Dynamic responses of physiological indexes in maize leaves to different spraying fertilizers at varying concentrations

The dual role of nutrient uptake by plant roots and leaves is one of the main advantages of sprinkler fertigation, while an improper solution concentration suppresses plant physiology and even causes foliar burns. To explore the suitable solution concentrations of nitrogenous fertilizer, phosphate fertilizer and potassium fertilizer, field experiments were conducted at two sites in the North China Plain during the 2019 and 2021 growing seasons of summer maize. The foliar relative chlorophyll content (SPAD), foliar light energy conversion capacity ( F v / F 0 ) and maximum light energy conversion efficiency ( F v / F m ) prior to and after fertilizer solution spraying were measured and compared. In the experiments, six urea concentrations (0.10 − 3.20%), eight monoammonium phosphate concentrations (0.03 − 4.80%) and seven potassium sulfate concentrations (0.10 − 4.80%) were tested during the jointing stage (V6), flare opening stage (V12), heading stage (VT) and filling stage (R2) of summer maize. The results showed that after spraying fertilizer solution, the spatiotemporal variability in F v / F 0 reached moderate from the weak spatiotemporal variability observed prior to spraying. The SPAD values reached moderate from the weak spatiotemporal variability only after spraying nitrogen fertilizer from V6 to VT and after spraying potassium fertilizer from V12 to R2. All the changes in the index variability suggested a great influence of foliar nutrient absorption on plant physiology. Averaged over 5 days following nutrient spraying during the whole season, the average increments synthesized by SPAD, F v / F 0 and F v / F m were 1.60, 1.33, and 1.21 times, and the average reductions were 0.62, 0.78 and 0.62 times, respectively. Depending on the fertilizer type and spraying opportunity, the influence of the fertilizer solution on plant physiology changed greatly. To maximize the relative chlorophyll content and photosynthetic capacity of foliar plants resulting from fertilizer solution spraying, the recommended urea solutions were 0.10 − 0.80%, 0.40%, 0.25 − 0.40% and 0.25 − 0.40% during the V6, V12, VT and R2 stages, respectively. For monoammonium phosphate, the suggested concentrations were 0.06 − 0.15%, 0.06 − 0.15%, 0.03 − 0.40% and 0.03 − 0.80%, respectively. Spraying potassium sulfate at a concentration of 0.10 − 0.40% during the V12 and VT stages would benefit plant growth.