It is postulated that definition of the availability of nutrients in soil t for plant uptake, will not be satisfactory, unless there is consideration of the plant's role as the absorber. The amount of nutrients absorbed by plants from soil can be related to i) the initial concentration in the soil solution, ii) the capacity of the soil to maintain this concentration (the buffer power), iii) the ease of movement of the nutrient to an absorbing root, and iv) the plant demand. These ideas are the foundation of models which successfully describe the nutrient uptake by single roots, growing in an infinite quantity of soil. The aim of the present work was to extend the approach used to explain uptake by single roots, to complete root systems. The requirements for the work are: (i) a theoretical description of nutrient flow to an absorbing, multiple root system; (ii) experiments for examining the proposed hypotheses. When a root absorbs a nutrient, there is a depletion in the nutrient concentration at the root surface. In a system of many roots, the zones of nutrient depletion around each root overlap. This reduces the effective initial concentration in the soil solution. So, in a multiple root system, the soil around each root is limited. The extent of overlap depends on the diffusion coefficient of the nutrient, the plant demand, and the interroot distance. The consequence is a lowering of the concentration at each root surface, below that of a similar root absorbing alone. An electrical analogue (Sanders et al. 1971) of diffusion of solutes to groups of absorbing roots was used to simulate nutrient uptake by plants from soil. The analogue was particularly useful for investigating the general consequences of different plant and soil conditions. To interpret specific plant uptake data, a more flexible computer model of diffusion and mass flow to a root system of variable density, with any specified uptake properties, was developed. For workers interested in an accuracy of ± 20%, an equation for calculating uptake, by systems similar to those which the computer model treats, is presented, which can be solved on a desk calculator. To test the model, experimental data on nutrient uptake, root dimensions and distribution, and soil conditions, during the growth of whole plants in soil was obtained. The computer model predicted the measured plant uptake wall, when values of the plant demand coefficient (which related uptake rate to the external solution concentration) given is the literature, from solution culture work under similar conditions, were used. It is concluded that the theory is an adequate representation of the simple plant-soil system used in the experiments. The expression, relating plant demand to concentration in the soil solution, was simulated on the electrical analogue. The effects of pattern, density, radius and demand coefficient of roots, on the course of uptake of solutes, of varying degrees of mobility, were investigated. Quantitative interrelations between soil and plant characteristics were established, which are discussed in the light of earlier concepts of mobility and availability of nutrients in soil. The uptake of a solute by any root system is roughly determined by the plant demand coefficient and the product of the solute diffusion coefficient, D, the absorption time, t, and the root density, L. The product DtL, for potassium, may often be is the range where root pattern affects uptake. This can be estimated graphically. Theory suggests that the uptake rate of K and K is the plant experiments was reduced by interroot competition. In both experiments, if supply was by physical processes only, the plants were absorbing K from the soil near to a maximum rate, which was set by transport through the soil. In those circumstances, the rate of uptake into a plant is limited by the length of root. Movement through the soil was easily able to supply the plant's requirement of N, until the total quantity was exhausted. It is deduced that this will usually be the case in British arable soils. A major problem, in the experimental determination of plant uptake from soil, results from the inaccessibility of the roots. A technique was devised for estimating the length and pattern of living roots of individual plants, without excessive labour. Radioactive roots are detected by autoradiography as they intersect planes of soil, and the root length par unit volume and rooting pattern follow easily. If two plants are labelled with different isotopes, their root systems can be distinguished. Any spatial interactions between the root systems are detected by the method, and the causes can be inferred. If the roots are extracted from the soil, their length can be automatically measured with an Image Analysing Computer.

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Made available in DSpace on 2015-03-26T13:55:12Z (GMT). No. of bitstreams: 1 texto completo.pdf: 240793 bytes, checksum: eeb362298c55405471ae4aeda1bb3acd (MD5) Previous issue date: 2012-07-18 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / This study aimed to evaluate the effects of the live yeast and inactive yeast autolyzed on the voluntary intake, digestibility coefficient, efficiency of microbial protein synthesis, characteristics of the ruminal environment - pH, volatile fatty acids (VFA), rumen ammonia nitrogen (RAN), and balance of nitrogen compounds of cattle feed with high concentrate levels. The experiment was carried out from November, 2010 to February, 2011. Five Nellore heifers with 300 kg ± 39.5 of initial body weight and fitted with rumen canullaes, were used and distributed in a 5 x 5 Latin square design, with five treatments, five animals and five experimental periods lasting 15 days. These 15 days were divided in seven days to the animal s adaptation and the other eight days were for the collection of data and materials. Five additives/levels in the same basal diet were evaluated, as follow: negative control (without additives); positive control (1% of the diet dry matter of sodium bicarbonate and magnesium oxide in the proportion of 4:1); live yeast (10 g/day); inactive yeast autolyzed in the doses of 15 and 30 g/day. The experimental diets consisted of two concentrates based on corn and soybean meal, that differed only by the presence or absence of sodium bicarbonate and magnesium oxide, containing 20% of corn silage, dry matter basis, and calculated to weight gain of 1.2 kg per animal per day, second NRC (2000). The use of additives didn t alter (P>0.05) dry matter intake (DM), and intake of organic matter (OM), crude protein (CP), ether extract (EE), neutral detergent fiber corrected for ash and nitrogenous compounds (NDFap), non-fiber carbohydrates (NFC) and total digestible nutrients (TDN). Only the EE digestibility coefficient was influenced (P<0.05) by the treatments, showing higher values to the treatments positive control and inactive yeast autolyzed in the dose of 30 g/day; the negative control was the treatment that presented the lower EE digestibility coefficient; the treatments inactive yeast autolyzed in the dose of 15 g/day and live yeast didn t differ from the others. The digestibility coefficient of DM, OM, CP, NDFap, NFC and the content of TDN were not affected (P>0.05) by the treatments. Effects were not detected (P>0.05) among treatments on the nitrogen intake, fecal nitrogen excretion, urinary excretion of nitrogen, balance of nitrogen compounds, nitrogen utilization efficiency in relation to N intake and to N absorbed and efficiency of microbial protein synthesis. There were no treatments effects (P>0.05) on the ruminal pH average, RAN, total production and molar ratio of VFA and in the ratio acetate:propionate. The evaluated blood metabolites, glucose, creatinin and urea, were not influenced (P>0.05) by the studied additives. / Objetivou-se investigar o efeito da levedura viva e levedura inativa autolisada sobre consumo voluntário, coeficientes de digestibilidade, eficiência de produção de proteína microbiana, características do ambiente ruminal - pH, nitrogênio amoniacal ruminal (NAR), ácidos graxos voláteis (AGV) e balanço de compostos nitrogenados de bovinos alimentados com dietas de alto concentrado. O experimento foi conduzido entre novembro de 2010 e fevereiro de 2011. Foram utilizadas cinco novilhas Nelore, de aproximadamente dois anos de idade, com peso corporal médio inicial de 300 ± 39,4 kg, fistuladas no rúmen, distribuídas em delineamento em quadrado latino 5 x 5, com cinco tratamentos e cinco períodos com 15 dias de duração. Destes 15 dias, sete foram destinados à adaptação dos animais e os oito dias restantes para realização de coletas de dados e material.. Avaliou-se cinco diferentes aditivos/níveis em uma mesma dieta basal: controle negativo (sem aditivos); controle positivo (bicarbonato de sódio e óxido de magnésio na proporção de 4:1 da matéria seca da dieta); levedura viva na dose de 10 g/animal/dia e levedura inativa autolisada nas doses de 15 e 30 g/animal/dia. As dietas experimentais consistiram de dois concentrados à base de milho e farelo de soja, que diferiam entre si somente pela presença ou não de bicarbonato de sódio e óxido de magnésio, contendo 20% de silagem de milho, base da matéria seca e calculada para proporcionar ganho de peso de 1,2 kg/animal/dia, segundo o NRC (2000). O uso de aditivos não alterou (P>0,05) o consumo de matéria seca (MS), matéria orgânica (MO), proteína bruta (PB), extrato etéreo (EE), fibra em detergente neutro corrigida para cinzas e proteína (FDNcp), carboidratos não fibrosos (CNF) e nutrientes digestíveis totais (NDT). Somente o coeficiente de digestibilidade (CD) do EE foi influenciado (P<0,05) pelos tratamentos, apresentando maiores valores para os tratamentos controle positivo e levedura autolisada na dose de 30 g/dia; o controle negativo foi o tratamento que apresentou a digestibilidade do EE mais baixa; os tratamentos levedura autolisada na dose de 15 g/dia e levedura viva não diferiram estatisticamente dos anteriores. Os demais CD, CDMS, CDMO, CDPB, CDFDNcp, CDCNF e o teor de NDT não foram afetados (P>0,05) pelos tratamentos. Não foram detectados efeitos (P>0,05) dos tratamentos sobre o consumo de nitrogênio, excreção fecal de nitrogênio, excreção urinária de nitrogênio, balanço de compostos nitrogenados, eficiência de utilização do nitrogênio em relação ao nitrogênio consumido e ao nitrogênio absorvido e eficiência de produção microbiana. Os tratamentos não influenciaram (P>0,05) a média do pH ruminal, a concentração de NAR, a produção total e proporções molares de AGV e a relação acetato:propionato. Os metabólitos sanguíneos avaliados, glicose, creatinina e ureia, não foram influenciados (P>0,05) pelos aditivos estudados.

Made available in DSpace on 2015-03-26T13:55:14Z (GMT). No. of bitstreams: 1 texto completo.pdf: 605913 bytes, checksum: 567cf7b52ccdd329ffc64b287c636d4d (MD5) Previous issue date: 2012-10-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This dissertation was prepared from data generated in two experiments with procedures for the in situ isolation of indigestible neutral detergent fiber (iNDF) and indigestible acid detergent fiber (iADF) using sheep. The first experiment aimed to determine the in situ incubation time needed for the isolation of iNDF, and investigate the occurrence of mineral contamination in long term incubations in sheep. Samples concentrates, roughages and faeces were used. All samples were ground through in a cutting mill utilizing sieve with pores of 2mm diameter. Subsequently, the samples were placed in 4 x 5 cm non-woven textile fabric (NWT - 100g / m²) bags at the rate of 20 mg of dry matter (DM) / cm ² of exposed area and incubated in the rumen of four male sheep. This procedure was repeated four times, and incubated at every period groups among animals. The following incubation times were used: 0, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, 240 and 312 hours. After the bags had been removed, the contents of neutral detergent fiber (NDF) and neutral detergent insoluble ash (NDIA) of the residues were analyzed. The NDF degradation profiles were interpreted independently for each material by a non-linear logistic model. The profiles of availability of mineral associated with undegraded NDF were interpreted by a asymptotic model of the first order. Incubation times in sheep of 168 hours are recommended for isolation of NDFi. The content of mineral associated with undegraded NDF stabilized on average 28,9 hours after incubation, showing that samples were not contaminated by mineral, beyond that naturally associated with NDF. In the second experiment, the objective was to evaluate the influence of concentrate level in the diet on the estimates of roughages iNDF and iADF, and, incubation time needed for the in situ isolation of these fractions in sheep. The following forages were used for in situ procedures: in natura sugarcane, Tifton 85 hay, corn straw and corn silage. The samples processing and packaging were carried out following the procedures used in the first experiment. The treatments consisted on diets with different roughage (R): concentrate (C) proportions: 100V: 0C; 80V: 20C, 60V: 40C, 40F: 60C. Treatments were assigned to four male sheep breed, rumen using a Latin square design 4 x 4. The same incubation times used in the first experiment were applied in this experiment. After removal of the bags, they had their NDF and ADF contents analyzed sequentially. The degradation profiles were initially interpreted individually for each forage in each treatment using a non-linear logistic model. For each incubated roughage, the adjusted models were compared to check the effect of treatments on the indigestible fractions (iNDF and iADF) estimates and the fiber degradation rate. It was observed treatment effect (P <0.05) on the iNDFi and iADF estimates for in natura sugarcane and corn silage. It was observed influence of the treatments (P <0.05) on the degradation rates of NDF and ADF to the four roughages It is recommended that for in situ procedures using sheep fed up to 20% concentrate, incubations times of 120 and 144 hours be used for isolation of iNDF and iADF, respectively. / Esta dissertação foi elaborada a partir de dados gerados em dois experimentos com procedimentos para o isolamento da fibra insolúvel em detergente neutro indigestível (FDNi) e fibra insolúvel em detergente ácido indigestível (FDAi) em procedimentos in situ em ovinos. No primeiro experimento, objetivou-se determinar o tempo de incubação in situ, necessário para o isolamento da FDNi e, investigar a ocorrência de contaminação mineral em amostras incubadas no rúmen de ovinos por longos períodos. Foram utilizadas amostras de alimentos concentrados, volumosos e fezes. Todas as amostras foram processadas em moinho de facas utilizando peneira com poros de 2 mm de diâmetro. Posteriormente, as amostras foram acondicionadas em sacos de tecido não tecido (TNT, gramatura 100g/m²) de dimensão igual a 4 x 5 cm, na proporção de 20 mg de matéria seca(MS)/cm² de superfície exposta e incubados no rúmen de quatro ovinos machos, sem raça definida, fistulados no rúmen. Tal procedimento foi repetido por quatro vezes, incubando-se a cada período os grupos em animais distintos. Utilizaram-se os tempos de incubação: 0, 12, 24, 48, 72, 96, 120, 144, 168, 192, 216, 240 e 312 horas. Após a retirada dos sacos, foram determinados os teores de FDN e cinzas insolúveis em detergente neutro (CIDN). Os perfis de degradação da FDN foram interpretados de forma independente para cada material por meio de modelo logístico não linear. Os perfis de disponibilização da CIDN foram interpretados por meio de modelo assintótico de primeira ordem. Recomenda-se tempo de incubação in situ em de 168 horas para isolamento da FDNi em ovinos. Os teores de CIDN dos resíduos não degradados estabilizaram-se em média 28,9 horas após a incubação, demonstrando que as amostras não apresentaram contaminação mineral além daquela naturalmente associada à FDN. No segundo experimento, objetivou-se avaliar a influência do nível de concentrado da dieta sobre as estimativas da FDNi e FDAi de alimentos volumosos e os tempos de incubação in situ necessários para o isolamento destas frações em ovinos. Foram utilizadas para os procedimentos in situ amostras dos alimentos: cana-de-açúcar in natura, feno de tifton 85, palha de milho e silagem de milho. O processamento e acondicionamento das amostras foram realizados seguindo os procedimentos utilizados no primeiro experimento. Os tratamentos constituíram-se de dietas com diferentes relações volumoso(V):concentrado(C): 100V:0C; 80V:20C; 60V:40C e 40V:60C. Os tratamentos foram designados a quatro ovinos machos, sem raça definida, fistulados no rúmen por meio de um delineamento quadrado latino 4 x 4. Utilizou-se os mesmos tempos de incubação utilizados no primeiro experimento. Após a retirada dos sacos, estes tiveram seus teores de FDN e FDA analisados de forma sequencial. Os perfis de degradação foram inicialmente interpretados de forma individual para cada alimento em cada tratamento através de modelo logístico não linear. Procedeuse, para cada alimento incubado, a comparação entre os modelos ajustados, de modo a verificar o efeito dos tratamentos sobre as estimativas das frações indigestíveis (FDNi e FDAi) e taxa relativa à dinâmica de degradação ruminal. Observou-se efeito de tratamento (P<0,05) sobre a estimativa da FDNi e FDAi da cana-de-açúcar e silagem de milho. Para todos os alimentos foi observada influência dos tratamentos (P<0,05) sobre as taxas de degradação da FDN e FDA. Recomenda-se, para procedimentos in situ, em ovinos alimentados com até 20% de concentrado, a utilização de incubações de 120 e 144 horas, para isolamento da FDNi e FDAi, respectivamente.