Michael Mazurana

Sistemas de preparo de solo: alterações na estrutura do solo e rendimento das culturas

A introducao e intensificacao no uso do sistema de semeadura direta no Brasil nas ultimas decadas desenharam um novo cenario na agricultura brasileira, aumentando a preocupacao com as caracteristicas fisicas dos solos. O objetivo deste trabalho foi avaliar a implicacao que diferentes sistemas de preparo de solo impoem sobre algumas caracteristicas fisicas de um Argissolo Vermelho inicialmente sob uso com campo natural. Cinco metodos de preparo de solo foram ensaiados: semeadura direta (SD), escarificacao (E), semeadura direta com escarificacao a cada dois anos (SDE2), escarificacao com escarificador munido de rolo destorroador (ER) e escarificacao seguida de gradagem (EG). Foram avaliados: densidade do solo, macroporosidade, microporosidade e porosidade total, resistencia mecânica do solo a penetracao, infiltracao de agua no solo e rendimento das culturas. Os valores de densidade do solo, resistencia mecânica do solo a penetracao e microporosidade aumentaram em detrimento da diminuicao da macroporosidade. A densidade do solo foi menor nos sistemas de preparo com maior grau de mobilizacao do solo, sendo os maiores valores observados para o sistema SD e os menores para o sistema EG. A taxa de infiltracao de agua apresentou-se maior no sistema ER, seguido pelos sistemas EG, SD e SDE2, ao passo que o rendimento das culturas foi maior nos sistemas com menor mobilizacao de solo.

Capacidade de suporte e compressibilidade de um argissolo, influenciadas pelo tráfego e por plantas de cobertura de inverno

One of the most effective practices in preventing soil compaction is to apply stresses below the bearing capacity of the soil, often estimated by the pre-compression stress (σp). To evaluate the effects of cover crops and tractor traffic on σp and compression index (CI), a field experiment was initiated in 2002 on sandy clay loam Paleudult, in Southern Brazil (Rio Grande do Sul State). Treatments under no-tillage involved winter fallow and two winter cover crops (black oats and black oats + vetch, which was substituted in 2006 by oilseed radish - Raphanus sativus L.) in the plots and two traffic conditions (with and without wheel-tractor traffic) in the subplots. Undisturbed soil cores were sampled in June and November 2006 to determine soil physical properties as well as σp and CI by uniaxial compression tests in an oedometer. Before oedometer tests, soil cores were equilibrated at different water tensions. Regardless of time and traffic conditions, winter fallow showed the highest σp value and the lowest CI value at 0.03-0.06 m. As the soil became drier, differences in σp between winter fallow and cover crops were reduced. In five years, seven wheel-tractor passages increased σp only in the surface layer (0.03-0.06 m), without altering CI. The use of cover crops and absence of traffic reduced the soil bearing capacity and increased soil susceptibility to compaction due to the reduction in soil bulk density and increase of macropores.

Resistência mecânica do solo e força de tração em hastes sulcadoras de semeadoras-adubadoras em sistema de integração lavoura-pecuária

A integracao lavoura-pecuaria, realizada mediante a implantacao de pastagens no inverno e a semeadura de milho ou soja no verao, constitui-se numa alternativa para a diversificacao de atividades e ampliacao dos lucros. Animais em pastejo, principalmente em areas agricolas manejadas sob semeadura direta, podem resultar na compactacao adicional do solo, diagnosticada geralmente pelo aumento de resistencia do solo a penetracao (RP). Com o objetivo de avaliar a correlacao entre RP e forca de tracao (FT) medida em hastes sulcadoras de semeadoras-adubadoras, nos anos de 2004 e 2005, foi conduzido um experimento em Sao Miguel das Missoes - RS, em Latossolo Vermelho (0.540 kg kg-1 de argila). Os tratamentos consistiram em quatro intensidades de pastejo, que resultaram em alturas de pastagem de 10; 20; 30 e 40 cm, e de testemunha sem pastejo, organizados em DBC, com tres repeticoes. Avaliou-se a RP, no final do periodo de pastejo, e na semeadura da soja, obteve-se a FT exigida nas hastes sulcadoras de semeadoras-adubadoras. A RP e a FT aumentaram com o incremento na intensidade de pastejo. A correlacao entre essas variaveis foi significativa, comprovando que e possivel avaliar o estado de compactacao do solo por meio da medicao da FT requerida pelas hastes sulcadoras de semeadoras-adubadoras.

Padrão de afilhamento em arroz afetado pela presença dos íons amônio e nitrato

Rice development is affected by nitrogen, specially its tillering pattern which is determined by number of tillers. Tillers synchronism with main stem is related to leaves emission rate and both traits affect the number of productive culms potential. Tiller emission and synchronism of leaf development between main stem and tillers were studied in rice plants (cv IRGA 417) cultivated in a hydroponic solution (Hoagland) under three N concentrations (1, 5 e 10 mmol L-1), each with different proportion of N-NH4+ and N-NO3- (100:0; 75:25; 50:50; 25:75). The different proportions under 1 mmol L-1 were similar for tiller number, synchronism, and productive culms. All traits (tiller number, synchronism and productive culms) were negatively affected when higher levels of N-NH4+ ion (5 and 10 mmol L-1 - 100 and 75% of N ions) were supplied to plants. Nevertheless, when N-NO3- ion was present in at least 50% of the solution, the detrimental effects were not found. When N was at 1 mmol L-1, rice plants tolerate N-NH4+ ion presence, independently of the presence of N-NO3- ion. At higher N concentrations, it is necessary at least 50% of N-NO3- ion in order to avoid detrimental effects on tillering.

Propriedades físicas do solo e crescimento de raízes de milho em um argissolo vermelho sob tráfego controlado de máquinas

Soil functions can be hampered by compaction induced by inadequate management. Some soil physical properties are indicators of the existence of compacted layers that can affect the root development of crops. Agricultural practices, e.g., planting of cover crops to improve soil properties, can mitigate the compaction-related problems. The aim of this study was to evaluate the physical attributes of soil and plants, grown under controlled conditions. In an Ultisol under no-tillage with two winter cover crops (fallow and oat + vetch) and controlled machine traffic (no traffic -NT, before traffic - BT and after traffic - AT), we evaluated the pre-consolidation pressure, penetration resistance, soil bulk density, porosity, and average diameter of aggregates. Undisturbed soil samples were collected before and after traffic, filled into PVC pots and placed in a greenhouse. Three corn seeds were sown per pot and grown for 25 days under different conditions of water availability. After this period, the leaf area and the fresh and dry matter of corn shoots and roots were determined. Regardless of the layer, bulk density was not affected by the soil cover, but was influenced by machine traffic. Macroporosity in the fallow plot was affected by traffic to a depth of 0.10 m, indicating the reduced capacity of this system to resist disturbances, evidenced also by the lower pre-consolidation pressure. Resistance to penetration increased with depth, and was related to higher density, lower macroporosity and higher pre-consolidation pressure. Without water stress, maize root growth was positively influenced by machine traffic. Under the tested experimental conditions, no-tillage with crop rotation was more resilient to soil disturbances than the other system.

Atributos físicos e químicos de um argissolo vermelho, em pomar orgânico de citros com manejo da vegetação nas entrelinhas

The management in organic citrus orchards is differentiated with respect to conventional orchards. Thus, it was aimed to evaluate some physical and chemical attributes of a typic ultisol and productivity of a mandarin orchard, cv. Montenegrin under organic production system, with different vegetation management between the lines. The treatments were: harrowing, mowing, lodging with coulter and log dragging. The evaluation of the physical attributes occurred under the canopy and in the machinery traffic area, in the depths of 0.0-0.1 and 0.1-0.2 m. The chemical fertility of the soil was determined in the layer of 0.0-0.1, 0.1-0.2 and 0.2-0.4 m, while the fruit yield was estimated from central plants of each portion. Machine traffic negatively affected the physical attributes of soil below the interface patch, although it was not restrictive to fruit yield. In all treatments there was an increase of organic matter in the topsoil, and the levels of P, K+, Ca2+ and Mg2+ in the three soil layers in relation to the adjacent area with native vegetation. The handling with harrowing showed significantly higher productivity in relation to the management with mowing.

Soil susceptibility to compaction under use conditions in southern Brazil

O grau de compactacao do solo e intensificado pelo seu inadequado manejo, sendo a compactacao depente do tipo de solo, uma vez que mesmo sob condicoes identicas de uso, diferentes solos tem diferentes habilidades para suportar a carga. O objetivo deste estudo foi avaliar a susceptibilidade a compactacao de diferentes classes de solos sob sistema plantio direto (PD) em relacao ao estado original. Assim, i) solos com o mesmo material de origem apresentam distinta resistencia a compressao com o aumento do tempo adopcao do PD; ii) os indicadores mais sensiveis desta mudanca sao os da relacao massa: volume e volume: volume e; iii) existe uma relacao entre resistencia e suscetibilidade a compactacao com a quantidade e o tipo de oxido. As amostras de solo foram coletadas em areas sob PD e sob condicao natural (CN), a fim de avaliar o impacto imposta pelo PD sobre os atributos densidade e porosidade, tensao de pre-compressao e indice de compressibilidade e relaciona-los com o tipo de oxido e conteudo. Os resultados mostram que a densidade e a macroporosidade foram os mais afetados pelo uso agricola em PD, independentemente do tipo de solo, ou seja, a sua dinâmica esta mais relacionada com o uso do solo e menos com as caracteristicas mineralogicas. A resistencia do solo e suscetibilidade a compactacao foram maiores no solo desenvolvido em basalto, seguido por aqueles desenvolvidos em arenito e granito. Tanto o teor de materia orgânica e tipo e concentracao de oxidos de ferro foram relacionados com a resistencia do solo e susceptibilidade a compactacao.

Qualidade de um Argissolo submetido a práticas de manejo recuperadoras de sua estrutura física

The aim of this study was to evaluate the effectiveness of alternative managements in restoring a physically degraded soil after eight years. For this, an experiment managed with direct sowing (no tillage) is being conducted since 2002, in Eldorado do Sul, RS, in an Ultisol that initially was degraded naturally with a high degree of compaction. Treatments consisted of three soil cover crops in winter (fallow, oat + vetch and forage radish), two depths (0.12 and 0.21 m) of operation of the shank of fertilizer and seed drill and three traffic conditions (tractor movements, harvester and no traffic). In summer corn and soybeans are sown in annual rotation. There was an increase in the levels of soil organic matter and of its fractions, which resulted in reduced values of density and increased macroporosity and total porosity of soil. Soil bulk density was lower in soil condition not without agricultural machinery traffic. The conversion of naturally degraded field into a system of grain production using integrated management alternatives with no tillage system restores the physical quality of soil to carry out appropriately its functions.

Balanço de nutrientes em povoamento de Eucalyptus saligna implantado sobre Cambissolo Háplico no RS

The forest system fragility can be evaluated through nutrient balance, with an emphasis in the cycling efficiency to maintain or elevate of productivity of system. The objective of this study was to evaluate the effects of different soil tillage systems on nutrient losses transported by erosion on an Inceptisol with Eucalyptus saligna. Four tillage systems were tested: interrupted deep chiseling with residue (SIR), continuous deep chiseling with residue (SCR), continuous deep chiseling without residue (SSR) and mechanical pitting (CME). The SIR system showed the greatest nutrient losses. The loss of nutrients was higher by water erosion, in the following order, K > Ca > Mg > P > Cu > B. SIR and SSR tillage systems had the highest levels of nutrients in shoots and lower nutritional balance, respectively.