Pedro Luiz Oliveira de Almeida Machado

Impact of oil contamination and biostimulation on the diversity of indigenous bacterial communities in soil microcosms

The aim of this study was to analyse the effect of oil contamination and biostimulation (soil pH raise, and nitrogen, phosphate and sulphur addition) on the diversity of a bacterial community of an acidic Cambisol under Atlantic Forest. The experiment was based on the enumeration of bacterial populations and hydrocarbon degraders in microcosms through the use of conventional plating techniques and molecular fingerprinting of samples directly from the environment. PCR followed by denaturing gradient gel electrophoresis (DGGE) was used to generate microbial community fingerprints employing 16S rRNA gene as molecular marker. Biostimulation led to increases of soil pH (to 7.0) and of the levels of phosphorus and K, Ca, and Mg. Oil contamination caused an increase in soil organic carbon (170-190% higher than control soil). Total bacterial counts were stable throughout the experiment, while MPN counts of hydrocarbon degraders showed an increase in the biostimulated and oil-contaminated soil samples. Molecular fingerprinting performed with 16S rRNA gene PCR and DGGE analysis revealed stable patterns along the 360 days of experiment, showing little change in oil-contaminated microcosms after 90 days. The DGGE patterns of the biostimulated samples showed severe changes due to decreases in the number of bands as compared to the control samples as from 15 days after addition of nutrients to the soil. Results obtained in the present study indicate that the addition of inorganic compounds to soil in conjunction with oil contamination has a greater impact on the bacterial community than oil contamination only.

Soil management under no-tillage systems in the tropics with special reference to Brazil

Because of cost reductions and soil erosion control, no-tillage is being rapidly adopted by farmers in the Americas, particularly in the humid and sub-humid tropics. Compared to conventional tillage (tillage operations resulting in <30% cover of plant residue remaining on the surface), no-tillage combined with crop rotation involving cover crops increases soil organic matter content, whilst improving soil fertility. This was mostly evident at 0–5 cm depth. Further successful adoption by farmers, including smallholder farmers from different regions, depends on improvements of various aspects, from edaphological constraints (e.g. in Brazil) to social and infrastructural limitations (e.g. in West and Central Africa). Special emphasis is given to the effects of no-tillage on soil organic matter and the consequences on some chemical (e.g. subsoil acidity, fertilizer management) and physical properties of soils (e.g. soil compaction, aggregate stability). Research imperatives for regional improvement or adaptation of such a conservation tillage are emphasized together with social and economical aspects for its adoption.

Estoques de carbono e nitrogênio e distribuição de frações orgânicas de latossolo do cerrado sob diferentes sistemas de cultivo

This study was carried out to evaluate the effect of cultivation systems on soil carbon and nitrogen contents and on the distribution of light and heavy fractions of soil organic matter (SOM). Density and particle-size fractionations were used to isolate free light fraction (FLF), intra-aggregate light fraction (ILF) and heavy fractions (HF) of a Red-Yellow Latosol from a field experiment at Embrapa Rice and Beans in Goias, Brazil. Treatments consisted of a combination of soil tillage and crop rotation. Soil tillage systems utilized were no-tillage (NT) and conventional tillage (mouldboard ploughing followed by light disc harrowings - CT), under two crop rotations: fallow/rice - fallow/soybean and sunhemp/rice - millet/soybean. As a reference, soil samples were collected from a non-cultivated area nearby the field experiment. All samples were analyzed at Embrapa Soils between January and August 2000. Compared to the forest site, soil cultivation led to a decrease of 50 % in the C and N contents, under both tillage systems. Decreased C and N storages in the cultivated soils were less for ploughed soils than soils under no-tillage. The largest proportion (60-90 %) of C and N was associated with the finest soil particles, with ploughing increasing this tendency. The C content of light fractions decreased due to the replacement of the Cerrado vegetation by cropping systems. Light fraction of the soil organic matter was a sensitive indicator of changes in SOM content caused by cropping systems.

Total C and N storage and organic C pools of a Red-Yellow Podzolic under conventional and no tillage at the Atlantic Forest Zone, south-eastern Brazil

A 15-year experiment in a clayey Red-Yellow Podzolic in the tropical highlands of Vicosa, Brazil, was studied in 2000, aiming to evaluate the impact of different management systems (no tillage, disk plowing, heavy scratcher + disk plowing, and heavy scratched) on the total organic carbon (TOC), total nitrogen (TN), and several organic carbon pools. A natural forest, adjacent to the experimental area, was used as reference. The greatest TOC and TN as well as microbial biomass C (CMB), light fraction C (CFL), and labile organic carbon (CL) stocks were observed in the Atlantic Forest, compared with all other systems. The long-term cultivation (±70 years) of this area, prior to the installation of the experiment, has led to soil degradation, slowing the C recovery. No tillage had the higher C and N stocks and greater CL pool at the surface (0–10 cm), indicating improvement in soil nutrient status, although none of the systems presented potential to sequester C-CO2. Sustainable tropical agricultural systems should involve high residue input and conservative soil management in order to act as a C-CO2 sink. The C stocks in the CMB, CFL, and CL compartments were more reduced in relation to the natural vegetation with higher intensity management than the TOC stocks. This result indicates that these C compartments are more sensitive to changes in the soil management.

Propriedades espectrais da matéria orgânica leve-livre e leve intra-agregado de dois latossolos sob plantio direto e preparo convencional

Este trabalho teve como objetivo estudar a natureza quimica das fracoes leves-livres (FLL) e leves intra-agregado (FLI) da materia orgânica do solo, obtidas pelo fracionamento fisico do solo por densidade, por meio da espectroscopia na regiao do infravermelho, para verificar se tais fracoes constituem compartimentos distintos da materia orgânica do solo. Foram analisadas amostras de Latossolos de dois estados do Brasil (RS e GO), submetidos a plantio direto e preparo convencional, em distintos sistemas de rotacao de culturas. A analise por infravermelho revelou diferencas contrastantes entre os compartimentos orgânicos estudados. Os espectros de IV da fracao leve-livre apresentaram configuracao semelhante aos dos residuos vegetais, indicando que ela se encontra em estadios iniciais de transformacao. Nao foram observadas diferencas estruturais na FLL entre os distintos sistemas de preparo e rotacao de culturas. Os espectros de IV da FLI apresentaram bandas de absorcao N-H e C-O de polissacarideos menos intensas e em maior conjugacao, em relacao aos espectros da FLL, caracteristicas de material mais humificado. Foi observada ainda uma maior transformacao estrutural da fracao leve intra-agregado em solos sob preparo convencional, quando comparada a FLI de solo sob vegetacao natural e plantio direto. Os indices de hidrofobicidade (IH) e de condensacao (IC), determinados a partir de relacoes entre as bandas de absorcao de grupamentos - CH3 alifaticos, C-O de polissacarideos e C=O conjugados, permitiram identificar as diferencas na recalcitrância e condensacao das fracoes leves. Constatou-se que ambos os indices foram significativamente maiores para a materia orgânica intra-agregado, por consequencia de seu maior grau de humificacao.

Produção e ciclagem de nutrientes por plantas de cobertura nas culturas de arroz de terras altas e de soja

The cover crops in no-till system can contribute to the formation of mulch and nutrient cycling to annual crops in succession. The objective of this study was to evaluate biomass production and nutrient cycling of cover crops sown in the second growing season, in crop rotation after upland rice and soybean, in no-tillage and conventional tillage systems, on a Red Latassol of Rio Verde, state of Goias, from April 2008 to April 2010. The experiment was evaluated in randomized strips, in a 5 x 6 factorial design, with four replications. In the horizontal strips two soil management systems (after three years of no-tillage and conventional systems) were evaluated and the cover crops in the vertical strips. Biomass and ground cover and nutrient cycling rates were only evaluated in the no-till treatments, in a 5 x 6 factorial arrangement, where the plots were subdivided, corresponding to six harvest dates of dried biomass 0, 15, 30, 60, 90 and 120 days after cutting of the cover crops. The following cover crops were sown in the second growing season: Brachiaria ruziziensis, Pennisetum glaucum and B. ruziziensis + Cajanus cajan and a fallow treatment as reference. Biomass production and the rates of soil cover and nutrient accumulation and release by cover crops as well as rice and soybean yield were evaluated. B. ruziziensis and B. ruziziensis + C. cajan performed best in biomass production, ground cover and nutrient accumulation at the end of the cover crops. The nutrients N and K had the highest concentration in the biomass, and the highest nutrient release to the soil was observed for K and P. The highest rice yield was observed when grown in no-tillage on crop residues of P. glaucum and B. ruziziensis, while soybean yields did not differ in the treatments.

Influence of organic and mineral fertilisation on organic matter fractions of a Brazilian Acrisol under maize/common bean intercrop

In 1984, a field experiment was initiated in Coimbra, State of Minas Gerais, Brazil, involving the combination of 3 levels of mineral fertilisers at control (0); 10 kg N/ha, 15 kg P/ha, and 17 kg K/ha (MF1); 20 kg N/ha, 30 kg P/ha, and 34 kg K/ha (MF2); and 2 levels of organic compost at control (0) and 40 m3/ha (OC) in a maize/common bean intercrop. Soil samples were collected (0–0.10 and 0.10–0.20 m) in 2000 to evaluate the impact of mineral and organic compost on total carbon (TOC) and nitrogen (TN) stocks and on organic carbon pools of a Ferric Acrisol (Chromosol in the Australian Soil Classification). Additional soil samples were collected from an adjacent site covered by secondary Atlantic Forest as a reference. The conversion of forest to agriculture caused a reduction in most of TOC, TN, and microbial biomass carbon, free-light fraction carbon (CLF), and non-labile carbon. The carbon pools in cultivated plot were enhanced by the addition of compost alone. At both depths, TOC and TN stocks were higher (P < 0.05) in the MF2 + OC than MF2 treatment. Compared to soils that have received mineral fertiliser alone or combined with compost, the stocks of labile organic carbon, TN, and CLF were significantly affected (P < 0.05) by the sole application of compost.

Modelagem de funções no cálculo dos índices DRIS

O objetivo deste trabalho foi modelar o fator k e as funcoes DRIS para a diagnose foliar de mangueiras cultivadas. Dez pomares comerciais, no estagio de producao, localizados no vale do Rio Sao Francisco, foram monitorados, mensalmente, durante dois anos, por meio da coleta de amostras foliares para determinacao dos teores de N, P, K, Ca, Mg, B, Fe, Mn, Zn e Cu. Os dados foram testados quanto a normalidade e as relacoes entre as concentracoes dos nutrientes foram usadas para calcular as normas DRIS, obtendo-se media, variância e limites maximo e minimo de cada relacao dentro da populacao amostrada. Os nutrientes foram classificados como macronutrientes de resposta frequente (MAF) (N, P e K), macronutrientes de resposta rara (MAR) (Ca e Mg); micronutrientes de resposta frequente (MIF) (B, Fe, Mn e Zn) e, micronutrientes de resposta rara (MIR) (Cu). Funcoes DRIS foram desenvolvidas para cada classe de nutrientes. O modelo desenvolvido expressa o balanco nutricional das plantas cultivadas ajustado a cada nutriente e reflete o comportamento biologico das plantas como resultado da variacao da disponibilidade dos nutrientes.

Atributos biológicos do solo em pastagens de diferentes idades no sistema de integração lavoura‑pecuária

The objective of this work was to evaluate the effect of the pasture (Urochloa brizantha) component age on soil biological properties, in a crop-livestock integrated system. The experiment was carried out in a Brazilian savannah (Cerrado) area with 92 ha, divided into six pens of approximately 15 ha. Each pen represented a different stage of the pasture component: formation, P0; one year, P1; two years, P2; three years, P3; and final with 3.5 years, Pf. Samples were taken in the 0-10 cm soil depth. The soil biological parameters - microbial biomass carbon (MBC), microbial biomass respiration (C-CO2), metabolic quotient (qCO2), microbial quotient (qmic), and total organic carbon (TOC) - were evaluated and compared among different stages of the pasture, and between an adjacent area under native Cerrado and another area under degraded pasture (PCD). The MBC, qmic and TOC increased and qCO2 reduced under the different pasture stages. Compared to PCD, the pasture stages had higher MBC, qmic and TOC, and lower qCO2. The crop-livestock integrated system improved soil microbiological parameters and immobilized carbon in the soil in comparison to the degraded pasture.

Ciclagem de nutrientes por plantas de cobertura e produtividade de soja e arroz em plantio direto

The objective of this work was to evaluate nutrient cycling by cover crops and its influence on the performance of the rotation between upland rice and soybean. The crops were sown under no-tillage, in a Rhodic Haplustox, in the Cerrado region of the state of Goias, Brazil. The cover crops were sown mechanically, also under no-tillage, after the harvest of soybean (3/25/2008) and rice (4/7/2009). A randomized complete block design was used, split-plotted in time, with four replicates. The treatments consisted of the following cover crop species, besides fallow: Urochloa ruziziensis, U. brizantha, Pennisetum glaucum and U. ruziziensis + Cajanus cajan. The evaluation of the remaining nutrient in straw was performed at 0, 15, 30, 60, 90, and 120 days from the desiccation date of the cover crops. Urochloa ruziziensis and U. brizantha were the most efficient in the accumulation and release of nutrients, especially potassium. Urochloa ruziziensis is the most suited species for use as a cover crop previous to upland rice cultivation under no-tillage. However, none of the cover crop species significantly affect soybean grain yield.