Study on the effect of harvesting frequency on cassava foliage for cassava hay production and its nutritive value

A Phengvilaysouk and M Wanapat^*

Livestock Research Center, National Agriculture and Forestry Research Institute,
Ministry of Agriculture and Forestry, P O Box 811,Vientiane, Lao PDR
ammalyp@yahoo.com
* Tropical Feed Resources Research and Development Center (TROFREC), Department of Animal Science, Faculty of Agriculture,
Khon Kaen University, Khon Kaen 40002, Thailand

Abstract

This experiment was carried out to investigate the effect of harvesting frequency on yield and nutritive value of cassava foliage. It was arranged in a Randomized complete block design (RCBD). Two treatments were two different ages of cassava foliage of initial harvesting, at 2 and 4 months; (IC₂) and (IC₄). The subsequent harvestings for both were at every 2 months until the cassava foliage was 8 months old. Cassava (Rayong 5, RY₅) was cultivated as a monoculture for all plots; each plot was 5x10 m (50 m²), and 150 kg/ha of commercial fertilizer (46-0-0, N-P-K) was applied to cassava crop at the start.
 

The results showed that cassava foliage yield was significantly different (P<0.05) among harvesting times within the treatments. For the initial harvesting at 2 months of age (IC₂), DM yield was highest in the second harvest (H₂) and was lowest in the fourth harvest (H₄) (3.2 and 1.2 tonnes/ha, respectively). For the treatment of initial harvesting at 4 months of age (IC₄), DM yield was greatest in the first harvest (H₁) (3.3 tonnes/ha) and was lowest in the third harvest (H₃) (1.2 tonnes/ha). The foliage yield at each harvesting time significantly decreased (p<0.05) with the crop age. However, total DM yield was not significantly different among treatments. Total DM yields of IC₂ and IC₄ were 7.1 and 6.5 tonnes/ha, respectively. The fiber contents, NDF, ADF and ADL, were significantly (p<0.05) higher in IC₄ than IC₂, especially in the first harvest (H₁) (56.4, 37.5 and 14.6%, respectively). In contrast, CP was significantly higher in IC₂ (21.5%). Based on this study, it is concluded that different initial harvesting of cassava foliage at 2 months (IC₂) and 4 months of age (IC₄) had no major affect on the quantity of the foliage, with yields of 7.1 vs 6.5 tonnes/ha, respectively, but affected the chemical composition of cassava, especially of CP (21.5% vs 20.5%) and NDF (48.1% vs 52.4%), respectively.

Keywords: Cassava foliage; initial harvesting; cassava hay production; chemical composition

Introduction

Cassava or tapioca (Manihot esculenta, Crantz) is an annual tuber crop grown widely in tropical and sub-tropical countries. This plant is well known for adaptation to poor soil conditions, to be drought resistant and to be pest tolerant (Chantaprasam and Wanapat 2003). Several varieties of cassava are found in Lao PDR, including ordinary cassava, red cassava, yolk cassava, Japanese cassava, mottled cassava and the animal feed cassava (Biodiversity Country Report 2003). Generally, cassava is a crop traditionally grown for root production. Cassava root is regarded as a reserve food for people because it is an excellent energy source, and leaves are available as crop residues when the root is harvested (Vongsamphanh 2003). Cassava foliage is one of the most important crops for farmers, because it contains a high content of proteins. According to Allen (1984) cassava leaf has a high crude protein (CP) concentration (16.7 to 39.8% CP) which consisted of various essential amino acids in proportions close to those of soybean meal(Atchara Limsila et al 2002). However, the intake and digestibility could be low due to the high level of condensed tannins (Reed et al 1982; Onwuka 1992).

Recently, several researchers have paid attention to cassava in integrated crop-livestock farming systems in several Asian countries. Preston (2002) reported that new research information about the use of cassava foliage as animal feed is becoming available. The potential use of cassava hay (combined leaves, stems and petiole) was reported by Wanapat et al (1997) and then by Wanapat (2000a; 2000b), who also reported that planting cassava for hay making aimed to increase digestible biomass. In addition, cassava tubers contain high levels of starch while the leaves have been used as a high protein source when collected at tuber harvesting time (Wanapat 2001). Alternatively, systems for making hay from cassava foliage by harvesting the whole upper green part at early growth stage (3-4 months), and every 2-3 months subsequently until one year by cutting the whole crop at 30 cm above ground could reduce the condensed tannin content and increase the protein content (25% of DM), resulting in a higher nutritive value (Wanapat 2003). Cassava can also be managed as a semi-perennial crop with repeated harvesting of foliage at 2-3 month intervals (Preston and Rodríguez 2004). It is very important that new high-yielding cassava varieties and highly effective cultivation technologies are developed (Wenquan Wang 2002).

The purpose of this study was to determine the effect of initial harvesting of cassava foliage at 2 and 4 months, and subsequent harvestings at 2 months until 8 months of age, on cassava hay yield and chemical composition under the rain-fed conditions of Lao PDR.
 

Materials and methods

Location

The experiment was conducted at the Livestock Research Center (Nam Xuang), 44 km from Vientiane City, Lao PDR, under rain fed conditions on a sandy loam soil. The pH of the soil was 4-5. There are two seasons, dry (November-April) and rainy (May-October). The average temperature was approximately 27^oC. The experiment was started in March 2006 and finished in January 2007.

Experimental design

The experiment was arranged in a Randomized complete block design (RCBD) with 2 treatments and 6 replications. Cassava was cultivated in monoculture for all of the plots and each plot was 5x10 m (50 m²). The experiment consisted of the following two treatments:

• IC₂ = Initial harvesting of cassava foliages at 2 months and subsequent harvesting every 2 months until 8 months of age.
• IC₄ = Initial harvesting of cassava foliages at 4 months and subsequent harvesting every 2 months until 8 months of age.

Soil preparation and cultivation of cassava

Soil was ploughed by using a tractor to break down the soil structure without harrowing. The area was divided into 12 plots. The size of each plot was 5x10 m. Rayong 5 [RY₅] was cultivated in monoculture at the beginning of the rainy season (March). Cassava stems were used at length of 15-20 cm for planting with 90x60 cm spacing in each plot. Weeding was done monthly and commercial fertilizer (46-0-0 of N-P-K) was applied initially and after at every harvest (150 kg/ha).

Harvesting of cassava and chemical analysis

Initial harvesting of cassava foliage was done at 2 months (IC₂) and at 4 months (IC₄) of growth. The subsequent harvest was done at every 2 months of growth until the foliage was 8 months old. Cassava foliage IC₂ was harvested 4 times and IC₄ was harvested 3 times. Harvesting of IC2 treatment was at 2 months when the plants were 90-120 cm in height. They were harvested at 40-50 cm above the ground, and treatment of IC4 was harvested when the foliage was 150-180 cm in height, cutting at 90-100 cm, only green part of foliage. The cassava foliage comprised young stems, leaves and petioles. They were harvested between 08:00h - 10:00h to avoid yield fluctuation. The foliage was measured for fresh yield in individual plots.

The samples 1 kg were randomly sampled of each plot and divided into two parts, one for separate proportions of leaves, petioles and stems, and the other for analysis of dry matter (DM), ash and crude protein (CP), according to (AOAC 1990). Neutral-detergent fiber (NDF), acid-detergent fiber (ADF) and acid-detergent lignin (ADL) were determined by the procedure of Goering and Van Soest (1970). Condensed tannins (CT) in cassava hay were analyzed by the Vanillin-HCL method (Burns 1971 modified by Wanapat and Poungchompu (2001).

Statistical analysis

Data were subjected to Analysis of Variance (ANOVA) according to RCBD using the General Linear Model (GLM) of Minitab Software Version Release 14 (2003). Treatment means that showed significant differences at the probability level of (P<0.05) were compared by using Tukey's pairwise comparison procedures. The following model was:

Y_ij = µ +B_i + T_j + E_ij

Where: 

Y_ij = Observation in block i (I=1-6) and treatment j (j=1-2),

µ = Overall mean,

B_i = Block effect,

T_j = Treatment effect,

E_ij = Error.
 

Results

Yield and chemical composition of cassava foliage

Leaf accounted for a higher proportion than petiole and stem of the whole crop. Within initial harvesting of cassava foliage at 2 months (IC₂), the highest DM yield was 3.2 tonnes/ha, obtained at second harvesting (H₂) while within initial harvesting of cassava foliage at 4 months (IC₄) it was 3.3 tonnes/ha, obtained at first harvesting (H₁). Highest total yield was found at IC₂ compared with IC₄ (7.1 vs 6.5 tonnes/ha) (Table 1).

Crude protein contents were similar under each initial harvesting, ranging from 19.7 - 22.2% but were significantly different between IC₂ and IC₄ (21.5 vs 20.5%, respectively). The fibrous fractions, NDF, ADF, ADL were found to be different (p<0.05) under each initial harvesting and especially when compared between two initial harvesting times (IC₂ and IC₄). It was apparent that initial harvesting at 2 months resulted in lower contents of all fibrous fractions (Table 2).

Economical returns

Economical returns of cassava foliage are shown in Table 3. The total expenditures for IC₂ and IC₄ are significantly different. Treatment IC₂ resulted in higher expenditure compared to IC₄ (1,693 and 1,451 USD), respectively. The costs of cassava hay for IC₂ and IC₄ were not significantly different, 0.2 USD/kg of DM. However, cassava foliage at IC₂ had a higher quality, because of higher levels of protein and lower levels of fiber.

Discussion

Cassava foliage yield

In the current study, initial harvesting of cassava foliage at 2 months (IC₂) and at 4 months (IC₄) showed that total dry matter yield ranged from 7.1 to 6.5 tonnes/ha, respectively, but was not significantly different between IC₂ and (IC₄. These results agreed with Wanapat (2001), who found that the DM yield of cassava hay ranged from 2-8 tonnes/ha, depending on variety, cultivation practice and use of fertilizer. This is in contrast with results from the study of Chantaprasarn and Wanapat (2003), who demonstrated that DM yield of cassava foliage ranged from 0.3 to 4.0 tonnes/ha when harvested at 3 months after planting under traditional cultivation. DM yield of both treatments was slightly higher than the value obtained by Khang and Preston (2005a) who reported a cassava foliage KM₉₄ dry matter yield of 4.3 tonnes/ha. A similar result was also obtained by Duong and Preston (2005), who found that dry matter yield of cassava foliage was increased from 4.3 to 5.4 tonnes/ha when the cassava was fertilized with effluent at 5 tonnes DM/ha. Poungchompu et al (2001) also reported that DM yields were relatively high (3.6 to 4.4 tonnes/ha) for 3 cuttings, with a first harvest at 3 months after planting and every 2 months thereafter, and with planting on ridges and manure application.

The results in the present study were basically lower than the finding of Wanapat et al (2005), who reported that cassava production without legume intercropping and with cowpea, Stylosanthesguianensis and Phaseoluscalcaratus intercropping produced 12.6, 10.9, 11.4 and 11 tonnes DM/ha of cassava foliage, respectively. DM yield of cassava foliage was significantly reduced by subsequent harvesting and with the age of the cassava plants. This finding is in agreement with Vongsamphanh and Wanapat (2004), who showed that yield of RY₇₂ and a local variety was linearly decreased with harvest time after planting, and Chantaprasarn and Wanapat (2003), who showed that cassava foliage yield was increased by frequent harvesting intervals. A similar result was also obtained by Sinthuprama et al (1983). Plant spacing and frequency of cutting have been shown to have a significant effect on the combined yield of cassava (Petlum et al 2001). However, cassava foliage yield when harvested at 2-month intervals could be maintained over a 2 year period when goat manure or bio-digester effluent was applied at the rate of 180 kg N/ha after every harvest (Preston 2001). There are several possible explanations for this result on the different yields of cassava foliage, such as it differences in study site, seasonal conditions, planting space, fertilizer management, subsequent harvestings, and differences in variety (Gomez and Valdivieso 1984; Simwambana et al 1992). Fertilizer management can affect foliage yield, as reported by Molina and El-Sharkawy (1995), as can the factor of age at first cutting and interval between cuttings (Lockard et al 1985; Simwambana et al 1992; Tung et al 2001; Hong et al 2003).

The present results show that leaf proportion ranged from 46.4 to 48.5% when harvested at IC₂ and IC₄, respectively. However, these values were lower than the results of Meyrelles et al (1977), who found the leaf proportion of cassava foliage was 52%. In addition, leaf proportion was higher when the crop was fertilized with effluent from a bio-digester, and ranged from 60 to 66% (Khang and Preston 2005a). This finding agrees with Nguyen Phuc Tien et al (2003,) who showed that leaf proportion of cassava foliage associated with Flemingia ranged from 60 to 63%. It has been found that cassava hay harvested at 4 months after planting had a leaf proportion of 61.6% (Wanapat 2002).

The present results concerning the chemical composition of cassava hay are in agreement with those from Khang and Preston (2005a; 2005b), who reported that CP content in cassava foliage ranged from 18.7 to 20.5% when intercropped with Flemingia, and from 18.6 to 20.7% with application of effluent from a bio-digester. In present study, CP content in cassava foliage ranged from 19.7 to 22.2%. Wanapat et al (1997) reported that the CP value in cassava hay (whole crop) was 24.9%, compared with 20.6-22.0% CP in the study of Poungchompu et al (2001). These results were lower than the values obtained by Kiyothong and Wanapat (2003), who found that CP content ranged from 21.6 to 21.9% in cassava hay as sole crop. Vongsamphanh and Wanapat (2004) also found that CP ranged from 22.6 to 25.8% when harvested at 3 month intervals, and Wanapat et al (2005) reported cassava foliage intercropped with legumes had a protein content that ranged from 20.2 to 24.1% CP in the first and second year, respectively.

Concentrations of the fibrous components of cassava hay, NDF, ADF and ADL were 48.1, 30.5, 10.7 and 52.4, 33.4, 12.3% when harvested at IC₂ and IC₄, respectively. The values of NDF, ADF and ADL in this study were higher than those reported by Chantaprasarn and Wanapat (2003), and than those obtained by Man and Wiktorsson (2001; 2002). NDF content ranged from 35.3 to 37.6% when foliage was grown with and without effluent applied (Khang and Preston 2005a). It can be suggested that when cassava was grown as monoculture, the fibrous fraction was slightly higher compared to cassava intercropped with legumes, and that the differences were probably due to differences in harvesting time.

Condensed tannins (CT) in cassava hay harvested at IC₂ and IC₄ were from 3.6 to 3.5%, respectively, and tended to decrease with subsequent harvestings. These results are in agreement with those (3.4%) of Vongsamphanh and Wanapat (2004), and are slightly lower than the values obtained by Poungchompu et al (2001) and Kiyothong and Wanapat (2003). The level of condensed tannins in the present study tended to decline with frequent harvesting, and was similar to the values obtained by Hong et al (2003). Wanapat (2002) also reported that CT was generally higher in mature cassava leaves than in cassava hay harvested at a young growth stage. However, a level of CT of between 2-4% is considered to be favorable for ruminants as rumen by-pass protein (Wanapat 2001). If the level of CT in the feed exceeds 6% of dry matter, it will reduce feed intake and digestibility (Barry and Manley 1984).
 

Conclusions and recommendations

• Based on this experiment, it can be concluded that different initial harvesting intervals of cassava foliage affected chemical composition, but not the quantity of cassava hay.

• Early initial harvesting of cassava foliage showed that the crude protein content tended to be higher and fibrous fractions lower in IC₂.

• Further research should be carried out on factors affecting the yield of cassava foliage and feeding method in different farming systems.

• It would be interesting to assess the effects of intercropping with legumes, and to consider integrated crop-livestock systems in terms of animal manure application to improve cassava foliage yield on-farm.
   

Acknowledgements

The author would like to express most sincere thanks to the Swedish International Development Agency (Sida), Department for Research Cooperation with Developing Countries (SAREC), through the MEKARN regional project for funding this thesis research, and to the National Agriculture and Forestry Research Institute (NAFRI), Livestock Research Center (LRC) and Tropical Feed Resources Research and Development Center (TROFEC), Department of Animal Science, Faculty of agriculture, Khon Kaen University, Thailand for permission to use research facilities and for their cooperation.
 

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