Eloy Antonio Pauletto

Resistência mecânica à penetração de um Planossolo submetido a diferentes sistemas de cultivo

O conhecimento das caracteristicas e propriedades dos solos de varzea do RS, utilizados atualmente com a cultura do arroz irrigado, torna-se essencial para a adocao de praticas que envolvam irrigacao, drenagem, correcao da acidez e da fertilidade, principalmente quando se deseja obter altos niveis de produtividade, com menor custo e com menores possibilidades de degradacao destes solos e do ambiente onde estao situados. Dentro deste panorama, avaliou-se a compactacao de um Planossolo cultivado sob diferentes sistemas de manejo, atraves da resistencia mecânica do solo a penetracao. Camadas compactadas foram identificadas, de forma mais acentuada, na profundidade intermediaria (0,10-0,20 m) nos sistemas com maior utilizacao da mecanizacao agricola (T2 - sistema de cultivo continuo de arroz e T3 - sistema de cultivo de arroz x rotacao de culturas). Observou-se que, em todos os sistemas, houve aumento dos valores de resistencia mecânica do solo a penetracao em relacao a testemunha (T6 - solo mantido sem cultivo), principalmente na camada intermediaria (0,10-0,20 m), quando o solo foi submetido ao sistema de cultivo continuo de arroz (T2). Os tratamentos T3 (sistema de cultivo de arroz x rotacao de culturas) e T5 (sucessao de culturas: soja (sistema convencional) x arroz (sistema de semeadura direta)) apresentaram os valores mais altos de resistencia a penetracao, provavelmente em decorrencia da baixa umidade e dos efeitos do cultivo e da utilizacao de maquinas responsaveis pela deformacao da estrutura do solo.

ESTABILIDADE DE AGREGADOS DE UM PLANOSSOLO SOB DIFERENTES SISTEMAS DE MANEJO

The wetland soils in the state of Rio Grande do Sul present wide variation in their morphological, physical, chemical and mineralogical characteristics due to the heterogeneity of the parent material and different degrees of hydromorphism. Since their main uses for flooded rice and cattle breeding are frequently low-profit activities, the introduction of dry land crop species in rotation and/or succession with flooded rice has been called for. By broadening the spectrum of wetland soil use, a better weed control for flooded rice and an enhanced physical state of the degraded soil by management systems of reduced soil disturbance would become possible. In this context, the effect of tillage systems on the aggregation state of an Albaqualf has been evaluated: conventional tillage (CT), minimum tillage (MT), no tillage (NT) and pre-germinated (PG), by means of the following attributes: distribution of stable water aggregates in different size classes and mean weight diameter (MWD) of the aggregates. The experiment has been conducted since 1995/96 and is installed in the Estacao Experimental de Terras Baixas (Experimental Station Lowlands-ESL) of Embrapa (Brazilian agricultural research organization), Clima Temperado, district of Capao do Leao (RS). After three years, the NT system favored an aggregate formation of larger sizes, originating largest MWD, while the system PG pushed the largest aggregate concentration of the soil into the smallest size class, with the smallest aggregate MWD. The MWD was lineal and positively correlated with the organic C, not presenting any correlation with the clay dispersed in water.

Planosol soil sample size for computerized tomography measurement of physical parameters

Computerized tomography (CT) is an important tool in Soil Science for noninvasive measurement of density and water content of soil samples. This work aims to describe the aspects of sample size adequacy for Planosol (Albaqualf) and to evaluate procedures for statistical analysis, using a CT scanner with a 241Am source. Density errors attributed to the equipment are 0.051 and 0.046 Mg m-3 for horizons A and B, respectively. The theoretical value for sample thickness for the Planosol, using this equipment, is 4.0 cm for the horizons A and B. The ideal thickness of samples is approximately 6.0 cm, being smaller for samples of the horizon B in relation to A. Alternatives for the improvement of the efficiency analysis and the reliability of the results obtained by CT are also discussed, and indicate good precision and adaptability of the application of this technology in Planosol (Albaqualf) studies.

Persistência dos efeitos da escarificação sobre a compactação de Nitossolo sob plantio direto em região subtropical úmida

O objetivo deste trabalho foi avaliar a persistencia dos efeitos da escarificacao sobre a compactacao de Nitossolo Vermelho, manejado sob plantio direto (PD), na regiao subtropical umida do Brasil. O experimento foi realizado em blocos ao acaso, com quatro repeticoes e seis tratamentos, constituidos pelo tempo de manutencao do solo sob PD apos escarificacao: PD continuo por 24 meses apos escarificacao, realizada em setembro de 2009; PD continuo por 18 meses apos escarificacao, realizada em marco de 2010; PD continuo por 12 meses apos escarificacao, realizada em setembro de 2010; PD continuo por seis meses apos escarificacao, realizada em marco de 2011; plantio realizado em solo recem escarificado, em setembro de 2011; e PD continuo e sem escarificacao (testemunha). As especies cultivadas na area foram: milho, safra 2009/2010; trigo, em 2010; soja, safra 2010/2011; centeio, em 2011; e milho, safra 2011/2012. Os efeitos dos tratamentos foram avaliados a partir de parâmetros fisicos do solo e de parâmetros morfologicos e produtivos da cultura do milho, na safra 2011/2012. A escarificacao do Nitossolo sob plantio direto, em regiao de clima subtropical umido, nao aumenta a produtividade de graos de milho, e os seus efeitos sobre a estrutura do solo nao persistem por mais de 18 meses.

Conteúdo de carbono orgânico em planossolo háplico sob sistemas de manejo do arroz irrigado

Nos solos de varzea da regiao Sul do Rio Grande do Sul, onde um milhao de hectares sao cultivados com arroz irrigado por alagamento em diferentes sistemas de manejo, a influencia da condicao de ma drenagem e alternância entre ciclos de oxidacao e reducao sobre o conteudo de C orgânico do solo (COS) e pouco conhecida. Este estudo foi realizado em um experimento de longa duracao (21 anos), localizado no municipio do Capao do Leao, RS, com o objetivo de avaliar o efeito de sistemas de manejo do arroz irrigado sobre os estoques de COS e das fracoes fisicas da materia orgânica em um Planossolo Haplico. O fracionamento fisico da materia orgânica do solo foi realizado pelo metodo densimetrico, em amostras de solo coletadas das camadas de 0-0,025; 0,025-0,05; 0,05-0,10; e 0,10-0,20 m, nos tratamentos: ST- Sistema tradicional de cultivo um ano com arroz (preparo convencional) e dois anos com pousio; APC- Sistema de cultivo continuo de arroz (preparo convencional) e controle de invasoras com herbicida; APD- Sucessao azevem/arroz (plantio direto); e SN- Solo mantido com vegetacao natural (campo nativo). O sistema com arroz/azevem em plantio direto APD foi mais eficiente em manter os estoques de COS e da fracao leve livre ate 0,05 m de profundidade, em comparacao com o ST e APC. A fracao leve oclusa nao se mostrou sensivel aos efeitos dos diferentes sistemas de manejo, sugerindo para o solo de varzea baixa eficiencia da protecao fisica da MOS por oclusao em agregados, o que pode estar relacionado aos efeitos da condicao de ma drenagem no processo de agregacao. A umidade excessiva no inverno e o alagamento durante os cultivos de arroz estariam proporcionando agregacao transitoria entre cultivos. A quantidade de CO nesse Planossolo, tanto entre os sistemas de cultivo quanto em profundidade, deve-se principalmente a fracao pesada, que e a fracao mais estavel e mais dificil de ser degradada.

Efeito de semeadora com haste sulcadora para ação profunda em solo manejado com plantio direto

The adoption of no-till in the humid subtropical region of Brazil based on only two precepts of conservation agriculture, soil disturbance restricted to the crop row and crop residue maintained as soil cover, has led to stratification of soil chemical properties in the 0-20 cm soil layer and physical degradation of the subsurface layer (from approximately the 5-20 cm depth), which may make for lower yields during short term droughts. The aim of this study was to evaluate the residual effect of a seed drill/fertilizer applicator equipped with fixed shanks, set at four different depths, for the sowing of maize (Zea mays L.), in mitigation of chemical and physical problems in a Latossolo Vermelho distrofico humico (Rhodic Hapludox) under no-till for more than ten years. The treatments were: T1 = shank extremity at 5 cm depth; T2 = shank extremity at 10 cm depth; T3 = shank extremity at 15 cm depth; and T4 = shank extremity at 17 cm depth. The crop profile method was used to evaluate soil physical properties (bulk density, total porosity, macroporosity, and soil resistance to penetration) at eight and ten months after sowing the maize. The chemical properties (pH in water; available P and K; exchangeable Ca, Mg, and Al; potential acidity; and organic matter) were evaluated in layers every 2.5 cm from the 0-22.5 cm depth. The seed drill/fertilizer applicator equipped with fixed shanks for ripping the soil was able to mitigate soil physical and chemical problems, both at eight and 12 months after sowing.

Densidade de um planossolo sob sistemas de cultivo avaliada por meio da tomografia computadorizada de raios gama

A sustentabilidade do arroz (Oryza sativa L.) irrigado em solos de varzea esta alicercada na utilizacao da rotacao e sucessao de culturas, fundamentais para o controle do arroz-vermelho e preto. Os reflexos sobre os atributos dos solos de varzea merecem estudos em especial sobre a compactacao do solo. O objetivo deste trabalho foi identificar camadas compactadas em Planossolo submetido a diferentes sistemas de cultivo e preparo, avaliando-se a densidade do solo (Ds) pela Tomografia Computadorizada de Raios Gama (TC). A analise foi realizada em um experimento de longa duracao, conduzido de 1985 a 2004, na Estacao Experimental da Embrapa Clima Temperado, Capao do Leao, RS, num delineamento experimental em blocos ao acaso, com sete tratamentos, cada um com quatro repeticoes (T1 - um ano de arroz com preparo convencional do solo seguido de dois anos de pousio; T2 - cultivo continuo de arroz com preparo convencional do solo; T4 - rotacao de arroz e soja (Glycine max L.) com preparo convencional do solo; T5 - rotacao de arroz, soja e milho (Zea maiz L.) em preparo convencional do solo; T6 - plantio direto de arroz no verao em sucessao do azevem (Lolium multiflorum L.) no inverno; T7 - rotacao de arroz sob plantio direto e soja sob preparo convencional do solo; T8 - testemunha: solo sem cultivo). A Tomografia Computadorizada de Raios Gama permitiu detectar que o plantio direto de arroz no verao em sucessao do azevem no inverno nao resultou na formacao de camadas compactadas; a utilizacao de dois anos de pousio, no sistema de producao de arroz irrigado, nao foi suficiente para evitar a formacao de uma camada superficial compactada; e a rotacao de arroz, soja e milho com preparo convencional do solo apresentou duas camadas compactadas (0,0 a 1,5 cm e 11 a 14 cm), indicando que essas podem limitar a producao agricola nesse sistema de producao em Planossolos.

Teor e qualidade de substâncias húmicas de planossolo sob diferentes sistemas de cultivo

The objective of this study was to evaluate and compare the content and chemical characteristics of humic substances (SHs) of an Albaqualf under different soil management systems. Soil samples were collected in a long-term field experiment (19 years) from the 0-0.025; 0.025-0.05 and 0.05-0.20m layers and from the top of the B horizon. The following treatments were evaluated: APC-continuous rice crop system under conventional tillage and weed control with herbicides; APD-no-tillage system with rye-grass in the winter and rice in the summer, and SN-soil under natural condition with native grassland. The SHs and the non-humic fraction (NH) were obtained by chemical fractioning. The content of total soil carbon and those occurring as SHs and NH were determined by the Walkley-Black and spectrophotometric methods, respectively. To determine the chemical and molecular characteristics of the SHs, UV-visible and infrared spectroscopy techniques and elementar analyses were employed. In comparison to the soil under natural condition (SN), the no-tillage system (APD) maintained total soil organic carbon concentrations as well as the content of SHs. The conventional tillage reduced soil total organic carbon and the content of SH in the upper layers (<0.05m). The proportion of fulvic acid in relation to the total soil organic carbon increased with soil depth, suggesting the mobilization of this fraction along the profile. The soil management system affected the composition of the organic matter mainly in the 0 to 0.025m layer, where the SH showed a lower decomposition and higher polaricity degree and contained smaller proportion of aliphatic structures than SH in the APD system.

Recuperação da qualidade estrutural, pelo sistema plantio direto, de um Argissolo Vermelho

Soils with high sand content in the A horizon are prone to degradation processes, depending on management system used. This study had as objective to evaluate the degradation of a Hapludalf formed from granite, located in the Passo do Pilao watershed in Pelotas county, cultivated under conventional system, and its recovery by no-tillage system, compared to two native systems, namely grass field and forest. The experiment was setup in an agricultural area, in April of 1995, with the cultivation of Avena strigosa plus Vicia vilosa, both for conventional system and no-tillage. An area under native grasses and another with native forest were sampled for comparison. Soils samples were colleted from the layers of 0-0.05m, 0.10-0.15m and 0.20-0.25m, to determine the soil texture, porosity, densities, water retention, aggregate stability and distribution, and organic carbon content. The cultivation systems increase the soil bulk density and reduce total porosity, microporosity, water retention and availability, compared with native systems such as grass field and forest. The conventional system reduces organic carbon content and aggregate stability, whereas no-tillage, after five years, increases, somewhat, the organic carbon content in the surface layer, but increases aggregate stability to values near of those for native systems. The aggregate stability had direct relationship with organic carbon content up to an upper limit of 25g kg-1. The bulk density, macroporosity, S parameter, organic carbon content and aggregate stability are good indicators of the changes observed in the soil management systems. For the Hapludalf formed from granite, there was recovery of the properties related to soil structure stability, but in those related to soil bulk density and porosity no recovery was observed.

Perennial grasses for recovery of the aggregation capacity of a reconstructed soil in a coal mining area in southern Brazil

The construction of a soil after surface coal mining involves heavy machinery traffic during the topographic regeneration of the area, resulting in compaction of the relocated soil layers. This leads to problems with water infiltration and redistribution along the new profile, causing water erosion and consequently hampering the revegetation of the reconstructed soil. The planting of species useful in the process of soil decompaction is a promising strategy for the recovery of the soil structural quality. This study investigated the influence of different perennial grasses on the recovery of reconstructed soil aggregation in a coal mining area of the Companhia Riograndense de Mineracao, located in Candiota-RS, which were planted in September/October 2007. The treatments consisted of planting: T1- Cynodon dactylon cv vaquero; T2 - Urochloa brizantha; T3 - Panicum maximun; T4 - Urochloa humidicola; T5 - Hemarthria altissima; T6 - Cynodon dactylon cv tifton 85. Bare reconstructed soil, adjacent to the experimental area, was used as control treatment (T7) and natural soil adjacent to the mining area covered with native vegetation was used as reference area (T8). Disturbed and undisturbed soil samples were collected in October/2009 (layers 0.00-0.05 and 0.10-0.15 m) to determine the percentage of macro- and microaggregates, mean weight diameter (MWD) of aggregates, organic matter content, bulk density, and macro- and microporosity. The lower values of macroaggregates and MWD in the surface than in the subsurface layer of the reconstructed soil resulted from the high degree of compaction caused by the traffic of heavy machinery on the clay material. After 24 months, all experimental grass treatments showed improvements in soil aggregation compared to the bare reconstructed soil (control), mainly in the 0.00-0.05 m layer, particularly in the two Urochloa treatments (T2 and T4) and Hemarthria altissima (T5). However, the great differences between the treatments with grasses and natural soil (reference) indicate that the recovery of the pre-mining soil structure could take decades.