Rice Straw Varieties Research Articles

Chemical composition, cell wall features and degradability of stem, leaf blade and sheath in untreated and alkali-treated rice straw

Three dominant morphological fractions (i.e. leaf blade (LB), leaf sheath (LS) and stem) were analysed for chemical composition and ruminal degradability in three rice straw varieties. In one variety treated with alkali, cell wall features were also characterized using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy. The highest concentrations of cell wall carbohydrates (hemicellulose and cellulose) were observed in LS, whereas the highest concentrations of non-fibre (silica, phenolic compounds and CP) and lignin were recorded for LB. The stem had the lowest silica and hemicellulose contents but intermediate levels of other components. In terms of ruminal degradability, stem ranked higher than LB, which was followed by LS. Hemicellulose was found to be less degradable than either dry matter or cellulose in all the three fractions investigated. FTIR results indicated that the highest levels of hydrogen bonding, esterification and crystallinity within the cell wall components belonged to LS. In the alkaline treatment, these indices decreased to a larger extent for leaf fractions and a greater improvement was achieved in the degradability of LB and LS compared with that of stem. In the 24-h ruminal incubation, the silicified layer of epidermis and the underlying cell walls showed a rigid structure in the control fractions, whereas the treatment with NaOH resulted in crimping of the silicified cuticle layer and the loss of integrity in cell structure. Despite the highest silica and lignin contents observed in LB, LS showed the lowest degradability, which might be due to its high level of hydrogen bonding, crystallinity and esterification within its cell wall components as well as its high hemicellulose content.

Cellulose solvent- and organic solvent-based lignocellulose fractionation enabled efficient sugar release from a variety of lignocellulosic feedstocks

Developing feedstock-independent biomass pretreatment would be vital to second generation biorefineries that would fully utilize diverse non-food lignocellulosic biomass resources, decrease transportation costs of low energy density feedstock, and conserve natural biodiversity. Cellulose solvent- and organic solvent-based lignocellulose fractionation (COSLIF) was applied to a variety of feedstocks, including Miscanthus, poplar, their mixture, bagasse, wheat straw, and rice straw. Although non-pretreated biomass samples exhibited a large variation in enzymatic digestibility, the COSLIF-pretreated biomass samples exhibited similar high enzymatic glucan digestibilities and fast hydrolysis rates. Glucan digestibilities of most pretreated feedstocks were ∼93% at five filter paper units per gram of glucan. The overall glucose and xylose yields for the Miscanthus:poplar mixture at a weight ratio of 1:2 were 93% and 85%, respectively. These results suggested that COSLIF could be regarded as a feedstock-independent pretreatment suitable for processing diverse feedstocks by adjusting pretreatment residence time only.

Evaluation of the life cycle of bioethanol produced from rice straws

This study evaluated the life cycle of bioethanol produced by enzymatic hydrolysis of rice straw. Net energy consumption, CO2 emission and production costs were estimated to determine whether environmentally preferable and economically viable bioethanol can be produced from rice straws. Two varieties of rice straw (Koshihikari and Leafstar), three energy scenarios (F-E-RH: Fuel-Electricity-Residues used for Heat; F-E-RE: Fuel-Electricity-Residues used to generate Electricity; F-RE: Fuel-Residues used to generate Electricity) and three types of primary energy (heavy oil; LNG: liquefied natural gas; agri-residues) were considered. The net energy consumption, CO2 emission and production costs were estimated to be 10.0–17.6MJ/L, −0.5 to 1.6kg/L and 84.9–144.3¥/L (1 US$≈100¥), respectively, depending on the feedstock and scenarios of this study. A shift in energy scenarios or in the type of primary energy (heavy oil to LNG or agri-residues) not only reduces emissions and production costs of bioethanol from rice straw, but may also reduce the fluctuation in production cost over time and risk on investment, which would encourage more investment in this sector.

A techno-economic and environmental evaluation of the life cycle of bioethanol produced from rice straw by RT-CaCCO process

Japan has set an ambitious goal to produce bioethanol from abundant biomass in views to offset some of her greenhouse gas (GHG) emissions. This study attempts to evaluate the life cycle of bioethanol produced from the most common variety of rice straw in Japan (cv. Koshihikari) by enzymatic hydrolysis. Three scenarios are established in the evaluation process. The net energy consumption, CO2 emission and production costs are estimated to determine if environmentally friendly and economically viable bioethanol can be produced from rice straw in Japan. The net energy consumption, CO2 emission and production costs are estimated to be 10.43–11.56 GJ/m3, 1106.34–1144.94 kg/L and 88.54–137.55 k¥/m3 (1 US$≈100¥), respectively depending on the scenarios of this study. This study reveals that despite a bit of environmental benefits, the economic viability is doubtful unless innovative technologies along with the renewable energy policy and stakeholders participation are considered. A shift in scenarios not only reduces the production cost, but may also minimize the risk of soil degradation and productivity loss and encourage more stakeholder participation and investment in the bioethanol industry in Japan.

Improvement of Fermentation Quality of Rice Straw Silage by Application of a Bacterial Inoculant and Glucose

The improvement of the fermentation quality of rice straw silage by application of lactic acid bacteria (LAB) and glucose was investigated in this study. Sixteen rice varieties were harvested at the maturity stage and the rice straw was ensiled with LAB inoculant (1×10 5 cfu/g of fresh weight) and glucose (2% of fresh weight). Inoculation with LAB improved the fermentation as reflected in reductions in pH, acetic acid (by 3.7 to 78.3%), butyric acid (by -6.0 to 100.0%) and ammonia nitrogen (by 1.0 to 71.7%) concentrations, and increases in lactic acid (by 43.9 to 282.9%) and crude protein concentrations compared with the control. Application of LAB plus glucose was more effective in improving fermentation quality than LAB alone. The variety of rice straw which contained relatively high levels of water soluble carbohydrates (WSC) tended to obtain better fermentation quality. The results suggested that LAB application and selection of rice varieties whose straw contained high levels of WSC were effective in improvement of the fermentation quality of rice straw silage.

The response of rice straw varieties to urea treatment

Sixteen rice straw varieties comprising 6 single-crop and 10 double-crop varieties were treated with 40 g/l urea solution (50 g straw per 200 ml of solution) for 21 days at 27 °C and total and insoluble ash, crude protein, neutral detergent fibre and in vitro digestibility (IVD) were measured after samples were dried at 60 °C to constant weight. The mean IVD values across treatments for the single-crop varieties were 0.500, 0.480, 0.418 and 0.499 for all fractions (whole straw, stem, leaf sheath, and leaf blade), corresponding values for the double-crop varieties were higher, 0.560, 0.598, 0.542 and 0.627, respectively. The untreated IVD values across varieties were 0.496, 0.497, 0.404 and 0.462 for whole straw, stem, leaf sheath, and leaf blade; and for urea treated, 0.564, 0.581, 0.556 and 0.665, respectively. Urea treatment caused a decrease in neutral detergent fibre exclusive of residual ash (NDFom) and in increase in IVD of all fractions ( P<0.001). Single-crop fractions were all lower in IVD ( P<0.001), and all fractions except whole straw were higher in NDFom ( P<0.05) than double-crop varieties. Based on criterion variables selected from step-wise discriminant analysis, single- and double-crop varieties clustered separately before but together after urea treatment which may be important in selecting genetic varieties. Regression analysis showed, in general, fractions with a lower IVD intercept responded better to urea treatment evaluated by relatively higher regression coefficients of 0.39, 0.67, 0.79 and 0.80, respectively for whole straw, stem, leaf sheath, and leaf blade. The effect of the untreated stem, leaf sheath, and leaf blade IVD on the IVD of untreated and urea-treated whole straw was described by single and multiple regressions where the most important fraction was the leaf blade IVD for urea-treated whole straw IVD and the leaf sheath IVD for the untreated whole straw IVD. Multiple regressions, although they had higher R 2, did not show any fraction to be more important than found in the simple regressions. It is concluded that although urea-treatment may result in a better response in poorer quality straws, rice straw varieties with a high leaf sheath IVD would improve the quality and utilisation of whole straw without urea treatment whereas high leaf blade IVD would improve the quality and utilisation of whole straw with urea treatment.

Rumen fermentation and microbial biomass synthesis indices of tropical feedstuffs determined by the in vitro gas production technique

This study was conducted to establish rumen fermentation characteristics and microbial biomass synthesis indices for the feed ingredients commonly used in the manufacturing of compounded cattle feeds and/or in feeding large ruminants in Bangalore and surrounding districts of Karnataka state, India. The feed samples selected for the study included 8 protein sources, 9 energy sources, 8 varieties of finger millet straw (FMS) and 12 varieties of rice straw (RS). The fermentation characteristics were studied by measuring the gas production in vitro and by fitting cumulative gas production against time of incubation in the exponential model, Y = D [1 − e − k* t ], where Y is gas volume at time t, D is potential gas production (ml/g DM) and k (h −1) is rate at which gas is produced. The D and k for protein sources, energy sources, FMS and RS were 234.7 ± 53.1 and 0.123 ± 0.032, 402.8 ± 51.8 and 0.076 ± 0.021, 261.6 ± 16.4 and 0.064 ± 0.011, 254.8 ± 16.8 and 0.033 ± 0.005, respectively. The feed samples were incubated again to determine the cumulative gas production and true digested organic matter (TDOM) at time of half asymptotic gas production ( t 1/2). The TDOM was calculated as the difference between OM incubated and the OM residue at t 1/2 after refluxing with neutral detergent solution. The ratio of milligram TDOM to milliliter gas produced at t 1/2 (partitioning factor (PF)) was regarded as an index of efficiency of microbial biomass synthesis (EMBS) on the assumption: (i) carbon of TDOM is quantitatively distributed between microbial biomass and the sum of fermentative gas and short chain fatty acids (SCFAs); and (ii) gas production is stoichiometrically related to SCFAs. The PF, for the respective group of feedstuffs varied from 3.86 to 6.48, 3.28 to 4.53, 2.73 to 3.72 and 2.55 to 3.23. Using ingredients for which the PF was determined, six mixed diets were formulated to differ in PF with finger millet straw as roughage component (700 g/kg as is) across all the diets. Evaluation of these diets for gas production and PF revealed significant associative effects up to 12 h after incubations. Therefore, it is concluded that the range in the PF of the tested feed ingredients is wide enough to facilitate ingredient selection for higher PF or in other words higher EMBS. However, since the associative effect of ingredients influence gas production and PF of mixed diets, the limitations in using gas production kinetics and PF of the ingredients to achieve a desirable fermentation characteristics of mixed diets should be realized.

The degradability of straw from single‐ and double‐crop rice varieties

AbstractThe degradation of two single‐crop and six double‐crop rice straw varieties was compared before and after urea treatment. The single‐crop varieties were taller, later maturing, lower in grain yield, contained more stem and were lower in the degradability of their straw than the double‐crop varieties before urea treatment. This suggests that breeding for improved agronomy could also improve the straw. Single‐crop varieties responded better to urea than the double. Principal component and cluster analyses showed that the distinction between single‐ and double‐crop varieties before urea treatment were not evident after it. The leaf fraction of all straw varieties responded better than the stem to urea. Copyright © 2003 Whurr Publishers Ltd

The effect of agronomic improvement and urea treatment on the nutritional value of Malaysian rice straw varieties

The objectives of the study were to estimate the effect of agronomic improvement on rice straw nutritional value and to compare the response of straw varieties to urea treatment. The agronomic characteristics (i.e. grain yield, days to maturity, culm height and morphological composition) and straw characteristics (i.e. chemical composition and in vitro dry matter digestibility (IVD)) before and after 4% urea treatment of two single-crop and six double-crop rice varieties were measured. The single-crop varieties were taller, 89 cm versus 78 cm, late maturing, 130 days versus 122 days, lower in grain yield, 1450 kg/ha versus 4382 kg/ha and contained more stem, 48% versus 28%, than the double-crop varieties. The total ash, neutral detergent fibre (NDF), insoluble ash, IVD and crude protein (CP) of the single-crop varieties averaged 18.0, 60.9, 6.2, 41.2 and 6.0%, respectively, in comparison with 17.8, 63.5, 5.2, 54.0 and 3.3%, respectively, for the double-crop varieties. Covariance-adjusted means of the single-crop varieties after urea treatment were 20.4, 64.5, 6.5, 64.4 and 11.6%, respectively, and corresponding estimates for the double-crop varieties were 19.5, 61.7, 9.2, 59.6 and 5.2%, respectively. The IVD and CP of straw, respectively, improved and declined ( P<0.05) with improvements in agronomic characteristics. The relationship between IVD ( y) and grain yield ( x) was explained by the equation: y=35.9+0.004 x ( P<0.001, R 2=0.91). Varietal response to urea treatment was not uniform with respect to IVD and CP. The relationship between IVD after ( y) and before ( x) urea treatment was explained by the equation: y=41.5+0.38 x ( P<0.01, R 2=0.77) indicating that the single-crop varieties of lower initial IVD responded better to urea treatment. Principal component analysis ranked the single-crop varieties lower than the double-crop varieties based on their agronomic and untreated straw characteristics, but higher in their straw characteristics after urea treatment. Cluster analysis classified the single- and double-crop varieties separately. Consequently, the genetic distance between them was larger than within them. Results show that improving the agronomic qualities of rice may concurrently improve straw characteristics and that urea treatment may be suitable for improving straws of poor quality only.

Rice Straw, It`s Quality and Quantity as Affected by Storage Systems in Bangladesh

The effects of current storage practices on the nutritive quality and the level of mycotoxin contamination of rice straw were studied in four selected villages of Mymensingh district of Bangladesh. Farmers were allowed to store the same variety of rice straw in both improved and traditional systems. Straw samples were collected from both the stores and analysed for nutrient composition and in vitro digestibility. Chemical analysis of rice straw showed that storage methods had no significant (P>0.05) effect on OM, CP and ME contents of rice straw. However, improved storage method significantly (P<0.01) increased nitrogen free extract, in vitro dry matter digestibility and in vitro organic matter digestibility of rice straw compared with those of traditional storage method. Chemical analyses for mycotoxin content in the rice straw of traditional storage showed lower level of Fumonisin and no detectable level of Aflatoxins (B , B , G and G ). The results suggest that 1 2 1 2 improved storage system is essential since it increases the quality of rice straw in respect of nutrient composition as well as in vitro digestibility. A definite conclusion regarding the mycotoxin level can only be made after two or three years of monitoring.

In sacco degradability, chemical and morphological composition of 15 varieties of European rice straw

The aim of this study was to evaluate the variability in chemical and morphological variables of European rice straw varieties and to relate these variations to changes in in sacco degradation. Fifteen rice straw varieties were analyzed for their chemical and morphological compositions. Ground (2 mm) straw was incubated in the rumen of three ruminally cannulated cows for 24 and 72 h for in sacco degradability measurements. Results were analyzed by principal component analysis (PCA) and equations are proposed for degradation of rice straw in the rumen according to morphological and chemical variables. Both chemical and morphological characteristics presented great variability. Mean values, on a dry matter (DM) basis (%), for ash, silica, crude protein (CP), ash-free neutral detergent fiber (NDF), ash-free acid detergent fiber (ADF), and acid detergent lignin (ADL), were 11.2, 6.8, 3.9, 75.8, 45.7 and 9.3 respectively. Mean values, on a DM basis (%), for stem (internodes+nodes), leaf blade, leaf sheath and chaff were 22.7, 32.7, 35.8 and 7.5 respectively. Variation in the in sacco degradation (%) of DM and organic matter (OM) was observed among straw varieties at 24 and 72 h: 30.4 (26.6–36.3) and 50.3 (43.6–57.6) for DM degradation; 29.0 (23.6–35.6) and 50.2 (42.2–58.7) for OM. The principal component analysis discriminated degradation parameters with botanical and chemical parameters. Degradation (%) was positively related to total leaves and leaf blade fractions and hemicelluloses, and negatively related to stem fraction, NDF, cellulose and lignin. Cumulative equation with both leaf blades (morphological variable) and hemicelluloses (chemical variable) explained 62 and 66% of variation in OM degradation at 24 and 72 h, respectively.

Nutritional properties of the leaf and stem of rice straw

The proportion of the leaf blade, leaf sheath and stem fractions in six rice straw varieties averaged 30, 40 and 30%, respectively. In vitro dry matter digestibility (IVD) of these fractions, estimated by the cellulase-neutral detergent solution procedure, was 503, 513 and 610 g/kg, respectively. The lower IVD of the blade and sheath was due to lower degradation parameters estimated by a simple technique of incubating samples in a cellulase-buffer solution at 38°C for 3, 6, 12, 24, 48 and 72 h. Treatment with 4% urea solution for 21 days increased the IVD and the degradation characteristics of the leaf fraction more than the stem but treatment with a 4% sodium hydroxide (NaOH) solution for 21 days improved the IVD and degradability characteristics of all straw fractions to the same extent. The leaf had a lower neutral detergent fibre (NDF), higher total and insoluble ash than the stem. Urea treatment which increased total ash but decreased insoluble ash in the leaf were increased in the stem. NaOH treatment increased total and insoluble ash in all fractions. The NDF content, lower in the untreated leaf compared to the stem, was unaffected by but decreased after urea and NaOH treatment, respectively. Crude protein (CP) content, similar between untreated straw fractions, increased after urea but decreased after NaOH treatment .Principal component scores of the leaf and stem fractions derived from a principal component analysis of the analysed variables showed that the leaf ranked higher in nutritive value than the stem before and after chemical treatment. The high leaf content of modern rice straw varieties should therefore promote the utilisation of rice straw as a ruminant feed.

Differences in the nutritive value of two rice straw varieties as influenced by season and location

Two varieties of rice straw, MR 84 and MR 77, harvested from three locations and over two consecutive cultivation seasons, were compared for their botanical composition, chemical composition and in vitro dry matter digestibility (IVD). For both varieties, botanical composition was not significantly different between seasons ( P > 0.05) but the IVD of whole straw was significantly higher in the main season ( P < 0.01). The proportion of stem and blade and the contents of ash and silica were significantly different between locations ( P < 0.01). Canonical correlations between seasons and between locations were significant ( P < 0.01) and positive for chemical composition and IVD suggesting that varietal differences were consistent across these environmental influences.

The use of multivariate statistics to evaluate the response of rice straw varieties to chemical treatment

The use of multivariate statistics to evaluate the response of rice straw varieties to chemical treatment

A comparison of ten rice-straw varieties grown at two different altitudes during a wet and a dry season, using the in vitro cumulative gas production technique

In vitro cumulative gas production was used to evaluate a series of rice straws for their fermentability. The straws comprised ten different varieties which had been grown at two locations (higher and lower altitudes), during two seasons (wet and dry). Curves were fitted, and the resulting parameters, DM loss and gas yield, were tested for significant differences by an analysis of variance using the Tukey test. Significant differences between the parameters of the fitted curves were found between the offered and refused straw, the material grown at different altitudes, the material from the wet and dry seasons, and between varieties. Significant interactions were found between the environmental factors and cultivar, for the offered and refused feeds.

Factors contributing to varietal differences in the nutritive value of rice straw

The proportion in whole straw, chemical composition and in vitro dry matter digestibility (IVD) of the leaf blade, leaf sheath and stem (including inflorescence) fractions of 32 varieties of rice straw harvested from the same location, year and season, were measured. The composition and IVD of whole straw was then calculated. The mean proportion of blade, sheath and stem was 32.4%, 25.5% and 41.0%, respectively, in whole straw. Stem had a significantly higher IVD (58.9%), lower insoluble ash (6.9%) and lower total ash (18.9%) but a higher neutral detergent fibre (NDF, 62.7%) and lower crude protein (CP, 3.4%) than blade or sheath. For whole straw, the range in composition and IVD was: NDF, 54.2–63.2%; IVD, 44.4–64.7%; CP, 2.0–5.3%; insoluble ash, 6.2–14.4; total ash, 16.6–25.1%. Canonical correlation analysis showed that varietal differences in the composition and IVD of whole straw were significantly correlated ( P < 0.001) with varietal differences in these parameters in the blade, sheath and stem fractions. Varietal differences in whole straw were not significantly correlated ( P > 0.05) to their leaf, sheath and stem proportions or to their agronomic characteristics (culm height, days to maturity and grain yield). There is thus potential for breeding and selecting rice varieties with good straw and agronomic characteristics.

In vitro digestibility studies of some local and high yielding varieties of rice straw ( Oryza sativa)

Five local and four high-yielding varieties (HYV) of rice straw ( Oryza sativa) were analysed for their various chemical constituents. The HYV rice straw samples were found to contain more glucose and xylose residues and less crude protein than those of the local varieties. Ash and silica contents were high in both groups. Extensive in vitro rumen digestibility studies showed that the HYV rice straw generally had higher dry matter disappearance (DMD) and organic matter disappearance (OMD) values compared with the local varieties. The in vitro rumen degradation patterns of cellulose, hemicellulose and bound p-coumaric and ferulic acids in rice straw cultivars ‘BR14’ and ‘Balam’ were similar. Klason lignin degradation was low in both the samples. Alkali treatment increased the DMD and OMD values of all the samples by an average of 14% and 15%, respectively.

Varietal differences in the chemical composition and in vitro digestibility of rice straw

SummaryFour varieties of rice straw, MRl, MR71, MR84 and MR27, were separated into the following botanical fractions; inflorescence, stem, leaf blade and leaf sheath. The relative proportion of each fraction in whole straw was estimated and analysed for its chemical composition and in vitro digestibility (IVD). The composition and IVD of whole straw was then calculated. Cluster analysis showed that MRl was distinct from the other varieties. This could be attributed to a high proportion of stem (32·3%), high IVD (36·9%), low insoluble ash (4·0%) and a low silica content (2·7%) in the whole straw. The genetic distance between any two varieties ranged from 5·4 × 10-3 to 47·8 × 10-3 and was largest between MRl and the other varieties. Cluster analysis also showed that within a variety, the chemical composition and IVD of the stem, leaf blade and leaf sheath were similar, suggesting that sampling errors may be reduced if the inflorescence, which comprises 7–13% of the whole straw, is excluded when the material is analysed. Stepwise and canonical discriminant analyses indicated that the important variables to be measured when comparing straw varieties were IVD, crude protein and insoluble ash.

Solubility of mineral elements present in ruminant feeds

SUMMARYEight feeds were treated with seven solvents and the proportion of seven mineral elements (Ca, Mg, P, Na, K, Cu, Zn) released was assessed. Six of the feeds were from Sri Lanka (Panicum maximum ecotype Guinea A, Glyricidia maculata, Artocarpus heterophyllus, untreated and urea-treated rice straw, and rice bran) and two from the Netherlands (maize silage and wheat straw). The solvents were water, tris buffer, rumen fluid from a cow deprived of (RF -) or fed (RF +) mineral supplements, neutral detergent solution with (NDS +) or without (NDS -) EDTA, and acid detergent solution (ADS).Both the type of feed and the solvent significantly influenced (P &lt; 0·01) the amount of dry matter loss and the proportion of minerals released. Maize silage released over 80% of its minerals, except Cu, in water and tris buffer, probably because of the low pH (3·7) during ensiling. The other feeds differed widely in their ability to release minerals. In general, P, Na and K. were more soluble in water than Ca, Mg and Zn.Mineral concentration in RF influenced not only the amount of minerals released, but also the extent of sorption by the feed. The latter effect was more pronounced in feeds with low mineral concentration, maize silage being no exception.Treatment with NDS+ and ADS removed all minerals except Cu. With all feeds, 12–34% and 5–34% of the Cu remained in the ND and AD residues, respectively, indicating its association with the cell wall. Results of the NDS- treatment showed that some of the Ca and Mg may be associated with the cell wall.Comparison of the feeds across the different solvents tested indicated that, in terms of absolute quantity of mineral released, G. maculata could be a good source of Ca, Mg, K and Cu, and that rice bran is a good source of P and Zn. The variety of rice straw tested released high amounts of Na. A. heterophyllus is rich in available Ca.

Rumen degradation of straw 9. Effect of cellulase and ammonia treatment on different varieties of rice straws and their botanical fractions

ABSTRACTThe composition and degradability of four varieties of rice straw were examined. The varieties were tall or short and early or late maturing. The straws and their botanical parts (leaf blade plus leaf sheath, internode, node and chaff) varied in acid-detergent fibre, ash and silica contents, but not in nitrogen and neutral-detergent fibre. There were some trends but no significant difference in proportions of parts between varieties. Milled samples of whole straw and its parts were either untreated, treated with a cellulase preparation plus propionic acid, treated with ammonia, or treated with cellulase then ammonia. Rumen degradability was measured by incubating the samples in polyester bags suspended in the rumen of sheep. The soluble fraction and potential degradability were greater in untreated short and early than in tall and late varieties, but rates of degradation did not vary significantly. Internode was more degradable than leaf. Cellulase and/or ammonia treatments increased the soluble fraction, especially in tall and late varieties, and increased potential degradabiiity except in internode. Degradability correlated positively with ash and silica contents.