Chemical and physical properties of Sarawak (East Malaysia) rice straws

H Nori, S A Sani and A A Tuen*

Faculty of Resource Sciences and Technology, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
* Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak, 94300 Kota Samarahan, Sarawak, Malaysia
nhollena@frst.unimas.my

Abstract

Samples of straw from two varieties of rice, namely Biris and Saratani were collected and separated into leaf (including leaf blade and sheath) and stem fraction and were analyzed for chemical composition and predicted digestibility. The grain yield, straw yield, grain to straw ratio and leaf to stem ratio were determined in terms of dry matter.

Varietal differences in the straw chemical composition were significant where Saratani had higher concentration of organic matter (P<0.01) and digestibility (P<0.01) while Biris produced higher concentration of acid detergent lignin (ADL) (P<0.001), acid detergent fiber (ADF) (P<0.05) and ash (P<0.01). Between the two varieties, Saratani variety is superior to Biris in view of the higher grain yield, grain to straw ratio and digestibility.

The result showed that rice variety with good agronomic characteristics produced straw with better nutritive quality.

Key words: agronomic characteristics, nutritive quality, variety

Introduction

Rice straw has been used as ruminant feed in traditional livestock farming communities in Asia. It is used to meet part of the nutrient requirements of ruminants in the rice-producing areas during the cropping season and in dry or drought periods. Rice straw is usually categorized as poor quality roughage, but its feeding value can vary over a wide range.  It was reported that rice straws from Malaysia showed great variability in their chemical composition (Vadiveloo 1995; Nori et al 2006), proportion of morphological fractions (Vadiveloo 2000; Nori 2005) and digestibility as estimated by in vitro (Vadiveloo 2003; Nori et al 2006) measurements. However, these previous studies only provide information on the properties of Peninsular Malaysian rice straw varieties but straw cultivars from Borneo, especially Sarawak which is located in East Malaysia have not been explored and studied. In terms of geographical location, Peninsular Malaysia and Borneo Island (where East Malaysia is located) are 650 km apart and separated by the South China Sea. Malaysia region has a monsoon climate, but only the east coast of Peninsular Malaysia has a real rainy season. The wettest season on the west coast of the peninsular is between September and December; on the east coast and in Sabah and Sarawak is between October and February. It has been reported that environmental factors such as location, weather and planting season contributes to variability in chemical composition and digestibility of rice straw (Vadiveloo and Phang 1996; Shen et al 1998; Summers et al 2001).

This present study was conducted to evaluate the chemical composition and agronomic characteristics of straws from Sarawak rice varieties, namely Biris (traditional variety) and Saratani (modern variety).

Materials and methods 

Rice straw

Two varieties of rice, Biris and Saratani, were hand harvested from the farmer’s field in Kota Samarahan district of Sarawak, East Malaysia, in March 2007. Biris is a traditional rice variety where as Saratani is a commercial, modern rice variety. Eight samples were collected for each variety. The grains were separated from the straw following harvest. Approximately 1 kg of the straws was separated into leaf (including blade and sheath) and stem fractions.  The straw samples were oven-dried at 60 ^oC for 48 hours and ground to pass through a 1 mm sieve in a hammer-mill for chemical analysis.  

Chemical and physical analysis

The ground samples (leaf and stem fractions) were analyzed in the laboratory for crude protein, neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), ash and silica.  The crude protein and ash were determined by Association of Official Analytical Chemist (AOAC 1984).  Chemical composition for NDF, ADF and ADL were analyzed according to the procedures of Goering and Van Soest (1970) and silica was determined according to the method as described by Smith et al (1971). The organic matter and cellulose content were obtained by calculation. The digestible dry matter (DDM) was calculated based on Pioneer Forage Manual, A Nutritional Guide (Holland and Kezar 1990):

Digestible Dry Matter (DDM) = 88.9 – (%ADF x 0.779)

The plant physical (agronomic) properties such as leaf to stem ratio, grain to straw ratio, grain yield, straw yield and stem height were recorded.

Statistical analysis

The data were analyzed by using a paired T-test to evaluate significant differences between two rice varieties. The analysis was run on a SAS Version 6.12 statistical package.

Results and discussion 

Chemical composition

The chemical composition and dry matter digestibility in each botanical fractions of two rice varieties are shown in Table 1.

Between the varieties, Biris has the highest concentration of ADF (P<0.05), ADL (P<0.001) and ash (P<0.01) where as Saratani has the highest dry matter digestibility (P<0.01) and organic matter (P<0.01) content. Crude protein concentration in the stem fraction of Biris is higher (5.34%) than Saratani. The concentration of crude protein in the leaf fraction did not differ significantly (P>0.05) between the varieties. However, the highest crude protein content of 5.34% reported in this study is still below the critical level of 7% which is necessary for voluntary feed intake in ruminants. Therefore, rice straw should not be used as a sole feed for ruminants but only recommended as a replacement for part of the forage in a ration. High content of silica is found deposited in the leaf fraction of Biris (19.6%) (P<0.05). Silica that is absorbed and metabolized by forage crops has been found to be an important factor in reducing the digestibility of cell wall constituents (Agbagla-Dohnani et al 2003). Saratani has higher cellulose content in the leaf fraction (P<0.01). The cellulose content in the stem fraction for both varieties was not significantly different (P>0.05). NDF content was observed to be highest in the stem fraction of Biris (57.6%) and leaf fraction of Saratani (57.2%).

Physical properties

The physical properties of two rice varieties are given in Table 2.

Saratani variety bear higher grain yield of 3.47 t/ha (P<0.05) and grain to straw ratio of 0.99 (P<0.01). On the other hand, Biris had higher straw yield of 4.87 t/ha (P<0.001) and leaf to stem ratio of 1.13 (P<0.05). There was no varietal differences in the stem height (P>0.05). Some farmers consider the straws from high yielding varieties to be less acceptable to animals (Hilmersen et al 1984). In contrast, our results showed that variety Saratani, which is a commercial and modern variety, with higher grain yield and harvest index produced straw with better nutritive quality in view of its higher digestibility rate. Our result is also supported by other researchers (Devasia et al 1976; Vadiveloo 2003) who reported that straws from new high yielding varieties of rice produce better nutritive quality than the traditional varieties. Plant breeders have become interested in varieties that would have both high grain yield and high straw digestibility to improve the total crop utilization ratio (Bainton et al 1991). 

Conclusion 

• The superiority of Saratani variety should be confirmed in animal feeding experiments.

• Varietal differences in the nutritive quality of rice straw provide an opportunity for plant breeders to improve straw quality through breeding and selection. 

• The release of rice varieties with good straw and agronomic characteristics will benefit both rice and animal breeders.

References 

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AOAC 1984  Official Methods of Analysis, 14th edition.  Association of Official Analytical Chemists, Washington, DC.

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Goering H K and van Soest P J 1970  Forage fiber analysis.  Apparatus, reagents, procedures and some applications.  USDA Agricultural Handbook No. 379.

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Received 20 April 2009; Accepted 24 April 2009; Published 5 August 2009

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