Aino Victor Ávila Jacques

A queima das pastagens naturais: efeitos sobre o solo e a vegetação

The effects of fire and alternative managements on soil and vegetation of native pastures were revised from several research works, jointing personal observations developed during almost 40 years in range areas of Rio Grande do Sul, Brazil. Soil parameters such as potential acidity; aluminum concentration; basis saturation; and others were considered with vegetation parameters such as production and quality of green forage dry matter during the year; botanical composition; volumetric amount of water in soil; nutrients cycling through the forage and dead material; etc. The general conclusion based on the results of the revised works, is that the burning of natural pastures, in the high altitude region of Southern Brazil, must be avoided as a routine practice, because it is detrimental to the environment, reduces the forage yield and quality, and it is not a sustainable practice.

Relações planta-animal em ambiente pastoril heterogêneo: padrões de deslocamento e uso de estações alimentares

This study assessed how the displacement patterns and feeding station used can be affected by sward heights of 4, 8, 12 and 16 cm. A randomized complete design was used with two replication in time and space. The animals were evaluated by 45- minute grazing tests, to determine the number of bites, number of feeding stations and number of steps using counters, except for number of bites, which was registered by the IGER Behaviour Recorder device. A positive correlation was observed between sward height and herbage mass, and negative correlation between sward height and herbage bulk density. Differences between female calves and ewes were observed in all variables evaluated. The number of feeding station per minute decreased quadratically with increasing sward height. The number of bites per feeding station and time per feeding station increased quadratically with increasing sward height and were affected negatively by the lower herbage bulk density in the upper strata of the higher sward heights. Female calves, at 12 cm sward height, carried out more bites per feeding station and remained longer at each feeding station. The same behaviour was observed for ewes at 8 cm sward height. As less feeding stations were used, as a response to the previous variables, the animals walked more with slower steps. Thus, at sward heights between 8 and 12 cm the animals remained more time grazing each feeding station and covered longer distances searching for new grazing sites.

Acumulação de Forragem e Material Morto em Pastagem Nativa sob Distintas Alternativas de Manejo em Relação às Queimadas

It was studied five management systems of native pasture, under grazing, from Rio Grande do Sul State: with biennial burning for more than 100 years, without burning for 32 years with or without mowing, and pasture improvement for 7 and 24 years. The forage accumulation and the senescent material detached from the plant, were evaluated using grazing exclusion cage. The experimental design was a completely randomized with three replications. The systems without burning were more productive and among these the forage accumulation was similar among without burning and without mowing and the improvement treatments with annual accumulation higher than 9,000 kg/ha of green forage dry matter. The litter was higher with treatment without burning and without mowing, lower with burning, and intermediate with other treatments. The alternative management showed to be more productive and more sustainable as compared with burning practices.

Qualidade da forragem de pastagem nativa sob distintas alternativas de manejo

n Burning of native pasture affects soil, botanical composition, species development, and forage quality. It was studied five management systems of native pasture under grazing condition: biennial burning for more than 100 years; without burning for 32†years with or without mowing; and pasture improvement for 7 and 24†years. The experimental design was a completely randomized one, with three replications. Crude protein and in†vitro organic matter digestibility were greater in im- proved and mowed areas. The level of N did not differ among treatments, while the levels of P, K, Ca and Mg were greater in improved area as compared to other treatments. The tissue nutrient quantity accumulated, as result of forage production, was greater in the systems without burning.

Estratégias de manejo da oferta de forragem para recria de novilhas em pastagem natural

O experimento foi realizado com o objetivo de avaliar o desenvolvimento de novilhas de corte dos 15 aos 28 meses de idade mantidas em pastagem natural sob diversos manejos da oferta de forragem. Avaliaram-se quatro ofertas fixas ao longo do ano (4, 8; 12 e 16% do peso vivo, PV) e tres ofertas de forragem variaveis (8-12; 12-8; e 16-12%, de modo que o primeiro valor corresponde a oferta utilizada na primavera e o segundo aquela empregada no restante do ano). Foram utilizadas novilhas de corte mesticas sob pastejo continuo com taxa de lotacao variavel para avaliacao do peso vivo, do escore de condicao corporal, do ganho medio diario e da aptidao reprodutiva pela dosagem de progesterona no sangue. Para caracterizacao do pasto, foram avaliadas a massa de forragem (MF), a altura do pasto (ALT) e a area efetivamente pastejada (AEP). Na oferta de forragem de 4%, os animais apresentaram reducao acentuada de peso no fim do verao e outono, por isso, essa oferta de forragem foi eliminada. O peso vivo, o escore de condicao corporal e o ganho medio diario nao diferiram entre as ofertas de forragem; as variacoes ocorreram somente entre as estacoes. Aos 26 meses de idade, a probabilidade de estro das novilhas nao diferiu entre as ofertas de forragem, embora a oferta de forragem de 16-12% tenha resultado em probabilidade de estro de 50%. Aos 28 meses de idade, a oferta de forragem de 16-12% resultou em maior probabilidade de estro (86%) e nao diferiu das ofertas de 16% (50%) e 8-12% (50%), as quais promoveram estrutura do pasto mais adequada, ou menos limitante, ao habito de pastejo das novilhas.

CARACTERÍSTICAS DE UM LATOSSOLO VERMELHO SOB PASTAGEM NATURAL SUJEITA À AÇÃO PROLONGADA DO FOGO E DE PRÁTICAS ALTERNATIVAS DE MANEJO

Soil samples were taken, in 1998, from distinct layers (0-2.5; 2.5-5.0; 5-10 and 10-30cm) in fields with native pasture under grazing, submitted to burning and alternative management practices (without burning with or without mowing, and improved for 7 and 24 years), in the Campos de Cima da Serra region, RS, Brazil. The experimental design was a completely randomized, with three replications. The improvement of native pasture increased the value of pH and the levels Ca, Mg, P and base saturation, and reduced the potential acidity. Biennial burning increased the potential acidity and reduced Mg. The mowing treatment increased the level of Mg and base saturation, and decreased the potencial acidity in the soil surface in comparison to the system without burning and without mowing. Systems without burning were more efficient in water conservation and soil cover.

Adaptação das plantas ao fogo: enfoque na transição floresta - campo

The presence of grassland alternating with Araucarian forest in Southern Brazilian plateau, has surprised the scientists, as to be in force the current climate, of greater precipitation than in remote times, the tendency would be the development of forest vegetation. Disturbances, specially fire-grazing interaction and low temperacture in the region, are the greater responsible for the boundaries and expansion of broadleaf forest, and dominance of that vegetation type. The grassland and forest vegetation submitted for long period to recurrent fires have developed strategies to tolerate, avoid or respond to fire. The response of individual plants involve morphological and physiological changes, while at the community level such changes are observed in the dinamics of association among species. Under range conditions, the grasses are the most fire tolerant component in the community, due to the continuous growth of intercalar meristems and also to the new shoots which grow below soil surface or protected in old sheat leaf. Fire stimulates flowering in plants whose growth form is able to avoid greater loss of matter during the burning period. Fire also promotes the release of seeds due to changes in temperature or the release of substances from smoke. At the community level, fire effects on the plants ocurr in relation to the way of surviving and nature and localization of regeneration tissues. The plant behaviour in relation to burning may be classified as dependent (stimulus to reproduction), resistant (stimulus to new shoot), or plants that avoid fire (annual cycle). Therefore, fire has complex effects on the vegetation structure, resulting that tolerant and sensitive species have had different preference patches in the environment.

COMPOSIÇÃO FLORÍSTICA DE UMA PASTAGEM NATURAL SUBMETIDA A QUEIMA E MANEJOS ALTERNATIVOS

The botanical and floristic composition of native pasture, submitted to burning and alternative management practices, was evaluated during one year. The treatments were: biennial burning for more than 100 years; no burning - with or without mowing; and improved with lime, annual fertilization and sod-seeding of cool season species for 7 and 24 years. Forage accumulation within grazing exclusion cage was collected and sorted into species groups. The floristic composition was estimated with BOTANAL method based on the frequency and coverage of species along a transect. The experimental design was completely randomized, with three replications. Improvement of pasture promotes good native warm season grass species, sedges and legumes. Burning stimulates the development in Piptochaetium montevidense, to detriment of warm season grasses, legumes and senescent material. The species Paspalum notatum, P. paniculatum and Desmodium incanum has greater contribution under improved and mowed treatments. The biennial burning stimulates species of Andropogon and Schizachyrium genera and also opportunistic species. The alternative management with no burning, rotational grazing and deferment, promotes greater floristic richness, and species with better nutritive value.

Disponibilidade e valor nutritivo de forragem de leguminosas nativas (Adesmia DC.) e exóticas (Lotus L.)

RESUMO - O genero Adesmia DC. possui 17 especies nativas no Brasil, distribuidas nos Estados do Sul, cuja importância esta vinculada a sua adaptacao ao solo e clima regionais, alem de ser de crescimento hibernal (temperadas). Este trabalho teve o obj etivo comparar o padrao de acumulo de materia seca (MS) e valor nutritivo de forragem de A. latifolia, A. punctata e A. tristis, tendo como padrao Lotus corniculatus (cornichao) e L. uliginosus. O ensaio foi realizado em casa de vegetacao durante 210 dias (4000 graus-dia). A disponibilidade de forragem (DF) foi similar entre A. latifolia (276 g MS/m 2 ) e cornichao (275 g MS/m 2 ) e entre A. tristis (201g MS/m 2 ) e L. uliginosus (192 g MS/m 2 ), sendo que A. punctata apresentou a menor DF (155 g MS/m 2 ). A. latifolia caracterizou-se pela maior precocidade na DF, devido ao crescimento mais rapido em relacao as demais especies, sugerindo seu potencial para utilizacao dur ante a estacao fria. Em relacao as analises de qualidade, o teor de proteina bruta (PB) nas folhas de A. latifolia foi de ate 21,6% e a DIVMO atingiu 72,3%. Os maiores conteudos de PB e DIVMO foram encontrados nas folhas de cornichao, 30,3 e 75,8%, respectivamente. A. tristis apresentou DIVMO muito baixa nos caules (34,9 a 44,7%), o que poderia limitar seu consumo por bovinos. Concluiu-se que, entre as especies de Adesmia estudadas, A. latifolia detem o maior potencial forrageiro, sugerindo a continuidade de estudos com a especie.

Nodulação e fixação biológica de nitrogênio de Adesmia latifolia e Lotus corniculatus em vasos de Leonard

Adesmia latifolia is a forage legume native from Southern Brazil which is outstanding due to stoloniferous growth habit and for forage production during the cool season. The Lotus corniculatus (birdsfoot trefoil) is a forage usually utilized as cool season species in subtropical and temperate regions. For both species, however, there is a reduced number of scientific works related to the nodule type and biological nitrogen fixation (BNF). This work had the purpose to analyze such processes in these species and also to compare their morphological development under different nitrogen sources: mineral-N (ammonium nitrate - 5%), symbiotic-N (inoculation) and without nitrogen (control). The experiment was carried out in greenhouse conditions, utilizing Leonard Jars with nutritive solution; the substrate consisted of mixture of sand, vermiculite and charcoal. It was a randomized complete design with four replications. At the end of 65 days the plants were harvested and evaluated for length and volume of roots, number and weight of nodules, dry matter (DM) accumulation and BNF. A. latifolia stand out for the character number of nodules (126/jar) and total nodule weight (82.22 mg DM/jar) as compared to birdsfoot trefoil with 82 nodules/jar and 20.25 mg DM/jar. The BNF was more effective in A. latifolia, whose inoculated plants produced an average of 37% of DM that was obtained by plants supplied with mineral-N, while birdsfoot reached only 15% of DM production with BNF. The amount of symbiotic fixed nitrogen was 43.12 mg N/jar in Adesmia and 9.92 mg in birdsfoot trefoil.