefficient use of rainwater and yield reduction. Super absorbent polymers (SAPs) have been studied as soil amendments in arid and semi-arid environments, but little is known about potential use for drought stress mitigation in humid subtropical climates under rainfed conditions. This study investigated the potential of three K-based SAPs (Stockosorb 660, Hydrosource and SuperAB A200) to act as water reservoirs during periods of drought. In the laboratory, SAPs mixed with sandy soil were tested for water absorption capacity (WAC) and re-swelling capacity, saturated hydraulic conductivity (Ks), water holding capacity (WHC) and storage of simulated rainfall. SAPs showed high WAC, reswelling capacity, reduced Ks and increased soil WHC with performance dependent more on SAPs concentration than SAPs type. The three SAPs effectively reduced rainwater transport and increased soil water storage during simulated rainfall. In North Carolina, USA, an outdoor pot study with corn in loamy sand soil under rainfed conditions tested the effects of the three SAPs at three concentrations (0.15%, 0.30% and 0.45% w/w) on rainwater transport/storage, biomass production, and biomass rainwater productivity (WPbiomass). Under field conditions, 41.76% of rainwater was percolated in the absence of SAPs while in SAPs-amended soil (0.45% w/w) only 4.8%, 5.5% and 6.02% was lost by percolation, for Stockosorb 660, Hydrosource and SuperAB A200, respectively. The retained rainwater resulted in higher leaf water potential leading to enhanced plant growth and WPbiomass. Stockosorb 660 performed best in terms of rainwater saving, while Hydrosource was the most effective in terms of plant growth and WPbiomass. The results suggest that SAPs soil amendment is a potential approach to mitigate drought stress under rainfed conditions in humid subtropical climates.