The purpose of this study was to elucidate the regulatory mechanisms of planting density on fertilization and kernel-setting characteristics in summer maize under drip fertigation conditions, and to clarify the relationship between planting density and kernel number per ear as well as yield formation under integrated water-fertilizer management.

In 2023-2024, this experiment selected the medium-large ear type maize variety Denghai 605 (DH605) and the small ear type maize variety MY73 as test materials. It set up a traditional water and fertilizer management method (QG) with border irrigation and one-time base application of fertilizer before sowing, as well as a drip irrigation integrated water and fertilizer management method (DG). With a gradient of 15 000 plants/hm², a total of 8 planting densities ranging from 15 000 to 120 000 plants/hm² were set up to explore the impact of planting density on the fertilization and seed-setting characteristics and yield formation of summer maize under the integrated water and fertilizer management of drip irrigation.

Compared with the QG treatment, the plant height and specific leaf area density (SDLA) of both DH605 and MY73 varieties increased under QG treatment, and the differentiation process of male and female spikes accelerated. The number of florets on the male spike increased, while the abortion rate decreased. The number of filaments, total florets, and fertilized florets on the female spike increased, and the seed setting rate and total seed setting rate improved too. The anthesis-silking interval (ASI) shortened by about 1 day, the empty spike rate decreased, and the maximum yields increased by 7.6% and 6.4%, respectively. Under different water and fertilizer management conditions, as planting density increased, the plant height and SDLA of both varieties increased, but the development of male and female spikes was inhibited: the number of florets on the male spike decreased, and the abortion rate increased; the number of silk-spinning and fertilized florets on the female spike decreased, and the fertilization rate and total fertilization rate of florets first increased and then decreased; under high-density conditions, the ASI extended by about 1 day, the empty spike rate and bald tip length increased, and the yield showed a trend of first increasing and then decreasing. In addition, the differentiation process of male and female spikes in MY73 was faster than that in DH605, with a shorter ASI, lower plant height, and larger SDLA. The decrease in the seed setting rate and total seed setting rate with increasing SDLA was not significant, and the planting density for achieving maximum yield was higher.

Under the conditions of this experiment, excessive planting density would have a significant negative impact on fertilization and fruiting characteristics, thereby affecting the establishment of grain number per ear and hindering yield improvement. Compared with traditional irrigation methods, drip irrigation water fertilizer integration technology could effectively alleviate the negative impact of high-density conditions on the fertilization and fruiting characteristics of summer maize, thereby increasing yield. DH605 and MY73 reached their maximum yields at planting densities of 60 000 plants/hm² and 75 000 plants/hm², respectively.