Renato Borges de Medeiros

Potencial alelopático do capim-annoni-2 (Eragrostis plana Nees) na germinação de sementes de gramíneas perenes estivais

Among plant strategies to invade and dominate the plant community, the release of alelochemicals is prominent. These compounds are present in all plant parts, principally, in root exudates, leaves and their degraded parts. They are released in the environment through volatile or soluble emanations, translocated in water. Capim-annoni-2 is an invasive exotic Poaceae of rangeland vegetation with allelopatic potential. To test this effect, plant structures from the mid part of capim-annoni-2 were collected and cut in small pieces of 0.5cm and placed in three covering levels of 0, 50 and 100% in gerboxes covered with germitest blotters over the cut material. A hundred seeds of Paspalum notatum Flugge, P. regnellii Mez, Megathyrsus maximus B. K. Simon and S. W. L. Jacobs, Setaria sphacelata (Schumach) Staff and C. E. Hubb ex Chipp and Lactuca sativa L., were placed to germinate as controls. A randomized complete block design was used with four replications. The allelopatic effect was observed on the seed germination after the beginning of capim-annoni-2 plant tissue decomposition. Seeds with high speed germination, such as M. maximus and P. reginelli as well as L. sativa, escaped the allelopatic effect. The most damaged species in their germination course were P. notatum e S. sphacelata. The germination injury was proportional to the gradient increase of the capim-annoni-2 covering tissue with the exception of P. reginelli which showed, at 50% capim-annoni-2 covering level, an increase in germination, but at 100% level there was a significant germination reduction. The capim-annoni-2 allelopathic effects occur during plant tissue decomposition. Seeds with precocious germination escape these effects. The late germination of P. notatum and S. sphacelata exposed them to the capim-annoni-2 allelopathic effects. P. reginelli germination was stimulated at 50% covering level to capim-annoni-2, but at maximum level there was a significant germination decrease in its seeds.

Influência de sistemas de rotação de sementes de gramíneas forrageiras temperadas na composição do banco de sementes invasoras no solo

Due to changing cropping practices in perennial grass seed crops in western Oregon, USA, alternative rotation systems are being considered to reduce weed infestations. Information is generally lacking regarding the effects of alternative agronomic operations and herbicide inputs on soil weed seed bank composition during this transition. Six crop rotation systems were imposed in 1992 on a field that had historically produced monoculture perennial ryegrass (Lolium perenne L.) seeds. Each system plot was 20 x 30 m, arranged in a randomized complete block design, replicated four times. Twenty to thirty soil cores were sampled in June 1997 from each plot. The weed species composition of the cores was determined by successive greenhouse grow-out assays. In addition to seed density, heterogeneity indices for species evenness, richness, and diversityViable seeds of several native plant species present difficulties to germinate. Two trials were carried out to identify appropriate methodology to overcome seed dormancy in Operculina macrocarpa and Operculina alata. In the first one, the seeds of Operculata macrocarpa were submitted to the following treatments: dry cooling; wet heat; immersion in peroxide, immersion in hot water, immersion in sulfuric acid; wet cooling; mechanical scarification; soaking in potassium nitrate; and the control. Percentage of germination, hard seeds and dead seeds were determined. In the second trial, seeds of Operculina macrocarpa and Operculina alata were scarified and sown on paper and sand substrates and set to germinate under five different environmental conditions: continuous light and constant temperature (25oC), continuous light and alternating temperatures (20oC/16h-35oC/8h), continuous darkness and constant temperature, continuous darkness with alternating temperatures (20oC/16h-35oC/8h), and alternating light and temperatures (light/35oC/8h-darkness/20oC/16h). Percentage and time to germination were determined. Mechanical scarification was the most efficient method to break dormancy in Operculina macrocarpa; towel paper, temperature between 20-30oC and darkness were appropriate conditions for seed germination of Operculina macrocarpa and Operculina alata.

Soil seed bank variation patterns according to environmental factors in a natural grassland

5 ABSTRACT - This research aimed to determine the soil seed bank and its relationship with environmental factors that have an influence in the distribution of the vegetation above the ground in an excluded area of natural grassland in the South of Brazil. Most of the 122 identified species in the seed bank were perennials. Data analysis indicated three distinct community groups, according to the size and composition of the soil seed bank in lowlands with permanent wet soils, in lowlands and in other areas. In general, lowlands were characterized by low-fertility soils, high moisture and aluminum contents, being spatially homogeneous habitats and, therefore, more restricted to vegetation heterogeneity than other parts of the relief. Environmental factors most associated with soil seed bank size and composition were relief position and their co-related soil variables such as: soil moisture content, potassium content, organic matter, basic saturation of cation exchange soil capacity, exchangeable basics sum of the soil and clay soil content. According to that, relief position, associated with combined effects of soil chemical properties related to it, determines the observed variation pattern of the soil seed bank, as a reflection of the vegetation above the area.

Comportamento de ovinos em gestacao e lactacao sob pastejo em diferentes estadios fenologicos de azevem anual

This work was carried out at the field to evaluate the grazing sheep behavior conducted in annual ryegrass (Lolium multiflorum Lam.) on vegetative, pre-flowering and flowering stages. Ewes at the end of pregnancy and at the beginning of lactation maintained in a 1.3 ha paddock were evaluated in terms of grazing time, bite rate, bite size, leaf:stem ratio of ingested pasture estimated by hand-plucking method. Daily grazing time/h of 9.65, 10.97 and 10.68, bite rates/min of 52.65, 51.93 and 40.63 and the bite weight g/bite of 0.064, 0.055 and 0.048 were observed for vegetative (VS), pre-flowering (PS) and flowering stages (FE), respectively. This behavior resulted in forage intake rates of 4.48%, 3.91% and 2.72% of body weight on VS, PS an FS, respectively These evolutions were accompanied by reduction of the leaf:stem ratio of available forage (4.36:1, 1.11:1 and 0.17:1) which were in accordance to the qualitative limitation that occurs in the flowering stage. These data showed that until pre-flowering stage, the strategies desenvolved by the animals allowed an adequate intake forage, while that in the flowering stage the low quality pasture determinated a decrease intake, being this considerate insufficient to attend nutritional necessities of lactating ewes and respective lambs.

Banco de sementes do solo em área agrícola sob diferentes sistemas de manejo estabelecida sobre campo natural

Knowledge of the ecology of soil seed banks (SSB) contributes to improving integrated weed SSB management systems in croplands established in natural grassland areas. The aim of this study was to evaluate the effect of different cropping systems, established in a natural grassland field (Depressao Central of Rio Grande do Sul, 30o05´S, 51o40´O, altude 46m, rainfall 1398mm), on the SSB. Three different tillage-crop rotation systems were imposed (no-tillage - NT, reduced tillage - RT, and conventional tillage - CT) in three plots arranged in seven blocks. Two SSB evaluations were carried out in each tillage system, one in May and the other in October/ 2002. The SSB was evaluated by sampling soil cores, which were germinated in a glasshouse, and seedlings were counted and identified. Edaphic variables were registered to relate with collected data. The results indicated that different tillage systems affected the SSB composition, and that certain species responded differently to these influences. The NT system resulted in higher BSS wealth, a lower number of Brachiaria plantaginea seeds, a higher number of Sida rhombifolia seeds, but inverse values were recorded for RT and CT systems. The spatial soil seed bank distribution presented high heterogeneity among cropping systems. Edaphic variables, specially organic matter, pH and phosphorous, showed associations with the variation in SSB composition.

Forage yield and nitrogen nutrition dynamics of warm-season native forage genotypes under two shading levels and in full sunlight

The successful achievement of a highly productive understorey pasture in silvopastoral systems depends on the use of well-adapted forage genotypes, showing good agronomic performance and persistence under shading and grazing. In this study, the herbage dry matter yield (DMY) and nitrogen nutrition dynamics were determined in three native warm-season grasses (Paspalum regnellii, Paspalum dilatatum and Paspalum notatum) and a forage legume (Arachis pintoi) under two shading levels compared with full sun. The experiment was conducted in the Campanha region, Bage, state of Rio Grande do Sul, Brazil, during two evaluation cycles (2008/2009 and 2009/2010). Three shade cloth levels (0%, 50% and 80% of light restriction) were applied to the forage genotypes in a split plot design, in which shading levels were the main plot and forage genotypes were the subplots, with three replications. P. regnellii showed the highest accumulated DMY (1500 and 1700 g m-2, respectively, for the first and second evaluation cycles) at all shading levels and showed no DMY decreased under the heavy shade (80%). Average DMY over the four genotypes under the 50% shade level was higher or equal compared with full sun. Influence of rainfall was observed on the DMY performance of all genotypes: the positive effect of moderate shading (50%) on P. dilatatum and P. notatum DMY was associated to a low soil water availability status. Increased shading level resulted in high nitrogen nutrition index values on grasses, in comparison with full sun. All genotypes performed well under the moderate shading level, but the DMY of both P. regnellii and P. dilatatum and the herbage N content in P. notatum and A. pintoi of all genotypes stood out, showing that those main genotypes are promising to grow in silvopastoral systems at the Campanha region in southern Brazil.

Sheep behavior at the pregnancy and at the lactation grazing on different phenological stages of annual ryegrass

This work was carried out at the field to evaluate the grazing sheep behavior conducted in annual ryegrass (Lolium multiflorum Lam.) on vegetative, pre-flowering and flowering stages. Ewes at the end of pregnancy and at the beginning of lactation maintained in a 1.3 ha paddock were evaluated in terms of grazing time, bite rate, bite size, leaf:stem ratio of ingested pasture estimated by hand-plucking method. Daily grazing time/h of 9.65, 10.97 and 10.68, bite rates/min of 52.65, 51.93 and 40.63 [...]

Prevention of natural grassland invasion by Eragrostis plana Nees using ecological management practices

The objective of this research was to evaluate the effects of different types of disturbance on the ability of the natural grassland to avoid the invasion of Eragrostis plana Nees (South African lovegrass). The experiment was carried out in Dom Pedrito, Rio Grande do Sul, Brazil, in an area free of South African lovegrass, from Feb. 2004 to Apr. 2007. The treatments were: 1) grassland management regimes: exclusion; low grazing intensity (rotational grazing), ±10 cm; and high grazing intensity (continuous grazing), ±5 cm; 2) initial levels of soil disturbance: high grassland, ±10 cm; low grassland, ±5 cm height; and low grassland with scarified soil; 3) fertilization regimes: without fertilization; phosphorus; and nitrogen. The experimental design was a split-split-plot type in complete blocks, with three replicates. Three winter cultivated species - Trefoil repens L., Lotus corniculatus L., Lolium multiflorum Lam. and South African lovegrass -were sown in 54 split-splitplots (split-plots: low grassland, and low grassland with scarified soil). The other 27 split-split-plots (split-plots: high grassland) were sown only with South African lovegrass. The grassland height, plant number of South African lovegrass, grassland dry mass and photosynthetic active radiation intercepted (FARint) at the soil level were recorded. The fertilization regimes did not influence the South African lovegrass plant number. The initial levels of soil disturbance and grassland management regimes influenced the invasion of South African lovegrass. The invasion was favored by the lower grassland height and lower forage mass, higher intensity of the soil disturbance, and higher FARint due to the continuous grazing. On the contrary, higher grassland height, higher forage mass, lower soil disturbance and lower FARint, associated with rotational grazing or exclusion, showed higher potential to control the invasion of South African lovegrass in the natural grassland.

Controle de invasão biológica por capim-anonni em margem viária mediante a introdução de gramíneas

The objective of this study was to control biological invasion by Eragrostis plana Nees (South African lovegrass) on a roadside by introducing competitor grasses associated with soil management and fertilization practices. The experimental design was a complete randomized block with split-plots parcels and three replications. In the parcels, it was evaluated two practices of soil treatments: subsoil tillage plus disc harrow tillage and application of limestone and phosphorous; and only subsoil tillage and, in the split-plots, the following grass species: Megathyrsus maximus (Jacq.) B. K. Simon & S. W. L. Jacobs; Setaria sphacelata (Schumach.) Stapf & C. E. Hubb.; seed mixture of three native grasses, Paspalum notatum Alain ex Flugge, Paspalum regnelli Mez and Paspalum urvillei Steud.; evaluated by comparison to an exclusion subplot (control). In the floristic surveys, which were performed on January 8th 2005, and after planting, in January 26th and June 25th, 2006, a high floristic richness was observed, with 86 botanical species distributed in 29 families and 21% of exotic species. The subsoil tillage plus disc harrow tillage, limestone and fertilization associated with the introduction of M. maximus or with S. sphacelata were the treatments which contributed most to reduce E. plana frequency. The native grasses present in the roadside vegetation Paspalum plicatulum Mitchx, Piptochaetium montevidense (Spreng.) Parodi and the introduced native species Paspalum urvillei have potential to control E. plana invasion.

Efeito de diferentes sistemas de pastejo sobre o desempenho de suínos mantidos em pastagem de trevo-branco (Trifolium repens L.)

This trial was carried out to determine the effect of continuous, alternated or rotational grazing systems on the performance of pigs (feed intake, weight gain, feed conversion and backfat thickness), in the growing and finishing phases, as well as the forage availability and chemical composition of a white clover pasture (Trifolium repens L.). Thirty-six castrated pigs were allotted to a randomized complete-block experimental design with three treatments and three replications. Twelve feedlot pigs were kept on a rearing system. No significant differences were found between grazing systems on parameters of animal performance and forage on offer. However, significant differences were observed on the pasture chemical composition between the grazing systems studied. Pigs reared on white clover pasture consumed from 13.41 to 15.92% less feed and showed smaller backfat thickness and weight gain than pigs reared in the confined system. No significant differences on feed conversion between feedlot pigs and pigs under pasture conditions were observed.