Produtividade e acúmulo de nitrato nos frutos da abóbora "Tetsukabuto" em função da adubação nitrogenada

Abstract

The importance of hybrid winter squash ("Tetsukabuto" type) is rising in Brazil, especially in Minas Gerais state, but few studies have been carried out in relation to fertilization. We evaluated yield and nitrate accumulation in fruits of hybrid winter squash ("Tetsukabuto" type) depending on the nitrogen fertilization in Viçosa, Minas Gerais state, Brazil. The randomized block experimental design was used, arranged in a 2×5 factorial design, with two nitrogen sources (ammonium sulphate and ammonium nitrate) and five nitrogen doses (0; 50; 100; 200 and 400 kg ha-1), and four replications. The number of fruits per plant, average fruit mass, fruit yield and nitrate accumulation in the fruits were evaluated. No significant effects of nitrogen sources and of the interaction between nitrogen sources and nitrogen doses was found on the productive characteristics of the hybrid winter squash, but these characteristics were increased depending on the N doses applied. The highest number of fruits/plant (6.9 units), highest average fruit mass (1.76 kg/fruit) and highest fruit yield (17.16 t ha-1) were obtained in the doses 339, 217 and 260 kg -1 of N, respectively. The rates of N for maximum economic efficiency were 251 and 238 kg ha-1, resulting in fruit yields of 17.15 and 17.07 t ha-1, for the ammonium sulfate and ammonium nitrate, respectively. Nitrate accumulation in fruits employing N doses in the form of ammonium sulfate was not verified. However, the nitrate content in the fruits presented lineal increment depending on the N doses in the form of ammonium nitrate. At the highest N rate, the nitrate content in the fruit fresh matter was 406 mg kg-1. However, this nitrate content value does not represent risk for human health.