Fabiane Machado Vezzani

UMA VISÃO SOBRE QUALIDADE DO SOLO

Soil quality (SQ) has become a major research issue among soil scientists since the early 1990s, following the recognition of the role soils play in terms of agricultural sustainability and environmental quality. This review aims to discuss the state of the art concerning soil quality and look into the proposed indicators for its evaluation. Most part of the research work in the literature is focused on the identification of a soil attribute that would serve as a SQ indicator (SQI) underlying the evaluation of soil degradation and the estimation of research needs and funding, as well as a critical evaluation of soil management practices. Some authors have proposed criteria for the definition of a SQI. In this literature review three major approaches were clearly identified: search for soil attributes to be used as SQI; organic matter as SQI; and SQ as a result of processes in the soil-plant system. It was concluded that the understanding of the soil as a system represents the most significant advance and that therefore the identification of soil management practices to achieve SQ are more important than the effort to obtain a SQ indicator. From this point of view, soil should be treated as an open system where the non-equilibrium thermodynamics theory is applicable and the SQ emerges from the interactions of the soil-plant-biota system. The agricultural systems that enhance SQ are those where the soil is intensively cultivated with plants preferably of different species, and without tilling.

Agregação e estoque de carbono em argissolo submetido a diferentes práticas de manejo agrícola

A estrutura fisica e uma propriedade essencial para que o solo cumpra adequadamente suas funcoes e tenha qualidade. Com o objetivo de avaliar a contribuicao de praticas de manejo na recuperacao da agregacao de um solo fisicamente degradado, estudou-se a distribuicao de agregados estaveis em agua e particulas simples em classes de diâmetro (9,51-4,76; 4,76-2,00; 2,00-0,25; 0,25-0,053; < 0,053 mm) e o estoque de C na camada superficial de 0-7,5 cm de um Argissolo Vermelho distrofico tipico da Depressao Central do Rio Grande do Sul sob sistemas de manejo. Em parcelas experimentais com 17 anos, avaliaram-se os sistemas: solo mantido sem plantas e sem revolvimento (Descoberto); plantio direto de Lablab purpureus e milho (Zea mays) (Lablab/m); plantio direto de Cajanus cajan e milho (Guandu/m); e pastagem perene de Digitaria decumbens (Pangola). Em parcelas experimentais com 15 anos, avaliaram-se os sistemas: preparo convencional e plantio direto de Avena strigosa e milho (pc a/m e pd a/m, respectivamente) e Avena strigosa + Vicia sativa e milho + Vigna unguiculata (pc av/mc e pd av/mc, respectivamente). Avaliaram-se, tambem, area de lavoura de graos em preparo convencional conduzida por 30 anos (Lavoura) e area de campo nativo (CN), representando a condicao degradada e o ecossistema nativo deste solo, respectivamente. As avaliacoes foram realizadas em amostras de solo indeformadas coletadas em duas epocas (setembro de 1999 e setembro de 2000), compondo seis repeticoes por sistema de manejo. Os dados foram analisados por meio da analise de variância, e o teste de Tukey (5 %) foi utilizado para verificar as diferencas entre os sistemas de manejo. O CN apresentou 76,4 % de solo agregado, distribuidos em 63,8 % de macroagregados e 23,6 % de particulas simples, com estoque de C de 20,0 Mg ha-1 na profundidade de 0-7,5 cm. O uso agricola com revolvimento intenso do solo e baixa adicao de residuos (sistema Lavoura) reduziu a proporcao de solo agregado para 49,9 % e aumentou a de particulas simples para 50,1 %. O estoque de C reduziu para 11,8 Mg ha-1 na profundidade de 0-7,5 cm. A partir dessa condicao, o sistema sem revolvimento de solo, com maior diversidade de especies de plantas e grande adicao de residuos (pd av/mc) elevou, em 15 anos, a proporcao de solo agregado para 70,7 %, e a dos macroagregados, para 53,5 %. A pastagem perene (Pangola) elevou a proporcao de solo agregado para 74,1 % e a dos macroagregados para 61,8 %, igualando-se ao CN. Os sistemas pd av/mc, Guandu/m e Lablab/m recuperaram os estoques de C no nivel do CN. No entanto, a Pangola, que apresentou os maiores indices de agregacao do solo, teve o estoque de C inferior ao desses sistemas, enfatizando a acao positiva do sistema radicular denso na recuperacao da agregacao do solo.

Water, Sediment and Nutrient Retention in Native Vegetative Filter Strips of Southern Brazil

Vegetative filter strips (VFS) are areas adjacent to watercourses with the purpose of reducing sediment and nutrients contained within runoff water from cropland. The aim of this study was to evaluate the retention of water, sediment and nutrients in VFSs with 5, 10, 20 and 30 m widths exposed to simulated runoff water. The VFS chosen for this study were populated by native herbaceous vegetation with a predominance of grasses from South of Brazil. To simulate runoff water, a flow of 30 L min -1 was applied to all plots. Simulated runoff water contained 3.22 g L -1 of sediment and the nutrients concentration was 62.2; 40.9 and 170.3 mg L -1 de P, NH 4-N and NO 3-N,

Forage yield and quality on soil subjected to phosphorus rates in subtropical grassland of Brazil

Phosphorous application effects were evaluated on ryegrass dry matter (DM) accumulation, root development and plant tissue concentration of phosphorus, nitrogen and carbon aiming to determinate the nutritional status of the pasture, as well as to verify the possibility to establish a phosphorus dilution curve for this pasture. Also, the development of phosphorus and ryegrass cultivated with the residual effect of phosphorus fertilization was determined. The experiment was carried out in Pinhais County - Parana State on a Cambisol with very low phosphorus levels. The experiment was of random blocks design and treatments consisted of five phosphorus rates of triple superphosphate (0, 45, 90, 180 and 360 kg P2O5 ha-1) applied to soil surface with four replications. Phosphorus fertilization promoted linear increments in the soil phosphorus availability and resulted, in the first year, in early pasture production and higher phosphorus content in the plant. Nitrogen and carbon contents were not affected. Phosphorous application increased ryegrass DM accumulation in all periods, ranging from 16 to 2826 kg DM ha-1 at flowering stage, for zero and 360 kg P2O5 ha-1, respectively. Root density was positively influenced by phosphorus supply, and the rate of 45 kg P2O5 ha-1 was effective for maximum root development. The residual effect of phosphorus fertilizer provided enhancement of yield and phosphorus plant concentration for both sorghum and ryegrass in the second year.

Carbono e nitrogênio nas frações granulométricas da matéria orgânica do solo, em sistemas de culturas sob plantio direto

Soil quality in no-till systems is related to the crop systems and may be evaluated through particulate organic matter (>53 ∝m) stock due to the functionality this property provides to the soil and its sensitivity to management practices. Aiming to assess soil quality no-till crop systems, this study was carried out through a long-term experiment (21 years) in a Latossolo Vermelho distrofico tipico (typical Oxisol) in Ponta Grossa, PR, Brazil. Six crop systems were assessed. Wheat-TR (Triticum aestivum L.), soybean-SO (Glycine max L.), corn-MI (Zea mays L.), oat-AV (Avena strigosa Schreb.) as a cover crop, vetch-ER (Vicia villosa Roth) as a cover crop, ryegrass-AZ (Lolium multiflorum Lam) for hay, or alfalfa-AL (Medicago sativa L.) for hay comprised the following systems: TR-SO (reference), ER-MI-AV-SO-TR-SO, ER-MI-TR-SO, AV-MI-TR-SO, AZ-MI-AZ-SO and AL-MI (corn every three years). The stocks of total organic carbon (COT) and total N (NT) and C and N in particulate (>53 ∝m) and mineral-associated organic matter (<53 ∝m) were determined at 0-5, 5-10 and 10-20 cm. The semiperennial AL-MI system had the greatest COT and NT stocks in the 0-20 cm layer (63.6 Mg ha-1 COT and 4.6 Mg ha-1 NT), and increased annual sequestration rates in relation to the TR-SO baseline system (0.23 Mg ha-1 year-1 COT and 0.03 Mg ha-1 year-1 NT). The AL-MI system also had the highest C and N stocks in the particulate organic matter in the same layer (12.5 and 0.91 Mg ha-1, respectively) due to its higher C addition from root plant matter and the physical protection of organic crop litter. The ER-MI-TR-SO system had the lowest C and N stocks in the 0-20 cm layer with values of totals stocks of 57.8 and 4.03 Mg ha-1, respectively, and without an increased annual sequestration rate because the stocks were similar to the TR-SO baseline system; C and N stocks in particulate organic matter were 10.4 and 0.67 Mg ha-1, respectively. This tendency was repeated for individual layers with a significant difference between systems in the 0-5 cm layer and no significant difference in the 5-10 and 10-20 cm layers. The particulate organic matter contributed around 30 % to total C stocks in the 0-5 cm layer on average in the systems. Crop rotations with species that have active root systems for a longer time, such as the semi-perennial AL-MI system, could increase total C and N stocks, especially the particulate organic matter, which promote soil functionality and, consequently, greater soil quality.

Dejeto líquido bovino em plantio direto: perda de carbono e nitrogênio por escoamento superficial

The use of manure in agricultural system is a possibility to dispose of the waste generated in animal production, but improper use can cause environmental problems. The general objective of this study was to evaluate carbon and nitrogen concentrations and losses in runoff in four doses of liquid dairy manure (0, 60, 120, 180 m3 ha-1 yr-1) applied to a silt clay loam Oxisol with 13 % slope, in no-till with soybean, oat, corn, and wheat in crop rotation. The runoff was collected for two years and seven months in 60 L containers after every rain with runoff from at least one plot. Soluble nutrients were analyzed in runoff samples filtered through a 0.45 µ m membrane and total nutrients in unfiltered samples. The application of liquid dairy manure reduced the losses of organic carbon and nitrogen, with positive consequences for water quality. However, higher rates tended to increase the concentrations of these elements and, consequently, reduce water quality. The weighted average concentrations of nitrate were below the limit allowed by Brazilian legislation, but ammonium exceeded the threshold values, indicating the need of control measures to prevent the runoff from reaching the water bodies, even in no-tillage systems. It should be pointed out that these data were obtained under low potential polluting conditions, i.e, on 13 % slope, low rainfall and with a minimum interval of ten days between manure application and rainfall. Further studies should also evaluate nitrate leaching.