Effect of rates and forms of nitrogen splitting on corn in the Brazilian Cerrado of Piau State

Zea mays crop has been standing out in the Brazilian Cerrado of Piaui State, located in the Northeastern Brazil. However, despite the high technology level utilized, yield levels are still below the expectation, mainly due to the mismanagement of nitrogen (N). This experiment was conducted in field using single-cross hybrid 30F53 from Pioneer®. The experiment was conducted as completely randomized blocks design with nine treatments and four replications. The treatments consisted of five rates of N as urea, equivalent to 0, 60, 120, 180 and 240 kg N ha-1. It was applied twenty kg N ha-1 at sowing and the rest as topdressing. The splits comprised the application of 50% at the four expanded leaf stage (V1) + 50% at the eight expanded leaf stage (V2) or total rates at four expanded leaf stage. Leaf N content, leaf relative chlorophyll content, plant height, ear height, stem diameter, yield, grains per ear and rows per ear, grains per row, 1000 grains weight and agronomic efficiency index were measured. Nitrogen significantly increased agronomic characteristics of corn and the highest grain yield was obtained with 190.65 kg ha-1 N. Plant height, relative chlorophyll content, leaf N content, plant biomass, stem diameter, thousand seed weight, yield and agronomic efficiency index were positively influenced by the rates of nitrogen. The split of topdressing in twice was not suitable in the dystrophic Yellow Latosol of the Piaui Cerrado. Plant height, relative chlorophyll content, ear insertion height, stem diameter, grains per ear and rows per ear, grains per row and agronomic efficiency index positively correlated with grain yield.   Key words: Agronomic efficiency index, yield, relative chlorophyll content.