Luiz Fernando Carvalho Leite

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.

Decomposição e liberação de nutrientes de resíduos vegetais depositados sobre Latossolo Amarelo no Cerrado Maranhense

In the no-tillage system the use of cover crops is a widely adopted alternative to increase the sustainability of the agricultural system. This study aimed to evaluate the decomposition rate and total nitrogen (N), phosphorus (P) and potassium (K) release from the biomass of natural bush fallow and cover crops (Brachiaria sp., millet and Brachiaria sp. + millet intercrop), cultivated on a Yellow Latosol in the savanna of the Maranhao State. The experiment was carried out under no-tillage system after maize harvesting. Dry matter production, decomposition rate and nutrient release (N, P and K) at twenty-day intervals, until one hundred days after biomass cutting were evaluated. Millet or Brachiaria sp. mono or intercropped and natural bush fallow showed similar decreases in their decomposition in the first sixty days, with losses of 10; 13; 16 e 12% respectively. The highest and lowest rate of N release was observed on millet and Brachiaria sp. + millet intercrop, respectively. Among the nutrients, K was the earliest released in all treatments. The Braquiaria sp. is the cover crop with greater resistance to decompose, keeping the residue on the soil for longer periods in the Cerrado of Maranhao State.

Soil organic carbon and biological indicators in an Acrisol under tillage systems and organic management in north-eastern Brazil.

No-tillage and organic farming are important strategies to improve soil quality. This study aimed to quantify the effects of the tillage systems and organic management on total organic carbon (TOC), labile C (CL), and biological indicators in an Acrisol in north-eastern Brazil. Five systems were studied: NV, native vegetation; NT/ORG, no-tillage plus organic fertiliser; NT/CHE, no-tillage plus chemical fertiliser; NT/CHE/ORG, no-tillage plus organic and chemical fertiliser; CT/CHE, conventional tillage plus chemical fertiliser. Soil samples were collected in the 0–0.10 and 0.10–0.20 m depths. TOC stocks were higher in NT/CHE/ORG (0–0.10 m, 14.0 Mg/ha; 0.10–0.20 m, 13.0 Mg/ha) and NT/ORG (0–0.10 m, 12.6 Mg/ha; 0.10–0.20 m, 11.6 Mg/ha) than in CT/CHE and NV systems. CL stocks were higher in NT/ORG (3.61 Mg/ha) at 0–0.10 m and in NT/ORG, NT/CHE, and NT/CHE/ORG at 0.10–0.20 m. At 0–0.10 m, microbial biomass C content was higher in the NT/CHE/ORG (190 mg/kg) and NT/ORG (155 mg/kg). Soil microbial respiration rate was similar in all systems. However, qCO2 was higher in the NT/CHE and CT/CHE systems, suggesting a stress in the soil microbial biomass. No-tillage and organic management promoted positive changes in soil organic carbon and soil microbial properties and improved soil quality.

Atributos químicos e estoques de carbono e nitrogênio em argissolo vermelho-amarelo sob sistemas agroflorestais e agricultura de corte e queima no norte do Piauí

Slash and burn farming practices have caused land degradation in the state of Piaui. This problem has stimulated the adoption of land use sustainable alternatives such as agroforestry systems. This work aimed to evaluate changes in the chemical characteristics and carbon and nitrogen stocks in Acrisol under six (SAF6) and ten year (SAF10) old agroforestry systems, agriculture with a three year (SE3) ecological basis, slash and burning practices (ACQ), and native forest (FN) in the northern state of Piaui. Soil samples, in the dry and humid periods, were collected in the 0-10 cm depth. Chemical soil properties, total organic carbon (TOC) and total nitrogen (TN) were evaluated. SAF10 showed lower Al +3 content (0.02 cmolc dm-3) in relation to the other systems. In the dry season, P content in SAF10 (12.27 mg dm-3) was six to seven times larger than ACQ and FN, respectively. The highest values of TOC and TN were observed, in the dry season, respectively, in the SAF10 (48.54 Mg ha-1 and 4.43 Mg ha-1) and SAF6 (43.30 Mg ha-1 and3.45 Mg ha-1). Agroforestry systems improved soil quality and can be considered conservation strategy for northern Piaui.

Microbiological process in agroforestry systems. A review

Soils around the world are degraded due to inappropriate management practices. There is thus the necessity to find more conservationist agricultural systems. Agroforestry system is an alternative system that helps prevent land degradation while allowing continuing use of land to produce crops and livestock on a sustainable basis. Agroforestry system is a form of sustainable land use that combines trees and shrubs with crops and livestock in ways that increase and diversify farm and forest production while also conserving natural resources. This system enhances organic carbon accumulation in soils by the inclusion of cover crops and permanent vegetation, which is expected to increase the soil microbial biomass. The use of microorganisms aims at improving nutrient availability for plants. Currently, there is an emerging demand to decrease the dependence on chemical fertilizers and achieve sustainable agriculture and agroforestry. Arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria, and the association of rhizobia with leguminous plants are mutualistic symbioses of high economic importance for increasing agricultural production. The biological nitrogen fixation (BNF) process is an economically attractive and ecologically sound method to reduce external nitrogen input and improve the quality and quantity of internal resources. BNF by associative diazotrophic bacteria is a spontaneous process where soil nitrogen is limited and adequate carbon sources are available. However, the ability of these bacteria to contribute to increased crop yields is only partly a result of BNF. The successful use of legumes is dependent upon appropriate attention to the formation of effective symbioses with root nodule bacteria. An essential component for increasing the use of legumes is the integration of plant breeding and cultivar development, with appropriate research leading to the selection of elite strains of root nodule bacteria. An expansion of the utility of inoculants is also necessary to develop a broad conceptual framework and methodology that is supported by scientific arguments; it is destined to impact assessment of the use of new biological products in agriculture.

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.

Caracterização da fauna edáfica em sistemas de manejo para produção de forragens no Estado do Piauí

Resumo - O objetivo desse trabalho foi avaliar a distribuicao da fauna em funcao da umidade do solo em diferentes sistemas de manejo para a producao de forragens com capim-Tifton 85 (Cynodon dactylon Pers. x C. niemfuensis Vanderys), capimTanzânia (Panicum maximum Jacq. cv. Tanzânia), capim-Andropogon (Andropogon gayanus Kunth), Leucena (Leucaena leucocephala (Lam.) R. de Wit.) tendo como controle uma Mata dos Cocais. A coleta da fauna foi feita utilizando-se armadilhas do tipo Pitfall em duas epocas do ano: setembro de 2007 e marco de 2008, periodo seco e chuvoso, respectivamente. Os sistemas com capim-Tifton, capim-Tanzânia e Leucena mostraram maior numero de individuos nos dois periodos avaliados. A queimada ocorrida no capim-Andropogon antes da primeira coleta resultou em uma reducao na abundância e diversidade da fauna edafica. Os maiores valores em riqueza, diversidade e uniformidade de fauna foram obtidos na amostragem realizada no periodo umido. A mata mostrou maior diversidade e equitabilidade nos dois periodos avaliados. Em situacao de estresse hidrico alguns grupos como Formicidae e Collembola predominaram nos sistemas de manejo diminuindo a uniformidade, enquanto no periodo umido varios grupos mostraram boa representatividade o que favoreceu a uniformidade. A analise multivariada de componentes principais evidenciou que os sistemas com mata, capim-Tifton e capim-Tanzania e Leucena mostraram associacao com varios grupos da fauna edafica nos dois periodos avaliados enquanto que o sistema com capim-Andropogon, que sofreu queimada, apresentou afinidade apenas com o grupo Heteroptera, no periodo seco. Plavras-chave - Leguminosa arborea. Pastagem. Sazonalidade.

Atributos químicos e estoques de carbono em Latossolo sob plantio direto no cerrado do Piauí

No-tillage adoption has been considered a viable alternative for sustainable soil use. This work aimed to evaluate the influence of no-tillage system with different times of adoption and conventional tillage on chemical attributes and carbon stocks in an Oxisol of the savannah of Piaui in Northeastern Brazil. Soil samples in the 0-5, 5-10, 10-20 and 20-40 cm layers were collected in conventional tillage (CT) no-tillage (NT) with 2 (NT2), 4 (NT4) and 6 (NT6) years of adoption and native forest (NF). The following chemical properties were evaluated: pH, extractable P, exchangeable cations, Al, potential acidity (H+Al), total organic carbon (TOC) and microbial biomass carbon (Cmic). NT adoption increased pH, extractable P and exchangeable cations contents. Compared to conventional tillage, TOC and Cmic stocks increased 34 and 99% (NT2), 47 and 92% (NT4) and 61 and 108% (NT6), respectively, in the superficial layer (0-20 cm). No-tillage adoption improves chemical attributes and increases total organic carbon and microbial carbon and its continuous use contributes to soil quality in savannah soils of Piaui state.

Estoques e frações de carbono orgânico em Latossolo Amarelo submetido a diferentes sistemas de manejo

The objective of this work was to determine the effects of soil management systems on the stocks and fractions of organic carbon of an Oxisol (Xantic Ferralsol), in the cerrado of the state of Piaui, Brazil. The following systems were evaluated: a three-year-old conventional tillage; a three- and a five-year -old no-tillage system, using millet as cover crop; and a nine-year-old no-tillage, using millet as cover crop for seven and forage (Urochloa brizantha) for two years. A native cerrado area was used as a reference. Soil samples were collected in the wet and dry seasons from 0.00-0.05, 0.05-0.10, 0.10-0.20, and 0.20-0.40 m depths for determining: total organic carbon and nitrogen contents and stocks; humic substances content; and humification index. The highest carbon contents were observed in the soil under cerrado, at 0.00-0.05 m depth, in both seasons. However, the highest stocks of carbon and nitrogen as well as the highest contents of humic substances were verified in the soil with no-tillage system for five and nine years, in both seasons, at all evaluated depths. The highest humification index was also observed in these soils, in the dry season. No-tillage associated with cover crops decreases soil organic matter mineralization, increases soil carbon stocks in depth, and favors carbon sequestration in cerrado areas of Piaui state.

Qualidade química do solo e dinâmica de carbono sob monocultivo e consórcio de macaúba e pastagem

This study aimed to evaluate the effects of the cultivation of acrocomia palm (Acrocomia aculeata) intercropped or not with pasture on the chemical quality and carbon pools of an Oxisol of the Savanna of Maranhao state. Four land use systems were studied: acrocomia, pasture, acrocomia intercropped with pasture and savanna native vegetation. Soil samples were collected up to 60 cm depth for determination of chemical attributes and soil organic carbon contents and stocks. The highest values of P, K, Ca and Mg were observed in the soil under pasture. Total organic carbon stocks and labile carbon content were higher under native vegetation up to 60 cm followed by acrocomia intercropped with pasture system. Higher values of microbial biomass carbon and microbial quotient were verified in the soil under pasture in all depths. Pasture is important to be intercropped with acrocomia since it increases the soil fertility levels and soil carbon stocks favoring the improvement of the soil quality in the Savanna of Maranhao state.