Taro (Alocasia odora (C) Koch, Xanthosoma nigra (vell) Stellfeld and Colocasia esculenta (L) schott) in Central Vietnam: biomass yield, digestibility and nutritive value

Du Thanh Hang and Nguyen Trung Kien

Hue University of Agriculture and Forestry,
Hue, Central Vietnam
hangduthanh@yahoo.com.vn

Abstract

The biomass yield of four popular varieties of Taro, traditionally grown in the sandy soil of Thua Thien Hue province, was documented. The varieties were: Ao trang [Colocasia Esculenta (L) Schott (Green Sterm)]; Chia voi [Colocasia Esculenta (L) Schott (Light Green Stem)], Tim [Alocasia Odora C.Koch (purple sterm)] and Quang [Xanthosoma nigra (vell) stell feld]. The DM percentage in the leaves was double and crude protein triple that in the petioles. Total oxalate was up to 50% higher in petioles than in leaves and tended to be lower in the An Trang and Chia Voi varieties compared with the Quang and Tim varieties. On a DM basis leaves and petioles each contributed about 50% of the total biomass. Yields were similar for  Ao Trang, Chia voi, and Tim and much lower for the Quang variety. Assuming that harvests continued at 30 day intervals throughout the year then annual yields for the An Trang variety would be of the order of 250 tonnes/ha of fresh biomass and 4.2 tonnes/ha of crude protein.ng

Four castrated male F1 (Mong Cai x Large White) pigs with initial weight of 40 ± 0.3 kg were allocated to a 4*4 Latin square to measure total tract digestibility and nitrogen utilization of diets including 50% of ensiled taro foliage. The control diet (RM) was a 50:50 mixture of rice bran and maize meal supplemented with minerals and vitamins. The other 3 diets had ensiled Taro foliage (leaves + petioles) replacing 50% of the RM diet (TS50), or the TS50 diet with 5% rice wine by-product (TS50WB) or with addition of 0.2% synthetic methionine (TS50M). Feed DM intake did not differ among the four diets, but there were differences in nutritive value. Apparent digestibility of OM was lower, but that of crude fibre was higher when ensiled Taro foliage replaced 50% of the maize-rice bran. Nitrogen retention and biological value of the dietary protein were  increased with incorporation of Taro silage in the diet, and by addition of rice wine by-product. There were no benefits from supplementation with synthetic DL-methionine.

Key words: biological value, methionine, pigs, rice wine-by-product

Introduction

Vietnam with a hot and humid climate has good conditions for growing Taro (Colocasia esculenta). According to Nguyen Thi Ngoc Hue (2005), there are ten main varieties of Taro grown for tubers in the North of Viet Nam. In Thua Thien Hue province in central Vietnam, eight varieties are grown (Du Thanh Hang and Preston 2010; Ngo Huu Toan and Preston 2010), some for tubers and some for the stems (petioles) used as vegetable in popular dishes such as "Com hen" and "canh chua bac ha". Some Taro cultivars are grown for feeding to pigs. Taro has a high biomass yield, which depends on the season, climate, fertilizer application, time of harvesting, defoliation and purpose of use. According to Ngo Huu Toan and Preston  (2010), the yield of fresh biomass can be from 250 to 370 tonnes/ha. Taro leaves are rich in protein while the stems (petioles) are rich in soluble carbohydrates (Rodríguez and Preston 2009). The main limitation toTaro foliage as feed for pigs is the presence of oxalate salts, however, these can be reduced by cooking, soaking and ensiling (Du Thanh Hang et al 2011). 

The objective of this study was to document the biomass yield of some popular Taro varieties grown in the coastal region of Central Vietnam and to determine the nutritive value for pigs of diets in which the ensiled foliage (leaves + petioles) replaced 50% of a traditional diet of equal parts of maize grain and rice bran. The effect of supplements of rice wine by-product and synthetic methionine was also investigated. 

Materials and methods

 Experiment 1: Biomass yield and chemical composition of selected Taro varieties

Location 

The experiment was carried out in Phú Đa village, Phu Vang district of Thua Thien Hue province to document the biomass yield of four popular varieties of Taro growths  traditionally grown in the sandy soil of Thua Thien Hue province.

Experimental design

The treatments were the four varieties: Ao trang [Colocasia Esculenta (L) Schott (Green Sterm)]; Chia voi [Colocasia Esculenta (L) Schott (Light Green Stem)], Tim [Alocasia Odora C.Koch (purple sterm)] and Quang [Xanthosoma nigra (vell) stell feld]. They were arranged with 4 replicates in a 4*4 Latin square design with plots ​​measuring 2.5*4m. The total experimental area was 200m².  The varieties were planted at a distance of 20 cm between plants and 60 cm between rows. Fertilization before planting was with 200 kg organic manure and 10 kg of NPK fertilizer applied to the overall area of 200m².  After each harvest a further application was made to the experimental area of  200 kg organic manure and 10 kg super phosphate.

The first harvest was made 60 days after planting, with two subsequent harvests at 30 day intervals. The whole plant was harvested with leaves and petioles being weighed separately. At each harvest, samples (10%) of the leaves and petioles of each species were taken for analysis of dry matter, protein and oxalate salts.

Experiment 2: Digestibility and nitrogen retention in pigs fed diets containing 50% ensiled taro with or without rice wine by product and synthetic methionine 

Location 

The experiment was done in the experimental farm of the University.

Experimental design

Four castrated male F1 (Mong Cai x Large White) pigs with initial weight of 40 ± 0.3 kg were allocated to a 4*4 Latin square to measure total tract digestibility and nitrogen utilization of diets including 50% of ensiled taro foliage. The control diet (RM) was a 50:50 mixture of rice bran and maize meal supplemented with minerals and vitamins (Table 1). The other 3 diets had ensiled Taro foliage (leaves + petioles) replacing 50% of the RM diet (TS50), or the TS50 diet with 5% rice wine by-product (TS50WB) or with addition of 0.2% synthetic methionine (TS50M).  

Each experimental period included 7 days for adaptation and five days for collection of samples (feeds, feces and urine).

Ensiling the Taro foliage

Taro leaves and petioles were ensiled by first chopping into small pieces (2-3 cm,), then wilting under shade overnight and then mixing with 3% molasses (fresh basis), prior to sealing in polyethylene bags for 21 days. 

Chemical analyses

Samples of feed and refusals were dried at 60⁰C for 24 h and ground through a 1 mm sieve prior to chemical analysis according to the standard methods of AOAC (2002). Dry matter (DM) was measured by drying fresh samples at 105⁰C for 24 h. Crude protein (N*6.25). was determined on fresh samples by the Kjeldahl method Ash was the residue after ashing the samples at 600⁰C.  

The total oxalate contents were determined using the method outlined by Savage et al (2000). Duplicate samples (0.5 g of finely ground material) were weighed into 125 ml flasks and 40 ml of 0.2 M HCl added. The beakers were placed in a water bath at 80°C for 15 min. The extract was allowed to cool and then transferred quantitatively to a 100 ml volumetric flask and made up to volume with 0.2 M HCl. A 45 ml aliquot of each extract was centrifuged at 2889 RCF (Varifuge 3.0R, Heraeus, Hanau, Germany) for 15 minutes before the supernatant was filtered through a 0.45 μm cellulose nitrate filter.

Statistical analysis

Analysis of variance was performed using the general linear model (GLM) procedure of Minitab (2010). 

Results and Discussion

The DM percentage in the leaves was double and the crude protein triple that in the petioles (Table 2). Total oxalate was up to 50% higher in petioles than in leaves and tended to be lower in the An Trang and Chia Voi varieties compared with the Quang and Tim varieties. 

The fresh yield of the petioles was almost double that of the leaves; however, on a DM basis leaves and petioles each contributed about 50% of the total biomass (Table 3). Yields were similar for  Ao Trang, Chia voi, and Tim and much lower in the Quang variety. Assuming that harvests continued at 30 day intervals throughout the year then annual yields for the An Trang variety would be of the order of 250 tonnes of fresh biomass, similar to the low end of the range (250 to 370 tonnes/ha/year) reported by Ngo Huu Toan and Preston (2010).    

The DM content of leaves increased in the 2^nd and 3^rd harvests compared with the first harvest (Table 4). The same trend was seen for the DM content of the petioles as between the 3^rd and first harvests. The oxalate content of leaves and petioles declined after the first harvest. The crude protein content in leaves and petioles did not change between harvests. 

 Feed DM intake did not differ among the four diets (Table 5). 

 OM apparent digestibility was lower when ensiled Taro foliage replaced 50% of the maize-rice bran (Table 6). By contrast apparent digestibility of crude protein was similar among all diets other than the diet with added methionine which was lower than the rest. Apparent digestibility of crude fiber was highest when the rice wine by-product was included in the diets.

 Urine volume was higher on all diets containing ensiled Taro foliage. This apparent diuretic effect of ensiled Taro silage was also reported by Malivanh et al (2012) and was attributed to the need to excrete oxalate salts in the urine.  

N retention was increased when ensiled Taro foliage replaced 50% of the maize-rice bran in the diets (Table 6). When N retention was expressed as percent of N intake and of N digested there appeared to be a major benefit from inclusion of 5% of rice wine by-product in the diet. Similar positive effects on N retention from addition of rice wine by-product to diets rich in ensiled Taro foliage were reported by Manivanh et al (2012). 

Conclusions

• The DM percentage in Taro leaves was double and crude protein was triple that in the petioles.

• On a DM basis leaves and petioles each contributed about 50% of the total biomass. Assuming that harvests were made at 30 day intervals throughout the year then annual yields of Taro foliage (leaves plus petioles) would be of the order of 250 tonnes of fresh biomass.

• Coefficients of apparent digestibility of organic matter were reduced but those for crude fiber were increased when ensiled Taro foliage replaced 50% of the maize-rice bran in the diet.

• Daily N retention and the biological value of  the dietary protein were increased when ensiled Taro foliage replaced 50% of the maize-rice bran in the diet, with additional benefits to biological value when 5% of rice wine by-product was also added.

Acknowledgments

The authors would like to thank each of the farmers who permitted us to carry out experiments in their farms. The authors also gratefully acknowledge the support from the MEKARN project, funded by Sida (Sweden).

References

AOAC 2002 Official methods of analysis of AOAC International. 17th edition. 1st revision. Gaithersburg, MD, USA, Association of Analytical Communities.

Du Thanh Hang and Preston T R 2009 Taro (Colocacia esculenta) leaves as a protein source for growing pigs in Central Viet Nam. Livestock Research for Rural Development. Volume 21, Article #164. http://www.lrrd.org/lrrd21/10/hang21164.htm

Du Thanh Hang and  and Preston T R 2010  Effect of processing Taro leaves on oxalate concentrations and using the ensiled leaves as a protein source in pig diets in central Vietnam. Livestock Research for Rural Development. Volume 22, Article #68. http://www.lrrd.org/lrrd22/4/hang22068.htm

Du Thanh Hang, Binh L V, Preston T R and Savage G P 2011 Oxalate content of different taro cultivars grown in central Viet Nam and the effect of simple processing methods on the oxalate concentration of the processed forages. Livestock Research for Rural Development. Volume 23, Article #122.  http://www.lrrd.org/lrrd23/6/hang23122.htm

Manivanh N, Ngoan L D and Preston T R 2012 Apparent digestibility and N retention in growing pigs fed rice bran supplemented with different proportions of ensiled Taro foliage (Colocacia esculenta) and rice distillers’ by-product. Livestock Research for Rural Development. Volume 24, Article #67. http://www.lrrd.org/lrrd24/4/noup24067.htm

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Rodríguez L and Preston T R 2009 A note on ensiling the foliage of New Cocoyam (Xanthosoma sagittifolium). Livestock Research for Rural Development. Volume 21, Article #183. http://www.lrrd.org/lrrd21/11/rodr21183.htm

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Received 29 March 2012; Accepted 17 November 2012; Published 2 December 2012

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