Interaction of deep placed controlled-release urea and water retention agent on nitrogen and water use and maize yield

Controlled-release urea has been widely adopted to increase nitrogen (N) use efficiency and crop production, and these effects can range widely depending on water availability in soil. However, limited information is available on the interaction of controlled-release urea placement depth with water retention agent (WRA) on N and water use and the yield of crops. The objectives of this study were to assess the consequences of this interaction on N and water use and the maize (Zea mays L.) yield by a split-plot design with WRA as the main plots and five application methods of urea as sub-plots. The five application methods consisted of inter-row side dressing of conventional urea at 5 cm and 10 cm depths, inter-row side dressing of controlled-release urea at 5 cm and 10 cm depths, and deep placement of the controlled release urea at a 15 cm depth. Soil water stocks, dry matter accumulation, 1000-grain weight, grain-filling rate, N and water use efficiencies, and economic benefits were evaluated. The results revealed that the year, WRA, urea, and their interactions had significant effects on N and water use efficiencies, yield and benefits. When controlled-release urea was placed deep, soil water stocks were higher from the male tetrad stage to maturity and evapotranspiration (ET alpha) increased. Deep placement of controlled-release urea at a 15 cm depth without WRA enhanced the agronomic efficiency of N and water. The yield and net income were increased compared with controlled-release urea at a 5 cm depth. The combination of WRA and deep placement of controlled-release urea at a 15 cm depth had a significant effect on water use efficiency. However, this combination had no significant effects on N use efficiency, yield and benefits. WRA used with conventional urea can maintain higher soil water stocks, and increase the dry matter production, grain-filling rate, N and water use efficiencies. The differences were more significant during the dry season. Conventional urea at a 10 cm depth with WRA enhanced N and water use efficiencies, yield and net income by 6.5, 3.2, 6.5 and 4.2% respectively when compared with conventional urea without WRA. Thus, the best solution to obtain higher yield, water and N use efficiencies, and net income is placing controlled-release urea at 15-cm depth without WRA. When controlled-release urea is not available, placing conventional urea at a 10-cm depth combined with WRA is an interesting alternative for farmers. (C) 2016 Elsevier B.V. All rights reserved.