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

As plantas de cobertura em sistema de plantio direto pode contribuir na formação de palhada e ciclagem de nutrientes para as culturas em sucessão. O objetivo deste trabalho foi avaliar a produção de matéria seca e ciclagem de nutrientes por plantas de cobertura semeadas em safrinha no desempenho do arroz de terras altas e da soja semeados em rotação, em sistemas plantio direto e preparo convencional, em Latossolo Vermelho do município de Rio Verde, Goiás. O estudo foi realizado no período de abril de 2008 a abril de 2010. Utilizou-se o delineamento em faixas com fatorial 2 x 5 com quatro repetições. Nas faixas horizontais foram testados os dois sistemas de manejo do solo (plantio direto e convencional) e nas faixas verticais, as plantas de cobertura. As avaliações de matéria seca, taxa de cobertura do solo e ciclagem de nutrientes foram realizadas apenas nos tratamentos plantio direto, em que as parcelas foram subdivididas em seis épocas de coletas de matéria seca após a dessecação das plantas de cobertura, o que ocorreu aos 0, 15, 30, 60, 90 e 120 dias a partir da dessecação de manejo das plantas de cobertura, perfazendo um fatorial 5 x 6. As plantas de cobertura, semeadas em safrinha, foram as seguintes: Brachiaria brizantha, B. ruziziensis, Pennisetum glaucum e B. ruziziensis + Cajanus cajan e o pousio. Avaliaram-se a produção de matéria seca, a taxa de cobertura do solo, o acúmulo e liberação de nutrientes pelas plantas de cobertura e a produtividade do arroz na safra 2008/09 e da soja na safra 2009/10, semeados em rotação. As espécies B. ruziziensis e B. ruziziensis + C. cajan destacaram-se na produção de matéria seca, taxa de cobertura do solo e acúmulo de nutrientes no final do período de entressafra. Os nutrientes com mais acúmulos nas matérias secas foram N e K, e as maiores taxas de liberação no solo foram observadas nos elementos K e P. As maiores produtividades de arroz sob plantio direto foram obtidas sobre palhadas de P. glaucum e B. ruziziensis, enquanto a cultura da soja não apresentou diferenças em sua produtividade nos tratamentos estudados.

Soil chemical properties related to acidity under successive pig slurry application

Pig slurry application as soil manure can alter the chemical properties of the soil and affect its acidity, modifying the environment for crop growth and development. The objective of this study was to evaluate the chemical properties related to soil acidity subjected to successive applications of pig slurry. The experiment was conducted in May 2000, in an experimental area of the Federal University of Santa Maria (UFSM) under no-tillage and lasted until January 2008. Nineteen surface applications of 0, 20, 40, and 80 m³ ha-1 of pig slurry were performed, during a period of 100 months and the soil sampled in the end (layers 0-2, 2-4, 4-6, 6-8, 8-10, 10-12, 12-14, 14-16, 16-18, 18-20, 20-25, 25-30, 30-35, 35-40, 40-50 and 50-60 cm). The application of pig slurry increased soil pH values, an effect that could reach the depth of 8 cm without affecting the potential acidity values. The applications also resulted in accumulation of Ca and Mg exchangeable levels in the surface layers, increasing base saturation and reducing Al saturation. Long-term applications induced an increase in organic matter in the deeper layers. However, the effect of this residue on the potential CEC was less significant and restricted to the surface layers.

Structural quality of a no-tillage red latosol 50 months after gypsum aplication

Gypsum application may enhance the soil quality for plants in terms of soil chemical and physical properties. The objective of this study was to evaluate the effects of gypsum application on the structural quality of a no-tillage Red Latosol. The experiment was initiated in September 2005 in Guarapuava-PR, with gypsum applications of 0; 4; 8; and 12 Mg ha-1 on the soil surface. In November 2009, two soil blocks were sampled from the 0-0.3 m layer for visual evaluation of the soil structure quality (Sq) and to determine the aggregate-tensile strength (ATS). Soil penetration resistance (PR) and gravimetric moisture (H%) of the 0-0.300 m layer were evaluated, and soil cores were collected (layers 0.000-0.075 and 0.075-0.150 m), to determine soil bulk density (BD), total soil porosity (TP), microporosity (Mi), and macroporosity (Ma). Data were subjected to analysis of regression at 5 %. No significant effects of gypsum application on ATS and H % of aggregates were observed, but for Sq, a quadratic effect (0.000-0.075 m) and linear increase (0.075-0.150 and 0.150-0.300 m) were stated, indicating soil quality decrease, although Sq remained mostly below 3.0, with good to intermediate soil quality. Soil PR increased with gypsum, but also remained below critical levels. No effect was observed for soil H % at the moment of PR determination on the field. The gypsum applications decreased BD in the 0.075-0.150 m layer, and increased PT and Ma, while in 0.000-0.075 m some Ma was converted to Mi, without affecting PT and BD. These last results indicate a gain in soil structural quality by gypsum applications, but the higher scores of soil structure and values of soil penetration resistance, though still below thresholds, should be monitored to prevent limitations to soil use in the future.

Consistência hidrológica de modelos digitais de elevação (MDE) para definição da rede de drenagem na sub-bacia do horto florestal Terra Dura, Eldorado do Sul, RS

O desenvolvimento da erosão hídrica ocorre em resposta ao modo como a água se move através e sobre uma determinada paisagem. O modelo digital de elevação (MDE) deve, portanto, ser o mais preciso possível, uma vez que constitui a base para a análise do relevo. Este trabalho teve como objetivo definir um modelo digital de elevação hidrologicamente consistente (MDEHC) e o método de direção de fluxo mais adequado para a definição da rede de drenagem na sub-bacia do horto florestal Terra Dura, município de Eldorado do Sul, RS. Foram testados os modelos gerados com os interpoladores Topogrid e redes triangulares irregulares (Triangulated Irregular Network -TIN) linear (TIN L) e TIN natural neighbor (TIN NN). A qualidade em relação às análises hidrológicas foi avaliada por meio da comparação das curvas de nível geradas pelos modelos testados com as curvas originais da sub-bacia (escala 1:10.000); da avaliação da quantidade de áreas planas; e da comparação da drenagem gerada pelos modelos a partir dos métodos de direção de fluxo Deterministic (D8) e Deterministic infinity (D∞ ou D infinito) com a drenagem original. Entre os modelos avaliados, o Topogrid apresentou maior consistência hidrológica, verificada na melhor continuidade das curvas de nível (menos arestas) e maior detalhamento da área de drenagem e divisores, acarretando menor quantidade de áreas planas e caminhos de fluxo mais detalhados, independentemente do método de direção de fluxo utilizado. Em relação à rede de drenagem, o método distribuído D∞ obteve melhor desempenho na descrição dos caminhos de fluxo, comparado ao método de direção única D8. O MDEHC Topogrid associado ao método D∞ proporcionou a identificação mais precisa dos caminhos preferenciais do fluxo que formam a rede de drenagem.

Replication of an ivg protocol to estimate bioaccessible arsenic in materials from a gold mining area in Brazil

Tests for bioaccessibility are useful in human health risk assessment. No research data with the objective of determining bioaccessible arsenic (As) in areas affected by gold mining and smelting activities have been published so far in Brazil. Samples were collected from four areas: a private natural land reserve of Cerrado; mine tailings; overburden; and refuse from gold smelting of a mining company in Paracatu, Minas Gerais. The total, bioaccessible and Mehlich-1-extractable As levels were determined. Based on the reproducibility and the accuracy/precision of the in vitro gastrointestinal (IVG) determination method of bioaccessible As in the reference material NIST 2710, it was concluded that this procedure is adequate to determine bioaccessible As in soil and tailing samples from gold mining areas in Brazil. All samples from the studied mining area contained low percentages of bioaccessible As.

Propriedades físicas do solo e produtividade de arroz irrigado em diferentes sistemas de manejo

O Estado do Rio Grande do Sul é o maior produtor de arroz irrigado do País, com destaque para a região da Fronteira Oeste. O objetivo deste trabalho foi avaliar propriedades físicas do solo e a produtividade de arroz irrigado por inundação em plantio direto e convencional, em níveis de palha residual de arroz em plantio direto. O delineamento experimental foi inteiramente casualizado, com quatro experimentos e 10 repetições nos experimentos 1, 2 e 3 e seis no experimento 4. Os sistemas de manejo foram: experimento 1 (E1), sistema PD (E1PD) e sistema convencional com duas gradagens na camada de 0-7 cm + remaplan (E1C), em área de um ano de cultivo de arroz, após sete anos de pousio do cultivo de arroz e semeadura de azevém no inverno, com pastejo animal o ano todo; experimento 2 (E2), sistema PD (E2PD) e sistema convencional (E2C), após campo nativo; experimento 3 (E3), sistema PD (E3PD) e sistema convencional (E3C), após plantio direto de arroz irrigado durante dois anos em área de campo nativo; e no experimento 4 utilizaram-se quatro níveis de palha residual antes da semeadura do arroz. A produtividade de arroz irrigado por inundação não diferiu entre os sistemas plantio direto e convencional. A massa seca residual do arroz antes da semeadura não influenciou a produtividade de arroz irrigado por inundação.

Microbial biomass and activity in litter during the initial development of pure and mixed plantations of Eucalyptus grandis and Acacia mangium

Studies on microbial activity and biomass in forestry plantations often overlook the role of litter, typically focusing instead on soil nutrient contents to explain plant and microorganism development. However, since the litter is a significant source of recycled nutrients that affect nutrient dynamics in the soil, litter composition may be more strongly correlated with forest growth and development than soil nutrient contents. This study aimed to test this hypothesis by examining correlations between soil C, N, and P; litter C, N, P, lignin content, and polyphenol content; and microbial biomass and activity in pure and mixed second-rotation plantations of Eucalyptus grandis and Acacia mangium before and after senescent leaf drop. The numbers of cultivable fungi and bacteria were also estimated. All properties were correlated with litter C, N, P, lignin and polyphenols, and with soil C and N. We found higher microbial activity (CO2 evolution) in litter than in soil. In the E. grandis monoculture before senescent leaf drop, microbial biomass C was 46 % higher in litter than in soil. After leaf drop, this difference decreased to 16 %. In A. mangium plantations, however, microbial biomass C was lower in litter than in soil both before and after leaf drop. Microbial biomass N of litter was approximately 94 % greater than that of the soil in summer and winter in all plantations. The number of cultivable fungi and bacteria increased after leaf drop, especially so in the litter. Fungi were also more abundant in the E. grandis litter. In general, the A. mangium monoculture was associated with higher levels of litter lignin and N, especially after leaf drop. In contrast, the polyphenol and C levels in E. grandis monoculture litter were higher after leaf drop. These properties were negatively correlated with total soil C and N. Litter in the mixed stands had lower C:N and C:P ratios and higher N, P, and C levels in the microbial biomass. This suggests more effective nutrient cycling in mixed plantations in the long term, greater stimulation of microbial activity in litter and soil, and a more sustainable system in general.

Nutrients in soil layers under no-tillage after successive pig slurry applications

Successive applications of pig slurry to soils under no-tillage can increase the nutrient levels in the uppermost soil layers and part of the nutrients may be transferred to deeper layers. The objective was to evaluate the distribution of nutrients in the profile of a soil after 19 pig slurry applications under no-tillage for 93 months. The experiment was conducted from May 2000 to January 2008 in an experimental area of the Federal University of Santa Maria, southern Brazil, on a Typic Hapludalf. The treatments consisted of pig slurry applications (0, 20, 40 and 80 m³ ha-1) and at the end of the experiment, soil samples were collected (layers 0-2, 2-4, 4-6, 6-8, 8-10, 10-12, 12-14, 14-16, 16-18, 18-20, 20-25, 25-30, 30-35, 35-40, 40-50 and 50-60 cm). The levels of mineral N, available P and K and total N, P and K were evaluated. The 19 pig slurry applications in 93 months promoted migration of total N and P down to 30 cm and available P and K to the deepest layer analyzed. At the end of the experiment, no increase was observed in mineral N content in the deeper layers, but increased levels of available P and K, showing a transfer of N, P and K to layers below the sampled. This evidences undesirable environmental and economic consequences of the use of pig slurry and reinforces the need for a more rational use, i.e., applications of lower manure doses, combined with mineral fertilizers.

Soil losses from typic cambisols and red latosol as related to three erosive rainfall patterns

Rainfall erosivity is one of the main factors related to water erosion in the tropics. This work focused on relating soil loss from a typic dystrophic Tb Haplic Cambisol (CXbd) and a typic dystrophic Red Latosol (LVdf) to different patterns of natural erosive rainfall. The experimental plots of approximately 26 m² (3 x 8.67 m) consisted of a CXbd area with a 0.15 m m-1 slope and a LVdf area with 0.12 m m-1 slope, both delimited by galvanized plates. Drainpipes were installed at the lower part of these plots to collect runoff, interconnected with a Geib or multislot divisor. To calculate erosivity (EI30), rainfall data, recorded continuously at a weather station in Lavras, were used. The data of erosive rainfall events were measured (10 mm precipitation intervals, accuracy 0.2 mm, 24 h period, 20 min intervals), characterized as rainfall events with more than 10 mm precipitation, maximum intensity > 24 mm h-1 within 15 min, or kinetic energy > 3.6 MJ, which were used in this study to calculate the rainfall erosivity parameter, were classified according to the moment of peak precipitation intensity in advanced, intermediate and delayed patterns. Among the 139 erosive rainfall events with CXbd soil loss, 60 % were attributed to the advanced pattern, with a loss of 415.9 Mg ha-1, and total losses of 776.0 Mg ha-1. As for the LVdf, of the 93 erosive rainfall events with soil loss, 58 % were listed in the advanced pattern, with 37.8 Mg ha-1 soil loss and 50.9 Mg ha-1 of total soil loss. The greatest soil losses were observed in the advanced rain pattern, especially for the CXbd. From the Cambisol, the soil loss per rainfall event was greatest for the advanced pattern, being influenced by the low soil permeability.

Methane efflux in rice paddy field under different irrigation managements

Paddy rice fields may contribute to methane (CH4) emission from soil due to anaerobic conditions after flooding. Alternatives to continuous flooding irrigation in rice have been developed to mitigate CH4 efflux into the atmosphere. This study aims to investigate the effects of irrigation managements in the CH4 efflux during the rice growing season. An experiment was carried out at in Santa Maria, Rio Grande do Sul State, Brazil, during 2007/08 and 2009/10 growing seasons. The treatments were continuous flooding and intermittent irrigation in 2007/08 and continuous flooding, intermittent irrigation and flush irrigation in 2009/10. Intermittent irrigation is effective in mitigating CH4 efflux from rice fields when climatic conditions enable water absence during cultivation, but its efficiency depends on the electrochemical soil conditions during the flooding cycles.

Adubação nitrogenada para milho com o uso de plantas de cobertura e modos de aplicação de calcário

O sistema plantio direto (SPD) é uma realidade na região dos Cerrados, mas alguns questionamentos persistem nesse tipo de manejo como o modo de realização da calagem e a dose de nitrogênio (N) a ser adotada em cultura comercial, em relação às culturas precedentes. Desse modo, objetivou-se avaliar modos de aplicar o calcário na implantação do SPD e o efeito de culturas de cobertura precedentes sobre a necessidade de adubação nitrogenada da cultura do milho, durante diferentes anos agrícolas. O delineamento experimental utilizado foi de blocos casualizados, em esquema fatorial 5 x 2 (modos de aplicação do calcário x culturas de cobertura) e posterior divisão em três subparcelas, referentes às doses de N (0, 90 e 180 kg ha-1). Foram avaliados quatro modos de aplicação de calcário: incorporado a 0-0,2 m, em out./2001; dose total em superfície aplicada, em out./2001; aplicação de 1/2 da dose, em out./2001, e 1/2, em ago./2002, na superfície; e aplicação de 1/3 da dose recomendada, em mar./2001, + 1/3, em out./2001, e 1/3, em ago./2002, também em superfície. Além de um tratamento testemunha (sem calcário) e duas culturas de cobertura, crotalária e milheto. Os diferentes modos de calagem não alteraram a produtividade de grãos de milho. O cultivo de milho após crotalária apresentou melhor desempenho e menor demanda de adubação nitrogenada, quando comparado ao cultivado após milheto.

Nitrogênio, carbono e compactação do solo como fatores limitantes do processo de recuperação de matas ciliares

A recuperação de áreas de floresta, principalmente de matas ciliares, tornou-se fator-chave para a adequação ambiental da agricultura, com o propósito de proteger os recursos hídricos e a biota. Entretanto, o cultivo agrícola tradicional, além de ter alterado a ciclagem de nutrientes com a perda de matéria orgânica, biomassa e atividade microbiana, causou também a compactação do solo, o que influencia a posterior implantação de reflorestamentos. O objetivo deste trabalho foi identificar quais atributos do solo (físicos, químicos e microbiológicos) mais influenciam o teor de C, N, P e umidade da serapilheira em áreas de mata ciliar com diferentes idades de recuperação (20, 10 e cinco anos), em comparação com uma área nativa (NT). A partir da ANOVA e dos testes de médias (Duncan) e correlação (Pearson), foram verificados quais atributos acompanham o tempo de recuperação e qual a relação entre eles. A análise multivariada de partição da inércia a partir da análise de redundância (pRDA) foi feita a fim de identificar quais atributos do solo foram mais importantes para discriminar entre as áreas, com base nos teores de C, N, P e umidade da serapilheira encontrados nessas áreas. Maior relação C/N da serapilheira foi encontrada nas áreas de 20 (26,8) e de cinco (29,9) anos. Entre os atributos microbiológicos avaliados, observou-se que a respiração basal do solo (C-CO2), o carbono da biomassa microbiana (CBM) e a atividade das enzimas desidrogenase e urease foram diretamente proporcionais ao aumento da idade das áreas. O C e N totais do solo, o N-NO3, o nitrogênio da biomassa microbiana (NBM), a atividade das enzimas desidrogenase e urease, bem como a macroporosidade correlacionaram-se positivamente e a microporosidade, negativamente, com o C e N da serapilheira. A partir da pRDA, o NBM e o carbono total do solo foram os atributos mais importantes para explicar o teor de N e C da serapilheira; a explicação compartilhada foi mais da metade de toda a explicação observada ou 28,2 %. A melhoria das condições físicas do solo e a adição de matéria orgânica que resultam na formação de uma serapilheira mais rica em N pode ser uma forma de melhorar as condições microbiológicas e químicas do solo e de acelerar o processo de recuperação.

Wheat yield and physical properties of a brown latosol under no-tillage in south-central Paraná

Soil management influences the chemical and physical properties of soil. Chemical conditions have been thoroughly studied, while the role of soil physical conditions regarding crop yield has been neglected. This study aimed to analyze the wheat yield and its relationship with physical properties of an Oxisol under no-tillage (NT). The study was carried out between 2010 and 2011, in Reserva do Iguaçu, State of Paraná, Brazil, on the Campo Bonito farm, after 25 years of NT management. Based on harvest maps of barley (2006), wheat (2007) and maize (2009) of a plot (150 ha), zones with higher and lower yield potential (Z1 and Z2, respectively) were identified. Sampling grids with 16 units (50 x 50 m) and three sampling points per unit were established. The wheat grain yield (GY) and water infiltration capacity (WIC) were evaluated in 2010. Soil samples with disturbed and undisturbed structure were collected from the 0.00-0.10 and 0.10-0.20 m layers. The former were used to determine soil organic carbon (Corg) levels and the latter to determine soil bulk density (BD), total porosity (TP), macroporosity (Mac), and microporosity (Mic). Soil penetration resistance (PR) and water content (SWC) were also evaluated. The wheat GY of the whole plot was close to the regional average and the yield between the zones differed significantly, i.e. 22 % higher in Z1 than in Z2. No significant variation in Mic was observed between zones, but Z1 had higher Corg levels, SWC, TP and Mac and lower BD than Z2 in both soil layers, as well as a lower PR than Z2 in the 0.00-0.10 m layer. Therefore, soil physical conditions were more restrictive in Z2, in agreement with wheat yield and zone yield potential defined a priori, based on the harvest maps. Soil WIC in Z1 was significantly higher (30 %) than in Z2, in agreement with the results of TP and Mac which were also higher in Z1 in both soil layers. The correlation analysis of data of the two layers showed a positive relationship between wheat GY and the soil properties TP, SWC and WIC.

Effects of tillage systems on physical properties of a cohesive yellow argisol in the northern state of Espírito Santo, Brazil

Tillage systems are a key element of the technology of crop production, both with a view to crop yield and from the perspective of soil conservation and sustainability of the production system. The aim of this paper was to evaluate the effects of five tillage systems on the physical properties of a cohesive Yellow Argisol. The experiment was installed in the field on January 21, 2011 and lasted 260 days, in an area previously used as pasture with Brachiaria grass without liming or fertilization, but irrigated by a low pressure spray system. The treatments, in five replications and in a randomized block design, consisted of: 1) disk plow (twice) + disk harrow + ridge-furrow tillage (raising a ridge along the planting row), 135 days after transplanting (DP + RID); 2) disk plow (twice) + disk harrow (DP no RID); 3) subsoiler (SB); 4) disk plow (twice) + disk harrow + scarification with three shanks along the plant row (DP + SPR); and 5) disk plow (twice) + disk harrow + scarification with three shanks in the total area (DP + STA). In all tillage systems, furrows were mechanically opened for the papaya plants. After the treatments, the mechanical resistance to penetration was determined, followed by soil moisture, mean weight diameter (MWD), geometric mean diameter (GMD), bulk density (BD), macroporosity (Ma), microporosity (Mi), and number of fruits per plant. There were differences in penetration resistance (PR) between treatments. The subsoiler was more effective to decrease RP to a distance of 0.35 m from the plants, perpendicular to the plant row. The scarifier resulted in a lower PR than DP or SB, even at the depth of 0.40 m, and it was more effective at greater distances perpendicular to the plant. All tillage systems induced a PR between 2.0 and 3.0 MPa at the depth with the highest concentration of papaya tree roots (0-0.25 m), improving the physical conditions to this depth. There was no statistical difference among the treatments for BD, Ma, Mi, MWD, and GMD at a depth of 0.20 m. The disk plow changed the physical properties of the soil most intensely to a depth of 0.20 m. The use of scarification, reduced tillage with a forest subsoiler, or ridge-furrow tillage did not improve the physical properties in the rhizosphere. Reduced tillage with a forest subsoiler resulted in a lower number of fruits per plant than all other treatments, which did not differ from each other.

Doses de lodo de esgoto compostado em produção de tapete de grama esmeralda imperial

A eficiência da adubação nitrogenada para gramados pode ser aumentada com a utilização de fontes de liberação lenta, como composto de lodo de esgoto, que, em razão das suas características, pode ser um substituto de parte ou do total da adubação inorgânica para as gramas. Não foram encontrados resultados referentes à utilização de lodo compostado na cultura da grama, no Brasil. Objetivou-se com este trabalho avaliar o efeito de doses de composto de lodo de esgoto na produção da grama esmeralda Imperial. Os tratamentos foram constituídos de cinco doses de composto de lodo de esgoto (0, 12, 24, 36 e 48 Mg ha-1, base seca), mais um tratamento com adubação inorgânica (300 kg ha-1 N, 80 kg ha-1 P2O5 e 200 kg ha-1 K2O). Os compostos orgânicos presentes no composto têm diferentes taxas de mineralização, liberando aos 120 dias após a aplicação do lodo mais Mg (100 %), K (90 %) e N (67 %) do que S (57 %), P (40 %) e Ca (31 %). A utilização do composto de lodo na cultura da grama Imperial proporcionou adequado fornecimento de nutrientes, quando aplicado superficialmente, em doses maiores que 36 Mg ha-1. As doses de composto proporcionaram, após a colheita do tapete, aumento linear da acidez potencial e do teor de matéria orgânica, P, S, Fe, Cu, Mn, Zn, As, Cu e Ni e redução linear do pH, do teor de Ca e Mg e da saturação por bases do solo. O aumento das doses do composto de 0 a 48 Mg ha-1 reduziu a massa dos tapetes de grama, atingindo valores de 4,0 kg/tapete, quando a maior dose foi aplicada. Altas doses também proporcionaram os maiores valores de resistência dos tapetes na ordem de 35 e 33 kgf, com as doses de 36 e 48 Mg ha-1, respectivamente.