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Varia??o de atributos e din?mica de carbono e nitrog?nio em Organossolos em fun??o de uso e manejo agr?cola no Rio de Janeiro. / Changes in attributes and dynamics of carbon and nitrogen in Histosols due to agricultural use and management in Rio de Janeiro.Soares, Paula Fernanda Chaves 15 February 2011 (has links)
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Previous issue date: 2011-02-15 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico - CNPQ / The Histosols are characterized by high organic content, distinguishing this class from others in
the Brazilian System of Soil Clasification. Because of this characteristic they are more fragile
in face of agricultural use and management than mineral soils. The agricultural drainage is the
most important practice that changes soil properties and it is the cause of subsidence, which
impacts on other attributes. On the other hand, Histosols are an important natural reservoir of
carbon in the soil. However, there are few studies on the dynamics of carbon and nitrogen and
potential contribution of greenhouse gases as a result of agricultural usage. The study aims to
identify changes in edaphic attributes and dynamics of carbon and nitrogen of Histosols in a
floodplain environment in State of Rio de Janeiro, according to types of land use and
agricultural management. Three areas with different managements were selected. Two areas are
located in Macae municipality, under pasture and annual crop rotation, and the third in Santa
Cruz, in Rio de Janeiro city, cultivated with cassava (Manihot esculenta). They were evaluated:
chemical and physical attributes, including aggregate stability and specific attributes of
Histosols; content soil organic matter (SOM), carbon in the fractions - humin (HUM-C), humic
acid (HAF-C) and fulvic acid (C-FAF); stocks of C and N; and flux of gases CO2 and N2O
from soil to atmosphere. In general, the area cultivated with cassava had the highest values for
the exchangeable cations at all depths; in the first sampling the H value varied from 32.1 to
33.2 cmolc kg-1, and Ca from 20.4 to 15.7 cmolc kg-1. In the second sampling K and P (5.16 to
4.36 cmol c kg-1, and 4 mg kg-1, respectively) were highest in the cassava crop area. The levels
of (SOM) were highest in the pasture for the two sampling periods, with values ranging from
306.3 to 249.0 g kg-1 (WB method) and 297.8 to 278,5 g kg-1 (oven method) for the first
sampling, and from 303.2 to 153.9 g kg-1 (WB) and 322.9 to 176.1 g kg-1 (oven) in the second
period, indicating that this usage is less aggressive to the soil. The physical properties of
Histosols may be used to indicate degree of subsidence. Thus, the high values of particle
density and bulk density (1.9 and 0.8 Mg m-3); the total volume of pores that ranged from 54 to
60% with the lowest values in the two samplings; and minimum residue and mineral material
highest than other usages (0.49 to 0.44 cm and 85.1 cm-1 to 80.7%, respectively) in the cassava
area point to the high subsidence ot these soil. As for SOM chemical fractionation, the C_HUM
indicated that this fraction had highest expression in all areas. In the second sampling the
cassava area showed the lowest values of C-HUM (79.05 to 76.27 g kg-1), followed by C_FAH
(44.56 to 40.05 g kg-1) and C_FAF (20.37 to 14.36 g kg-1). The stocks of C and N were highest
in the pasture area, indicating better preservation of SOM, with values from 72.93 to 117.12 mg
kg-1 for C and from 8.35 to 2,67 mg kg-1 for N. The values of CO2-C flux were within the range
of variation proposed by the IPCC, where the highest emission value corresponded to 0.09 Mg
CO2 ha-1 day-1 in the pasture area. The values of N2O-N flux were lower than the emission rate
proposed by the IPCC, with the highest value around 270 g N2O-N m-2 day-1 in the area with
beans. In general, the area with pasture management stood up as management that caused the
least damage to the Histosols properties, among the land use evaluated. / Os Organossolos caracterizam-se pelo alto teor de material org?nico, que distingue essa classe
das demais no Sistema Brasileiro de Classifica??o de Solo. Ainda, por essa caracter?stica s?o
solos mais fr?geis diante do uso e manejo agr?cola que solos com dom?nio de minerais. Dentre
as pr?ticas que mais alteram as propriedades ed?ficas, a drenagem ? a mais importante e ?
respons?vel pelo processo de subsid?ncia com impactos em v?rios atributos. Por outro lado, os
Organossolos s?o importante reservat?rio natural de carbono no solo. Ainda assim s?o poucos
os estudos sobre a din?mica de carbono e nitrog?nio e o potencial de contribui??o com gases de
efeito estufa diante do manejo agr?cola. O estudo visa identificar altera??es nos atributos
ed?ficos e na din?mica de carbono e nitrog?nio de Organossolos em ambiente de v?rzea no
Estado do Rio de Janeiro, em fun??o de tipos de uso e manejo agr?cola. Foram selecionadas tr?s
?reas com manejos distintos. Duas ?reas localizam-se em Maca?, com pastagem e rota??o de
culturas anuais, e a terceira em Santa Cruz, no Rio de Janeiro, com mandioca (Manihot
esculenta). Foram avaliados: atributos qu?micos e f?sicos, incluindo estabilidade de agregados e
atributos espec?ficos de Organossolos; teores de mat?ria org?nica do solo (MOS) e o teor de C
nas fra??es humina (C-HUM), ?cido h?mico (C-FAH) e ?cido f?lvico (C-FAF); estoques de C
e N; e fluxos dos gases CO2 e N2O do solo para a atmosfera. Em geral, a ?rea com mandioca
apresentou os maiores valores para o complexo sortivo em todas as profundidades; na primeira
coleta o H variou de 32,1 a 33,2 cmolc kg-1, e o Ca entre 20,4 e 15,7 cmolc kg-1. Na segunda
coleta destacam-se os valores de K e P (5,16 e 4,36 cmolc kg-1 e 4 mg kg-1, respectivamente)
tamb?m maiores na ?rea com mandioca. A MOS mostrou maior teor na ?rea de pastagem para
as duas coletas, com valores variando entre 306,3 a 249,0 g kg-1 (m?todo WB) e 297,8 a 278,5
g kg-1 (m?todo da mufla) na primeira coleta, e para a segunda coleta de 303,2 a 153,9 g kg-1
(WB) e 322,9 a 176,1 g kg-1 (mufla), o que indica que esse manejo ? menos agressivo ao solo.
As propriedades f?sicas dos Organossolos podem indicar o seu grau de subsid?ncia. Assim, os
valores altos de densidade da part?cula e densidade do solo (em torno de 1,9 e 0,8 Mg m-3) mais
o volume total de poros, que variou de 54 a 60% sendo os menores nas duas coletas, e o res?duo
m?nimo e material mineral com valores maiores (0,49 a 0,44 cm cm-1 e 85,1 a 80,7%,
respectivamente) indicam para a ?rea de mandioca maior grau de subsid?ncia. No
fracionamento qu?mico da MOS o C_HUM indicou que essa fra??o teve maior express?o em
todos as ?reas. Na segunda coleta a ?rea de mandioca apresentou os menores valores de CHUM
(79,05 a 76,27 g kg-1) seguidos de C_FAH (44,56 a 40,05 g kg-1) e C_FAF (20,37 a
14,36 g kg-1). Os estoques de carbono e nitrog?nio foram mais altos no solo sob pastagem,
indicando melhor conserva??o da MOS, com valores entre 117,12 e 72,93 Mg kg-1 para C e
8,35 e 2,67 Mg kg-1 para N. Os valores de fluxo de C-CO2 estiveram dentro da faixa de
varia??o proposta pelo IPCC, em que o maior valor de emiss?o correspondeu a 0,09 Mg CO2
ha-1 dia-1 na ?rea de pastagem. Os valores de N-N2O foram menores que a taxa de emiss?o
proposta pelo IPCC, com o valor mais elevado em torno de 270 ?g N-N2O m-2 dia-1 e na ?rea
com feij?o. Em geral, a pastagem se destacou como o manejo que causou menor altera??o nas
propriedades dos Organossolos, dentre as formas de uso da terra avaliadas.
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