Adubação nitrogenada em videira: perdas e mineralização de nitrogênio

Abstract

Since 1980, native fields of the Campanha Gaúcha from Rio Grande do Sul State (RS) have been incorporated into the grape production. In this region, vines has been cultivated under sandy soils with low organic matter content; therefore they have a low nitrogen (N) supply capacity and inputs of N through organic or mineral sources are necessary. Although, some N may be lose by volatilization or leaching. In addition, the amount of N mineralized along the plant s cycle is unknown. The objective was to evaluate N loses by volatilization and leaching, such as to quantify the N mineralization rates in soils cultivated with vines and fertilized with different sources of N. In order to evaluate the loses, two experiments were carried out in Cabernet Sauvignon vines in Rosário do Sul (RS). The experiment 1 consisted on the installation of lysimeters on the rows and application of 0, 40, 80 and 120 kg N ha-1, as urea, to collect and analyze the mineral N leached. On the experiment 2, urea was applied in amounts of 0, 20, 40, and 80 kg N ha-1 year-1. Also, application of 40 kg N ha-1 year-1 of organic compost and 40 kg N ha-1 year-1 as polymer coated urea were used to evaluate the N volatilization as N-NH3. To evaluate the mineralization rates, incubations were carried out at the laboratory during 141 days, using Sandy Typic Hapludalf soils, collected from 0-20 cm layer. In the moment of incubation, an amount of 40 Kg N ha-1 of organic compost, polymer coated urea and urea were added on the soils. One sample was collected from a native field as reference treatment. Mineral N concentration in the leached solution, especially along the vine sprouting, increased according to the fertilizers rates applied on the sprouting beginning. The fluxes and loses of N-NH3 from vine soils to the atmosphere had increased according to the mineral N rate. Polymer coated urea and organic compost showed the lowest loses of N-NH3 by volatilization. A higher mineralization was observed up to the 38th day of incubation when polymer coated urea and urea was distributed on soil surface. The N releasing of compost applied on vine soils has a better synchronism to the plant requirements, comparing to polymer coated urea or urea. The N storage in the soil, which may be mineralized of native or vine fields, is able to supply the vine requirements.