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Nitrogen (N) wheat requirements in southeastern Buenos Aires province are determined by soil sampling at pre-planting (0-60 cm). Nevertheless, soil sampling at tillering could be a more precise tool for diagnosing N deficiencies due to N losses during initial stages of growing seasons as a consequence of excessive water in the soil profile. The objective of this study was to validate the methodology of N diagnostics and N application at planting or tillering at the different sites and years insoutheastern Buenos Aires province. An additional objective was to analyze the possibility of estimating N-NO3- levels up to 60 cm soil depths using soil N-NO3- contents up to 40 cm. In 6 of 10 sites, applications of N at tillering increased grain yield significantly compared to fertilization at planting. Relative yield (RY) was related to mineral N content (0-60 cm) at planting (r²= 0.73) or tillering (r²= 0.80). Response thresholds for 95% of RY were 152 kg N ha-1 and 126 kg N ha-1 for fertilization at planting or tillering, respectively. Soil N-NO3- content up to a soil depth of 60 cm was highly associated with N-NO3- content to the 40 cm depth for both sampling moments (r²= 0.98 and 0.90 for planting and tillering, respectively). Soil N-NO3- content from 0 to 60 cm can be estimated using soil N-NO3- content from 0 to 40 cm. [ABSTRACT FROM AUTHOR]