Objectives The effects of different nitrogen, phosphorus and potassium fertilizer combinations on maize yield formation were studied under high-temperature stress during flowering stage, aiming to provide a nutrient management strategy for alleviating heat damage in maize.

Methods A pot experiment was conducted using a heat-tolerant cultivar MY73 and a heat-sensitive cultivar Xianyu 335 (XY335). Five fertilization treatments were applied: nitrogen alone (N), nitrogen-phosphorus (NP), nitrogen-potassium (NK), nitrogen-phosphorus-potassium (NPK), and no fertilizer control (CK). High temperature stress (mean 40.7℃) and normal temperature (mean 29.5℃) treatment were imposed at the tasseling stage for 8 days. Leaf photosynthetic characteristics were measured one day before the end of high-temperature treatment. At maturing stage, plant biomass, ear traits, grain yield and quality were determined.

Results 1) Under high temperature, the grain yield of both MY73 and XY335 significantly decreased by 36.2%−46.8% and 39.9%−58.8%, respectively, compared with normal temperature. Under high temperature, the yield of both cultivars increased progressively in the order of N, NP, NK, and NPK. Compared with CK, the yields of MY73 in the four treatments increased by 18.1%, 34.5%, 42.5%, 54.8%, yields of XY335 increased by 14.2%, 34.4%, 87.4%, 102.5%, respectively, under high temperature. For both the heat-tolerant cultivar MY73 and the heat-sensitive cultivar XY335, there was no significant yield difference between NK and NPK treatment under high temperature. 2) Under high temperature, the ear length, ear diameter, kernel number per ear, and 100-grain weight of both maize cultivars decreased across fertilizer treatments, with MY73 decreased by 10.5%−18.6%, 4.8%−10.2%, 13.7%−25.8%, and 17.0%−19.3%, respectively, XY335 decreased by 14.2%−28.7%, 14.1%−21.0%, 33.0%−45.4%, and 14.0%−20.5%, respectively. The NPK treatment resulted in the highest values for all the ear traits. It was found that there was no significant difference in ear traits between the NK and NPK treatments for MY73, whereas the ear length and kernel number per ear of XY335 under the NK treatment were significantly lower than those under the NPK treatment. 3) High temperature reduced the net photosynthetic rate (Pn) of MY73 and XY335 by 24.3%−32.0% and 23.3%−41.8%, respectively. Under high temperature, the Pn of both cultivars increased progressively with treatments from N to NPK. Compared with CK, the Pn of MY73 increased by 4.7%, 16.6%, 20.0%, and 31.3%, respectively, and the Pn of XY335 increased by 20.3%, 34.9%, 37.9%, and 46.2%, respectively, with the NPK treatment consistently performing the best. 4) Temperature and fertilizer had significant effects on crude fat and crude protein in grains, respectively, while the cultivar factor primarily influenced lysine and crude starch content. The crude starch content of MY73 was higher than that of XY335 in all fertilization treatments under both temperature conditions.

Conclusions High temperature during the tasseling stage reduced ear length, ear diameter, kernel number per ear, and 100-grain weight, leading to yield loss, with a greater reduction in the heat - sensitive cultivar XY335 than in the heat-tolerant cultivar MY73. Under high - temperature stress, fertilization stimulated the net photosynthetic rate, enhanced ear traits, and ultimately increased grain yield, thereby alleviating heat-induced yield suppression. The combined application of NPK showed the most significant mitigation effect and improved the comprehensive heat-tolerance coefficient of both cultivars.