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The use of 15N tracers in blends of N-fertilizers contributes to determining the N derived from each N-fertilizer in the plant, improving the recommendation in the field. However, to evaluate the contribution of two 15N-labeled fertilizers to maize nutrition is an expensive process, and it is challenging to manufacture 15N-labeled controlled-release urea (CRU) considering a polymer-sulfur coated urea (PSCU). The objective of this study was to evaluate, in a field experiment, two methods to quantify the N derived from the PSCU (NdfPSCU) in maize plant using two blends (70% PSCU + 30% urea (U) and 30% PSCU + 70% U) applied in three ways (incorporated, broadcast and split application). The first method quantifies the NdfPSCU by subtracting the total N uptake in the N treatment by the sum of the N uptake in the control treatment (without N-fertilizer application) and the N derived from the U (NdfU) in the plant quantified with 15N. The second method quantifies the NdfPSCU using 15N (precise and direct method). Despite the first method is less expensive than the second it underestimated the NdfPSCU in four maize growth stages in Rhodic Eutrustox soil, being necessary the use of 15N in the PSCU to quantify the NdfPSCU with blends of PSCU + U. [ABSTRACT FROM AUTHOR]

Blends of controlled-release urea (CRU) and conventional urea can be an alternative to conventional fertilization to improve nitrogen use efficiency (NUE) and reduce costs when applied as a single application to agricultural crops. Different indexes of NUE, grain yield, nutrient uptake and partitioning in maize (Zea mays L.) were investigated in field experiments. The treatments consisted of a single rate of 180 kg N ha−1 with different proportions of polymer-sulfur coated urea (PSCU) and conventional urea (U) applied incorporated at sowing (0.05 m below and 0.1 m to the side of the seed row) at two tropical sites (Site 1, Typic Haplustox; Site 2, Rhodic Haplustox) in Brazil. A control treatment (without urea-N) and a treatment with conventional urea management (UCM: 20% of urea-N applied as basal fertilizer and 80% of N applied as top dressing) were also included. This study demonstrates that blends of PSCU and U are efficient in supplying N throughout the maize cycle at a Typic Haplustox site when applied in a single application incorporated at sowing, resulting in high yields and adequate macronutrient uptake. PSCU improved NUE index compared to U and UCM. There was not response for N fertilization in the Rhodic Haplustox site. [ABSTRACT FROM AUTHOR]