Resposta do inhame submetido a diferentes fontes e doses de fertilizantes nitrogenados no Estado do Maranhão, Brasil

This study was carried out at the State University of Maranhao, Sao Luis, Brazil from January to November 2012. We assessed the behavior of the yam Dioscorea cayenensis 'Da Costa', fertilized with different rates and sources of nitrogen (N). The experimental design was randomized, with treatments in a 6 x 2 factorial design. The factors were represented by six rates of N fertilization (0, 50, 100, 150, 200, and 250 kg.ha(-1)) and two sources (ammonium sulfate and urea) by using four replicates. We evaluated the mean mass, commercial root yield, leaf N content, starch content in the tubers, and percentage of tubers with symptoms of nematode infection (dry and thick skins). The maximum values for the mean masses of commercial tubers were 2.5 and 1.9 kg with doses of 130 and 160 kg of N ha(-1) from ammonium sulfate and urea, respectively. Doses of 130 and 154.3 kg of N ha(-1) produced the maximum yields of commercial tubers of 19.7 and 14.9 t.ha(-1) with ammonium sulfate and urea fertilization, respectively. The maximum levels of foliar N by using urea and ammonium sulfate were 36.5 and 29.3 g.kg(-1), respectively, at a dosage of 250 kg.ha(-1). The maximum starch contents of 25.7 and 28.3 % were obtained at doses of 114 and 116 kg of N ha(-1) of ammonium sulfate and urea, respectively. The percentage of tubers infected with nematodes was 10% when the N source was urea and 15.6% when the source was ammonium sulfate, both at a dosage of 250 kg.ha(-1).