Osmar Rodrigues Brito

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.

Fertility and acidity status of latossolos (oxisols) under pasture in the Brazilian Cerrado

The Cerrado region, with over 50 million hectares of cultivated pasture, provides 55% of Brazilian beef production. Previous investigations have shown that about 70-80% of this pasture is affected by some kind of degradation, leading to low productivity. However, until now, few surveys have been carried out on a regional scale. The aim of the present work is both to assess the fertility and acidity levels of Cerrado soils under pasture and compare the variability of the soils characteristics on a regional scale. Two soil depths were sampled in different places within the studied area: (1) a surface horizon (0.0-0.2 m) in order to evaluate its fertility and acidity status for pasture, and (2) a subsurface horizon (0.6-0.8 m), used for classification. Most of soils had levels of nutrients below the reference values for adequate pasture development. Whatever the texture, about 90% of soils had low or very low availability of phosphorus. Only 7 to 14% of soils had low pH, high exchangeable aluminum, and aluminum saturation above the critical acidity level. Except for nitrogen, no significant difference was found between Latossolos Vermelhos and Latossolos Vermelho-Amarelos.

Disponibilidade de cobre, ferro, manganês e zinco em solos sob pastagens na Região do Cerrado

Este trabalho teve como objetivo descrever os teores totais e disponiveis de cobre, ferro, manganes e zinco e suas relacoes com a acidez, fertilidade, textura e mineralogia de latossolos sob pastagens na Regiao do Cerrado. Os solos estudados foram amostrados em tres regioes: as margens das rodovias GO-060 e BR-154, entre os municipios de Goiânia, GO, e Barra do Garcas, MT; no Distrito Federal, e nos municipios de Unai e Paracatu, noroeste de Minas Gerais. Coletaram-se 54 amostras na camada de 0–20 cm. Relacionaram-se as quantidades disponiveis de Cu, Fe, Mn e Zn (extraidos com DTPA) com seus teores totais, textura, mineralogia e variaveis quimicas dos solos, por meio da analise de componentes principais. Os teores totais e disponiveis desses elementos foram extremamente variaveis. A disponibilidade de Fe, Cu e Mn se relacionou principalmente com os teores de ferro cristalino e com o pH em agua. A disponibilidade de Zn se relacionou principalmente com a capacidade de troca cationica do solo. O Zn e, entre os micronutrientes avaliados, o mais frequentemente limitante ao desenvolvimento das pastagens na Regiao do Cerrado.

Root system and yield of sugarcane cultivated under different amounts of straw in southern Brazil.

The amount of straw of sugarcane needed to remain in field for sustainability of the production system and quantity that could be used in sectors such as cogeneration and production of bioethanol for optimization of power generation by the sector are unclear issues. The aim of this study was to evaluate the effect of different amounts of straw on the development of the sugarcane root system and yield using the variety SP 801816 in a Rhodic Eutrudox in southern Brazil. Six treatments were evaluated: 0 (no straw), 25, 50, 75 and 100% (20 Mg ha -1 ) of straw and straw burned at 60, 180 and 270 days after planting in 150 m 2 plots. Root samples were collected at 0.45 and 0.75 m from the planting line at depths of 0-0.10, 0.10-0.20, 0.20-0.40 and 0.40 to 0.60 m at harvest, and the stems of the plots were weighed to measure yield. In water stress period, the 50, 75 and 100% straw treatments promoted a greater root mass to 0.20 m deep, which was also reflected in the yield. The 50 and 75% straw treatments resulted in 25% greater yield than the 0 and 25% straw and straw burned, resulting in 28 Mg ha -1 more. The amount, 50% straw retention in the field is sufficient to increase the mass of the roots and, in turn, productivity, which is possible to remove the 50% surplus from the field for industrial processes for the production of energy, without the occurrence of damage to the crop.

Indicators of soil quality in the implantation of no-till system with winter crops

We assessed the effect of different winter crops on indicators of soil quality related to C and N cycling and C fractions in a Rhodic Kandiudult under no-till system at implantation, during two growing seasons, in Londrina PR Brazil. The experimental design was randomized blocks with split-plot in time arrangement, with four replications. The parcels were the winter crops: multicropping of cover crops with black oat (Avena strigosa), hairy vetch (Vicia villosa) and fodder radish (Raphanus sativus); sunflower (Heliantus annuus) intercropped with Urochloa ruziziensis; corn (Zea mays) intercropped with Urochloa; and corn; fodder radish; or wheat (Triticum aestivum) as sole crops. The subplots were the years: 2008 and 2009. Determinations consisted of total organic C, labile and resistant C, total N, microbial biomass C and N, the C/N ratio of soil organic matter, and the microbial quotient (qMic), besides microbiological and biochemical attributes, assessed only in 2009. The attributes significantly changed with the winter crops, especially the multicropping of cover crops and fodder radish, as well as effect of years. Despite stimulating the microbiological/biochemical activity, fodder radish cropping decreased the soil C in the second year, likewise the wheat cropping. The multicropping of cover crops in winter is an option for management in the establishment of no-till system, which contributes to increase the concentrations of C and stimulate the soil microbiological/biochemical activity.

Mineral nutrition and production of beans in areas managed with and without burning of organic residues and different fertilization types

The use of organic residues in agriculture has motivated the development of researches that seeks for the sustainability of the production. The agricultural use, in nature or in the form of compounds of twigs and branches resulting from the pruning of trees in urban centers can be considered as a source of organic fertilizer to various crops. Through a simulated situation of areas managed using the fire, this work was led to evaluate the effects of doses, burning of organic residues and fertilization types on the components of the production, leaf contents of macronutrients and on the yield of two cultivars of carioca beans (IPR Colibri and IPR Eldorado) cultivated in rotation system with corn crop. Two experiments were installed: Experiment I - with the burning of the residues; and Experiment II - without the burning of the residues. For each experiment it was used a randomized block design with three replications in a 4x2 factorial arrangement, in which the factors were four doses of organic residues (0, 15, 30 and 45 Mg ha -1 ) and two fertilization types (EOF: organic fertilization and OMF: organic mineral fertilization). To evaluate the effect of fire on the productivity of bean cultivars was performed a joint analysis between experiments I and II. The components of production, the leaf nutrients contents and the productivity of bean cultivars IPR and IPR Colibri Eldorado were always higher with organo-mineral fertilization. Comparing the experiments it was found that the productivity of the bean IPR Colibri was higher than on treatment without burning of residues associated with mineral fertilizer.