Resumo

BARRACO, Mirian  e  DIAZ-ZORITA, Martín. Momento de fertilización nitrogenada de cultivos de maíz en hapludoles típicos. Cienc. suelo [online]. 2005, vol.23, n.2, pp.197-203. ISSN 1850-2067.

In the sandy Pampas region, corn (Zea mays L.) grain production is partially related with soil N availability levels. Although N fertilization is common practice, the available information for the efficient use of N fertilizers is not well documented. Our objective was to determine the best N fertilization timing and the relationship between corn response to this practice and soil and crop properties. In Typic Hapludolls located in the northern part of the sandy Pampas region, 4 field essays were performed during the 2001 to 2003 growing seasons in Typic Hapludolls. Seven treatments were arranged in a factorial design with 2 main factors: (a) Urea fertilization with 0.0, 37.5, 75.0 or 150.0 kg ha^-1 and (b) fertilization timing (at planting or at the 6 leaves vegetative stage). Grain yields varied between 5023 and 14757 kg ha^-1 without interactions between N fertilization rates and fertilization timing. The available information did not show differences between N fertilization at planting or during vegetative growth. Ninety percent of the maximum grain yields were achieved when available N levels (N_{soil at planting} + N_fertilizer) was greater than 142 kg ha^-1 in the 0 to 60 cm soil layer. The green color intensity of the upper leaves only discriminated between crops with and without N fertilization, but it was not adequate for N diagnosis. In Typic Hapludolls from the sandy Pampas region N requirements for maximum corn grain yields can be predicted based on soil N measurements and the fertilization performed both at planting or during vegetative growth stages.

Palavras-chave : Pampas Region; Cereals; Urea; Soil Fertility; No Tillage; Soil N.

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