Effect of different rates of slow/controlled release urea on nitrogen content in spring maize in loess highlands

A field experiment was conducted under plastic film mulching conditions in the highlands of the Loess Plateau area to study the effects of different rates of different types of slow and controlled release urea (via basal application at reduced rate) on grain yield, nitrogen use efficiency and nitrogen accumulation in spring maize. The aim of the study was to determine the optimum type and application rate of slow or controlled release urea via simplified and efficient fertilization techniques for spring maize production in the study area. Spring maize cultivar used in the study was Zea mays L. cv. 'Xianyu335'. The experiment consisted of nine treatments—no N use (N0), farmer conventional N fertilizationcommon urea with application rate of 225 kg(N)·hm^-2, N225, common urea N reduction (application rate of 180 kg(N)·hm^-2, N180, and N rate reduction with six kinds of slow or controlled release ureaapplication rate of 180 kg(N)·hm^-2, i.e., resin coated urea (RCU), controlled loss urea (CLU), sulfur coated urea (SCU), urea formaldehyde (UF), polypeptide urea (PU) and stabilized urea (SU). Plant and soil (0-20 cm layer) samples were collected at different growth stages for analysis of grain yield, plant N accumulation and soil inorganic N concentration. The application of N fertilizer increased grain yield of maize by 28%-65% relative to N0. Compared with N225, N180 decreased grain yield by 19.1%. The application of RCU, UF, PU and SU did not significantly reduce grain yield, while the application of SCU and CLU increased grain yield by 4.5% and 2.7%, respectively. Compared with N225, N180 reduced net income by 2 051 ￥·hm^-2. A total of six slow or controlled release urea (except for UF) increased plant N accumulation, but increased N use efficiency by 2.26%-12.69% and net income by 347-1 747 ￥·hm^-2. The highest N use efficiency and economic benefits were observed under SCU and CLU treatments. Greater N uptake and N use efficiency in slow or controlled release urea treatments partly resulted from greater N release during huge bellbottom stage to silking stage. Slow or controlled release urea (including CLU and SCU) via basal application at reduced amount (by 20%) maintained grain yield, improved N use efficiency and economic benefits, and saved labor cost. Therefore, it was recommended for used as an option for simplified and efficient fertilization in spring maize production in similar areas in the Loess Plateau.