Objectives We studied the effects of potassium application dosages on the photosynthetic and fluorescence indicators and yield of spring maize under drip fertigation, to understand the beneficial roles of potassium during the growth stages, and to propose an optimal potassium application rate for maize production under drip fertigation in Ningxia Autonomous Region.

Methods A randomized block group experimental design was adopted in a field experiment, six potassium fertilizer dosages were setup, including K₂O 0, 60, 120, 180, 240, 300 kg/hm², and denoted as K0, K1, K2, K3, K4, K5, respectively. The relative chlorophyll content (SPAD), leaf area index (LAI), photosynthetic potential (LAD), and photosynthetic fluorescence parameters of spring maize leaves were monitored during the growing period, and the yields were investigated at harvest. The correlation of yield with the monitored indicators were analyzed.

Results Potassium application had a significant effect on spring maize LAI, showing an “S” trend of “slow-fast-slow”. Two-year results showed that the LAD pre- (V6−R1) and post-anthesis (R1−R6) accounted for about 20% and 80% of the total LAD in spring maize. The dry matter accumulation was mainly occurred after flowering. In 2022 and 2023 years, Pn (net photosynthetic rate), Tr (transpiration rate), Gs (stomatal conductance) and Ci (intercellular carbon dioxide concentration) all showed a trend of increasing and then decreasing with the increase of potash fertilizer dosage. Compared with K0, the average peak Pn and Ci values were all recorded in K3 treatment, which were 16.14% and 4.42% higher than those in K0 treatment. In the 2022 and 2023 years, the Fv/Fm in K3 treatment increased by 23.54% on average at R1 stage compared to K0 treatment. With the increase of potassium application, the yields all showed an increasing and then decreasing trend, and the maximum yield was achieved under K3 treatment, which was 15179 kg/hm² and 14964 kg/hm², respectively. Pearson correlation analysis showed that LAI affected maize yield in the late stage (P<0.05), and LAD did that across the whole growing period (P<0.01). Principal component analysis showed that the K3 treatment had the highest composite score for the optimization effect on maize yield.

Conclusions Reasonable potassium application dosage (180 kg/hm²) results in higher SPAD value, and PSII reaction center activity, thus improves the capacity of optical energy capture, absorption, conversion, and maximizes photochemical efficiency of spring maize, reduces heat dissipation, promotes the photosynthesis of spring maize, and promotes the conversion of dry matter, so as to improve the yield of spring maize. The optimal potassium application dosage is K₂O 155−202 kg/hm² for reaching the target maize yield of 15000 kg/hm² under drip fertitation in Ningxia.