Phosphorus cycling in a small watershed in the Brazilian Cerrado: impacts of frequent burning

Abstract

Plant productivity in many tropical savannas is phosphorus limited. The biogeochemical cycling of P in these ecosystems, however, has not been well quantified. In the present study, we characterized P stocks and fluxes in a well-preserved small watershed in the Brazilian Cerrado. As the Cerrado is also a firedominated ecosystem, we measured the P stocks and fluxes in a cerrado stricto sensu plot with complete exclusion of fire for 26 years (unburned plot) and then tested some predictions about the impacts of fire impacts on P cycling in an experimental plot that was burned three times since 1992 (burned plot). The unburned area is an ecosystem with large soil stocks of total P (1,151 kg ha -1 up to 50 cm depth), but the largest fraction is in an occluded form. Readily extractable P was found up to 3 m soil depth suggesting that deep soil is more important to the P cycle than has been recognized. The P stock in belowground biomass (0-800 cm) was 9.9 kg ha -1 . Decomposition of fine litter released 0.97 kg P ha -1 year -1 . Fluxes of P through bulk atmospheric deposition, throughfall and litter leachate were very low (0.008, 0.006 and 0.028 kg ha -1 year -1 , respectively) as was stream export (0.001 kg ha -1 year -1 ). Immobilization of P by microbes during the rainy season seems to be an important mechanism of P conservation in this ecosystem. Fire significantly increased P flux in litter leachate to 0.11 kg ha -1 year -1 , and added 1.2 kg ha -1 of P in ash deposition after fire. We found an increase of P concentration in soil solution at 100 cm depth (from 0.03 lg l -1 in unburned plot to 0.3 lg l -1 in the burned plot). In surface soils (0-10 cm) of the burned plot, fire decreased the concentrations of extractable organic-P fractions, but did not significantly increase inorganic-P fractions. The reduction of extractable soil organic P in the burned plot in topsoil and the increase of P in the soil solution at greater depths indicated a reduction of P availability and may increase P fixation in deep soils. Repeated fire events over the long term may result in significant net loss of available forms of phosphorus from this ecosystem.

Frações de fósforo e correlação com atributos edáficos sob sistemas de plantio direto e integração lavoura-pecuária no Cerrado Goiano

“…Este domínio ocupa cerca de 24% do território brasileiro, cobrindo aproximadamente 200 milhões de hectares e possui a segunda maior biodiversidade do planeta (BUSTAMANTE et al, 2006) Inúmeros estudos foram desenvolvidos neste domínio, sendo verificados, em maior proporção, pesquisas sobre a dinâmica dos elementos carbono e nitrogênio (BUSTAMANTE et al, 2006;SIQUEIRA NETO;BERNOUX, 2008;CARVALHO et al, 2010;COSTA JUNIOR et al, 2011;LOSS et al, 2012a) comparativamente ao fósforo (P) e ao seu fracionamento. Sobre a dinâmica do P, em solos do Cerrado são encontrados trabalhos com ênfase somente na vegetação natural de Cerrado (RESENDE et al, 2011;BUSTAMANTE et al, 2012) e trabalhos comparando diferentes sistemas de uso das terras com a vegetação original (Cerrado) (FONTANA et al, 2008;EBERHARDT et al, 2008;TIRLONI et al, 2009;PEREIRA et al, 2010;LOSS et al, 2012a).…”

“…Em relação ao P, este é um elemento muito importante para o desenvolvimento dos vegetais (NOVAIS; SMYTH; NUNES, 2007;RESENDE et al, 2011). Entretanto, os solos tropicais, sendo grande parte destes encontrados no domínio morfoclimático do Cerrado, apresentam, normalmente, baixa concentração de P disponível e alto poder de "fixação" ou "retenção" do P via adubação SMYTH, 1999;EBERHARDT et al, 2008).…”

“…Entretanto, essa dinâmica é muito complexa e dependente de vários fatores intrínsecos ao solo; tais como a textura (EBERHARDT et al, 2008;TOKURA et al, 2011), sistemas de manejo (FONTANA et al, 2008;PEREIRA et al, 2010) e adubações minerais e orgânicas TIRLONI et al, 2009;DAO;ROSOLEM, 2010;GUARDINI et al, 2012), além dos fatores ambientais -bióticos e abióticos (FERNÁNDEZ et al, 2008;RESENDE et al, 2011).…”

Edaphic Attributes of a Crop-Livestock Integration System in the Cerrado Biome

“…The dynamics of phosphorus (P) fractions, on the other hand, is much more complex and depend on various factors related to soil attributes, such as texture (Tokura et al, 2011), management system (Pereira et al, 2010;Bezerra et al, 2015), chemical and organic fertilization (TIRLONI et al, 2009;GUARDINI et al, 2012;BEUTLER et al, 2015) and environmental (biotic and abiotic) factors (RESENDE et al, 2011). Agricultural systems such as CLI, which aims the maintenance of plant cover with minor soil tilling, can modify the dynamics of P fractions (BEZERRA et al, 2015;BEUTLER at al., 2015).…”

Phosphorus Forms in Ultisol Submitted to Burning and Trituration of Vegetation in Eastern Amazon

“…The biogeochemical cycle of P is modified during vegetation and litter burning, by converting the organic P into orthophosphate (Certini, 2005), which is easily reactive with soils. Several studies have shown a relationship between vegetation burning and availability and quantities of P forms in soils (Giardina et al, 2000;Galang et al, 2010;Oliveira et al, 2011;Resende et al, 2011).…”