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Previous issue date: 2006-04-25 === Funda??o Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro === Despite sugarcanes Biological Nitrogen Fixation (BNF) research efforts which have been
carrying on in Brazil, most of its varieties still need nitrogen fertilizer complement, and the
cost of this supply trends to raise following the petroleum price. Thus, the scientific research
has worked on finding alternatives to nitrogen fertilizer through varieties with higher potential
to the BNF; crops practical handling that would be able to increase BNFs contribution; and
also, through selection and inoculation of bacterias lineage efficient to BNF. Seeking some of
these answers, three experiments were developed at Embrapa Agrobiologia in Seropedica-RJ
heading to identify the most efficient sugarcanes varieties to BNF based on balance
techniques of N-Total on the system soil/plant; 15N natural abundance; and 15N isotopic
dilution. The experiment results allowed concluding that: 1) The N total balance of soil/plant
system after 8 and 13 years of harvesting was positive to the most varieties studied, showing a
significant entry of nitrogen from de atmosphere by BNF to the soil/plant system; 2) The
varieties Krakatau, SP 70-1143, SP 79-2312 and SP 71- 6163 confirmed potential to BNF as
observed on previous studies; 3) The varieties RB 72-454, RB 82-5336, RB 75-8540 and RB
83-5089 showed high potential to BNF. 4) The soil type and the crops cycle have great
influence on the BFN contribution; 5) The BNF is an important source of N for the soil/plant
system; got a glimpse of right handling possibility (systems of sugar cane harvesting with
crop residue remaining on the soil surface) and with the utilization of efficient varieties to
BNF may be possible to reduce or even eliminate crops nitrogen fertilizers. === Apesar dos esfor?os da pesquisa em FBN na cultura de cana-de-a??car, que vem sendo
desenvolvida no Brasil, as soqueiras da maioria das variedades de cana-de-a??car ainda
precisam de uma complementa??o com fertilizantes nitrogenados, e o custo deste insumo
tende a elevar-se, acompanhando o pre?o do petr?leo. Assim, nos ?ltimos anos, a pesquisa
cient?fica, vem trabalhando em busca de alternativas ? aduba??o nitrogenada, atrav?s de
gen?tipos com maior potencial para FBN, pr?ticas de manejo da cultura que poderiam
amplificar a contribui??o da FBN e pela sele??o e inocula??o de estirpes de bact?rias
eficientes para FBN. Buscando alcan?ar algumas dessas respostas, na Embrapa Agrobiologia,
localizada em Serop?dica-RJ, foram instalados tr?s experimentos com o objetivo identificar as
variedades de cana-de-a??car mais eficientes para FBN, com base nas t?cnicas de balan?o de
N-total no sistema solo/planta, abund?ncia natural de 15N e dilui??o isot?pica de 15N. Os
resultados desses experimentos permitiram concluir que: 1) o balan?o de N-total do sistema
solo-planta ap?s 8 e 13 anos de cultivo foram positivos para a maioria das variedades
estudadas, mostrando um significativo ingresso de nitrog?nio proveniente da atmosfera via
FBN para o sistema solo-planta; 2) os gen?tipos Krakatau, SP 70-1143, SP 79-2312 e SP 71-
6163 confirmaram o potencial para FBN j? observados em estudos anteriores; 3) as
variedades RB 72-454, e RB 82-5336, RB 75-8540 e RB 83-5089 apresentaram alto potencial
para FBN; 4) o tipo de solo e o ciclo da cultura teve grande influ?ncia na contribui??o da
FBN; e 5) a FBN ? uma importante fonte de N ao sistema solo planta, e vislumbram a
possibilidade de que com o manejo adequado (colheita de cana crua) e com a utiliza??o de
variedades eficientes para FBN, talvez, seja poss?vel reduzir ou mesmo eliminar a aduba??o
com fertilizantes nitrogenados na cultura.
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