Respuesta del cultivo de maíz bajo siembra directa a la fuente y al método de aplicación de nitrógeno.

PABLO A. BARBIERI, HERNÁN E ECHEVERRÍA, HERNÁN R SAINZ ROZAS

Ciencia del Suelo

Asociación Argentina de la Ciencia del Suelo

Lugar: Bs As ; Año: 2003 p. 18 - 23

0326-3169

Nitrogen fertilization is a common practice in no-tillage (NT) corn. However, when fertilizers like urea are broadcasted on soil surface, volatilization losses could decrease crop nitrogen availability. A experiment was carried out at INTA Research Station, Balcarce, Argentina (37º45´ S; 58º18´ W), during 1998/99 and 1999/00 growing seasons. In 1998/99 treatments were: 1) without N, 2) urea (46-0-0) broadcasted on soil surface, 3) calcareous ammonium nitrate (CAN) and 4) urea incorporated (4 cm). In 1999/00 the same treatments were evaluated except CAN. Nitrogen rate (70 kg N ha-1) was applied at V6 stage. In both years were evaluated volatilization losses, chlorophyll content at flowering, aerial dry matter, accumulated nitrogen and grain yield in physiological maturity. In both years, volatilization losses from broadcasted urea were not larger than 7% of applied nitrogen. Volatilization losses from incorporated urea were lower than 0,1%. Grain yield was significantly increased by N fertilization (7480 and 9980 kg ha-1 without N, average N source, placement and years), but it was not different between N source or placement methods. Chlorophyll content was increased by nitrogen fertilization in both years, but it was similar between N source or placement methods. Nitrogen recovery efficiency (kg N uptake/kg N applied) as determined by difference method was not different between CAN and urea incorporated (0,90, average years) and this value was greater than urea broadcasted (0,75, average years). However, differences in nitrogen use efficiency (kg grain/kg N applied) between urea placement methods or nitrogen sources were similar, because physiological efficiency was greater for urea broadcasted than incorporated urea or CAN. Therefore, the incorporation of urea below residues would not be advantageous practice for Balcarce area, because volatilization losses were not high under theses conditions.  Key words: Nitrogen placement, no tillage, corn, ammonia volatilization, urea.