Co-application of soil superabsorbent polymer and foliar fulvic acid to increase tolerance to water deficit maize: photosynthesis, water parameters, and proline

Fulvic acid (FA) and superabsorbent polymer (SAP) are widely applied to improve crop growth and yield under water deficit conditions, but little is known about the changes in crop physiological parameters related to water deficit tolerance when SAP and FA are combined. A pot test with maize (Zea mays L.) plants was conducted to examine the combined effect on photosynthesis, leaf water, prolific, and growth under soil water deficit. Maize plants were subjected to two soil moisture conditions at the late crop growth phase: water deficit (WD, 50% field capacity) and well-watered (WW, 80% field capacity). The SAP (4.5 g m(-2)) was mixed into the soil layer at sowing and the FA solution (2 g L-1) was sprayed twice during water control. The combined application significantly improved maize grain yield under both watering conditions. The net photosynthesis rate, intrinsic quantum yield, fluorescent parameter (F-v/F-m), and chlorophyll content all improved with the combined application under both watering regimes. The compensating effect of combining chemicals on yield and photosynthesis parameters was higher than when applied alone under the two watering conditions. For prolonged and WD conditions, leaf proline and water content were higher under the combined treatment than when used separately. Under the WD conditions treated with FA and SAP, F-v/F-m, had positive significant correlations with leaf water content and osmotic potential; leaf proline did not show any correlations with either the osmotic potential or leaf water content. This result demonstrated that SAP and FA could be combined to maintain high leaf proline and improve photosynthesis to mitigate adverse effects of moderate water storage on maize growth.