Basal-topdressing trade-offs in maize production: Lower current N losses versus elevated soil residual N and subsequent losses in the Northeast China

Context or problem

In the Northeast China’s intensive maize (Zea mays L.) production, reliance on high nitrogen (N) fertilizer inputs elevates risks of residual soil N and environmental losses, yet the long-term N fates remain unquantified. Split application of N fertilizer significantly enhances maize productivity and N use efficiency, but trade-offs between current season N losses and residual N accumulation of basal and topdressing fertilizers are poorly resolved across seasons.

Objective or research question

The objectives of this study were to explore the fate of basal and topdressing N in maize production as affected by N application rates and hybrids, especially its distribution in the soil profile and contributions to grain yield.

Methods

In this study, a three-year field experiment was conducted in Northeast China with five N rates (0, 100, 200, 300, 400 kg N ha⁻¹) and two hybrids (XY335 and WK702). N fertilizers were applied in split applications before sowing (as basal N) and at nine-leaf stage (as topdressing N). The basal and topdressing N were labeled with ¹⁵N in 2020, respectively, to trace the fate during the experimental years. Grain yield, N content of maize and N distribution in the soil profile were investigated in 2020–2022.

Results

When N rate increased from 0 to 400 kg ha⁻¹, grain yield increased from 4.2 to 13.6 t ha⁻¹ in XY335 and from 4.3 to 12.4 t ha⁻¹ in WK702. XY335 increased grain yield by 8.3 %-14.3 % than WK702, especially under N rate of 200–400 kg ha⁻¹. The ¹⁵N content of XY335 was higher than that of WK702 regardless of N rates and N sources. There was no significant difference in ¹⁵N content of maize plant among N rates, except 100 kg ha⁻¹. In the first year, basal and topdressing N did not differ in content within maize plant regardless of N rates and hybrids. In subsequent years, the content of topdressing N was higher than that of basal N within plant, especially under higher N rates. Grain yields were positively correlated with basal and topdressing N, even when their magnitudes were small (less than 4 kg ha⁻¹) in the third year. In term of N fate, basal N reduced N losses in the first year but increased soil residual N and subsequent N losses compared with topdressing N. WK702 reduced N losses by increasing soil residual N, although its plant N uptake was lower than that of XY335. The content of basal and topdressing N reduced with soil depth in the first two year while increasing in the third year. Basal N was higher than topdressing N regardless of soil layers, especially growing WK702. Grain yield exhibited a concave function with soil N content, where the soil N content corresponding to the maximum yield increased in the first two years but decreased in the third year with soil depth.

Conclusions and implications

Basal N application significantly reduced seasonal N losses but increased residual N in the soil profile and subsequent N losses, especially under high N rates, compared with topdressing N. Moreover, maize genotypes enhanced the differences in N fate between basal and topdressing N. N-efficiency hybrid increased grain yield and N accumulation, while N-inefficiency hybrid reduced N losses via gains in soil residual N especially in the subsequent years. The findings of this study provide novel insights for optimizing N management to enhance maize N use efficiency and to mitigate N losses, thereby achieving sustainable agricultural development.