Emanuelle Mercês Barros Soares

Estoque de carbono e quantificação de substâncias húmicas em Latossolo submetido a aplicação contínua de lodo de esgoto

Este estudo teve como objetivo avaliar o efeito da aplicacao continua de doses de lodo de esgoto oriundo da Estacao de Tratamento de Esgoto de Barueri, SP, sobre os teores e estoques de C e sobre as alteracoes na distribuicao de substâncias humicas em Latossolo Vermelho distroferrico. O experimento foi instalado em 1999, no Campo Experimental da Embrapa Meio Ambiente, em Jaguariuna-SP; os dados foram obtidos apos a sexta aplicacao de lodo e cultivo sucessivo de milho. Foram utilizadas, nas diferentes parcelas experimentais, as seguintes doses acumuladas de lodo de esgoto (base seca): 0, 30, 60, 120 e 240 Mg ha-1, sendo estudados os tratamentos: (L0) testemunha sem adicao de lodo; e aplicacao de lodo de esgoto visando fornecer uma (L1), duas (L2), quatro (L4) e oito (L8) vezes a dose de N requerida pelo milho. Foram avaliados os teores e o estoque de C orgânico nas camadas de solo de 0-10, 10-20, 20-40 e 40-60 cm. Os teores de C associados as substâncias humicas foram avaliados na camada de solo de 0-10 cm. O teor e o estoque de C orgânico aumentaram com o acrescimo nas doses de lodo de esgoto aplicadas, ate a camada de solo de 0-20 cm. A maior parte (50-66 %) do C associado as substâncias humicas esta presente no solo na forma de humina, seguido por C-fracao acidos fulvicos e C-fracao acidos humicos, nesta ordem. A aplicacao de lodo de esgoto implica maior acumulo de substâncias humicas no solo, mas as proporcoes de C-humificado da materia orgânica nao sao alteradas.

Doses e fontes de nitrogênio na produtividade do eucalipto e nas frações da matéria orgânica em solo da região do cerrado de Minas Gerais

Apesar da grande quantidade de N acumulada em plantacoes de eucalipto de alta produtividade, o aumento em volume do tronco em resposta a aplicacao de N nao tem sido expressivo nem consistente. O objetivo deste trabalho foi verificar o efeito de doses e fontes de N sobre o crescimento e o acumulo de N em plantas de eucalipto, na serapilheira, alem do impacto nas fracoes da materia orgânica do solo (MOS). O experimento foi instalado em campo, no municipio de Itamarandiba-MG, em blocos ao acaso com tres repeticoes, consistindo da aplicacao em cobertura de doses (0, 60, 120 e 240 kg ha-1) e fontes de N distintas (sulfato de amonio e nitrato de amonio) em clone de eucalipto (AEC1528®). O efeito dos tratamentos sobre o crescimento e acumulo de N nas plantas foi avaliado aos 30 meses de idade, abatendo-se arvores com DAP medio e separando-as em lenho, casca, galhos e folhas, para determinacao da producao de materia seca e dos teores e conteudos de nutrientes das plantas. Amostras de solo e de serapilheira foram coletadas para analises de nutrientes. Os teores de C e N total da materia orgânica particulada (MOP) e da materia orgânica associada a fracao mineral (MOAM) foram determinados por espectrometria de massa de razao isotopica, apos separacao fisica da MOS. As analises estatisticas consistiram de analise de variância e de regressao. A aplicacao de adubos nitrogenados promoveu aumento no crescimento volumetrico do tronco e na materia seca da parte aerea. A dose de N como sulfato de amonio para obter 90 % da producao maxima foi de 74 kg ha-1, a qual resultou em incremento de 42,3 % no volume de tronco em relacao a testemunha sem adubacao nitrogenada. Na dose de 120 kg ha-1 de N, nao houve diferenca de resposta a aplicacao de sulfato de amonio e nitrato de amonio. Nao foram detectadas alteracoes nos estoques de C e N da MOS com a adubacao nitrogenada. No entanto, houve aumento da absorcao de Ca, Mg e S. A taxa de recuperacao aparente de N no campo foi maior na dose de 120 kg ha-1 de N, atingindo 34,4 %.

Modeling changes in organic carbon stocks for distinct soils in southeastern brazil after four eucalyptus rotations using the century model

Soil organic matter (SOM) plays an important role in carbon (C) cycle and soil quality. Considering the complexity of factors that control SOM cycling and the long time it usually takes to observe changes in SOM stocks, modeling constitutes a very important tool to understand SOM cycling in forest soils. The following hypotheses were tested: (i) soil organic carbon (SOC) stocks would be higher after several rotations of eucalyptus than in low-productivity pastures; (ii) SOC values simulated by the Century model would describe the data better than the mean of observations. So, the aims of the current study were: (i) to evaluate the SOM dynamics using the Century model to simulate the changes of C stocks for two eucalyptus chronosequences in the Rio Doce Valley, Minas Gerais State, Brazil; and (ii) to compare the C stocks simulated by Century with the C stocks measured in soils of different Orders and regions of the Rio Doce Valley growing eucalyptus. In Belo Oriente (BO), short-rotation eucalyptus plantations had been cultivated for 4.0; 13.0, 22.0, 32.0 and 34.0 years, at a lower elevation and in a warmer climate, while in Virginopolis (VG), these time periods were 8.0, 19.0 and 33.0 years, at a higher elevation and in a milder climate. Soil samples were collected from the 0-20 cm layer to estimate C stocks. Results indicate that the C stocks simulated by the Century model decreased after 37 years of poorly managed pastures in areas previously covered by native forest in the regions of BO and VG. The substitution of poorly managed pastures by eucalyptus in the early 1970´s led to an average increase of C of 0.28 and 0.42 t ha-1 year-1 in BO and VG, respectively. The measured C stocks under eucalyptus in distinct soil Orders and independent regions with variable edapho-climate conditions were not far from the values estimated by the Century model (root mean square error - RMSE = 20.9; model efficiency - EF = 0.29) despite the opposite result obtained with the statistical procedure to test the identity of analytical methods. Only for lower soil C stocks, the model over-estimated the C stock in the 0-20 cm layer. Thus, the Century model is highly promising to detect changes in C stocks in distinct soil orders under eucalyptus, as well as to indicate the impact of harvest residue management on SOM in future rotations.

COMPETITIVE SORPTION AND DESORPTION OF PHOSPHATE AND CITRATE IN CLAYEY AND SANDY LOAM SOILS

The increase of organic acids in soils can reduce phosphorus sorption. The objective of the study was to evaluate the competitive sorption of P and citrate in clayey and sandy loam soils, using a stirred-flow system. Three experiments were performed with soil samples (0-20 cm layer) of clayey (RYL-cl) and sandy loam (RYL-sl) Red Yellow Latosols (Oxisols). In the first study, the treatments were arranged in a 2 × 5 factorial design, with two soil types and five combinations of phosphorus and citrate application (only P; P + citrate; and citrate applied 7, 22, 52 min before P); in the second, the treatments were arranged in a 2 × 2 factorial design, corresponding to two soils and two forms of P and citrate application (only citrate and citrate + P); and in the third study, the treatments in a 2 × 2 × 6 factorial design consisted of two soils, two extractors (citrate and water) and six incubation times. In the RYL-cl and RYL-sl, P sorption was highest (44 and 25 % of P application, respectively), in the absence of citrate application. Under citrate application, P sorption was reduced in all treatments. The combined application of citrate and P reduced P sorption to 25.8 % of the initially applied P in RYL-cl and to 16.7 % in RYL-sl, in comparison to P without citrate. Citrate sorption in RYL-cl and RYL-sl was highest in the absence of P application, corresponding to 32.0 and 30.2 % of the citrate applied, respectively. With P application, citrate sorption was reduced to 26.4 and 19.7 % of the initially applied citrate in RYL-cl and RYL-sl, respectively. Phosphorus desorption was greater when citrate was used. Phosphorus desorption with citrate and water was higher in the beginning (until 24 h of incubation of P) in RYL-cl and RYL-sl, indicating a rapid initial phase, followed by a slow release phase. This suggests that according to the contact time of P with the soil colloids, the previously adsorbed P can be released to the soil solution in the presence of competing ligands such as citrate. In conclusion, a soil management with continuous input of organic acids is desirable, in view of their potential to compete for P sorption sites, especially in rather weathered soils.

Organic acid coated-slow-release phosphorus fertilizers improve P availability and maize growth in a tropical soil

In this paper, we report the results of studies on the solubility (water solubility trial) and the response by plants (greenhouse pot experiment using Zea mays) for four types of monoammonium phosphate fertilizers (Conventional MAP MAP1, MAP coated with a natural organic acid MAP2, MAP coated with a synthetic organic acid MAP3, and MAP coated with a peat humic organic acid MAP4) applied at five increasing doses (0, 100, 300, 600 and 1200 mg P dm-3) and pre-incubated with the soil for five lengths of time before planting (0, 15, 30 and 60 d). The coating with organic acids reduced the water solubility of the P fertilizers MAP4 provided a more gradual release of P over time. In the soil pot experiment, it was found that MAP1 required the highest dose to reach 90% of dry matter accumulation by the maize plant, followed by the Coated-Slow-Release Fertilizers (CSRF). The agronomic efficiency (AE) of P applied as the CSRF was 3 to 13% greater than that of MAP1. In addition, MAP4 led to higher values of AE (+11%) and apparent P recovery by maize (+41%) in comparison to MAP1. The physicochemical properties imposed by the chemical composition of the organic acid coatings generated fertilizers with distinct release rates and improved agronomic efficiencies.

Temporal decomposition sampling and chemical characterization of eucalyptus harvest residues using NIR spectroscopy and chemometric methods

Near-infrared (NIR) spectroscopy and chemometric methods were used to predict the chemical properties of decomposing eucalyptus harvest residues to better understand the decomposition process of these materials. Leaves, twigs, branches, and bark from a decomposition experimental set up in commercial plantations were sampled for one year. The contents of carbon (C), nitrogen (N), extractives (EX), acid-soluble lignin (SL), Klason insoluble lignin (KL) and holocellulose (HC) were determined by the reference method in the collected samples. Principal component analysis (PCA) was employed to distinguish the types of harvest residues throughout the decomposition period. Multi-residue regression models were built from the NIR spectra using partial least squares regression (PLS). Two feature selection methods, i.e., ordered predictors selection (OPS) and genetic algorithm (GA), were applied and compared. The OPS and GA did not differ statistically; however, compared with the GA, OPS was more computationally efficient and selected fewer variables. Using the PLS-OPS models, the root mean square errors of prediction (RMSEP) for C, N, EX, SL, KL and HC were 19.70, 0.08, 0.74, 0.39, 28.13 and 33.99, respectively, and the prediction correlations (Rp) for these properties were 0.94, 0.99, 0.99, 0.99, 0.96 and 0.98, respectively. PLS-discriminant analysis (PLS-DA) was used to classify the samples over the decomposition time and provided a good separation. Some mismatches obtained in the modeled classes were explained by the differences in the decomposition rate and changes in the chemical composition of the different harvest residue components that were evaluated. The results showed the feasibility of NIR spectroscopy and chemometric methods to evaluate the chemistry of decomposing eucalyptus harvest residues, indicating that these methods can be used as rapid and inexpensive alternatives to conventional methods to help understand the decomposition process.