Manejo do nitrogênio no milho em semeadura direta em sucessão a espécies de cobertura de solo no inverno e em dois locais: I - efeito sobre a absorção de N

The permanence of cultural residues on soil surface modifies the processes of immobilization and mineralization, reducing N availability to maize, especially in succession to grasses. The objective this study was to evaluate, in two locations, the effects of rate and timimg of N application in maize (0-0; 0-160; 30-130 and 60-100kg/ha, respectively, at sowing and sidedressed), in no-till system, established in two sowing dates after desiccation (1 and 20 days) of two winter cover crops (black oat and common vetch) and bare area without weeds, on N uptake. The research was conducted at two locations of the state of Rio Grande do Sul, Brazil, in the 1996/97 growing season. In Eldorado do Sul, N application at sowing was beneficial because it increased N uptake in relation to the treatment with total N sidedressed, regradless of the species of winter crop tested. At Passo Fundo, only in the stage of 3-4 leaves there was advantage of N application at sowing in relation to total sidedressed application. In the stages of 6-7 leaves, 10-11 leaves and of tasseling there were no differences among the treatments with N application. The delay of maize sowing date after desiccation in 20 days is a management practice that could be used, specially when maize follows black oat, since it increased, at the average at the N management systems, 54 e 75% N uptake, respectively in Eldorado do Sul and in Passo Fundo. N uptake by maize in succession to black oat was lower at Eldorado do Sul that in Passo Fundo, in all stages of development tested. The increment of N rate from 30 to 60 kg/ha did not increase N uptake by maize plants, regardless of cover crop in the winter.