Effects of nitrogen rates and application time on popcorn

Among the various limiting factors in the production of Brazilian popcorn, paucity of information on cultural practices is highlighted, with emphasis on the management of fertilizer, especially nitrogen (N) topdressing. This mineral nutrient is of great importance in several agronomic characteristics of corn plants, mainly components of production. The aim of this study is to evaluate the effects of N management on popcorn (Zea mays L. subsp. everta) in two growing seasons (during 2007 and 2008 agricultural years) in Maringá, Northeast of Parana, Brazil. Experiment was conducted as a factorial arrangement in randomized complete blocks design with four replications. The treatments were a combination of five N rates (0; 45; 90; 135; 180 kg ha), two seasons of topdressing applications (development stages V4 and V8) and two varieties of popcorn (BRS-Angela and IAC-125). The N topdressing rates increased plant height, leaf area index, and ear length, number of grains per row, thousand grain weight, and grain yield of popcorn. The highest yields (3.94 t ha and 3.24 t ha) were obtained with the estimated rates of 130.1 and 131.5 kg N ha for the cultivars BRS-Angela in V8 and IAC-125 at V4, respectively. On the other hand, the economic rates of N topdressing were 73.76 and 78.42 kg N ha for BRS-Angela and IAC-125 cultivars, respectively. The N rates and time of application did not influence the capacity for expansion, and only the effect in this genetic trait was observed.