Adubação nitrogenada em mandioca (Manihot esculenta Crantz): efeitos sobre o crescimento da cultura

Abstract

Cassava (Manihot esculenta Crantz) is one of the main sources of carbohydrates for human food in the tropics, part of the staple food of about 500 million people, mainly in developing countries. The literature on cassava nitrogenous fertilization is scarce. This study aimed to evaluate the effects of levels and nitrogenous fertilizer sources on dry matter and nitrogen accumulation in roots and aerial parts of cassava. The experiment was conducted at the Experimental Station of Itaguaí/PESAGRO-Rio in Seropédica, State of Rio de Janeiro, on a Red-Yellow Podzolic soil, in the period May 1999 to June 2000. The design of the field experiment was in randomized blocks with four repetitions, in a 3 x 5 factorial outline, made up of by three N sources (urea, nitrocalcium and ammonium sulphate) and five N levels (0, 60, 120, 180 and 200 kg N ha-1). Each plot had 64.0 m2 with 12 grooves, spaced at 1.0m. The planting was carried out on 28/05/1999 with cuttings of cultivar Saracura. The nitrogen levels were divided into two applications, the first half was applied planting and other half was applied 9 month later. Plants were harvested at 07, 11 and 13 months after planting and determined dry matter, total nitrogen, nitrate-N, amino-N, crude protein and soluble sugars in roots, leaves and stem. To 7 months after planting, urea showed higher total dry matter value. At 13 months, nitrocalcium and ammonium sulphate provided dry matter root yield 20 % higher than the urea. The N content in leaves was approximately 7 times bigger those the N root contents. The application of 30 kg N ha-1 resulted in increase of 11% in leaf N content. There was a cassava response to N application and can behave as a specie efficient responsive little.