Yield, nitrogen use and economic benefit of summer maize under different ratios of controlled-release and ordinary urea combination in normal and dry rainfall years

Objectives The yield and economic effects of controlled-release and ordinary urea combination in different ratios were compared in drought and normal rainfall years, which will help to realize more efficient use of controlled-release urea.

Methods The experiment was carried out in Shundian Town, Yuzhou City, Henan Province from 2017 to 2018. From June to September of 2017 and 2018, the rainfall were 210.9 mm and 533.9 mm, so 2017 and 2018 were defined as drought and normal year, respectively. Under the same N application rate of 180 kg/hm², the controlled release urea (CRU, N 45%) and ordinary urea (N 46%) was mixed in ratio of 1∶9, 2∶8, 3∶7, 4∶6, 5∶5, respectively, and topdressed in one time. Plant samples were taken at the main growing stages, and the N contents were analyzed. At maturity, yields were investigated, and soil inorganic N content was determined.

Result The maize yield in 2017 and 2018 was significantly different, those in the same treatment in 2017 was decreased by 36.5% to 53.4% than those in 2018. In 2018, compared with ordinary urea treatment, the maize yield was increased by 10.1% and the economic benefit by 15.8% in the treatment with the ratio of CRU and urea of 3∶7. In 2017, compared with urea, the maize yield decreased by 22.9%, and the economic benefit decreased by 56.7% in the treatment of CRU to urea ratio of 4∶6. Under the same combination treatment, N accumulation after maize blossom in 2018 was 108.0%–1175.7% higher, and N partial productivity was 57.4%–114.6% higher than in those in 2017. In 2017, the NO₃^–-N contents in surface soil of treatments were 52.3% to 131.9% higher than those in 2018. In 2018, the NO₃^–-N contents of 0–30 cm soil in the CRU treatments were all higher than that in urea.

Conclusion Compared with normal rainfall year, maize yields are decreased by 36.5%–53.4% due to drought, N accumulation and N partial factor productivity are also decreased, and soil N residue is increased by 52.3%–131.9%. In normal rainfall, the combined application of controlled release urea and ordinary urea can improve the N accumulation and economic benefits. Under the tested conditions, the recommended combination ratio of controlled-release and ordinary urea is 3∶7.