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1.
Brauns’ lignins present in the methanol extracts of fresh birch (Betula pendula) xylem and of sawn birch board subjected to vacuum drying were characterized by 1H and 13C NMR spectroscopy (1D and 2D), IR spectroscopy, gel permeation chromatography (GPC) and colour measurements (CIELab) in order to find out whether Brauns’ lignin could contribute to the colour change of sawn timber that occurred during vacuum drying. The two Brauns’ lignin samples contained about equal amounts of syringylpropane and guaiacylpropane units linked with β-O-4 and β–β side-chain structures. Molecular weight of the Brauns’ lignin of vacuum-dried birch board (acetylated: 5,200 g mol−1) was higher than that of the Brauns’ lignin of fresh birch wood (acetylated: 4,400 g mol−1). The Brauns’ lignin of vacuum-dried wood was also clearly darker and more prominently yellow and red; between the Brauns’ lignin samples was 23.59. The differences in the molecular weights and colours suggest that the Brauns’ lignin underwent a chemical change during vacuum drying of the wood and that this change may have affected the colour of the wood.  相似文献   

2.
Chemical changes in cell wall components of bamboo internode during steam explosion process were analyzed to investigate self-binding mechanism of binderless board from steam-exploded pulp. More than 30% of xylose on initial mass, which is a major hydrolyzate of bamboo hemicelluloses, was lost after steam explosion treatment. Bamboo lignin is characterized by the presence of ester- and/or ether-linked p-coumaric acid to lignin. The content of phenolic hydroxyl groups of lignin isolated from steam-exploded pulp was characterized 2.3 times higher than those of the extract-free bamboo internode due to the cleavage of β-O-4 linkages. Alkaline nitrobenzene oxidation of the bamboo lignin gave vanillin, syringaldehyde and p-hydroxybenzaldehyde as major products. The content of p-hydroxybenzaldehyde decreased after steam explosion treatment, indicating the cleavage of ester- and/or ether-linked p-coumaric acid. The total yield of erythronic and threonic acids in ozonation products of the extract-free bamboo internode lignin was 268 mmol (200 g lignin)−1, while those of lignins in the steam-exploded pulp and powdery fraction were 96 and 129 mmol (200 g lignin)−1, respectively, suggesting the significant cleavage of β-O-4 linkages during steam explosion treatment. The cleavage of β-O-4 linkages was also confirmed by 1H- and 13C-NMR spectroscopic observations.  相似文献   

3.
The colour parameters (CIE L*a*b*) of black locust (Robinia pseudoacacia L.) wood meals extracted with seven solvents and heated under saturate vapour at 120°C are measured and the UV–vis spectrum analysis of dioxane extractives is performed to investigate the influence of extraction and thermal treatment on wood discolouration. The results show that extractions with polar solvents such as water, ethanol and dioxane can cause substantial decrease of b* but have little effect on a* and that extractions with less or non-polar solvents such as chloroform, ether and hexane can hardly influence both a* and b*. Extractions with ethanol and dioxane can also increase the optical reflection (L*) and arise a higher ΔE change than that with less or non-polar solvents. Heat treatment has much more influence on colour parameters than extractions do. After heat treatment, the lightness index of all the samples declines but a* value increases. The discolouration during thermal treatment is mainly due to the existence of polar extractives. Tannins, flavonoids and hydroxyanthraquinones are found in the dioxane extractives. The heated dioxane extractives have an obvious absorption between 400 and 600 nm. The condensation of the tannin molecules and the oxidation of the hydroxyl groups in flavonol molecules make up the potential reason of the formation of new colour substances during heat treatment. The elimination of the dioxane extractives can effectively reduce the extent of thermally induced discolouration.  相似文献   

4.
A series of experiments were carried out to investigate the colour stability of chemically treated and thermally modified wood compared to non-modified wood during long term artificial UV light irradiation. One set of wood samples was vacuum-pressure impregnated with alkaline (pH 9.8) copper (II) ethanolamine aqueous solution, while another set of samples from the same wood block was thermally modified at 210°C and −0.90 bar for 2 h. The treated and modified wood samples along with the non-modified ones were exposed to artificial UV light with the wave length in the region of UVA (315–400 nm) and UVB (280–315 nm) intermittently for 500 h. Colour measurements were carried out throughout the irradiation period at an interval of 100 h according to CIEL*a*b* system, where the results are presented in terms of ΔE, ΔL*, Δa* and Δb* values. Better photo-stability in terms of colour changes was recorded for both treated and modified woods compared to the non-modified one. By means of EPR and DRIFT spectroscopic study it was shown that some degree of colour stability of treated and modified woods, achieved during artificial UV light irradiation, resulted from lignin modifications and monomers of phenolic compounds.  相似文献   

5.
This study aims to evaluate the chemical composition of wood and extractives of Pinus taeda and Schizolobium parahyba (guapuruvu) as potential feedstock for new applications in the biorefinery industry. For this purpose, their content of α-cellulose, hemicellulose, insoluble lignin, hot water solubility, NaOH1% solubility, inorganic materials (ash), and monomeric sugars by high-performance liquid chromatography was quantified. Attenuated total reflectance infrared spectroscopy and thermogravimetric analysis were also used to complete the physicochemical characterization of the studied woods. The extractives were obtained by soxhlet extraction with ethanol:toluene and dichloromethane and identified with pyrolysis-gas chromatography/mass spectroscopy technique. The results showed that guapuruvu wood has the higher amount of hemicellulose (16%) when compared to pine wood (10%), which resulted in higher solubility in alkali solution. Furthermore, in relation to other biomasses, the two woods presented more percentage of lignin and minor content of hemicelluloses. The P. taeda wood presented the highest percentage of extractives mainly composed of fatty acids and aromatic hydrocarbons, while guapuruvu wood had a higher percentage of phenolic compounds and also fatty acids. Both the materials have low content of extractives with dichloromethane and were mainly composed of lipophilic compounds.  相似文献   

6.
Heat treatment of Pinus pinaster and Eucalyptus globulus wood was carried out by hot air in an oven for 2–24 h at 170–200°C and by steam in an autoclave for 2–12 h at 190–210°C. The colour parameters L*, a* and b* were determined by the CIELAB method on radial, tangential and transverse sections of untreated and treated wood, and their variation with regard to the treatment (ΔL*, Δa* and Δb*) were calculated in percent. For untreated eucalypt wood, lightness (L*) varied between 54.1 and 63.8% with a* between 7.4 and 8.5, and b* between 15.7 and 19.9. For untreated pine wood, L* varied between 67.3 and 76.1%, a* between 6.9 and 7.6 and b* between 16.3 and 24.1. Oven heat-treated wood became darker (ΔL* about 50% for 4% mass loss), and this was more for eucalypt wood under the same treatment conditions. In general, the contribution of red (a*) and yellow (b*) colour decreased with heat treatment. The transverse section of the two species darkened less for both the treatments with small differences between radial and tangential sections. Lightness decrease was related to chemical changes; with good correlations with glucose (R 2 = 0.96), hemicelluloses (R 2 = 0.92) and lignin (R 2 = 0.86). As regards colour, the heat treatments showed an interesting potential to improve the wood quality for solid timber products from pine and eucalypt.  相似文献   

7.
The above-ground biomass and production, below-ground biomass, nutrient (NPK) accumulation, fine roots and foliar characteristics of a 8-year-old silver birch (Betula pendula) natural stand, growing on abandoned agricultural land in Estonia, were investigated. Total above-ground biomass and current annual production after eight growing seasons was 31.2 and 11.9 t DM ha−1, respectively. The production of stems accounted for 62.4% and below-ground biomass accounted for 19.2% of the total biomass of the stand. Carbon sequestration in tree biomass reaches roughly 17.5 t C ha−1 during the first 8 years. The biomass of the fine roots (d < 2 mm) was 1.7 ± 0.2 t DM ha−1 and 76.2% of it was located in the 20 cm topsoil layer. The leaf area index (LAI) of the birch stand was estimated as 3.7 m2 m−2 and specific leaf area (SLA) 15.0 ± 0.1 m2 kg−1. The impact of the crown layer on SLA was significant as the leaves are markedly thicker in the upper part of the crown compared with the lower part. The short-root specific area (SRA) in the 30 cm topsoil was 182.9 ± 9.5 m2 kg−1, specific root length (SRL), root tissue density (RTD) and the number of short-root tips (>95% ectomycorrhizal) per dry mass unit of short roots were 145.3 ± 8.6 m g−1, 58.6 ± 3.0 kg m−3 and 103.7 ± 5.5 tips mg−1, respectively. In August the amount of nitrogen, phosphorus and potassium, accumulated in above ground biomass, was 192.6, 25.0 and 56.6 kg ha−1, respectively. The annual flux of N and P retranslocation from the leaves to the other tree parts was 57.2 and 3.7 kg ha−1 yr−1 (55 and 27%), respectively, of which 29.1 kg ha−1 N and 2.8 kg ha−1 P were accumulated in the above-ground part of the stand.  相似文献   

8.
1 Introduction Agricultural residues are an important renewable bio- mass resource. The annual production is more than 600 million tons in China. With the reduction of fossil fuel resources, the new trend is to acquire chemicals and energy from renewable resources. To produce green chemicals and clean fuels by developing bio- mass, biorefinery technology is one of the more promising technologies and objectives. Bagasse consists of cellulose, hemicellulose and lignin. Earlier studies have sho…  相似文献   

9.
The effect of ultraviolet-visible light irradiation on changes in surface chemistry and morphology of moso bamboo (Phyllostachys pubescens Mazel) was investigated. Fourier transform infrared (FT-IR) and FT-Raman spectroscopy were used in combination to study chemical changes induced by exposure to artificial sunlight (xenon lamp) for up to 160 h, and the resulting physical changes of cell walls of bamboo surfaces were examined by scanning electron microscopy (SEM). FT-IR results showed that significant changes occurred in the lignin component as indicated by considerable decreases in the intensities of the characteristic aromatic lignin peak at 1512 cm−1 and other associated bands. This was accompanied by formation of new carbonyl groups at 1735 cm−1, resulting in photooxidation of bamboo surfaces. The photosensitive nature of bamboo lignin was also demonstrated by FT-Raman analysis, in which obvious decreases in intensities of Raman bands at 1604 and 1630 cm−1 mainly derived from lignin and free and esterified p-coumaric and ferulic acids were observed. SEM micrographs of the irradiated cross sections of bamboo revealed that significant damage occurred to the fiber walls, whereas the parenchyma cells exhibited slight distortion and some cracks occurred in the cell walls. The structures of cell corners and middle lamellae were nearly intact after irradiation.  相似文献   

10.
In order to understand the structural characteristics of lignin in triploid clones of Populus tomentosa and its changes in the processes of pulping and bleaching, milled wood lignin (MWL), lignin carbohydrate complex (LCC) and the residual lignin from kraft pulp (KP) and sulfite pulp (SP) were isolated and analyzed by Fourier transform infrared (FTIR) spectrum and 13C nuclear magnetic resonance (NMR). The most diagnostic peaks were assigned and the differences were discussed. The spectral patterns reveal that triploid P. tomentosa shows the specific features of hardwood from temperate areas, but in the spectrum of FTIR, the strength ratio of A 1270 cm−1 to A1226 cm−1 is 0.88, higher than the average of hardwood from temperate areas, which will make the lignin delignification more difficult during pulping and bleaching. The LCC from triploid P. tomentosa is mainly composed of xyloglucan and glucuronic acid, and other glucides have much lower ratio. In LCC FTIR, there are three peaks at 1 427, 1 329 and 1 046 cm−1, indicating that both semi-cellulose and cellulose could exist in LCC, and that there might be relationships between cellulose and lignin. Compared with the residual lignin from KP and SP, the condensed structure in KP is more than that in SP.  相似文献   

11.
The gymnemic acid contents in various organs of Gymnema sylvestre were investigated by High Performance Liquid Chromatography (HPLC) method. The results shows that the content of gymnemic acid in various organs, obviously different, was 54.29, 31.66, 28.82, 27.67, 25.39, 20.56 and 1.31 mg·g−1 DW in shoot tips, flowers, nodes, leaves, internodes, roots and seeds, respectively. The highest gymnemic acid content (54.29 mg·g−1 DW) was found in shoot tip, 1.96 fold higher than that in leaves (27.67 mg·g−1 DW). Maximum quantity of gymnemic acid (35.39 mg·g−1 DW) was observed in the young leaves, which was 1.52 times higher than that in old leaves (23.07 mg·g−1 DW). The content of gymnemic acid in young, middle and old internodes was 26.47, 25.77 and 23.94 mg·g−1 DW, respectively, all lower than that in leaves (27.67 mg·g−1 DW), whereas the content of gymnemic acid in young, middle and old nodes was 27.96, 28.81 and 29.66 mg·g−1 DW, respectively, all higher than that in leaves. The study provides the scientific evidences for the rational development and utilization of Gymnema sylvestre resources, since over exploitation of natural stands has caused depletion of these plants in nature. Foundation project: This work was supported by University Grants Commission, New Delhi (No. 33-88/2007 (SR))  相似文献   

12.
Structural characterization of lignin from wheat straw   总被引：1，自引：0，他引：1  
Enzyme/mild acidolysis lignin (EMAL) was isolated from wheat straw. The structural characterization of wheat straw EMAL was investigated by FT-IR, 1H NMR, quantitative 31P NMR and DFRC, and DEPT CH (θ = 135C°) techniques. The wheat straw EMAL was a GSH-lignin with β-O-4′ structures and several condensed units (β-5′, β-β′, β-1′, 5-5′) and vinyl ether moieties; the contents of DBDO substructures and total β-aryl ether in the wheat straw EMAL were 0.257 mmol·g−1 and 0.818 mmol·g−1, respectively. Meanwhile, the structure features of the hemicelluloses residues attached to lignin were also investigated using DEPT CH (θ = 135C°) spectra.  相似文献   

13.
Morphology and vertical distribution patterns of spruce and beech live fine roots (diameter ≤2 mm) were studied using a soil core method in three comparable mature stands in the Solling: (1) pure beech, (2) pure spruce and (3) mixed spruce–beech. This study was aimed at determining the effects of interspecific competition on fine root structure and spatial fine root distribution of both species. A vertical stratification of beech and spruce fine root systems was found in the mixed stand due to a shift in beech fine roots from upper to lower soil layers. Moreover, compared to pure beech, a significantly higher specific root length (SRL, P<0.05) and specific surface area (SSA, P<0.05) were found for beech admixed with spruce (pure beech/mixed beech SRL 16.1–23.4 m g−1, SSA 286–367 cm2 g−1). Both indicate a flexible ‘foraging’ strategy of beech tending to increase soil exploitation and space sequestration efficiency in soil layers less occupied by competitors. Spruce, in contrast, followed a more conservative strategy keeping the shallow vertical rooting and the root morphology quite constant in both pure and mixed stands (pure spruce/mixed spruce SRL 9.6/7.7 m g−1, P>0.10; SSA 225/212 cm2 g−1, P>0.10). Symmetric competition belowground between mixed beech and spruce was observed since live fine roots of both species were under-represented compared to pure stand. However, the higher space sequestration efficiency suggests a higher competitive ability of beech belowground.  相似文献   

14.
We investigated the impact of residual extractives on lignin determination by lignin content difference between unextracted and extracted pulps, residual extractives analysis, and lignin content contribution from model extractive compounds. There were two different kinds of extractives in aspen kraft pulp. The extractives impacting on kappa number determination were well removed in oxygen delignification; these were mainly unsaturated fatty acids. However, the extractives impacting on Klason lignin determination were largely resistant to oxygen delignification; these were mainly saturated fatty acids, sterols, and hydrocarbons. Oxidation of unsaturated fatty acids was the main reaction in oxygen delignification. These trends were confirmed by simulation of lignin content determination with three model extractive compounds (β-sitosterol, linoleic acid, and palmitic acid). The publication of this article was made possible by an Emachu Research Fund. The authors are grateful for the fund.  相似文献   

15.
A study to determine the best vegetative propagation protocol was carried out for two species of the endemic genus Cloezia for conservation and mining revegetation activities in New Caledonia. Effects of clonal capacities and auxin treatments on rooting of C. buxifolia and C. aquarum semi-hardwood cuttings taken from wild populations were evaluated in four experiments. Different phenotypes varied in their capacity to root (from 0 to more than 80%) and this underlines the importance of collecting cuttings from different plants when revegetation programs are based on vegetative propagation. The experiments evaluated the effectiveness of IBA at 5, 10 and 20 g kg−1, IAA at 5 and 10 g kg−1 and NAA at 1 and 2 g kg−1 treatments to enhance rooting of C. buxifolia tip cuttings and C. aquarum tip and stem cuttings compared to control cuttings with no applied auxin. With the exception of IAA, auxin treatments enhanced the percentage of cuttings with roots and significantly improved the number of roots per cutting and root length. In this study, the best treatment is 10 g kg−1 IBA for C. buxifolia. For C. aquarum, 20 g kg−1 IBA significantly enhances quantitatively and qualitatively rooting of both tip and stem cuttings.
Résumé  Cette étude porte sur la définition d’un protocole de multiplication végétative optimale de deux espèces du genre endémique Cloezia dans un but de conservation et de revégétalisation en Nouvelle-Calédonie. Quatre essais visent à déterminer les potentialités clonales de différents individus et l’effet de divers traitements hormonaux sur l’enracinement de boutures de C. buxifolia et C. aquarum. L’enracinement des boutures dépend du pied-mère sur lesquelles elles sont récoltées et peut varier de 0 à plus de 80%, ce qui indique l’intérêt de la méthode d’échantillonnage lors de la collecte des boutures. L’effet de traitements hormonaux à base d’AIB, AIA et ANA à différentes concentrations, respectivement de 5, 10 et 20 g kg−1, 5 et 10 g kg−1 et 1 et 2 g kg−1 est également étudié sur des boutures de tête de C. buxifolia et des boutures de tête et de tige de C. aquarum. Ces traitements améliorent le pourcentage d’enracinement et augmentent significativement le nombre de racines produites et la longueur des racines des boutures de Cloezia, à l’exception des traitements à base d’AIA. Dans cette étude, le meilleur traitement est 10 g kg−1 d’AIB pour C. buxifolia et 20 g kg−1 d’AIB pour C. aquarum.
  相似文献   

16.
Effects of side chain hydroxyl groups on pyrolytic β-ether cleavage of phenolic model dimers were studied with various deoxygenated dimers under pyrolysis conditions of N2/400°C/1 min. Although phenolic dimer with hydroxyl groups at the C α − and C γ −positions was much more reactive than the corresponding nonphenolic type, deoxygenation at the C γ -position substantially reduced the reactivity up to the level of the nonphenolic type. These results are discussed with the cleavage mechanism via quinone methide intermediate formation, which is activated through intramolecular hydrogen bonds between C α − and C γ − hydroxyl groups.  相似文献   

17.
Test samples of Japanese larch (Larix leptolepis) heartwood and Japanese beech (Fagus crenata) sapwood were heated for 22 h at constant temperatures (50°–180°C) under three water content conditions. Raman spectra of the samples were recorded before and after the heat treatments, and spectral changes in the range from 1000 cm−1 to 1800 cm−1 were evaluated using the difference spectrum method. For both wood species, the Raman band intensity at 1655–1660 cm−1 due mainly to the C=C and C=O groups in lignin clearly decreased with increasing heat-treatment temperature (HTT). The spectral change was thought to reflect the progress of condensation reactions of lignin molecules during the heat treatment. Moreover, the decrease in band intensity was considerably facilitated by the presence of water in the cell wall, suggesting that the condensation is closely related to the softening of lignin. From the spectral changes in the wavenumber region of 1200–1500 cm−1, it was considered that wood constituents are partially decomposed at the higher HTT. Part of this article was presented at the 53rd Annual Meeting of the Japan Wood Research Society, Fukuoka, March 2003  相似文献   

18.
An investigation was carried out in an Entisol at farmers’ field in Jaipur district, Rajasthan, India during 2002–2004 to evaluate the effect of traditionally grown trees on soil biological characteristics. Traditionally grown trees in farm lands for study consisted of Prosopis cineraria (L.), Dalbergia sissoo (Roxb.) ex DC, Acacia leucophloea (Roxb.) and Acacia nilotica (L.) Del. having a canopy diameter of 8 m. Results revealed significant and substantial improvement in soil biological activity in terms of microbial biomass C, N and P, dehydrogenase and alkaline phosphatase activity under different tree based agroforestry systems as compared to a no tree control (cropping alone). Soil microbial biomass C, N and P under agroforestry varied between 262–320, 32.1–42.4 and 11.6–15.6 μg g−1 soil, respectively, with corresponding microbial biomass C, N and P of 186, 23.2 and 8.4 μg g−1 soil under a no tree control. Fluxes of C, N and P through microbial biomass were also significantly higher in P. cineraria based land use system followed by D. sissoo, A. leucophloea and Acacia nilotica in comparison to a no tree control. Thus, it is concluded that agroforestry system at farmers’ field enhance soil biological activity and amongst trees, P. cineraria based system brought maximum and significant improvement in soil biological activity.  相似文献   

19.
The bark ofPteroceltis tatarinowii is a raw material for manufacturing Xuan Paper. The effects of Ca2+ concentrations on the accumulation of mineral elements in the bark, leaf and root ofPteroceltis tatarinowii were studied under controlled conditions. The types of Hoagland nutrient solution with three Ca2+ concentrations levels (200, 400 and 600 μg·g−1) and a control (without Ca2+ were designed to culturePteroceltis tatarinowii. After 6 months, contents of seven mineral elements including Ca, K, Mg, Mn, Zn, Cu and Na in the root, leaf and bark were analyzed. The results indicated that Ca accumulations content in the root, leaf and bark had positively relation with Ca2+ concentrations (200, 400, 600 μg·g−1), and the order of the Ca content in the three components was root>leaf>bark. Ca content in the root treated with 600 μg·g−1 Ca2+ concentrations was 5.5 times as high as that of the control, and about 1.4 times as high as that of the root treated in 200 and 400 μg/g Ca2+ concentrations respectively. On the contrary, K and Mg contents in the root, leaf and bark were negatively related to Ca2+ concentrations, especially in the bark, and their accumulation trend followed the order of leaf>root>bark. K content in the bark treated with 600 μg·g−1 Ca2+ concentrations was 39.3% of that of the control, and was 79.0% and 91.8% of that of the bark treated with 200μg·g−1 and 400μg·g−1 Ca2+ concentrations respectively; Mg content in the bark treated with 600μg·g−1 Ca2+ concentrations was 23.4% of that of the control, and was 27.1% and 35.4% of that of the bark treated with 200 and 400 μg·g−1 Ca2+ concentrations respectively. Compared with the control, the general tendency of Mn, Zn and Cu content decreased with increasing of Ca2+ concentrations and their contents were in the order: root>leaf>bark. Based on the results of this study, the experiment has been useful for providing academic bases in improving the bark quality ofPteroceltis tatarinowii on non-limestone soil. Foundation item: This paper is supported by National Natural Science Foundation of China (No. 39970608). Biography: Fang Shengzun (1963), male, Professor in Stiiviculture, Nanjing Forestry University, Nanjing 210027, P.R. China. Responsible editor: Zhu Hong  相似文献   

20.
Information is lacking on the potential of leguminous fodder trees such as Leucaena leucocephala as a feed resource to supplement the native forages in traditional grazing management systems in the tropics. Two studies were conducted (1) to assess traditional fodder banks’ forage nutritive potential on animal production, and (2) to investigate the effect of Leucaena leucocephala leaf meal (LLM) supplementation on growth of steers grazing standing hay basal forages in the dry season. The traditional forages had low nutritive values indicated by low mean crude protein (CP) of 23 g kg−1 dry matter (DM), and high fibre contents of 717, 546 and 153 g kg−1 DM for neutral detergent fibre (NDF), acid detergent fibre (ADF) and acid detergent lignin (ADL), respectively. The forages were poorly degraded in sacco and had low metabolisable energy (ME) (4.2–4.6 MJ kg−1 DM). Mean washing losses A, slowly degradable DM fraction, B, potential degradability, (A+B) and mean 48 h DM degradability (DMD) of grazing land forages were 70, 471, 541 and 326 g kg−1 DM, respectively. In the supplementation study, 16 growing steers (160.8±0.24 kg) were randomly allocated into four groups, in a completely randomized design. Four LLM treatment diets (T1, T2, T3 and T4), with four levels: 0, 0.4, 0.6 and 0.8 kg DM for control, low, medium and high LLM levels, respectively, were randomly allocated to the animals in the four groups for 70 days (d). LLM supplementation (p<0.05) improved mean weight gain from −0.30 to 0.26 kg steer−1 d−1, for T1 and T4, respectively. Steers on T4 gained (p<0.05) more weight compared to the animals in T1 and T2, though there was no (p>0.05) difference in weight gains between animals on T3 and T4 (0.14 vs. 0.26 kg steer−1 d−1, respectively). Standing hay basal forages alone could not sustain animal productivity during dry seasons unless corrected for protein. Higher levels of LLM supplementation prevented weight losses and improved the performance of grazing steers, a management practice thought appropriate to low income pastoralists in semiarid western Tanzania.  相似文献   

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