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The effect of variety and cultivation season on the chemical composition and in vitro organic matter digestibility of rice straw
Agricultural Wastes 18 (1986) 83-91
The Effect of Variety and Cultivation Season on the Chemical Composition and in vitro Organic Matter Digestibifity of Rice Straw Kshanika Sannasgala & M. C. N. Jayasuriya* Department of Animal Science, University of Peradeniya, Peradeniya, Sri Lanka A BSTRA CT An experiment was conducted with seven varieties of rice straw cultivated during two major growing seasons--the Maha (North-East Monsoon) and the Yala (South-West Monsoon)---to examine the influence of variety and cultivation season on chemical composition and in vitro organic matter digestibility (IVOMD) of whole plant and plant fractions. The whole plant IVOMD for the seven varieties varied from 30% to 45% with a mean of 35.2 +_3.9%. The stem fractions tended to have a higher 1VOMD than other fractions, particularly the leaf Although there appeared to be a seasonal influence on the digestibility of plant fractions, whole plant digestibility was not affected by the cultivation season. The chemical compositions of the different plant fractions showed a wide variation. The crude protein content was lowest in the stem and highest in the leaf The node had the lowest content of NDF, ADF and cellulose. However, these parameters had no direct influence on the digestibility of the fractions. It is clear that large variations exist in chemical composition and IVOMD of rice straws both between and within varieties. More extensive and controlled studies are needed to identify these factors and their influence on whole-plant digestibility.
INTRODUCTION Plants are not homogeneous but complex arrangements of roots, stems, leaves and inflorescence. Each o f these components is made up o f tissues * Present address: Animal Production and Health Section, International Atomic Energy Agency, Wagramerstrasse 5, PO Box 100, A-1400 Vienna, Austria. 83 Agricultural Wastes 0141-4607/86/$03'50 © Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain
84
Kshanika Sannasgala, M. C. N. Jayasuriya
designed for specific functions; leaves carry out most of the assimilation of carbon dioxide while node and internodes provide the supporting structure for leaves and transport of nutrients from the roots. Chemical and physical differences between tissues may therefore lead to differences in digestibility. Hacker & Minson (1981) reported that leaves from Gramineae can vary in digestibility from 18% to 84%, with a mean of 59%, while the digestibility of stems may range from 5% to 85%. Similar observations have also been reported by Minson (1982) and Purser (1982). Recently, Pearce (1984) suggested that the wide variability in chemical composition and digestibility of cereal straws could be due to both genetic and environmental factors affecting plant growth. If the varieties or cultivars within a species were bred from a limited gene pool, then pronounced differences might not be expected, but if a wider gene pool was used in the breeding of these varieties, then a wide variation could occur. Similarly, environmental conditions could have a substantial effect on rate and extent of development of plant species and therefore on digestibility at maturity and senescence. Literature is lacking on the contribution made by variety, plant fractions and cultivation season to chemical composition and digestibility of rice straw. In this study we examined the influence of variety of rice straw and cultivation during two major growing seasons of the year on chemical composition and in vitro organic matter digestibility of whole plant and plant fractions. An attempt was also made to correlate the influence of plant fractions to whole plant digestibility.
METHODS Samples of rice straw (1 kg each) from seven varieties grown at the two main rice breeding stations in Sri Lanka, Batalagoda and Bombuwela, were collected during the South-West Monsoon (Yala) and the NorthEast Monsoon (Maha) seasons of 1982. The four varieties BG 380-2, BG 400-1, BG 276-5 and BG 94-1 were from Batalagoda and the three varieties BW 100, BW 267-3 and BW 266-7 were from Bombuwela. Approximately 500g of each variety were separated into five components, leaf, leaf sheath (leaf base), stem (internode), node and panicle. Samples of the whole plant, as well as these components, were dried at
Digestibility of rice straw
85
65°C to constant weight and then ground to pass through a 1 mm sieve in a Christy Norris laboratory mill. Dry matter (DM), ash, crude protein and crude fibre contents of these samples were determined by conventional methods (AOAC, 1970). Neutral detergent fibre (NDF), acid detergent fibre (ADF), cellulose, permanganate lignin and silica were determined as described by Goering & Van Soest (1970). Hemicellulose content was calculated as the difference between N D F and ADF. Neutral detergent solubles (NDS) content was calculated by subtracting the N D F value from 100. In vitro organic matter digestibilities (IVOMD) of whole plant and plant fractions were determined by the method of McLeod & Minson (1978) using Onozuka 35 cellulase (Yakult Biochemicals Co. Ltd., Japan) of fungal origin (Oxysporus sp.). Linear relationships between IVOMD of the whole plant or plant fractions and the chemical, physiological or morphological characteristics of different varieties of straw were estimated. The effect of season, variety and plant fractions on each chemical component and IVOMD was statistically examined by the standard two-way analysis of variance procedure of Steel & Torrie (1960).
RESULTS A N D DISCUSSION At both breeding stations rice was cultivated under rainfed conditions with supplementary irrigation. Cultivation practices such as fertilizer application, weed and pest control were similar and carried out as recommended by the Department of Agriculture (DIAD, 1982). In each season straws were collected within 2 weeks of the grain harvest. Some morphological and physiological measurements and IVOMD made on the seven varieties of rice straw are presented in Table 1. The varieties represented a range of types with respect to plant height, age and grain yield. The culm-length varied from 620 to 870 mm. In general, new improved types such as BG 380-2, BG 276-5 and BG 94-1 had shorter culm length than the old traditional varieties. Grain yield and age at harvest also showed a considerable variation amongst the varieties. However, none of the measured characteristics had any significant relationship to the IVOMD of the whole plant. The IVOMD of the whole plant straw for the seven varieties varied
120 135 90 105 135 116 I 16
BG 380-2 BG 400-1 BG 276-5 BG 94-1 BW 100 BW 267-3 BW 266-7
640 840 620 650 870 770 820
Culm length (ram)
470 400 430 290 380 380 350
Leaf length (mm)
5.9 3-9 5"3 5.4 2.4 3-0 2.1
Grain yieM (tons ha- 1)
21.2 15.2 12-7 12.7 15-2 20-9 20.8
N-fertilizer requirement (kgha -l)
41.8 (38.6-45.2 + 3.7) 34-9 (32-6-37.9 + 2.6) 36-4 (33.6-40"0 + 3-2) 33-2 (30-9-35'4 + 2-5) 32"4 (30.2-33-9 ___1"7) 35.4 (34.0-37"0 + 1"5) 31-0 (30-2-32"5 + 1.5)
(%)
IVOMD a
a Mean values for both Yala and Maha seasons with range and standard deviation within parentheses. Whole plant straw.
Age (days)
Rice variety
TABLE 1 Some Morphological and Physiological Characteristics of Seven Varieties of Rice Straw
Digestibility of rice straw
87
from 30% to 45% (Table 1) with a mean of 35.2 ___3.9; the mean value being similar to that recorded in previous experiments with rice straw varieties in Sri Lanka (Jayasuriya, 1979; Jayasuriya & Perera, 1982). The chemical composition and IVOMD of whole plant and different fractions of straw for the seven varieties are given in Table 2. While Yala samples of both whole plant and plant fractions consistently showed higher contents of crude protein and hemicellulose, Maha samples showed higher values for ADF. Other cell-wall constituents showed no definite trend. There was a wide variation in composition amongst different plant fractions, considering the mean values for the two seasons. For example, the crude protein content varied from 3.4% to 5. 1%, being lowest in the stem and highest in the leaf. The node fraction appeared to have the lowest content of NDF, A D F and cellulose. The variation in hemicellulose content was marginal. The stem contained the highest amount of A D F and cellulose. Yet these parameters had no direct influence on the digestibility of the fractions. The IVOMD also showed a wide variation. Similar to observations made by Winugroho (1981) it was interesting to note that the stem fractions, both node and internode, tended to have higher IVOMD values than the ottiers, particularly the leaf fraction. This peculiarity appears to be true only of rice straw since both Winugroho (1981) and Purser (1982) reported higher digestibilities for leafy material than for stem material in wheat straw. One of the important observations arising from this investigation was the lack of any significant influence of the cultivation season on IVOMD of the whole plant. The two cultivation seasons Maha and Yala differ mainly in the amount of rainfall, the Maha season receiving a much higher rainfall (1300-1500mm) than the Yala season (300-1000mm). The lack of influence of cultivation season on IVOMD of straw has also been reported by Wilson (1973) and Roxas et al. (1985). Although no particular explanation can be attributed to this, the beneficial effects of high rainfall, making soil nutrients easily available to the plant, cannot be ignored. Although the range of IVOMD of the entire plant for the two cultivation seasons was very narrow (34.9-35.1%), some of the plant fractions showed much wider differences in their digestibilities. The leaf fraction during the Maha season had a digestibility of 39% while the same for the Yala season was 28%. Similarly, the leaf sheath also
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
11.4+3-5 (6.9-15-8) 11.8+_2"7 (6.7-15.0) 11.6 12.9_+3"5 (8-3 19'6) 10"8_+1"5 (8"9-12"8) 11"9 11.9_+3.3 (8-2-17-3) 10-8+_ 1"6 (8.5-12.7) 11.4 11.8_+1.2 (9-5-13.5) 9.9+_1.2 (8.3-12.3) 10-9 10.7_+2-0 (8.9 14-3) 10"5_+0'8 (8-9 11-9) 10-6 7.4_+1.5 (4-7-9.6) 8.3_+1-8 (6.2-10"9) 7-9
Ash
Figures within parentheses indicate the range.
Panicle
Node
Stem (internode)
Leaf sheath (leaf base)
Leaf
Whole plant
Plant ]raction
3.9_+0.8 (2.4-4-9) 5-8+_ 1-0 (4-2~6"8) 4-9 4-5+-0-4 (3"8 5 - 3 ) 5"6_+0-6 (4-64i-6) 5" 1 3.7+_0.4 (3"1-4-2) 4-2+_ 1.3 (2-1~6-4) 4.0 2-9_+0.4 (2.1 3.8) 3.8+_1.2 (2-3-6-0) 3-4 4.4_+0.5 (3-9 5.0) 5-4_+1"2 (4-2 7"2) 4.9 3-7_+0.9 (2.3-5.5) 4'5_+0-9 (3-5~'2) 4- I
Crude protein
69-3+5-5 (61"5 76.2) 76.3+_3-2 (72-0-80.2) 72"8 68.4+-4-3 (61.9-76-4) 72-7_+2"6 (69.7-77"8) 70.6 76.0+3.9 (69.2 82.1) 76.0_+4-0 (67.2 79-8) 76-0 72-3_+4.1 (63.4-77-2) 74.5_+6.1 (63-0-80.9) 73-4 62-9+_4-8 (58-1 71-5) 72-4+_6"1 (59-1-78'6) 67.7 67.6_+5.9 (60.9-80-8) 76"5_+4'4 (69.8-81"7) 72. I
NDF
50-4+_1.7 (47-8-53.3) 50"3+_1.9 (48.0-53-6) 50-4 48'3_+3"1 (42-3-51-0) 45"2_+2"3 (42.6~9.9) 46.8 56-6+_2.6 (53-0410-4) 47.9*4-9 (40.2-53-2) 52-2 54.9_+3-8 (47-3~1.0) 51.6+_3.3 (45.8-55-9) 53.3 43.7_+3-6 (36.4-46-8) 41-5_+5"1 (31.ff47-8) 42-6 50.2_+4-4 (43.4-55.4) 48.5-+7"2 (32.0-54.4) 49.4
ADF
Hemicellulose
34.4+_2.1 (30-4-36-1) 39-1 _+2.9 (33-24-2"5) 36-8 30-4_+3'0 (24.7-33"4) 29"6_+2-0 (30-6-33"3) 30-0 37.1+1-1 (35-4-39-3) 34.0+-4.9 (26-7-43.0) 35-6 39-9_+3"8 (32-8-45.6) 39.4_+7.9 (22-5-48"8) 39-7 28-3_+3-1 (23.5-32.7) 30-7+_3"3 (24.6-35'2) 29.5 32.7-+7.9 (16.0-43.1) 35-2+6"7 (22-4-43-3) 33-9
18.8+_5-1 (12-8-24.1) 25.9+_3-8 (18.7-30.3) 22.4 20.1_+6"2 (10-6~31'1) 27"6_+3"6 (20-5-31-9) 23-9 19-5+_4.2 (13.9-25-7) 28.2_+2.8 (25.7-34-3) 23-8 17.4_+2.0 (15-1 20.9) 23-0+_3-9 (14.7-28.1) 20-2 19.2_+5.9 (11-9-27.2) 30.9_+3-8 (23-4-34.7) 25-1 17.1_+5.4 (6.9-23.7) 28.0-+4-6 (23-5-37"6) 22.6
(g per IOOg dr;' matter)
Cellulose
9-2+_3.0 (5.0-11-8) 3-2+_ 1.6 (I.6-5-6) 6-2 8-8_+1.5 (6-5-11"3) 6-2_+1"2 (3.7-7"7) 7-5 10.7_+3-0 (6.9 16-8) 6.4_+ I-2 (4-6-8-2) 8-6 10-2+_1.9 (6-9-12.8) 7.2+_2-1 (3-7-9.8) 8.7 8-4_+1.7 (5.4-10.9) 6-3+_1"2 (4.2-7"7) 7.4 7.8+2.1(4.2-10-1) 7-2_+2"4 (2-7-10-4) 7.5
Permanganate lignin
6-7_+3.2 (2-3-11.5) 7-9_+ 1.8 (4-5-10-3) 7.3 8'5+-2"9 (5-1-12-9) 7"8_+2"3 (6-0-11-9) 8.2 8-5_+3-0 (4.8-14-2) 7-2+-2-1 (4.6-10.8) 7-9 4.3_+1.6 (1-8~.6) 3-7_+0-6 (2.9-4-4) 4.0 5-8_+2.1 (2-3-8-1) 5"2+1"7 (3-1-8-8) 5.5 5-9_+2.3 (1.8-9-8) 5-1-+2"8 (2-7-8"6) 5.5
Silica
30.7+_5-5 (23-8 38.5) 23.7_+3-2 (19-8-28.0) 27.2 31'6+-4.3 (23-6-38.1) 27"3+-2"6 (22-2-30'3) 29.5 24.0+_3.9 (17.9-30-8) 24.0+-4.0 (20.2-32-8) 24-0 27.7_+4.1 (22.8-36.6) 25.5+_6-1 (19.1-37-0) 26-6 37.1_+4-8 (28-8-41-9) 27"6-+6"1 (21-440.9) 32.4 32-4-+5.9 (19-2-39.1) 23-5-+4.4 (18-3-30"2) 27-9
NDS
35.1+_3.5 (30.2-38.6) 34.9+-4-5 (30.2-45.2) 35.0 38.8+-5'2 (31'8-46"0) 27:9_+6-2 (20"1-40"5) 33-4 34-2_+3.5 (30.1-36-8) 29-1 +_4.6 (24.7-35.8) 31.7 35.6_+6.2 (25-8-46.5) 37.3+_6.2 (27.4-47-5) 36.5 45.1_+4-3 (38.1-53-9) 44-3+_5-8 (35.4-55"3) 44-7 26-6_+2-4 (23.1-31-2) 31"2_+2"7 (27.3-33"8) 28.9
IVOMD o/o
TABLE 2 Chemical Composition and IVOMD of Whole Plant Straw and Fractions as Influenced by Two Cultivation Seasons, Maha and Yala (Each value represents a mean of seven varieties with standard deviation)
Digestibility of rice straw
89
showed a difference of 5% IVOMD units in favour of the Maha season. Within the stem fraction, node showed a higher digestibility than the internode. This agreed with the observations on barley straw by Manley & Wood (1978) who found that the node IVOMD was 39% compared to 30% in the internode. Winugroho (1981), likewise, reported IVOMD values of 41% and 58% for node and 27% and 54% for internode in wheat and rice straw, .respectively. In recent years, neutral detergent solubles (NDS) content has been used to characterise the quality of fibrous material, particularly of cereal straws. Pearce (1985) demonstrated a very clear relationship (r = 0.91) between NDS and IVOMD in wheat straw internodes. Samples of wheat straw were collected over a period of 5 weeks before grain harvest and 5 weeks after grain harvest, and the relationship IVOMD = 12-74 + 0.94 NDS was found, implying that the NDS fraction was 94% digestible and that the digestibility of wheat straw stem internodes was highly dependent on the NDS fraction. Similar observations were also reported for barley and rice straw internodes, although the relationship for rice straw was not as good as that for wheat and barley straw. Contrary to this observation, the NDS (NDF) content of the seven varieties of rice straw here showed a very poor relationship with IVOMD for whole plant as well as for plant fractions. Lack of a significant relationship of NDS with IVOMD was presumably because of the poor correlation for Maha samples (r = 0-43), as Yala samples showed a significant relationship (r = 0.88). However, when mean NDS values for the two seasons were considered (Table 2) the relationship came closer to reaching the level of significance at 5% (r = 0-68). This supports the view that, although IVOMD could be highly dependent on NDS'content, as previously shown by Pearce (1985), as well as by our own data for Yala samples, variability between varieties could bring about a poor relationship between the two factors. Other cell wall components also did not show any significant correlation with IVOMD, for both plant and plant fractions. The data reported here demonstrate the large variation that can exist in the chemical composition and IVOMD of rice straw, both between varieties and within a variety. The variation in digestibility among plant parts would seem to play an important role in determining the overall digestibility of the straw. More extensive and controlled studies are needed to differentiate the importance of different factors that affect digestibility.
90
Kshanika Sannasgala, M. C. N. Jayasuriya A C K N O W L E D G E M ENTS
The work reported here is part of a higher degree p r o g r a m m e of K. Sannasgala while on the research studentship from the Straw Utilization Project, Sri Lanka. The authors wish to thank Miss Margaret H e y m a n n for typing the manuscript. REFERENCES AOAC (1970). Official methods of analysis. (1 lth edn). Association of Official Agricultural Chemists, Washington, DC. DAID (1982). Department of Agriculture Information Division, Government Department of Agriculture, Sri Lanka. Goering, H. K. & Van Soest, P. J. (1970). Forage fibre analysis. Agriculture Hand Book No. 379. Agricultural Research Service, US Department of Agriculture, Washington, DC. Hacker, J. B. & Minson, D. J. (1981). The digestibility of plant parts. Herbage Abs., 51, 460-81. Jayasuriya, M. C. N. (1979). Sodium hydroxide treatment of rice straw to improve its nutritive value for ruminants. Trop. Agric., 56, 75-80. Jayasuriya, M. C. N. & Perera, H. G. D. (1982). Urea-ammonia treatment of rice-straw to improve its nutritive value for ruminants. Agricultural Wastes, 4, 143-50. Manley, A. C. & Wood, R. S. (1978). The analysis of fractions of cereal crops on three dates prior to harvest. Agric. Prog., 53, 71-6. McLeod, M. N. & Minson, D. J. (1978). The accuracy of the pepsin-cellulase technique for estimating the dry matter digestibility in vivo of grass and legumes. Anita. Feed Sci. Technol., 3, 277-87. Minson, D. J. (1982). Effect of chemical composition on feed digestibility and metabolizable energy. Nutr. Abs. Rev., 52, 591-614. Pearce, G. R. (1984). Factors contributing to variation in the nutritive value of fibrous agricultural residues. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), School of Agriculture and Forestry, University of Melbourne, Australia. 117-23. Pearce, G. R. (1985). Characteristics of cereal straw in relation to their digestion. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), International Development Programme of Australian Universities and Colleges, Canberra, Australia. 53-8. Purser, D. B. (1982). Factors affecting the quality of wheat straw in SouthWestern Australia. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), School of Agriculture and Forestry, University of Melbourne, Australia. 27-41. Roxas, D. B., Obsioma, A. R., Lapitan, R. M., Castillo, L. S., Momongan, V. C. & Juliano, B. O. (1985). The effects of variety of rice, level of
Digestibility of rice straw
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nitrogen fertilization and season on the chemical composition and in vitro digestibility of straw. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), International Development Program of Australian Universities and Colleges, Canberra, Australia. 47-52. Steel, R. G. D. & Torrie, J. H. (1960). Principles and procedures of statistics. McGraw-Hill Book Company, New York. Wilson, J. R. (1973). The influence of aerial environment, nitrogen supply and ontogenetical changes on the chemical composition and dry matter digestibility. Austr. J. Agric. Res., 24, 543-56. Winugroho, M. (1981). Studies on the utilization of cereal straws. MSc Thesis. University of Melbourne, Australia.
The Effect of Variety and Cultivation Season on the Chemical Composition and in vitro Organic Matter Digestibifity of Rice Straw Kshanika Sannasgala & M. C. N. Jayasuriya* Department of Animal Science, University of Peradeniya, Peradeniya, Sri Lanka A BSTRA CT An experiment was conducted with seven varieties of rice straw cultivated during two major growing seasons--the Maha (North-East Monsoon) and the Yala (South-West Monsoon)---to examine the influence of variety and cultivation season on chemical composition and in vitro organic matter digestibility (IVOMD) of whole plant and plant fractions. The whole plant IVOMD for the seven varieties varied from 30% to 45% with a mean of 35.2 +_3.9%. The stem fractions tended to have a higher 1VOMD than other fractions, particularly the leaf Although there appeared to be a seasonal influence on the digestibility of plant fractions, whole plant digestibility was not affected by the cultivation season. The chemical compositions of the different plant fractions showed a wide variation. The crude protein content was lowest in the stem and highest in the leaf The node had the lowest content of NDF, ADF and cellulose. However, these parameters had no direct influence on the digestibility of the fractions. It is clear that large variations exist in chemical composition and IVOMD of rice straws both between and within varieties. More extensive and controlled studies are needed to identify these factors and their influence on whole-plant digestibility.
INTRODUCTION Plants are not homogeneous but complex arrangements of roots, stems, leaves and inflorescence. Each o f these components is made up o f tissues * Present address: Animal Production and Health Section, International Atomic Energy Agency, Wagramerstrasse 5, PO Box 100, A-1400 Vienna, Austria. 83 Agricultural Wastes 0141-4607/86/$03'50 © Elsevier Applied Science Publishers Ltd, England, 1986. Printed in Great Britain
84
Kshanika Sannasgala, M. C. N. Jayasuriya
designed for specific functions; leaves carry out most of the assimilation of carbon dioxide while node and internodes provide the supporting structure for leaves and transport of nutrients from the roots. Chemical and physical differences between tissues may therefore lead to differences in digestibility. Hacker & Minson (1981) reported that leaves from Gramineae can vary in digestibility from 18% to 84%, with a mean of 59%, while the digestibility of stems may range from 5% to 85%. Similar observations have also been reported by Minson (1982) and Purser (1982). Recently, Pearce (1984) suggested that the wide variability in chemical composition and digestibility of cereal straws could be due to both genetic and environmental factors affecting plant growth. If the varieties or cultivars within a species were bred from a limited gene pool, then pronounced differences might not be expected, but if a wider gene pool was used in the breeding of these varieties, then a wide variation could occur. Similarly, environmental conditions could have a substantial effect on rate and extent of development of plant species and therefore on digestibility at maturity and senescence. Literature is lacking on the contribution made by variety, plant fractions and cultivation season to chemical composition and digestibility of rice straw. In this study we examined the influence of variety of rice straw and cultivation during two major growing seasons of the year on chemical composition and in vitro organic matter digestibility of whole plant and plant fractions. An attempt was also made to correlate the influence of plant fractions to whole plant digestibility.
METHODS Samples of rice straw (1 kg each) from seven varieties grown at the two main rice breeding stations in Sri Lanka, Batalagoda and Bombuwela, were collected during the South-West Monsoon (Yala) and the NorthEast Monsoon (Maha) seasons of 1982. The four varieties BG 380-2, BG 400-1, BG 276-5 and BG 94-1 were from Batalagoda and the three varieties BW 100, BW 267-3 and BW 266-7 were from Bombuwela. Approximately 500g of each variety were separated into five components, leaf, leaf sheath (leaf base), stem (internode), node and panicle. Samples of the whole plant, as well as these components, were dried at
Digestibility of rice straw
85
65°C to constant weight and then ground to pass through a 1 mm sieve in a Christy Norris laboratory mill. Dry matter (DM), ash, crude protein and crude fibre contents of these samples were determined by conventional methods (AOAC, 1970). Neutral detergent fibre (NDF), acid detergent fibre (ADF), cellulose, permanganate lignin and silica were determined as described by Goering & Van Soest (1970). Hemicellulose content was calculated as the difference between N D F and ADF. Neutral detergent solubles (NDS) content was calculated by subtracting the N D F value from 100. In vitro organic matter digestibilities (IVOMD) of whole plant and plant fractions were determined by the method of McLeod & Minson (1978) using Onozuka 35 cellulase (Yakult Biochemicals Co. Ltd., Japan) of fungal origin (Oxysporus sp.). Linear relationships between IVOMD of the whole plant or plant fractions and the chemical, physiological or morphological characteristics of different varieties of straw were estimated. The effect of season, variety and plant fractions on each chemical component and IVOMD was statistically examined by the standard two-way analysis of variance procedure of Steel & Torrie (1960).
RESULTS A N D DISCUSSION At both breeding stations rice was cultivated under rainfed conditions with supplementary irrigation. Cultivation practices such as fertilizer application, weed and pest control were similar and carried out as recommended by the Department of Agriculture (DIAD, 1982). In each season straws were collected within 2 weeks of the grain harvest. Some morphological and physiological measurements and IVOMD made on the seven varieties of rice straw are presented in Table 1. The varieties represented a range of types with respect to plant height, age and grain yield. The culm-length varied from 620 to 870 mm. In general, new improved types such as BG 380-2, BG 276-5 and BG 94-1 had shorter culm length than the old traditional varieties. Grain yield and age at harvest also showed a considerable variation amongst the varieties. However, none of the measured characteristics had any significant relationship to the IVOMD of the whole plant. The IVOMD of the whole plant straw for the seven varieties varied
120 135 90 105 135 116 I 16
BG 380-2 BG 400-1 BG 276-5 BG 94-1 BW 100 BW 267-3 BW 266-7
640 840 620 650 870 770 820
Culm length (ram)
470 400 430 290 380 380 350
Leaf length (mm)
5.9 3-9 5"3 5.4 2.4 3-0 2.1
Grain yieM (tons ha- 1)
21.2 15.2 12-7 12.7 15-2 20-9 20.8
N-fertilizer requirement (kgha -l)
41.8 (38.6-45.2 + 3.7) 34-9 (32-6-37.9 + 2.6) 36-4 (33.6-40"0 + 3-2) 33-2 (30-9-35'4 + 2-5) 32"4 (30.2-33-9 ___1"7) 35.4 (34.0-37"0 + 1"5) 31-0 (30-2-32"5 + 1.5)
(%)
IVOMD a
a Mean values for both Yala and Maha seasons with range and standard deviation within parentheses. Whole plant straw.
Age (days)
Rice variety
TABLE 1 Some Morphological and Physiological Characteristics of Seven Varieties of Rice Straw
Digestibility of rice straw
87
from 30% to 45% (Table 1) with a mean of 35.2 ___3.9; the mean value being similar to that recorded in previous experiments with rice straw varieties in Sri Lanka (Jayasuriya, 1979; Jayasuriya & Perera, 1982). The chemical composition and IVOMD of whole plant and different fractions of straw for the seven varieties are given in Table 2. While Yala samples of both whole plant and plant fractions consistently showed higher contents of crude protein and hemicellulose, Maha samples showed higher values for ADF. Other cell-wall constituents showed no definite trend. There was a wide variation in composition amongst different plant fractions, considering the mean values for the two seasons. For example, the crude protein content varied from 3.4% to 5. 1%, being lowest in the stem and highest in the leaf. The node fraction appeared to have the lowest content of NDF, A D F and cellulose. The variation in hemicellulose content was marginal. The stem contained the highest amount of A D F and cellulose. Yet these parameters had no direct influence on the digestibility of the fractions. The IVOMD also showed a wide variation. Similar to observations made by Winugroho (1981) it was interesting to note that the stem fractions, both node and internode, tended to have higher IVOMD values than the ottiers, particularly the leaf fraction. This peculiarity appears to be true only of rice straw since both Winugroho (1981) and Purser (1982) reported higher digestibilities for leafy material than for stem material in wheat straw. One of the important observations arising from this investigation was the lack of any significant influence of the cultivation season on IVOMD of the whole plant. The two cultivation seasons Maha and Yala differ mainly in the amount of rainfall, the Maha season receiving a much higher rainfall (1300-1500mm) than the Yala season (300-1000mm). The lack of influence of cultivation season on IVOMD of straw has also been reported by Wilson (1973) and Roxas et al. (1985). Although no particular explanation can be attributed to this, the beneficial effects of high rainfall, making soil nutrients easily available to the plant, cannot be ignored. Although the range of IVOMD of the entire plant for the two cultivation seasons was very narrow (34.9-35.1%), some of the plant fractions showed much wider differences in their digestibilities. The leaf fraction during the Maha season had a digestibility of 39% while the same for the Yala season was 28%. Similarly, the leaf sheath also
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
Mean
Yala
Maha
11.4+3-5 (6.9-15-8) 11.8+_2"7 (6.7-15.0) 11.6 12.9_+3"5 (8-3 19'6) 10"8_+1"5 (8"9-12"8) 11"9 11.9_+3.3 (8-2-17-3) 10-8+_ 1"6 (8.5-12.7) 11.4 11.8_+1.2 (9-5-13.5) 9.9+_1.2 (8.3-12.3) 10-9 10.7_+2-0 (8.9 14-3) 10"5_+0'8 (8-9 11-9) 10-6 7.4_+1.5 (4-7-9.6) 8.3_+1-8 (6.2-10"9) 7-9
Ash
Figures within parentheses indicate the range.
Panicle
Node
Stem (internode)
Leaf sheath (leaf base)
Leaf
Whole plant
Plant ]raction
3.9_+0.8 (2.4-4-9) 5-8+_ 1-0 (4-2~6"8) 4-9 4-5+-0-4 (3"8 5 - 3 ) 5"6_+0-6 (4-64i-6) 5" 1 3.7+_0.4 (3"1-4-2) 4-2+_ 1.3 (2-1~6-4) 4.0 2-9_+0.4 (2.1 3.8) 3.8+_1.2 (2-3-6-0) 3-4 4.4_+0.5 (3-9 5.0) 5-4_+1"2 (4-2 7"2) 4.9 3-7_+0.9 (2.3-5.5) 4'5_+0-9 (3-5~'2) 4- I
Crude protein
69-3+5-5 (61"5 76.2) 76.3+_3-2 (72-0-80.2) 72"8 68.4+-4-3 (61.9-76-4) 72-7_+2"6 (69.7-77"8) 70.6 76.0+3.9 (69.2 82.1) 76.0_+4-0 (67.2 79-8) 76-0 72-3_+4.1 (63.4-77-2) 74.5_+6.1 (63-0-80.9) 73-4 62-9+_4-8 (58-1 71-5) 72-4+_6"1 (59-1-78'6) 67.7 67.6_+5.9 (60.9-80-8) 76"5_+4'4 (69.8-81"7) 72. I
NDF
50-4+_1.7 (47-8-53.3) 50"3+_1.9 (48.0-53-6) 50-4 48'3_+3"1 (42-3-51-0) 45"2_+2"3 (42.6~9.9) 46.8 56-6+_2.6 (53-0410-4) 47.9*4-9 (40.2-53-2) 52-2 54.9_+3-8 (47-3~1.0) 51.6+_3.3 (45.8-55-9) 53.3 43.7_+3-6 (36.4-46-8) 41-5_+5"1 (31.ff47-8) 42-6 50.2_+4-4 (43.4-55.4) 48.5-+7"2 (32.0-54.4) 49.4
ADF
Hemicellulose
34.4+_2.1 (30-4-36-1) 39-1 _+2.9 (33-24-2"5) 36-8 30-4_+3'0 (24.7-33"4) 29"6_+2-0 (30-6-33"3) 30-0 37.1+1-1 (35-4-39-3) 34.0+-4.9 (26-7-43.0) 35-6 39-9_+3"8 (32-8-45.6) 39.4_+7.9 (22-5-48"8) 39-7 28-3_+3-1 (23.5-32.7) 30-7+_3"3 (24.6-35'2) 29.5 32.7-+7.9 (16.0-43.1) 35-2+6"7 (22-4-43-3) 33-9
18.8+_5-1 (12-8-24.1) 25.9+_3-8 (18.7-30.3) 22.4 20.1_+6"2 (10-6~31'1) 27"6_+3"6 (20-5-31-9) 23-9 19-5+_4.2 (13.9-25-7) 28.2_+2.8 (25.7-34-3) 23-8 17.4_+2.0 (15-1 20.9) 23-0+_3-9 (14.7-28.1) 20-2 19.2_+5.9 (11-9-27.2) 30.9_+3-8 (23-4-34.7) 25-1 17.1_+5.4 (6.9-23.7) 28.0-+4-6 (23-5-37"6) 22.6
(g per IOOg dr;' matter)
Cellulose
9-2+_3.0 (5.0-11-8) 3-2+_ 1.6 (I.6-5-6) 6-2 8-8_+1.5 (6-5-11"3) 6-2_+1"2 (3.7-7"7) 7-5 10.7_+3-0 (6.9 16-8) 6.4_+ I-2 (4-6-8-2) 8-6 10-2+_1.9 (6-9-12.8) 7.2+_2-1 (3-7-9.8) 8.7 8-4_+1.7 (5.4-10.9) 6-3+_1"2 (4.2-7"7) 7.4 7.8+2.1(4.2-10-1) 7-2_+2"4 (2-7-10-4) 7.5
Permanganate lignin
6-7_+3.2 (2-3-11.5) 7-9_+ 1.8 (4-5-10-3) 7.3 8'5+-2"9 (5-1-12-9) 7"8_+2"3 (6-0-11-9) 8.2 8-5_+3-0 (4.8-14-2) 7-2+-2-1 (4.6-10.8) 7-9 4.3_+1.6 (1-8~.6) 3-7_+0-6 (2.9-4-4) 4.0 5-8_+2.1 (2-3-8-1) 5"2+1"7 (3-1-8-8) 5.5 5-9_+2.3 (1.8-9-8) 5-1-+2"8 (2-7-8"6) 5.5
Silica
30.7+_5-5 (23-8 38.5) 23.7_+3-2 (19-8-28.0) 27.2 31'6+-4.3 (23-6-38.1) 27"3+-2"6 (22-2-30'3) 29.5 24.0+_3.9 (17.9-30-8) 24.0+-4.0 (20.2-32-8) 24-0 27.7_+4.1 (22.8-36.6) 25.5+_6-1 (19.1-37-0) 26-6 37.1_+4-8 (28-8-41-9) 27"6-+6"1 (21-440.9) 32.4 32-4-+5.9 (19-2-39.1) 23-5-+4.4 (18-3-30"2) 27-9
NDS
35.1+_3.5 (30.2-38.6) 34.9+-4-5 (30.2-45.2) 35.0 38.8+-5'2 (31'8-46"0) 27:9_+6-2 (20"1-40"5) 33-4 34-2_+3.5 (30.1-36-8) 29-1 +_4.6 (24.7-35.8) 31.7 35.6_+6.2 (25-8-46.5) 37.3+_6.2 (27.4-47-5) 36.5 45.1_+4-3 (38.1-53-9) 44-3+_5-8 (35.4-55"3) 44-7 26-6_+2-4 (23.1-31-2) 31"2_+2"7 (27.3-33"8) 28.9
IVOMD o/o
TABLE 2 Chemical Composition and IVOMD of Whole Plant Straw and Fractions as Influenced by Two Cultivation Seasons, Maha and Yala (Each value represents a mean of seven varieties with standard deviation)
Digestibility of rice straw
89
showed a difference of 5% IVOMD units in favour of the Maha season. Within the stem fraction, node showed a higher digestibility than the internode. This agreed with the observations on barley straw by Manley & Wood (1978) who found that the node IVOMD was 39% compared to 30% in the internode. Winugroho (1981), likewise, reported IVOMD values of 41% and 58% for node and 27% and 54% for internode in wheat and rice straw, .respectively. In recent years, neutral detergent solubles (NDS) content has been used to characterise the quality of fibrous material, particularly of cereal straws. Pearce (1985) demonstrated a very clear relationship (r = 0.91) between NDS and IVOMD in wheat straw internodes. Samples of wheat straw were collected over a period of 5 weeks before grain harvest and 5 weeks after grain harvest, and the relationship IVOMD = 12-74 + 0.94 NDS was found, implying that the NDS fraction was 94% digestible and that the digestibility of wheat straw stem internodes was highly dependent on the NDS fraction. Similar observations were also reported for barley and rice straw internodes, although the relationship for rice straw was not as good as that for wheat and barley straw. Contrary to this observation, the NDS (NDF) content of the seven varieties of rice straw here showed a very poor relationship with IVOMD for whole plant as well as for plant fractions. Lack of a significant relationship of NDS with IVOMD was presumably because of the poor correlation for Maha samples (r = 0-43), as Yala samples showed a significant relationship (r = 0.88). However, when mean NDS values for the two seasons were considered (Table 2) the relationship came closer to reaching the level of significance at 5% (r = 0-68). This supports the view that, although IVOMD could be highly dependent on NDS'content, as previously shown by Pearce (1985), as well as by our own data for Yala samples, variability between varieties could bring about a poor relationship between the two factors. Other cell wall components also did not show any significant correlation with IVOMD, for both plant and plant fractions. The data reported here demonstrate the large variation that can exist in the chemical composition and IVOMD of rice straw, both between varieties and within a variety. The variation in digestibility among plant parts would seem to play an important role in determining the overall digestibility of the straw. More extensive and controlled studies are needed to differentiate the importance of different factors that affect digestibility.
90
Kshanika Sannasgala, M. C. N. Jayasuriya A C K N O W L E D G E M ENTS
The work reported here is part of a higher degree p r o g r a m m e of K. Sannasgala while on the research studentship from the Straw Utilization Project, Sri Lanka. The authors wish to thank Miss Margaret H e y m a n n for typing the manuscript. REFERENCES AOAC (1970). Official methods of analysis. (1 lth edn). Association of Official Agricultural Chemists, Washington, DC. DAID (1982). Department of Agriculture Information Division, Government Department of Agriculture, Sri Lanka. Goering, H. K. & Van Soest, P. J. (1970). Forage fibre analysis. Agriculture Hand Book No. 379. Agricultural Research Service, US Department of Agriculture, Washington, DC. Hacker, J. B. & Minson, D. J. (1981). The digestibility of plant parts. Herbage Abs., 51, 460-81. Jayasuriya, M. C. N. (1979). Sodium hydroxide treatment of rice straw to improve its nutritive value for ruminants. Trop. Agric., 56, 75-80. Jayasuriya, M. C. N. & Perera, H. G. D. (1982). Urea-ammonia treatment of rice-straw to improve its nutritive value for ruminants. Agricultural Wastes, 4, 143-50. Manley, A. C. & Wood, R. S. (1978). The analysis of fractions of cereal crops on three dates prior to harvest. Agric. Prog., 53, 71-6. McLeod, M. N. & Minson, D. J. (1978). The accuracy of the pepsin-cellulase technique for estimating the dry matter digestibility in vivo of grass and legumes. Anita. Feed Sci. Technol., 3, 277-87. Minson, D. J. (1982). Effect of chemical composition on feed digestibility and metabolizable energy. Nutr. Abs. Rev., 52, 591-614. Pearce, G. R. (1984). Factors contributing to variation in the nutritive value of fibrous agricultural residues. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), School of Agriculture and Forestry, University of Melbourne, Australia. 117-23. Pearce, G. R. (1985). Characteristics of cereal straw in relation to their digestion. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), International Development Programme of Australian Universities and Colleges, Canberra, Australia. 53-8. Purser, D. B. (1982). Factors affecting the quality of wheat straw in SouthWestern Australia. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), School of Agriculture and Forestry, University of Melbourne, Australia. 27-41. Roxas, D. B., Obsioma, A. R., Lapitan, R. M., Castillo, L. S., Momongan, V. C. & Juliano, B. O. (1985). The effects of variety of rice, level of
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nitrogen fertilization and season on the chemical composition and in vitro digestibility of straw. In: The utilization of fibrous agricultural residues as animal feeds. (P. T. Doyle, (Ed.)), International Development Program of Australian Universities and Colleges, Canberra, Australia. 47-52. Steel, R. G. D. & Torrie, J. H. (1960). Principles and procedures of statistics. McGraw-Hill Book Company, New York. Wilson, J. R. (1973). The influence of aerial environment, nitrogen supply and ontogenetical changes on the chemical composition and dry matter digestibility. Austr. J. Agric. Res., 24, 543-56. Winugroho, M. (1981). Studies on the utilization of cereal straws. MSc Thesis. University of Melbourne, Australia.