Interferência e nível de dano econômico de papuã em milho em função de doses de nitrogênio

Abstract

The objective of this study was to evaluate the interference of Alexandergrass on maize and to determine the economic threshold level (ETL) of the weed on the crop with different doses of nitrogen applied in topdressing. The hybrid maize Agroeste AS1551 Pro 2, with single density (11,3 plants m-2) was used. Treatments were composed of different nitrogen doses in topdressing ranging from 0 to 345.6 kg ha of N associated to Alexandergrass populations ranging from 0 to 328 plants m-2. Weed population, leaf area, soil cover and shoot dry mass of Alexandergrass were evaluated as indicator of infestation. For the ETL statistics (number of papua m-2), high, medium and low values of productivity, maize price, herbicide efficiency and control cost were used in each fertilization situation. As higher doses of nitrogen as topdressing are applied to the crop, Alexandergrass interference on grain yield is lower. This relationship is closely linked with the values measured in the field, and it can be said that the same infestation of alexandergrass in a crop can interfere less in productivity if higher doses of nitrogen are applied. For the ETL there is a fertilization interval in which the addition of topdressed N is important (115.2 to 230.4 kg ha) and allows the occurrence of higher levels of infestation. For low N doses (57.6 kg ha), less than 4 plants m-2 could drastically affect the economical results. The high cost of larger amounts of nitrogen (288 and 345.6 kg ha) makes it most economic to control Alexandergrass earlier in the planting season.