Objectives In order to solve the problem of rational application of nitrogen (N) fertilizer in maize in the Yellow River Delta, we used the root layer real-time regulation technology of N and different fertilizer types to reveal the response of maize yield, N absorption and utilization efficiency and inorganic nitrogen content in surface soil under the field conditions. We also further discussed the effects of different N rates and N fertilizer types on maize yield and N efficiency in order to provide theoretical basis and technical support for the nitrogen management of regional maize production.

Methods Two-year field experiment was carried out in the agricultural high-tech industry demonstration park in the Yellow River Delta of Shandong Province in 2017 and 2018. ‘Zhengdan 958’ was used as the test maize cultivar. We designed a two-factor experiment, the main factor treatment consisted of five N application levels as follows: no N application (CK), optimal N application (Opt), 70% of optimal N application (Opt70%), 130% of optimal N application (Opt130%), farmer traditional N application (FNP). The split plot consisted of three N fertilizer types, ammonium sulfate, calcium ammonium nitrate and urea. Soil samples were collected from 0–60 cm and 0–90 cm soil layers at the six-leaf (V6) and tasseling stage (VT) for rapid measurements of nitrate N and inorganic N contents. The yield and biomass of the maize were investigated, and N contents in maize plant and grain were measured at harvest stage, and N uptake and N use efficiency were calculated.

Results According to the root layer real-time N regulation technology, the rates of fertilizer N were reduced by 41% and 63% in 2017 and 2018, compared with those in FNP, but the yield did not reduced significantly. There was no significant difference in biomass, grain N content, straw N content and N uptake among Opt, Opt130% and FNP. The N harvest index of Opt was increased by 7 and 6 percent points in two years, N partial productivity increased by 71% and 190%, and N utilization efficiency increased by 32 and 34 percent points, respectively compared with FNP. Compared with ammonium sulfate, the grain yield of urea and NH₄NO₃ under Opt treatment was increased by 15% and 8%, respectively in 2017. At maturity, the soil inorganic N contents in Opt treatment were decreased significantly by 29% in 2017 and 39% in 2018, compared with NFP.

Conclusions The employment of the root layer real-time regulation technology in the Yellow River Delta could significantly reduce the N fertilizer rate without a significant effect on grain yield, thereby greatly improving the N use efficiency. Under the optimum N application rate, calcium ammonium nitrate, and urea are more efficient in grain yields than ammonia sulfate.