Robélio Leandro Marchão

Macrofauna edáfica associada a plantas de cobertura em plantio direto em um Latossolo Vermelho do Cerrado

The objective of this work was to characterize soil fauna groups and to evaluate the effects of cover crops under no-tillage system, in a Cerrado Oxisol, in two evaluation periods. The cover crops: Crotalaria juncea, Cajanus cajan, Stylosanthes guianensis, Brachiaria brizantha, Brachiaria brizantha/Zea mays association, Pennisetum glaucum, Panicum maximum and Sorghum bicolor were cultivated from November to April of each year. Common bean was sown every September under centre pivot irrigation. The area of each plot was 60 m 2 . Soil monoliths (25x25 cm) were taken randomly from each plot, at 0-10 cm and 10-20 cm dephs, in April and September, 2005, and macrofauna was hand sorted. Identified groups in decreasing order of total density are: Formicidae, Oligochaeta, Dermaptera, Coleoptera, Hemiptera, Miriapoda, Isoptera, Araneae, Lepidoptera, Blattodea and Diptera larvae. Crotalaria juncea showed the highest macrofauna density, followed by B. brizantha, B. brizantha/Zea mays association, Sorghum bicolor, Stylosanthes guianensis, Cajanus cajans, Pennisetum. glaucum, Panicum maximum. The use of cover species in no-tillage system, associated with irrigation, promotes soil colonization by macrofauna.

Sistemas de integração lavoura-pecuária na região do Cerrado

O objetivo deste trabalho foi analisar os beneficios e as perspectivas potenciais de sistemas de integracao lavoura-pecuaria no processo de intensificacao de uso das areas em exploracao com lavoura de graos e pastagens no Cerrado, e apontar as principais lacunas de informacao sobre o sistema. Os principais beneficios da integracao lavoura-pecuaria sao: melhoria das propriedades quimicas, fisicas e biologicas do solo; reducao da ocorrencia de doencas, insetos-pragas e plantas daninhas; maior produtividade das plantas e dos animais; e reducao de riscos pela diversificacao de atividades. No entanto, a adocao do sistema de integracao lavoura-pecuaria ainda e pequena, provavelmente em virtude da maior complexidade desse sistema. Concentrar esforcos nos fatores que limitam a adocao desse sistema no Cerrado parece ser um ponto estrategico para novos estudos. A busca por melhoria na qualidade de cobertura de solo para o sistema plantio direto, por meio de gramineas forrageiras, pode auxiliar na adocao da integracao lavoura-pecuaria no Cerrado. A expectativa e de que a adocao de sistemas de integracao lavoura-pecuaria resulte em melhorias significativas na sustentabilidade socioeconomica e ambiental das propriedades e da sua regiao de influencia.

Evidence of limited carbon sequestration in soils under no-tillage systems in the Cerrado of Brazil

The Brazilian government aims at augmenting the area cropped under no-tillage (NT) from 32 to 40 million ha by 2020 as a means to mitigate CO2 emissions. We estimated soil carbon (C) sequestration under continuous NT systems in two municipalities in the Goiás state that are representative of the Cerrado. A chronosequence of NT fields of different age since conversion from conventional tillage (CT) was sampled in 2003 and 2011. Soil C levels of native Cerrado and pasture were measured for comparison. After about 11 to 14 years, soil C stocks under NT were highest and at the levels of those under natural Cerrado. Average annual rates of soil C sequestration estimated using the chronosequence approach were respectively 1.61 and 1.48 Mg C ha−1 yr−1 for the 2003 and 2011 sampling, and were higher than those observed using repeated sampling after eight years. The diachronic sampling revealed that the younger NT fields tended to show higher increases in soil C stocks than the older fields. Converting an extra 8 million ha of cropland from CT to NT represents an estimated soil C storage of about 8 Tg C yr−1 during 10 to 15 years.

Methods of soil organic carbon determination in Brazilian savannah soils

Several methods exist for determining soil organic carbon, and each one has its own advantages and limitations. Consequently, a comparison of the experimental results obtained when these methods are employed is hampered, causing problems in the comparison of carbon stocks in soils. This study aimed at evaluating the analytical procedures used in the determination of carbon and their relationships with soil mineralogy and texture. Wet combustion methods, including Walkley-Black, Mebius and Colorimetric determination as well as dry combustion methods, such as Elemental and Gravimetric Analysis were used. Quantitative textural and mineralogical (kaolinite, goethite and gibbsite) analyses were also carried out. The wet digestion methods underestimated the concentration of organic carbon, while the gravimetric method overestimated. Soil mineralogy interfered with the determination of carbon, with emphasis on the gravimetric method that was greatly influenced by gibbsite.

Uso e manejo do solo e seus impactos sobre a qualidade física

The rational use of the soil has been the subject of study and discussion due to search for technological alternatives that allow the adequate management of the soil and consequently, a sustainable agriculture. The objective of this study was to collect data about the hydro-physical quality and its relation to the impacts caused by soil management through a literature review, contributing to better understanding of existing information in the literature. The use of indicators of physical quality of soil permit the designation of most appropriate soil management practices, especially those exposed to intensive agriculture. A critical analysis of indicators of soil quality show that the index proposed by Reynolds et al. (2002) has limitations about its use, the optimal hydric interval presents good results, and the S index needs more works with the use of h (soil-water suction) as the independent variable. Thus, the indicators of physical quality of soil are useful for evaluating the state of soil conservation, to making possible the secure management of natural resources, however, the existing indicators present very high complexity of the implementation and acquisition costs, which configures opportunity for the development of new indicators of physical quality of soil.

Soil fertility status, carbon and nitrogen stocks under cover crops and tillage regimes

The aim of the present study was to evaluate the effects of cover crops on the soils chemical fertility, in particular its carbon and nitrogen content, in a Typic Acrustox under conventional and no-tillage corn systems. We hypothesized that the no-tillage system associates with cover crops maintains or increases soil carbon and nitrogen stocks and enhance soil fertility. The no-tillage system did not present higher carbon and nitrogen stocks than conventional tillage, but resulted in higher concentrations of exchangeable bases, higher CEC, and higher base saturation in the surface soil layer, mainly under use of Canavalia brasiliensis. Carbon and nitrogen stocks (up to 40 cm depth) differ significantly between the different cover crop species. The use of Mucuna pruriens and Canavalia brasiliensis allows maintain or increase soil C and N stocks. The no-tillage system results in higher accumulation of soil organic matter (0-5 cm), and appears very likely to enhance soil fertility. The use of Canavalia brasiliensis and Mucuna pruriens in succession to corn promotes carbon sequestration and can be used to enhance soil quality in Cerrado agroecosystems.

Qualidade física do solo sob sistemas de integração lavoura-pecuária

The objective of this work was to evaluate the physical quality of soil in integrated crop-livestock systems (ICL) in comparison to continuous pasture and native Cerrado. During two years (2005 and 2006), soil samples from a clayed Rhodic Ferralsol were collected from two layers (0-20 and 70-80 cm), in six areas under different crop rotation and ICL. Continuous pasture and native Cerrado were used as reference. The following physical and hydraulic properties were evaluated: bulk density, water saturation, total porosity, macroporosity, effective microporosity, effective saturation, lab and field-saturated hydraulic conductivity, and soil-water retention curve. All the cultivated systems caused impact on the physical and hydraulic properties of the 0-20 cm layer. The continuous pasture provided the best soil physical quality. In the comparison between years, only the soil under conventional tillage had its bulk density increased and its soil porosity decreased. The pasture in the rotation system with ICL, even after four years, does not restore soil physical quality in comparison to continuous pasture.

Characterization of cover crops by NMR spectroscopy: impacts on soil carbon, nitrogen and phosphorus under tillage regimes

The objective of this study was to investigate the chemical composition of cover crops by solid-state CPMAS 13C NMR spectroscopy and its effects on carbon, nitrogen and phosphorus in a Typic Acrustox. Cover crops (Crotalaria juncea, Canavalia brasiliensis, Cajanus cajan, Mucuna pruriens and Raphanus sativus) and natural fallow were studied in rotation with maize under conventional and no-tillage regimes. Tissues of Crotalaria juncea, Canavalia brasiliensis, Mucuna pruriens and Raphanus sativus were analyzed using CPMAS 13C NMR spectroscopy. Soil samples were collected at the end of the growing season of the cover crops (September 2002) and during the grain filling period in corn from 0-5 and 5-10 cm layers. Cajanus cajan presented the lowest content of polysaccharides and along with Mucuna pruriens presented the highest percentage of aromatic carbon compounds, reflecting the slow decomposition of highly lignified material. Carbon stocks were higher in the superficial soil layer and under no-tillage due to the accumulation and slower decomposition of plant tissues under these conditions. Increases in the C/N ratio of the soil with Mucuna pruriens and the C/P ratio with Cajanus cajan in the dry season were also related to slower rates of decomposition, caused by the large concentration of aromatic compounds in the tissues of these species. The higher C/P ratios found at 0-5 cm layer are due to higher values of P (Mehlich-1) at 5-10 cm (25 mg kg-1) layer and the higher concentration of carbon in the superficial soil layer as a result of the accumulation of plant residues.

Balanço energético da produção de grãos, carne e biocombustíveis em sistemas especializados e mistos

The objective of this work was to evaluate the energetic efficiency of mixed and specialized production systems of grain and meat, and the energy balance in bioenergy production. Agronomic data from 20-year farming with specialized and mixed agrosystems were used. As specialized agricultural systems, the following ones were evaluated: grass pasture; grass with legume pasture; and continuous grain production under no tillage or conventional plough tillage. As a mixed system, the integrated crop-livestock was evaluated under no tillage or conventional plough tillage. The agricultural activity were considered energy input, while grain yield and meat production the energy output. The agricultural products obtained in mixed systems showed energy balance and total production of renewable energy equivalent to the those yielded by the specialized systems. The energy balance of soybean biofuel showed positive values both in mixed and in specialized systems regardless of the soil tillage managements. Among the analyzed soybean and maize biofuels, the greatest energy balance was observed in maize bioethanol. The biofuels produced in all production systems show a positive energy balance and can be considered energetically sustainable.

Relationship between macrofauna, mineralogy and exchangeable calcium and magnesium in Cerrado Oxisols under pasture

The objective of this work was to assess the relationship between macrofauna, mineralogy and exchangeable calcium and magnesium in Cerrado Oxisols under pasture. Twelve collection points were chosen in the Distrito Federal and in Formosa municipality, Goias state, Brazil, representing four soil groups with varied levels of calcium + magnesium and kaolinite/(kaolinite + gibbsite) ratios. Soil macrofauna was collected in triplicate at each collection point, and identifi ed at the level of taxonomic groups. Macrofauna density showed correlation with contents of kaolinite, gibbsite and exchangeable Ca + Mg in the soils. Mineralogy and exchangeable Ca + Mg had signifi cant effects on taxonomic groups and relative density of soil macrofauna. The termites (Isoptera) were more abundant in soils with low exchangeable Ca + Mg; earthworms (Oligochaeta), in soils with high levels of kaolinite; and Hemiptera and Coleoptera larvae were more abundant in gibbsitic soils with higher contents of total carbon.