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En el sudeste bonaerense, los requerimientos de nitrógeno (N) del cultivo de trigo son estimados mediante el muestreo de suelos en presiembra (0-60 cm), sin embargo, el muestreo en macollaje podría resultar una herramienta de diagnóstico más precisa debido a la ocurrencia de pérdidas de N al comienzo del ciclo del cultivo como consecuencia de excesos hídricos. El objetivo de este trabajo fue validar la metodología de diagnóstico para aplicaciones de N al momento de la siembra o al macollaje en diferentes sitios y años en el sudeste bonaerense, además de analizar la posibilidad de estimar el nivel de N-NO3 - hasta los 60 cm usando como variable el contenido de 0-40 cm. En 6 de 10 sitios, la aplicación de N al macollaje produjo incrementos significativos de rendimiento respecto de la siembra. El rendimiento relativo (RR) en grano se relacionó con el contenido de N mineral (0-60 cm) al momento de la siembra (r²= 0,73) o al macollaje (r²= 0,80). Los umbrales de respuestas para el 95% del RR fueron de 152 kg N ha-1 y 126 kg N ha-1 para la fertilización al momento de la siembra y macollaje, respectivamente. Se determinó una estrecha asociación entre el contenido de N-NO3 - hasta los 60 y 40 cm de profundidad para los muestreos al momento de la siembra (r²= 0,98) y al macollaje (r²= 0,90). El contenido de N-NO3 - hasta los 60 cm para ambos momentos de muestreos puede ser estimado mediante el muestro de suelo hasta los 40 cm de profundidad.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 NNO 3 - 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.

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]