Objectives The Huanghuai Plain is a major wheat-producing region in China, and the selenium (Se) concentration in wheat grains is an important determinant of dietary Se nutrition. This study investigated the effects of Se fertilization on wheat Se biofortification and the fate of applied Se under traditional irrigation and integrated water-fertilizer management, with the aim of providing a theoretical basis and technical support for optimizing Se fertilization practices and wheat Se biofortification in the Huanghuai wheat region.

Methods  From 2023 to 2024, field surveys were conducted in farmers’ wheat fields at four locations: Qishan, Shaanxi Province; Yiyang, Henan Province; Cixian, Hebei Province; and Qihe, Shandong Province. Soil available Se and wheat grain Se concentrations were determined. Field experiments with different Se application rates were conducted under traditional irrigation in Qishan and Qihe, with Se application rates of 0, 100, 200, 300, and 400 g/hm² using Na₂SeO₃ as the Se fertilizer, and wheat yield was determined. From 2024 to 2025, field experiments were conducted at the four locations to evaluate different irrigation and Se application methods. Under traditional irrigation, two treatments were established: no Se application and basal application of Se at 400 g/hm²(TC and TB, respectively). Under fertigation, three treatments were established: no Se application, basal application of Se at 400 g/hm², and topdressing application of Se at 400 g/hm² (DC, DB, and DT, respectively). At maturity, grain and straw yields of wheat were measured; Se contents in different grain fractions and straw were analyzed; Se harvest index and Se use efficiency were calculated. Soil samples from 0–100 cm depth were collected to determine available Se content in each 20 cm layer.

Results  1) The field survey showed that wheat grain Se concentrations across the four sites ranged from 10.8 to 234.2 μg/kg, with a mean of 42.5 μg/kg. The soil available Se content varied between 2.1 and 19.2 μg/kg, indicating that both grain and soil were deficient in Se. 2) Se rate trials demonstrated that wheat yield increased with higher Se application rates. The maximum yield of 11488 kg/hm² was achieved at Se application rate of 300 g/hm², representing a significant increase of 22.8% compared to the non-Se treatment (P< 0.05). 3)Under different irrigation and Se application methods, Se treatments did not significantly affect wheat yield but significantly enhanced Se contents in grains, flour, and bran. The Se content in grains, flour, and bran of TB treatment reached 291.7, 244.3, and 373.5 μg/kg, respectively, and those in DB were 316.8, 313.8, and 404.9 μg/kg, respectively, and were 313.2, 244.6, and 339.3 μg/kg in DT treatment, respectively. No significant differences were observed in Se distribution among grain components between DB and DT treatments. Notably, flour Se content was lower than that in bran in Shaanxi, Hebei, and Shandong, whereas the opposite trend was found in Henan. The overall recovery efficiency of Se fertilizer across the four sites was low, averaging only 0.63%. Se application increased the Se harvest index (HI) to 67.6% in TB treatment, 71.9% in DB treatment, and 66.3% in DT treatment. Consequently, the Se allocation index in flour increased from 44.7% to 51.1%, with no significant difference between DB and DT treatment. Furthermore, Se application significantly increased available Se content in the 0–20 cm soil layer by 38.2%–238.0%, with varying degrees of increase observed in deeper layers; however, no significant differences were found between traditional irrigation and integrated water-fertilizer management within the same soil layers. Under traditional irrigation, the soil layers with significantly increased available Se extended to 0–60 cm in Shaanxi and Henan, 0–100 cm in Hebei, and 0–80 cm in Shandong; under selenium application via integrated water and fertilizer management, the increased soil layer depth is 0–100 cm in Shaanxi, Henan and Hebei provinces, while that in Shandong Province is 0–80 cm.

Conclusions  The Huanghuai wheat region is generally characterized by low soil available Se concentrations (2.1–19.2 μg/kg). Although Se fertilization significantly enhances grain Se levels, its efficiency remains low and is highly dependent on environmental and management factors. Notably, while integrated water-fertilizer management did not compromise Se content in grain products compared to traditional irrigation, it exacerbated Se leaching to deeper soil layers. Consequently, we recommend adopting basal Se application combined with reduced application rates under integrated water-fertilizer management to mitigate leaching risks and optimize Se utilization efficiency.