Effects of blend ratio of controlled-release urea and normal urea on yield, inorganic nitrogen content and nitrogen use efficiency of spring maize in the dryland area of Eastern Gansu Province

Objectives The basal application of all the fertilizers by using controlled release urea in spring maize in the dryland area of Eastern Gansu Province has demonstrated the satisfactory effect on yield increase. Here we studied the effects of mixed ratio of controlled release urea and normal urea from the points of yield, soil inorganic nitrogen (N) content, and enzyme activity, and the nitrogen use efficiency (NUE) of maize.

Methods Field experiments were conducted in 2020 and 2021 in Wutong, Zhenyuan county of Eastern Gansu, with the maize cultivar ‘Xianyu 335’ as test crop. The treatments included no fertilizer (N0), merely common urea (N0:10) and controlled rerelease urea control (N10:0), and the mixed application of controlled release urea and common urea and ratio of 3∶7, 5∶5, and 7∶3. Except N0, all the fertilizer treatments had the same N total input (225 kg/hm²). At maturating stage, maize yield, yield components and grain quality were investigated, and the NUE was calculated. The soil samples were collected at the same time for the determination of inorganic N content in 0−40 cm soil layer, and the enzyme activity in 0−20 cm layer.

Results Compared with N0, all the fertilizer treatments significantly increased maize yield by increasing grain number per ear and 100-grain weight. N5:5 treatment produced the highest average yield (16618 kg/hm²), which was 20.1% and 13.6% higher than N0:10 and N10:0. Compared with N10:0 and N0:10, N7:3 treatment enhanced net income by 7100 yuan/hm² and 5500 yuan/hm², increased output to input ratio by 16.3% and 15.2%. After maize harvest, the NO₃⁻-N contents in 0−40 cm soil layer in the N3:7, N5:5 and N7:3 treatments were lower than N0:10 and N10:0, while the NO₃⁻-N and NH₄⁺-N in 0−20 cm soil layer were higher than N0, showing the blocking effect of NO₃⁻-N leaching. All the N3:7, N5:5 and N7:3 treatments significantly reduced shoot N but enhanced grain N content, compared to N0:10 and N10:0, with the best effect in N7:3 treatment. The nitrate reductase and urease activities tended to increase with the increase of controlled release urea, while the activities of catalase, sucrase and nitrite reductase tended to decrease. Application of controlled release urea significantly increased N partial factor productivity, nitrogen fertilizer agronomic efficiency, nitrogen use efficiency and fertilizer contribution rate to yield. The 2-year average nitrogen fertilizer recovery efficiency of N7:3 was 39.3%, which was 33.1% and 21.9% higher than that of N0:10 and N10:0, respectively. N7:3 was also recorded the highest grain lysine content, and 3.1% and 4.0% higher protein content than N0:10 and N10:0, respectively.

Conclusions The mix application of controlled-release urea and common urea in ratio of 7∶3 completely as basal fertilizer is effective in maintaining high soil available N content in 0−20 cm layer and preventing the deep leaching of NO₃⁻-N across the whole maize seasons, so improving maize grain yield, quality, and production benefit, increasing nitrogen fertilizer efficiency, 7∶3 is a suitable mix ratio for controlled-release urea and common urea for the spring maize production in the Loess Plateau area of Eastern Gansu.