Effects of nitrogen fertilizer type and rate on maize yield and nitrogen use efficiency in the Yellow River delta

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.