Flávio Luiz Foletto Eltz

Atributos físicos do solo em sistema de integração lavoura-pecuária sob plantio direto

Soil compaction is one of the most important reasons for decrease in crop yield. The impact of animal trampling on integrated beef cattle raising-crop production systems were studied to evaluate the changes in soil physical properties (bulk density, porosity, soil resistance to penetration and soil water infiltration). The field experiment was carried out in Jari, in the mid- plateau region of Rio Grande do Sul State, Brazil. Three management systems of winter pastures (black oat; Avena strigosa Schreber + ryegrass; Lolium multiflorum Lam.) were studied under different grazing frequencies: (1) No grazing (NG), (2) grazing every 28 days (G28) and (3) grazing every fourteen days (G14). The summer crops soybean (Glycine max (L.) Merr.) or corn (Zea mays L.), as antecedent crop in rotation to the winter pastures, were also studied to measure the increasing or decreasing effects on compaction by animal trampling. The greatest effects of animal trampling were concentrated in the top soil layer (0 to 0.05 m), but under the highest grazing frequency (G14) macroporosity was reduced down to the 0.10-0.15 m layer. The soil resistance to penetration had peaks of 2.61 and 2.49 MPa in the G28 and G14 treatments, respectively, in the 0.05-0.08 layer. In the ungrazed areas the values remained lower, around 1.66 MPa. Soil water infiltration was significantly affected by animal trampling and by the previous summer crop. In the case of corn area, the soil was less sensitive to cattle trampling, unlike in the areas following soybean, where the highest grazing frequency (G14) reduced the water infiltration rates. Soybean induced higher values of macroporosity in the evaluated soil layers; when related with lower beef cattle density or ungrazed pastures, the rates of water infiltration and accumulated infiltration were higher.

Erosividade, coeficiente de chuva, padrões e período de retorno das chuvas de Quaraí, RS

The planning of agricultural and civil engineering activities must be based on knowledge of rainfall erosion potential. For Quarai, RS, Brazil, the rainfall erosivity and its relationship with precipitation and rainfall coefficient, rainfall patterns and rainfall return period were determined. Daily rainfall data from the 1966-2003 period were used. For each erosive rainfall the segments of the rainfall chart with the same intensity were separated and the data recorded in a worksheet. The mean precipitation and rainfall patterns were estimated, as well as the monthly and annual erosivity by the EI30 index (International System of Units), using the software Chuveros. The rainfall coefficient was calculated. Pearson correlations and linear regressions between the erosivity index EI30 and the mean annual precipitation and rainfall coefficient (Rc) were performed. The rainfall maximum intensity was calculated by the method of extreme distribution type I for different rainfall durations (1/6, 1/3, 1/2, 1, 2, 4, 8, 12, 24 and 48 h) and rainfall return periods (2, 5, 10, 20, 50 and 100 years). Equations were adjusted that relate the maximum intensity and rainfall duration to all return periods, by the method of simple linear regression, and the rainfall characteristics related in a graph. The mean annual values of EI30 (R factor of USLE) determined for Quarai, RS, Brazil, was 9,292 MJ mm ha-1 h -1 year-1. The following equations were obtained: EI30 = -754.37 + 13.50 p (r2 = 0.85) and EI30 = -47.35 + 82.72 Rc (r2 = 0.84). In relation to the total precipitation studied, 44 % of the number of rainfalls and 90 % of the volume were erosive. Of the total rainfalls evaluated, 44 % of the number and 90 % of the volume were erosive. Of the total erosive rainfall events, 51 % had an advanced, 25 % had an intermediate, and 24 % had a delayed hydrological pattern. Of the total volume of erosive rainfalls, 57 % showed and advanced pattern, 25 % intermediate, and 18 % a delayed pattern.

CONTROLLING SOIL EROSION AND RUNOFF WITH POLYACRYLAMIDE AND PHOSPHOGYPSUM ON SUBTROPICAL SOIL

Sandy soil, prone to intense soil erosion, is used for agriculture in the subtropics of Brazil. This study was conducted to determine whether soil amendments are effective for conserving topsoil by preventing water-induced erosion on a Brazilian sandy Alfisol soil (coarse-loamy, mixed, thermic Typic Paleudalf). A programmable rainfall simulator was used at the experimental station of the Federal University of Santa Maria, in a newly harvested black oat (Avena estrigosa L.) field that was moldboard plowed and disked twice. Plots were on bare tilled soil with 8% to 12% slopes. The soil treatments consisted of a single 5 Mg ha-1 surface application of byproduct phosphogypsum (PG), a single 20 kg ha-1 surface application of anionic polyacrylamide (PAM), a combined amendment (PAM+PG) with the same rates as above, and an unamended soil (control). Simulated rainfall average intensity was 25 mm h-1 with a 2 h duration. Sediment and runoff samples were collected at intervals during the experiment, and soil surface samples inside the plot were taken after the rain for surface crusting analysis. Total soil loss was significantly lower for the treatments than for the control and averaged 197, 278, 217, and 2181 kg ha-1, respectively for PG, PAM, PAM+PG, and control treatments. PAM and PAM+PG had steady-state runoff rates significantly less than that of the control. All of the amendments reduced soil sediment erosion (average 90% reduction) more than final runoff (average 35% reduction). Using amendments to reduce precipitation-induced erosion is a possible alternative conservation practice in this region of the world.

Efeito do manejo mecânico da palhada de aveia preta sobre a cobertura, temperatura, teor de água no solo e emergência da soja em sistema plantio direto

Black oat provides an excellent soil cover, and is a preferential winter crop mainly before soybean cultivation in Rio Grande do Sul, Brazil. The objective of this study was to evaluate the effects of black oat straw management on soil cover, soybean emergency, soil temperature and soil water content. The experiment was carried out during 1997/98, at the Federal University of Santa Maria, Santa Maria (RS), on a Typic Hapludalf soil. A completely randomized block design was used in a split-plot distribution with five replications. The main treatments with mechanical management of black oat straw were: (a) combined harvested straw; (b) not managed, stand-up straw; (c) straw rolled with a knife-roll; (d) disked straw; (e) mowed straw and (f) without straw cover and weed control. In the subplots, herbicide was applied with or without weed control at post emergency. The variables analyzed in the subplots with weed control were soybean emergency rate index, soil cover by straw, soil temperature and soil water content. It was observed that the stand-up and disked straw treatments reduced soil cover, respectively, by 20 and 74%, during the 53 days of evaluation; the maximum soil temperature was highest for the treatment without straw and weed control and lowest for the stand-up straw; excessive rainfall during the period of this study did not allow for differences in soil water content among the black oat straw management treatments. The soybean emergency rate index was not affected by the different types of black oat straw management, but was lowest in the treatment without straw.

Isolation and characterization of two plant growth-promoting bacteria from the rhizoplane of a legume (Lupinus albescens) in sandy soil

Two bacterial strains that amplified part of the nifH gene, RP1p and RP2p, belonging to the genus Enterobacter and Serratia, were isolated from the rhizoplane of Lupinus albescens. These bacteria are Gram-negative, rod-shaped, motile, facultative anaerobic, and fast-growing; the colonies reach diameters of 3-4 mm within 24 h of incubation at 28 oC. The bacteria were also able to grow at temperatures as high as 40 oC, in the presence of high (2-3 % w/v) NaCl concentrations and pH 4 -10. Strain RP1p was able to utilize 10 of 14 C sources, while RP2p utilized nine. The isolates produced siderophores and indolic compounds, but none of them was able to solubilize phosphate. Inoculation of L. albescens with RP1p and RP2p strains resulted in a significant increase in plant dry matter, indicating the plant-growth-promoting abilities of these bacteria.

Erosividade da chuva em municípios do Mato Grosso: distribuição sazonal e correlações com dados pluviométricos

The rainfall erosivity constitutes an indispensable factor for prediction of soil losses by water erosion. In this way, the present study was carried out with the objectives to model the relationship among the erosivity index (EI30) monthly values, obtained from rainfall chart data with the precipitation and monthly rainfall coefficient for four municipal districts (Canarana, Sao Jose of Rio Claro, Poxoreo and Vera) of Mato Grosso State; to determine the erosivity factor (R) obtained from rainfall data for the four municipalities, as well as its return period and its occurrence probability; and to study the EI30 annual, seasonal and monthly distribution in these four municipalities. The potential relationship between the rainfall erosivity index and the rainfall coefficient make possible to evaluate the monthly and annual rainfall erosivity with good reliability (ERM < 7%) for the municipalities of Canarana, Vera and Sao Jose of Rio Claro. However, for Poxoreo this good reliability is verified only for the annual erosivity. In the four municipalities the spring and summer seasons correspond to the period of larger erosivity, being responsible, except for Poxoreo, for 94% or more of the annual total erosivity.

Resistência à penetração e rendimento da soja após intervenção mecânica em latossolo vermelho sob plantio direto

Compaction negatively affects a number of soil properties, e.g., resistance to root penetration and water and nutrient availability to plants, restricting the photosynthetic rate, shoot growth and consequently, the yield. When soil compaction becomes limiting to crop development, mitigation measures must be adopted. The purpose of this study was to evaluate the residual effect of mechanical soil plowing and chiseling, by a seeder with soil breakers (disks and disks plus short ripper) as mitigation practice of the soil compaction under no-tillage (NT), on soil penetration resistance and soybean yield. In 2001, a study was conducted in Coxilha, in northern Rio Grande do Sul, on an Oxisol, in an area with a sequence of NT management. In this field, every year a treatment of mechanical soil decompression was applied, consisting of plowing and chiseling the soil under NT, before sowing the summer crop, reassuming the NT management after this intervention. The experimental design consisted of randomized blocks in a split-plot design with three replications. The treatments consisted of a combination of 13 systems of soil management in the main plots and two seed drill devices in the subplots. Thus, the management systems were evaluated by the control, represented by the uninterrupted maintenance of NT for 16 years, six NT management periods (7.5, 6.5, 5.5, 4.5, 3.5, and 2.5 years) after one intervention with mechanical disc plow + disc harrow (A) and the same six NT management periods after one mechanical intervention with chiseling (E). The levels in the subplots consisted of the action of a no-till seeder equipped with double discs reaching a depth of 7 cm and a seeder equipped with double disks + short ripper reaching a depth of 13 cm. Results indicated that the mitigating effect on compaction and on the improvement of soil structure of the mechanical intervention in soil under consolidated NT consisting of soil chiseling or plowing is short-lived, with a residual effect of up to two and a half years for penetration resistance. The use of a no-till seeder drill equipped with short ripper + disc seeder has potential for mitigation of soil compaction, by reducing mechanical penetration resistance in the 7-15 cm layer. Nevertheless, the residual effect of mechanical intervention for soil decompaction and the adoption of different devices for fertilizer application in the plant furrow were not effective in altering the soybean yield in the 2008/2009 growing season.

Organismos edáficos como bioindicadores da recuperação de solos degradados por arenização no Bioma Pampa

Edaphic organisms are sensible to environment alterations and have been used as indicators of soil quality changes. These modifications can be promoted by degradation or agradation events. The study area is located in Alegrete, Rio Grande do Sul. It was analyzed the role of epigeic soil fauna as bioindicator of soil degradation by arenizacao and its restoration by revegetation with Lupinus albescens Hook. & Arn., a native fabaceous of Bioma Pampa. The treatments were constituted of soil under natural covering with Lupinus albescens, degraded area recovered with Lupinus albescens by one year (T1), degraded area recovered with Lupinus albescens by three years (T3), degraded area (SA) and native grass field (CN). The sampling was made in February and May of 2006 with PROVID traps. It was determined the abundance of organisms at Order level, the organisms richness, the diversity and evenness Shannon’ index. The process of Arenizacao reduced the development of sampled edaphic populations, while revegetation showed positive effects in the recolonization of the area. Colembolla group was a good bioindicator of degradation and restoration effects. The Shannon diversity index was not satisfactory to evaluate the edaphic fauna if disconnected of other parameters.

RECOMENDAÇÃO DE ADUBAÇÃO NITROGENADA PARA TRIGO EM SUCESSÃO AO MILHO E SOJA SOB SISTEMA PLANTIO DIRETO NO PARAGUAI

Nitrogen is one of the nutrients wheat needs most, but is often not supplied neither in the right quantity nor at the right time. Because of the importance of nitrogen fertilization and the lack of information available in Paraguay, this study was developed to establish a nitrogen fertilizer recommendation for wheat under no-till. Six field experiments were carried out over a period of two years, in four Departments of Paraguay, considering the most important soils (Oxisols, Inceptisols and Ultisols) and regions (Alto Parana, Itapua, Amambay and Missiones). Five N rates (0, 30, 60 90, 120 kg ha-1) were applied to wheat (Triticum aestivum) after corn (Zea mays) and soybean (Glycine max), and the residual effect on wheat of N applied to the precedent corn crop was evaluated (0, 60, 120, 180 and 240 kg ha-1), in 5 x 8m plots, in a random block design with three replications. Economically, wheat after soybean responded positively to the N rate of 35 kg ha-1 with yields around 3.100 kg ha-1. After corn, wheat responded economically to doses of up to 30 kg ha-1 N and reached a grain yield of 2.100 kg ha-1. When the concentration of soil organic matter is higher than 4 %, a sufficient quantity of N is available without mineral N fertilization, for yields up to 2.500 kg ha-1. Wheat responded to residual N applied to corn with a yield increase from 1.800 kg ha-1 (0 kg ha-1) to 2.300 kg ha-1 (N applied to corn estimated at 213 kg ha-1, averaged across all sites).

Influência do fenômeno El Niño na erosividade das chuvas na região de Santa Maria (RS)

O fenomeno El Nino Oscilacao Sul (ENOS) altera o tempo e o clima em varios locais, provocando alteracoes na circulacao atmosferica que afetam os elementos meteorologicos e climaticos, principalmente a chuva, nas diferentes regioes do Brasil. Na regiao Sul do Pais, em anos de El Nino, fase positiva do fenomeno, a chuva e frequentemente acima da normal, e, em anos de La Nina, fase negativa do fenomeno, a chuva e frequentemente abaixo da normal. Algumas caracteristicas das chuvas sao alteradas pelo ENOS, como a frequencia de ocorrencia, a intensidade e a quantidade. Essas caracteristicas sao importantes para a definicao das chuvas erosivas. Entre os metodos de determinacao da erosividade das chuvas, o indice de erosividade EI30 e o mais usado no Rio Grande do Sul (RS). O objetivo deste trabalho foi determinar e associar o indice de erosividade EI30 com o fenomeno ENOS para a regiao de Santa Maria, RS. Usaram-se os dados diarios de chuva registrados em pluviogramas a partir de 1o de julho de 1978 a 30 de junho de 2008, coletados na Estacao Climatologica Principal de Santa Maria, RS. As chuvas individuais e erosivas foram identificadas nos pluviogramas, classificadas em anos de El Nino, La Nina e Neutros, e foi calculado o seu indice EI30. Foi realizada a analise de correlacao de Pearson e analise de regressao entre o EI30 e o Indice Oceânico do Nino (ION). A significância da regressao foi testada com o teste t, a fim de quantificar a associacao entre as duas variaveis, com vistas a possivel previsibilidade do potencial erosivo das chuvas a partir de anomalias de Temperatura da Superficie do Mar (TSM) no oceano Pacifico. Tambem foram classificadas as chuvas em padroes Avancado, Intermediario e Atrasado. O potencial erosivo das chuvas em Santa Maria e afetado pelo fenomeno ENOS, de modo que maior numero de chuvas tem maior potencial erosivo em anos de El Nino e em anos Neutros. A variabilidade do potencial erosivo das chuvas em Santa Maria e maior nos anos Neutros do que nos anos de anomalia da TSM. O padrao das chuvas e alterado em anos de anomalia da TSM, no sentido de que nos anos de El Nino ha aumento nas chuvas de padrao avancado e em anos de La Nina ha aumento nas chuvas de padrao atrasado; no padrao intermediario, ha diminuicao do numero de chuvas em anos de El Nino e La Nina, em comparacao com anos Neutros. A capacidade preditiva do potencial erosivo das chuvas em Santa Maria pelo indice ION e fraca.