Arminda Moreira de Carvalho

Comportamento de espécies de adubos verdes em diferentes épocas de semeadura e espaçamentos na região dos Cerrados

RESUMO - Com o objetivo de avaliar o crescimento e desenvolvimento de leguminosas utilizadas como adubos verdes, instalaram-se tres ensaios, em tres epocas de semeadura e dois espacamentos na regiao dos Cerrados, durante o ano agricola de 1991/1992, na area experimental da Embrapa-Centro Nacional de Pesquisa do Solo (CNPS), em Senador Canedo, GO. As especies avaliadas foram Crotalaria juncea L., mucuna-preta (Mucuna aterrima (Piper & Tracy) Merr.), guandu cv. Kaki (Cajanus cajan (L.) Millsp.) e Crotalaria ochroleuca G. Don. O delineamento experimental utilizado, dentro de cada epoca, foi o de blocos ao acaso com parcelas subdivididas, com tres repeticoes. Os resultados indicaram que C. juncea e C. cajan apresentaram as maiores producoes de fitomassa seca. O atraso da semeadura, em relacao ao inicio da estacao chuvosa, reduziu os rendimentos de fitomassas verde e seca produzidos pelas leguminosas, exceto pela mucuna-preta. Os espacamentos de 0,5 m e 0,4 m nao influenciaram o periodo para o florescimento e as producoes de fitomassas verde e seca. Termos para indexacao: Mucuna aterrima, Crotalaria juncea, Crotalaria ochroleuca, Cajanus cajan , adubacao verde. EVALUATION OF GREEN MANURES IN DIFFERENT SOWING DATES AND ROW-SPACINGS IN THE CERRADOS REGIONIn 1991/1992 growing season, three field experiments were carried out to evaluate the growth and development of sunn ( Crotalaria juncea), Crotalaria ochroleuca, black velvet bean ( Mucuna aterrima), pigeon pea cv. Kaki ( Cajanus cajan) as green manures at three sowing dates and two row spacings at Embrapa-Centro Nacional de Pesquisa de Solos (CNPS), Senador Canedo, GO, Brazil. The experimental design used was a complete randomized block with split-plot and three replicates . Highest yields of dry matter were obtained with C. juncea and C. cajan. The delay in sowing dates to the beginning of the rainy season, reduced yield of fresh and dry matter of all legume species, except black velvet bean. Row-spacings of 0,5 and 0,4 cm did not influence the time for flowering and the yield of fresh and dry matter.

Fitomassa e cobertura do solo de culturas de sucessão ao milho na Região do Cerrado

The objective of this study was to evaluate the biomass production and soil cover by different crops after maize cultivated in conventional tillage and no-tillage, in Cerrado conditions. The biomass of black oat, sunnhep, canavalia, pigeonpea, mucuna, sunflower and millet was obtained when they showed 50% of flowering. Soil coverage was evalluated at 30 and 60 days after sequential crops sowing, in August (during dry season), in October (at the beginning of the rainy season) and after 15 and 45 days of maize crop sowing. Mucuna showed the highest soil coverage rate during its growing. The biomass produced by sunflower had no efficiency for soil coverage. No-tillage showed the highest productions of biomass by sequential crops, compared to the conventional tillage system.

Decomposição de resíduos vegetais em latossolo sob cultivo de milho e plantas de cobertura

Soil degradation occurs as a consequence of intensive preparation associated with monocropping systems with deposition of residues that are rapidly decomposed. The objective of this study was to investigate the decomposition rates of different cover plants residues in Latosol (Oxisol) under conventional and no-tillage systems. The cover plants (Crotalaria juncea, Canavalia brasiliensis, Cajanus cajan, Mucuna pruriens, Helianthus annuus, Pennisetum glaucum, Raphanus sativus and natural fallow, as a control) were used in a succession with maize. The cover plants were cut when flowering reached approximately 50 % and remained on the soil until the sowing of the maize. In the conventional system, plant residues were incorporated in subplots with plough. Litter bags with 10 g of dry matter of each species were placed on the soil surface and covered with plant residues to determine the decomposition rate along the dry (60 and 90 days of incubation) and wet seasons (180, 210 and 240 days of incubation) under both systems. During soil preparation and herbicide application before the sowing of maize, the remaining bags were removed from the field and kept in cold storage (0 oC). After the sowing of maize, these bags were returned to the respective subplots, either on the surface for the no-tillage treatment or buried at 10 cm depth when under the incorporation treatment. The lowest decomposition rates were found for residues of Cajanus cajan Pennisetum glaucum, Mucuna pruriens, and natural fallow. Incorporation of plant residues accelerated the decomposition time, when compared to no-tillage system, except for Raphanus sativus. Maize yield was highest after the rotation with Canavalia brasiliensis.

Cover plants with potential use for crop-livestock integrated systems in the Cerrado region

The objective of this work was to evaluate the effects of lignin, hemicellulose, and cellulose concentrations in the decomposition process of cover plant residues with potential use in no-tillage with corn, for crop-livestock integrated system, in the Cerrado region. The experiment was carried out at Embrapa Cerrados, in Planaltina, DF, Brazil in a split plot experimental design. The plots were represented by the plant species and the subplots by harvesting times, with three replicates. The cover plants Urochloa ruziziensis, Canavalia brasiliensis, Cajanus cajan, Pennisetum glaucum, Mucuna aterrima, Raphanus sativus, Sorghum bicolor were evaluated together with spontaneous plants in the fallow. Cover plants with lower lignin concentrations and, consequently, higher residue decomposition such as C. brasiliensis and U. ruziziensis promoted higher corn yield. High concentrations of lignin inhibit plant residue decomposition and this is favorable for the soil cover. Lower concentrations of lignin result in accelerated plant decomposition, more efficient nutrient cycling, and higher corn yield.

Indicadores biológicos associados ao ciclo do fósforo em solos de Cerrado sob plantio direto e plantio convencional

The objective of this work was to evaluate the effects of no-till, conventional tillage and cover crops on biological indicators associated to the P cycle. The work was carried out on three adjacent areas on a Red- Yellow Oxisol: area I, a two-year experiment comparing the two management systems; area II, a six-year experiment, and area III, a native Cerrado vegetation. The soil was sampled at two depths (0-5 cm and 5-20 cm) in July/1998 and January/1999. The biological indicators evaluated were microbial biomass P, acid phosphatase activity, phosphate-solubilizing and total soil fungi and bacteria. Acid phosphatase activity and number of phosphate- solubilizing microorganisms, at the 0-5 cm depth, were significantly greater in the no-till soil, as compared to the conventional tillage. Differences between the tillage systems, regarding the biological indicators evaluated, were more pronounced in area II in which the no-till system had been established for a longer period. Microbial P decreased in the no-till Raphanus sativus treatment. P-solubilizing fungi increased in the presence of Cajanus cajan and Raphanus sativus, whereas the P-solubilizing bacteria increased in the presence of C. cajan. Highest activities of acid phosphatase were detected in the soil under native vegetation, evidencing the importance of organic P mineralization in this ecosystem.

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.

Manejo de plantas de cobertura na floração e na maturação fisiológica e seu efeito na produtividade do milho

O objetivo deste trabalho foi avaliar o efeito do manejo de plantas de cobertura na floracao e na maturacao fisiologica sobre a produtividade do milho cultivado em sucessao. O experimento, em delineamento de blocos ao acaso com parcelas subdivididas, foi realizado em Latossolo Vermelho, em sistema plantio direto, com nove especies. Foram avaliados: produtividade de materia seca; tempo de ciclagem dos residuos vegetais; teores de N das plantas de cobertura; e produtividade de graos e teores de N nas folhas do milho. As especies Pennisetum glaucum, Mucuna aterrima, Cajanus cajan e Canavalia brasiliensis apresentaram as maiores produtividades de materia seca na floracao. Na maturacao fisiologica, Sorghum bicolor, P. glaucum, C. brasiliensis, Crotalaria juncea e C. cajan apresentaram produtividades mais elevadas de fitomassa. Nao houve efeito da epoca de corte e da interacao planta de cobertura e epoca de corte sobre a produtividade do milho. As maiores produtividades de milho foram obtidos apos cultivo de Urochloa ruziziensis, C. juncea, C. brasiliensis, C. cajan, P. glaucum e Raphanus sativus, e estao relacionadas ao maior acumulo de materia seca e ao menor tempo de ciclagem dos residuos vegetais das plantas de cobertura.

Absorção de N, P e K por espécies de adubos verdes cultivadas em diferentes épocas e densidades num latossolo vermelho-escuro argiloso sob cerrados

Planting spacings and sowing dates may influence nutrient absorption. Therefore, a field experiment was carried out from 1991 to 1992, at the experimental station of Embrapa/Soil Research National Center, located in Senador Canedo, Goias, Brazil, to determine the N, P and K uptake levels in the aerial part of sunhemp (Crotalaria juncea), Crotalaria ochroleuca, black velvet bean (Mucuna aterrima) and pigeonpea cv. Kaki (Cajanus cajan), under three sowing times (beginning, middle and end of the growing season) and two spacings between the planting rows. The experiment was arranged in a randomized split plot design, with three replications, with the sowing dates in the main plots and the planting spacings in the split plots. The results indicated that there the levels of N, P and K uptake varied among the species. N, P and K uptake levels in the legume shoot dry matter were influenced by the sowing times, and the species x sowing time interaction was significant for N and P. Nevertheless, N, P and K uptake levels were not influenced by the spacings between the planting rows.

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.

Forms of phosphorus in an oxisol under different soil tillage systems and cover plants in rotation with maize

Phosphorus fractions play a key role in sustaining the productivity of acid-savanna Oxisols and are influenced by tillage practices. The aim of this study was to quantify different P forms in an Oxisol (Latossolo Vermelho-Amarelo) from the central savanna region of Brazil under management systems with cover crops in maize rotation. Three cover crops (Canavalia brasiliensis, Cajanus cajan (L.), and Raphanus sativus L.) were investigated in maize rotation systems. These cover crops were compared to spontaneous vegetation. The inorganic forms NaHCO3-iP and NaOH-iP represented more than half of the total P in the samples collected at the depth of 5-10 cm during the rainy season when the maize was grown. The concentration of inorganic P of greater availability (NaHCO3-iP and NaOH-iP) was higher in the soil under no-tillage at the depth of 5-10 cm during the rainy season. Concentrations of organic P were higher during the dry season, when the cover crops were grown. At the dry season, organic P constituted 70 % of the labile P in the soil planted to C. cajan under no-tillage. The cover crops were able to maintain larger fractions of P available to the maize, resulting in reduced P losses to the unavailable pools, mainly in no-tillage systems.