Incubación anaeróbica del suelo como diagnóstico de la respuesta a nitrógeno del maíz bajo siembra directa

There is a lack of information on the applicability of soil methods to evaluate maize response to nitrogen fertilization. The aims of this work were to determine the relationships between soil nitrate concentration (0-30 cm) at four-five leaves stage (V4-V5) of maize and soil anaerobic nitrogen incubation (Nan) with the response of maize to nitrogen fertilization. With this purpose 41 field experiments were conducted in the southeast of Buenos Aires Province (Argentina), between 1998 and 2001. The experiments were carried out with maize under no-tillage with a ramdomized complete block design with two treatments (0 and 60 kg N ha-1). Nan were determined on soil samples taken at sowing and incubated for seven days at 40oC. The response of maize to nitrogen fertilization was not related to soil nitrate concentration at V4 stage (r2 = 0,04). The use of these methods are not recommended for evaluating maize response to nitrogen fertilization. Otherwise, the response of maize was related to soil nitrate concentration at V5 stage (r2 = 0,27). The response of maize to nitrogen was related with Nan (if Nan 48.mg kg-1 the yield increment = 6 %). Nan was related with the time (years) since the last pasture (r2 = 0.39). These results suggest that Nan probably is associated with light carbon fractions and can be used to explain the response of maize to nitrogen fertilization in no-tillage systems.