Abstract: 【Objective】Urea ammonium nitrate solution (UAN) is a liquid nitrogen (N) fertilizer with nitrate-N, ammonium-N and amide-N and owns advantages of these N sources. This study aimed to investigate maize yield responses and N use efficiency of UAN in black soil region, and thereby provided scientific references for application and promotion of UAN in local maize production.【Method】Two field experiments were conducted in black soil region of Jilin province in 2015 and 2016, including seven fertilization treatments, i.e. No N fertilizer application (N0); 200 kg N·hm^-2 of urea as base fertilizer (U200); 200 kg N·hm^-2of UAN as base fertilizer (UAN200); 80 kg N·hm^-2 of urea as base fertilizer with 120 kg N·hm^-2 of urea as topdressing (U80-120); 80 kg N·hm^-2 of UAN as base fertilizer with 120 kg N·hm^-2 of urea as topdressing (UAN80-120); 64 kg N·hm^-2 of urea as base fertilizer with 96 kg N·hm^-2 of urea as topdressing (U64-96); 64 kg N·hm^-2 of UAN as base fertilizer with 96 kg N·hm^-2 of urea as topdressing (UAN64-96). All the topdressing were applied at jointing-bellbottom stage, and the fertilization depth was 12 cm below soil surface. Grain yield, yield characteristics, N uptake in plant, and soil mineral N content were measured at harvesting, as well as further N balance and the percentage of apparent recovery, residual and loss were also calculated.【Result】The results showed that N fertilization increased significantly grain yield and N uptake of maize in 2015 and 2016. In these two years, both the highest yields (10.3 and 11.9 t·hm^-2) and N uptake (187.4 and 288.2 kg·hm^-2) were observed under UAN200 treatment, while the lowest values were obtained under U64-96 treatment, which were 9.14, 10.2 t·hm^-2 and 159.1, 243.8 kg·hm^-2, respectively. With same application rates and methods, grain yields under UAN treatments were generally higher than those under urea treatments. Yield advantages was 6.1% for UAN200, 2.0% for UAN80-120 and 5.3% for UAN64-96 compared with the responding urea treatments in 2015, and these were 0.1%, 7.8% and 7.4% in 2016, respectively. The yield advantage in UAN treatments was mainly attributed to increased kernels number per ear and reduced bare tip length at maturity. With same application rates and methods, UAN treatments showed higher N uptake in plant but lower mineral N residual and surplus in soil after harvesting, thus obtained higher N use efficiency. UAN64-96 treatment reduced N input of 40 kg·hm^-2 compared with UAN200 treatment, but it still obtained grain yields of 9.6 and 11.0 t·hm^-2 in the two years, respectively, and which was similar with UAN200 treatment in 2015. Moreover, both the highest N recovery rates and lowest N loss rates were observed under UAN64-96 treatment, the former was 42.6% in 2015 and 52.0% in 2016, and the latter were 2.4% and 4.4%, respectively.【Conclusion】Compared with urea treatments, UAN treatments showed equal or higher maize grain yields and plants N uptake in black soil region when applied with same rates and methods, meanwhile soil N residual and surplus were relatively lower, and thereby resulting in higher N use efficiency and better environmental effect. Based on the integrated consideration of N application rate, grain yield, N use and loss, 160 kg N·hm^-2 of UAN was recommended to be applied for maize production in black soil region with two splits, i.e. 40% before planting and 60% at jointing-bellbottom stage.

Key words: urea ammonium nitrate solution (UAN), spring maize, black soil, grain yield, N uptake, N balance