Effect of intercropping on biomass yield and chemical composition of cassava

Suphawat Joomjantha and Metha Wanapat^*

Tropical Feed Resources Research and Development Center, Department of Animal Science,
Faculty of Agriculture, Khon Kaen University, Khon Kaen 40002, Thailand
jyjoe28@hotmail.com

Abstract

A randomized complete block design (RCBD) with 4 treatments and 4 replications was used to investigate the effect of various kinds of inter-cropping on yields and nutritive value of cassava foliage at 3 months of age. The cultivation treatments were: four rows of cassava without intercropping (control treatment, 4CF); four rows of cassava + two rows of Phaseolus calcaratus (4CF+2PC); four rows of cassava + two rows of sweet potato (4CF+2SP), and four rows of cassava + one row of Phaseolus calcaratus and one row of sweet potato (4CF+1PC1SP). The crops were grown on a sandy loam soil after ploughing and harrowing. Cassava was planted on ridges. Cattle manure was applied during harrowing at 300kg/ha. All foliages were initially harvested at 3 months after planting.

The results showed that intercropping of cassava foliage with two rows of sweet potato significantly increased cassava foliage yield when compared with control and other intercropping treatments (P<0.05). The cassava foliage yields were 2.1, 1.9, 2.6, and 1.9 tonnes/ha DM for 4CF, 4CF+2PC, 4CF+2SP and 4CF+1PC1SP, respectively. However, total DM yield of cassava and intercrops were highest in 4CF+1PC+1SP. There was no significant effect of intercropping on chemical composition of cassava foliage. The highest CP content (24.5% in DM) was obtained in cassava hay.

It is concluded that intercropping of cassava with sweet potato and Phaseolus calcaratus could increase foliage biomass and hence be recommended as a food-feed system especially under a small-holder farming system.

Keywords: Intercropping, Cassava foliage, Phaseolus calcaratus, Sweet potato, Food-feed system

Introduction

Cassava is grown widely in tropical countries. This plant is well known for its adaptability to poor soil condition, drought resistance and pest tolerance. It is a vitally important feed resource, which is abundantly available in the tropical countries. In Thailand, traditional cassava cultivation is for root production, as a human food and energy source for animals. Recently, managing cassava for foliage production has been found to have more potential as it is a high rumen by-pass protein source for ruminants and thus can improve production and reduce feed costs. Wanapat et al (1997) firstly reported the potential of cassava foliage made into hay (cassava hay), which combined leaves, stems and petiole, as a feed for ruminants. Alternatively, systems for making hay from cassava foliage by harvesting the whole upper green part at early growth stage (3-4 months) and thereafter every 2-3 months for subsequent harvests have been demonstrated and established by Wanapat et al (1997).

The potential of cassava-legumes inter-cropping as food-feed system for dairy farmers has been reviewed (Polthanee et al 2001). An advantage commonly claimed for intercropping systems is that they offer greater yield stability than sole cropping (Baker 1980; Rao and Willey 1980; Rao and Morgado 1984). Legume crops were intercropped with cassava such as cowpea, peanut and mungbean (Polthanee et al 2001), Flemingia (Dung et al 2005) Stylosanthes guianensis and Phaseolus calcaratus (Wanapat et al 2005). Cassava-legume intercropping systems usually increase the land use efficiency and economical return over solely cassava (Polthanee et al 2001) or long-term harvesting of cassava foliage showing benefits in saving costs of production which makes the system more sustainable for smallholder farmers (Wanapat et al 2005).

There is limited information on the biomass produced from the inter-cropped cassava-legumes systems or inter-cropped cassava with local fodder such as sweet potato, in terms of quality and feeding value for livestock. Wanapat et al (2005) reported that legume intercropping did not affect total yield and chemical composition of cassava foliage. Polthanee and Kotchasatit (1999) also reported that yield and root quality of cassava were not affected by the cassava-mung bean inter-cropping pattern. Dung et al (2005) reported that inter-cropping cassava with Flemingia resulted in higher and more stable yield of dry matter and crude protein content of cassava foliage. Moreover, inter-cropping cassava with Flemingia also improved soil fertility and decreased soil erosion (Dung et al 2005). It is very interesting in using sweet potato as intercrop with cassava foliage as human food and animal feed (food-feed system). It is a tropical root crop and has been grown exclusively for tuber production, mainly for human consumption (Ruiz et al 1981). Its leaves (SPL) also contain high crude protein (CP) content of 25.5-29.8% of DM.

The objectives of this study were to determine effect of cassava-legume (Phaseolus calcaratus ) or sweet potato inter-cropping on yield and chemical composition of cassava hay.

Materials and methods

Location

The experiment was conducted on farmer’s land in Khon Kaen, Thailand, from May to August, 2006. During this experiment the mean daily temperature, humidity and rainfall were 26.5^ºC, 80%, and 190 mm, respectively.

Experimental design and treatments

A randomized complete block design (RCBD) was used in the experiment with four treatments and four replications. The treatments were as follows:

4CF: Four rows of cassava cultivation without intercropping (4CF), Control

4CF+2PC: 4CF+ with two rows of Phaseolus calcaratus (4CF+2PC)

4CF+2SP: 4CF+ with two rows of sweet potato (Ipomoea batatas (L.) Lam) (4CF+2SP)

4CF+1PC1SP: 4CF+ with one row of Phaseolus calcaratus and one row of sweet potato (4CF+1PC1SP)

Land preparation and planting

The experiment was conducted during May to August, 2006. Land was ploughed and ridged then divided into sixteen plots (4.2x8.2 m each). Stems of cassava variety Rayong 72 with 15-20 cm length were used. Row spacing 40x60 cm (between stems and between rows) was used in all plots. Intercropping systems were done following the treatments above. Intercrops were grown in every 2 rows between 4 rows of cassava cultivation and two rows of cassava were grown as border rows. Weeding management was done two times for all experiment plots at the first and the second month after planting. Fertilizers were applied two times during preparation of the land using cattle manure at 2 tonnes/ha and 1 month after planting. All crops were rain-fed.

Data collection, analysis and sampling procedure

Three months after planting, cassava and intercrops were harvested. Harvesting of cassava foliage was done about 30 cm above ground by hand breaking. The samples were randomly collected and analyses of DM, CP and ash were done according to the procedure of AOAC (1990). Neutral-detergent fiber (NDF), acid-detergent fiber (ADF) and acid-detergent lignin (ADL) were determined according to the method of Van Soest et al (1991), condensed tannins by using the procedure of Burns (1971) as modified by Wanapat and Poungchompu (2001), and hydro-cyanic acid content spectrophotometrically (SpectroSC, LaboMed, inc. U.S.A.) with the 2, 4-quinolinediol-pyridine reagent (Lambert et al 1975).

2.6 Statistical analyses of data

All data were analyzed by ANOVA using the General Linear Model (GLM) of the SAS system for windows (SAS 1998). Treatment means were compared by using Duncan's New Multiple Range Test (Steel and Torrie 1980). The statistical model was:

Yij = µ + Bi + Tj+ Eij ,

where, Yij = observation in block i and treatment j, µ = Overall sample mean, Bi = Effect of block j, Ti = Effect of treatment i, Eij = Error

Results

The highest DM yield of cassava foliage was found in 4CF+2SP at 2.6 tonnes/ha (P<0.05) (Table 1). In addition, sweet potato intercropping (4CF+2SP) resulted in significantly higher cassava DM yield than Phaseolus calcaratus intercropping (2.6 vs. 1.9 tonnes/ha). Biomass DM yields with Phaseolus calcaratus (4CF+2PC) and sweet potato (4CF+2SP) were similar to that of the control while the combination of Phaseolus calcaratus and sweet potato as intercrops (4CF+1PC1SP) resulted in highest DM yield of 3.7 tonnes/ha (Table 2). Chemical composition of cassava foliage including CP, NDF, ADF, ADL, condensed tannin and hydro-cyanic acid (HCN) were similar across treatments. As compared among the three foliages, cassava hay, had highest CP content (24.5%) with slightly higher NDF and ADF contents and with similar CT and HCN values (Table 3).

Table 1. Yield and chemical composition of cassava foliage at 3 months of growth
Item	4CF	4CF+2PC	4CF+2SP	4CF+1PC+1SP	SEM
Fresh yield, tonnes/ha	9.9^a	8.9^a	12.1^b	9.0^a	0.65
DM yield, tonnes/ha	2.1^a	1.9^a	2.6^b	1.9^a	0.14
DM, %	22.7	20.6	22.4	20.9	1.55
	---------------------------% in DM--------------------------------
Ash	8.9	8.4	8.7	9.1	0.4
CP	24.4	24.6	23.8	23.7	0.8
NDF	50.3	46.9	48.8	50.9	1.2
ADF	41.2	39.8	39.5	40.1	1.8
CT	3.2	3.2	3.1	3.1	0.1
HCN (mg/100g)	1.9	2.0	2.0	2.0	0.2
^a,b,c Means in the same row with different superscripts differ (P<0.05) DM = dry matter, OM = organic matter, CP = crude protein, NDF = neutral-detergent fiber, ADF = acid-detergent fiber, CT= condensed tannin, HCN = hydro-cyanic acid, CF = cassava foliage, PC = Phaseolus calcaratus , SP = sweet potato, SEM = standard error of the mean 4CF = Four rows of cassava without intercropping 4CF+2PC = Four rows of cassava with two rows of Phaseolus calcaratus 4CF+2SP = Four rows of cassava with two rows of sweet potato (Ipomoea batatas (L.) Lam) 4CF+1PC+1SP = Four rows of cassava with one row of and one row of sweet potato

Table 2. Yield of cassava foliage at 3 months of age for control and inter-cropping systems
Item	4CF	4CF+2PC	4CF+2SP	4CF+1PC+1SP	SEM
Fresh yield, tonnes/ha
Cassava	9.9^a	8.9^a	12.1^b	9.0^a	0.65
Intercrops	10.3^a	8.0^a	6.6^a	15.2^b	1.75
DM yield, tonnes/ha
Cassava	2.1^a	1.9^a	2.6^b	1.9^a	0.14
Intercrops	2.2^a	1.9^a	1.5^a	3.7^b	0.4
Total yield, tonnes/ha
Fresh yield	20.2^ab	16.9^a	18.7^ab	24.3^b	2.05
DM yield	4.4^ab	3.9^a	4.2^ab	5.6^b	0.45
^a,b,c Means in the same row with different superscripts differ (P<0.05) DM = dry matter, CF = cassava foliage, PC = Phaseolus calcaratus , SP = sweet potato SEM = standard error of the mean, 4CF = Four rows of cassava without intercropping 4CF+2PC = Four rows of cassava with two rows of Phaseolus calcaratus 4CF+2SP = Four rows of cassava with two rows of sweet potato (Ipomoea batatas (L.) Lam) 4CF+1PC+1SP = Four rows of cassava with one row of and one row of sweet potato

Table 3. Chemical composition of cassava hay, sweet potato hay and Phaseolus calcaratus hay harvested at 3 months

Item	DM	Ash	CP	NDF	ADF	CT	HCN
	% …………………………..% inDM…....……………….						mg/100g
Cassava hay	89.6	9.5	24.5	49.9	40.7	3.2	1.9
Sweet potato hay	89.2	12.6	14.2	42	36.13	3.1	2.0
Phaseolus calcaratus hay	89.9	13.7	18.1	45.2	39.99	3.2	2.0
DM = dry matter, OM = organic matter, CP = crude protein, NDF = neutral-detergent fiber ADF = acid-detergent fiber, CT= condensed tannin, HCN = hydro-cyanic acid

Discussion

Wanapat et al (1997) reported that cassava grown in the dry season in the Northeast of Thailand resulted in 1.0 tonneha DM yield at 3 moths. However, cassava foliage yield was much higher where it was intercropped with leguminous plants (Wanapat et al 2005), namely cowpea and Phaseolus calcarlatus, when at 3 months after planting, yields were 2.1 and 2.3 tonnes DM/ha, respectively. Intercropping of leguminous fodder as food-feed between rows of cassava, such as Leucaena leucocephala or cowpea (Vigna unculata), enriches soil fertility and provides additional fodder. The effects of different harvesting intervals of cassava foliage yield ranged from 0.3 to 4.0 tonnes DM/ha, and were increased by frequent harvesting as reported by Chantaprasarn and Wanapat (2003). In the present study, yields of cassava in the control (without intercropping) were higher than reported by Wanapat et al (1997). The reason could be due to seasonal effect, since previous crops were grown in the dry season as compared to those grown in the rainy season. Intercropping of cassava foliage with Phaseolus calcaratus and /or sweet potato gave higher yield than in the control which was similar to that reported by Wanapat et al (2005). Higher cassava foliage yield was found in treatment of sweet potato intercropping when compared with other treatments. There is no research work available on intercropping of cassava foliage with sweet potato. The reason of higher yield of cassava foliage when intercropped with sweet potato in the present study could be attributed to the nature of crop canopies where sweet potato is a vine and Phaseolus calcaratus is a bush. This could affect the process of photosynthesis in the cassava crop.

Reports of the CP content of cassava foliage range from 20.2 t o 27.3 % in DM (Moore and Cock 1985; Wanapat et al 1997; Wanapat et al 2005; Poungchompu et al 2001; Chantaprasarn and Wanapat, 2003). In the present study, the CP of cassava foliage was 24.4, 24.6, 23.8, and 23.7% for 4CF, 4CF+2PC, 4CF+2SP, and 4CF+1PC1SP, respectively. The CP content of the cassava foliage was similar with the above reports. Ash content in cassava foliage in this study ranged from 8.4 to 9.1%. The result was higher than in previous studies (Wanapat et al 1997; Poungchompu et al 2001; Hong et al 2003; Kiyothong, 2003). The NDF and ADF of cassava foliage ranged from 46.9 to 50.9 and 39.5 to 41.2%. The values of NDF and ADF in this study were higher than those reported by Wanapat et al (1997). Poungchompu et al (2001) reported that NDF and ADF ranged from 57.5 to 58.8% and 31.0 to 32.0%, respectively. NDF was higher but ADF was lower than in the present study. Condensed tannins (CT) in this study were from 3.1 to 3.2% in DM. This result was slightly lower than the 3.8 to 4.2% as reported by Poungchompu et al (2001), Kiyothong (2003) and Vongsamphanh (2003). However, the nutritive value of cassava foliage will depend on the cultivar, age of plant, plant density, soil fertility, harvesting frequency and climate (Gomez and Valdivieso 1984; Wanapat et al 1997). Furthermore, planting space and frequent harvesting have been shown to affect the combined yield of the cassava foliage (Petlum et al 2001).

Conclusions

Intercropping affected yield but not chemical composition.
The cassava foliage yield was highest when intercropped with sweet potato. However, when considering total biomass yield, intercropping of cassava with sweet potato and Phaseolus calcaratus resulted in highest yield thus recommended as a food-feed system.
Nutritive values especially CP was found highest in cassava foliage or cassava hay as compared with sweet potato and Phaseolus calcaratus.
Intercropping of cassava could have potential in increasing cassava foliage for hay production and total combined biomass for ruminant feeding.

Acknowledgements

The authors were extremely grateful to the Swedish International Development Agency/Cooperation with Developing Countries (Sida-SAREC) for funding this thesis research. Special thanks are given to farmers who allowed the research to be conducted on their land. Appreciations are extended to the staffs of Tropical Feed Resources Research and Development Center (TROFREC), Department of Animal Science, Faculty of Agriculture, Khon Kaen University for assistance in cultivation, harvesting, hay making, sample collection and laboratory analysis.

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