Effects of blending of slow-release nitrogen fertilizer and urea on maize physiological characteristics and nitrogen uptake

Objectives To understand the effects of mixed regular and slow-release nitrogen fertilizers on maize physiological characteristics, nitrogen uptake and the distribution for effective reduction of soil NO₃^–-N leaching and improving of N use efficiency.

Methods An experiment was conducted at the Experimental Station of Water Saving Engineering, Northwest A&F University, with the tested soil of loam and maize cultivar of ‘Zhengdan 958’. A randomized complete block design with three kinds of nitrogen fertilizers and 4 N supply levels was used. Three nitrogen fertilizers were conventional urea (U), slow-release nitrogen fertilizer (S) and a mixture of slow-release nitrogen fertilizer and conventional urea with N ratio 7∶3 (SU). Four N application rates were 90 kg/hm² (N1), 120 kg/hm² (N2), 180 kg/hm² (N3) and 240 kg/hm² (N4), plus a control without N application (CK). A total of 13 treatments were established. The maize yield and physiological property, plant N content and soil NO₃^–-N concentrations were determined.

Results Compared with urea (U) and slow-release nitrogen fertilizer (S), the maximum total chlorophyll content with SU treatment was increased by 7.7% and 1.3% under N3 levels, while the maximum photosynthetic rate and transpiration rate were increased by 6.9%–88.6% and 3.4%–90.3%, respectively. Fertilizer SU treatment increased uptake and utilization of nitrogen. Under N3 level, the maximum plant nitrogen assimilation and grain nitrogen assimilation with SU treatment were 156.0 kg/hm² and 79.7 kg/hm², which were respectively increased by 8.1%–67.3% and 6.2%–54.1%, compared with the fertilizer U and S treatment. There was no significant difference in plant and grain nitrogen assimilation between U (N3) and S (N2) treatment. The highest grain yield (6200.4 kg/hm²) was achieved with the treatment of SU (N3), which was 20.7% and 19.8% higher than the treatments of U (N3) and S (N2), respectively. Compared with the fertilizers U and S treatment, SU treatment reduced soil N leaching by more uptake of soil nutrient at the 0–40 cm soil depth and reducing leaching of NO₃^–-N to deeper soil so as to improve N use efficiency and reduce the risk of soil environmental pollution.

Conclusions Applying the mixture of conventional urea and slow-release fertilizer at the N application rate of 180 kg/hm² is recommended for increasing chlorophyll content and photosynthesis of maize, promoting nitrogen uptake and reducing N leaching in the test area.