CARVALHO, C. J. R. de

COELHO, R. de F. R.

FIGUEIREDO, R. de O.

FONTENELLE, D. S.

ROMAN, A. L. C.

SÁ, T. D. de A.

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111Conferência Científica do LBAAnais de Trabaihos Completos27 a 29 de julho de 2004Academia de Tênis ResortBrasília, Brasil..'.-ntLBA Scientific ConferenceAbstract BookJuly 27-29, 2004Academia de TênisBrasília, Brazilhow total soil micronutrients vary across the field. A variety of approaches have been used to survey and map thegeographic distribution of soil micronutrient content at scales ranging from global to sites within single production fields.The present study investigates the spatial variation of sou micronutrients in a 63 ha pasture area located at Nova VidaRanch, Rondonia, Brazil. A regular 100 m grid was used for collecting a total of 195 soil samples at the 0-10, 10-20 and 20-30 cm layers. Soil samples were analyzed for Zn, Cu, Fe, Mn contents and also pH, total C, total N, P, K, Ca, Mg, and AI.Conventional statistical methods and geostatistics were performed in order to analyze soil properties spatial dependence.The spatial structure of the studied nutrients was analyzed and variogram models with a nugget component and two spatialcomponents were found to fit the experimental results. Semivariograms were best fitted by spherical and exponentialmodels. Two types of validation (cross and external) were conducted, indicating a lack of bias for the used predictionmodels. Contou r maps made by block kriging allowed to identify micro-regions with significantly high or low extractablenutrient contents. Maps of total soil micronutrient content can show where low micronutrient concentrations may causedeficiencies in plants and in the Iivestock that subsist on them.28.4-P: Effects of different land use systems in carbon, nitrogen and phosphorus cycles: comparison betweenslash-and-burn and chop-and-mulch systems.Roberta de Fátima Rodrigues Coelho, Bolsista DTI CNPQ/LBA, robpantoja@hotmail.comAndré Luiz Cote Roman, Bolsista Programa SHIFT, coteroman@yahoo.com.brCláudio José Reis de Carvalho, Embrapa Amazônia Oriental, carvalho.bel@terra.com.brRicardo de O. Figueiredo, Embrapa Amazônia Oriental, ricardo@cpatu.embrapa.br (Apresentador / Presenting)Tatiana Deane de Abreu Sá, Embrapa Amazônia Oriental, tatiana@cpatu.embrapa.brDanielle Santos Fontenelle, Bolsista ITI, CNPQ/LBA, dfagro@hotmail.comIn the traditional system of small-scale agriculture in Eastern Amazonia, land preparation prior to cropping is done byslashing and burning the fallow vegetation, to have access to nutrients, mainly phosphorus (P), from the ashes. With theintensification of land use the fallow period has been shortened, affecting consequently the biogeochemical functions ofsecondary vegetation, leading to its degradation. The alternative system, chop-and-mulch of the fallow vegetation,associated to the improvement of the fallow vegetation by planting fast growing leguminous trees, appears as an option toshorten the fallow period, increasing carbon accumulation (including soil organic matter) and nutrient cycling, while keepingthe fallow vegetation roots which act as a barrier to nutrient leaching. The consequences of burning to biogeochemicalprocesses have been reasonably studied, but little is known about the impact on carbon and nutrients accumulation derivedfrom the mulch, and on the mineralization or fixation promoted by the soil biota. To study these processes two plots (2 haeach) were set up with the following treatments: i) traditional slash-and-burn system; ii) alternative chop-and-mulchsystem (with fertilizer application). In both maize and cassava were cropped followed by a fallow phase (improved byplanting two leguminous tree species in the alternative system). We are evaluating: microbial biomass, C and N, activity ofenzymes associated to N and P mineralization, organic carbon accumulation and soil organic rnatter, NH4+, N03- and Pavailability, and organic P species, as well as vesicular arbuscular mychorrhizas (VAM) activity. Two years after landpreparation, the results show that the measured variables in the alternative system seem to be closer to what is found inthe original secondary vegetation.28.5-P: Response of the Soi! Microbial Community to Fertilization Practices in Agricultural and Native CerradoSystems in Brazi!Marirosa Molina, U.S EPA, molina.marirosa@epa.gov (Apresentador / Presenting)Laura Tillman Viana, University of Brasilia, Iviana@unb.brMercedes Maria Cunha Bustamante, University of Brasilia, mercedes@unb.brRichard G. Zepp, U.S. EPA, zepp.richard@epa.govAgricultural practices in the Cerrado (tropical savannah) and Amazon regions in Brazil have increased drastically during thelast decade causing dramatic changes in the nutrient and carbon cycling of native areas, and producing changes on themicrobial community structure. We compared microbial communities under a range of management practices whichincluded different native areas (savannah and forest), an agricultural site, and a Cerrado area subjected to fertilizationtreatments (N, P, N+P, Ca) using phospholipid fatty acid analysis (PLFAs) and fungal to bacterial ratios. In the nativeCerrado, samples were collected 10, 20 and 40 days after fertilizer application from four plots (15 x15m) per treatment in acompletely randomized designo Although the total PLFA concentration did not show significant differences among the sites,principal component analysis indicated that the structure of the microbial community varied as a function of the fertilizationtreatment and management practice (p<O.OOOl). In the fertilization experiment, N, P, and N+P treatments had a higherconcentration of Gram positive biomarkers than the control and exhibited similar microbial communities. P amendmentsproduced a higher fungal: bacterial ratio after 10 days of fertilization and was the only treatment showing a significantdifference in the ratios. Fungal: bacterial ratios were also significantly higher in the pasture site when compared to the ratiosobserved in the native savannah and Amazon soils. The higher ratio in the pasture site correlated with lower availability ofnitrogen and was a function of a decrease in the % composition of bacterial PLFAs. The results suggest a phosphoruslimitation on the fungal community inhabiting native Cerrado soíls, while in pastures, nitrogen seems to limit the bacterialcommunity, but has no effect on the fungi.28.6-P: Effect of ash deposition on soi! nitrogen availability in burned savannas of the Gran Sabana, Venezuela.Carlos Luis Méndez, Universidad Simon Bolivar, carlosmendez@etheron.net (Apresentador / Presenting)Bibiana Alejandra Bilbao, Universidad Simon Bolivar, bibiana_bilbao@hotmail.comEn Ia Gran Sabana, Parque Nacional Canaima (30000 km2), existe una alta incidencia de incendios, Ia mayoria de 105 cualesse inician en reas de sabanas. Los suelos de sabana son pobres, siendo el nitrogeno, uno de 105 nutrientes mas afectadospor el fuego. Este afecta el ciclo dei nitrogeno dei suelo directamente por calentamiento o indirectamente mediante Iaadicion de cenizas. En este trabajo se estudio el efecto de Ia deposicion de cenizas sobre Ia dinamica de nitrogenoinorganico dei suelo, a traves de incubaciones aerobicas en suelos de sabanas quemadas y no quemadas bajo distintostratamientos: a) adicion de cenizas provenientes de Ia combustion de biornasa, b) adicion de solucion de sacarosa, c) noadicion de fuente de carbono. Tanto en suelos quemados como no quemados Ia adicion de cenizas no afecto Iaamonificacion, mientras que Ia desaparicion dei nitrato parece haber sido estimulada solo en 105 suelos quemados, comoproducto quizas, de aumentos en Ia desnitrificacion e inmovilizaci<j:n microbiana. La adicion de sacarosa provoco Iainmovilizacion de Ia mayor parte dei nitrogeno inorganico en el suelo sin quemar, mientras que en suelo quemado solo seinmovilizo el amonio y se produjo un aumento dei nitrato. Los resultados muestran una interaccion entre Ia adicion decenizas y Ia quema, haciendo especifico el efecto de Ias cenizas sobre los procesos transformadores de nitrato, ademas de

Effects of different land use systems in carbon, nitrogen and phosphorus cycles: comparison between slash-and-burn and chop-and-mulch systems.

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