Livestock Research for Rural Development 19 (2) 2007 Guidelines to authors LRRD News

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Effect of increasing area of cassava (Manihot esculenta Crantz) relative to Flemingia (Flemingia macrophylla) on biomass yield, soil fertility and soil erosion

Ngo Tien Dzung and T R Preston*

Goat and Rabbit Research Center, Sontay, Hatay, Vietnam
dzungvbdp@yahoo.com
* University of Tropical Agriculture, TOSOLY, AA #48 Socorro, Colombia

Abstract

An experiment was carried out at the Goat and Rabbit Research Center, Sontay, Hatay, Vietnam, from February 2003 to November 2004 to measure effects on biomass yield, soil fertility and soil erosion in response to increasing ratio of rows of cassava rows to rows of the leguminous shrub Flemingia macrophylla in an inter-cropping system. Two rows of Flemingia were associated with 1, 2, 3, 4 and 5 rows of cassava. Flemingia was planted first and cassava 14 days later. Fertilizer was applied in the form of organic manure (from mixed cattle and buffalo excreta) before planting at the rate of 2 kg/m2 fresh weight in the first year and the same amount again in March the second year. No other fertilizers were applied during the experimental period. The first harvest was made when the cassava reached 100 cm in height and subsequent harvests of the re-growth from 56 to 75 days. All the foliages were removed at 30 cm above ground level.

Biomass yield of cassava and Flemingia in an inter-cropping system was improved by increasing the number of cassava rows relative to cassava in the first year, but decreased slightly in the second year. The maximum biomass yield was obtained in the system with 2 rows of cassava and two rows of Flemingia. The crude protein contentof the cassava foliage deceased as the area of cassava rlative to Flemingia increased. Soil fertility over a 24 month period increased in the plots with the highest ratio of Flemingia and decreased as the ratio of cassava to Flemingia was increased. Protein content in the cassava foliage decreased linearly with decreased in soil fertility. Soil erosion was high in all plots in the first year and was directly related to the relatve area planted with Flemingia. In the second year soil eroson was much less and was inversely related to the proportion of Flemingia n the inter-cropping system.

It is concluded that the optimum ratio of Cassava to Flemingia, in terms of biomass yield and maintenance of soil fertility, is two rows of each planted alternately.

Keywords: Biomass, bio-test, cassava, Flemingia, foliage, inter-cropping, soil fertility, soil erosion


Introduction

Cassava or tapioca (Manihot esculenta, Crantz) is an annual root crop grown widely in tropical and sub-tropical areas. It is a cash crop cultivated by smallholder farmers within the existing farming systems in many countries.   Growing and using cassava as a perennial forage was first proposed by Moore (1976) based on observations at CIAT in Colombia. High yields of foliage were obtained when cassava was managed as a semi-perennial crop with repeated harvesting of the foliage at 2-3 month intervals.  This idea was taken up in the Dominican Republic by  Ffoulkes and Preston (1978) who showed that the fresh foliage could be used as the sole source of protein and fibre for supplementing a liquid diet of molasses-urea for fattening cattle.  Growth rates were over 800 g/day and were not improved when 400 g/day of additional soya bean meal was given. However, although successful at the level of the animal the system could not be sustained agronomically.  Yields of foliage fell rapidly with successive harvests and were negligible by the fourth harvest, due to a lack of appreciation of the need to return to the soil the considerable amounts of nitrogen and other nutrients removed by repeated harvesting (T R Preston, unpublished observations). 

In studies on the use of cassava hay as cattle feed in Thailand Wanapat et al (1992, 1997, 2000)  described a combined forage/root management system for cassava with two or more harvests of the foliage prior to letting the root develop to maturity. More recent research, first in Vietnam (Preston et al 2000, 2001) then in Cambodia (San Thy and Preston 2000), has demonstrated that the cassava plant can be maintained as a semi-perennial forage crop for at least  2 years provided there is heavy fertilization either with goat manure or with the effluent from biodigesters charged with pig manure.  

Another approach to maintaining soil fertility is to plant the cassava in association with a forage legume such as Gliricidia sepium and Desmanthus virgatum (Preston et al 2000), Flemingia macrophylla (Ngo Tien Dzung et al 2003; Nguyen Phuc Tien et al 2003) and cow pea (Polthanee et al 2001).

Flemingia macrophylla is a leguminous shrub with high biomass yields that grows well in acid soils (Dinh Van Binh et al 1998). Flemingia improves soil fertility though return to the soil of organic matter from fallen dead leaves and by nitrogen fixation (Dinh Van Binh et al 1998; Andersson 2002). The foliage of Flemingia is relatively high in crude protein (about 17% in dry matter) but it can only replace about 15% of the diet of growing goats because of low palatability and low digestibility (Nguyen Thi Mui et al 2002). Recent research indicated that planting Flemingia and cassava in alternate double rows was better than alternate single rows in terms of total biomass yield, maintenance of soil fertility and reduced soil erosion, and that both these associations were superior to growing of cassava in monoculture (Ngo Tien Dzung 2003).

The overall objective of the present study was to develop a sustainable system for maintaining cassava as a semi-perennial forage crop for feeding to live stock. The hypotheses to be tested were:


Material and methods

Location and climate

The experiment was carried out from February 2003 to December 2004 on sloping land at 105o25' E and 21o06' N, 220m above sea level in the Bavi region, Hatay province, North Vietnam. The soil characteristics and composition at the experimental site were: pHKCl 4.24, organic matter (OM) 4.64%, Ntotal: 0.17%, K2Ototal 0.48% and P2O5 total 0.052%. In general, the soil is acid with low fertility and the OM has been reduced by erosion. Drought occurs frequently in the area.

The climate in the area is tropical- monsoon, with a wet season between April and November and dry season from December to March. Annual rainfall was 1874mm in 2003 and 1756mm in 2004 with a mean daily temperature from 19.7 to 31.5oC.

Treatments and experimental design

There were five treatments:

The plots were each 10*20m (200 m2) arranged as a randomized complete block design with 4 replications on 5000 m2 of sloping land. The slope of the plots ranged from 17.3 to 17.7%.

Crop establishment, management and measurements
Planting

The Flemingia was planted with 50 cm between the two rows and 5 cm between seeds. The cassava was planted with 50 cm between rows and 15 cm between stem cuttings (length of stem cutting was 20 to 25 cm). The cassava was planted first followed 14 days later by the Flemingia. Organic manure (from pigs, cattle and buffalo) was applied before planting and after 6 months of planting at the rate of 2 kg/m2. No other fertilizer was applied during the experimental period, which lasted for 2 years. Manure application was the same in all plots.

Harvesting

The first harvest was made when the cassava or Flemingia reached 100 cm in height (about 3 months after planting), all the foliage being removed at 30 cm above ground level. The same pattern was followed for the re-growth (about every 75 days). In each plot, 5 randomized sub-plots (4*4 m = 16m2) were chosen to estimate biomass yield, which was calculated as an average of the 5 sub-plots. The sub-plots were chosen without a zone around them. The roots from the cassava were harvested at the end of the two years of the experiment.

Measurements

Samples of foliage (Flemingia and cassava) and of cassava roots were taken from each of the 5 sub-plots and mixed prior to analysis for dry matter (DM) and nitrogen (N).

Soil sampling and biological test of soil fertility:
Biological test for soil fertility and soil analysis

At the beginning, and at 6-month intervals, samples of soil were taken from the plots for biological test of soil fertility (Nguyen Thi Mui et al 1996; Boonchan Chantaprasarn and Preston 2004) and for soil analysis. The soil samples were taken from each of the 5 sub-plots which were then bulked for each treatment/replicate. The growth periods of the maize in the biological test were 35 days in the summer season and 42 days in the winter season.

Soil erosion

At the lower limit of each plot, a canal system was established following the contour. The canals were 60 cm deep, 60 cm wide and 10 m long, and were lined by plastic sheet to catch the soil that was washed away. The soil loss was weighed after each rainfall.

Chemical analysis

The samples of the foliages, and the cassava roots, were analysed according to AOAC (1990) for DM and crude protein. Samples of soil were analysed for pHKCl (KCl 0.1M), OM, N, P and K, according to AOAC (1990).

Statistical analysis

The data were analysed statistically using the GLM procedure of the Minitab Software, version 13.1 (Minitab 2000). The treatment means which showed significant differences at the probability level of P<0.05 were compared with each other using Tukey's pair-wise comparison procedure (Minitab 2000). The model used in the analysis was:

Yij = µ + Ti +Bj + (TB)ij + eij

Where: Yij is dependent variable, µ the overall mean, Ti: treatment (i= 1,...5), Bj: block (j = 1; …4), (TB)ij: interaction between treatment and block and eij the experimental error


Results and discussion

Chemical composition of cassava and Flemingia foliages

There were contrasting results for composition of Flemingia and cassava foliage in the two years (Table 1).

Table 1: Mean values for content of  DM and crude protein (CP) in the foliage of cassava and Flemingia in each of the two years

 

Flemingia

Cassava

DM, g/kg

CP, g/kg DM

DM, g/kg

CP, g/kg DM

Year 2003

 

 

 

 

2FM-1CF

250a

148

239

171

2FM-2CF

249a

154

242

165

2FM-3CF

240ab

164

246

161

2FM-4CF

223ab

172

252

160

2FM-5CF

212b

175

253

159

SE mean

6.0

4.5

7.2

3.7

Year 2004

 

 

 

 

2FM-1CF

237a

177a

226

186

2FM-2CF

246ab

177a

231

186

2FM-3CF

250ab

174a

242

179

2FM-4CF

256b

163b

252

175

2FM-5CF

256b

163b

258

173

SE mean

3.9

2.1

6.7

3.4

a, b Means within columns within years,  without common  superscripts differ at P<0.05

As the ratio of cassava to Flemingia increased, there were increases in crude protein and decreases in DM content of the Flemingia foliage in the first year (2004) while the opposite trends were observed in the second year (Figures 1 and 2). By contrast, the DM content of cassava foliage increased and the crude protein decreased in both years as the ratio of cassava to Flemingia was increased (Figures 3 and 4).

Figure 1: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on DM content of foliage of Flemingia in each of the two years
Figure 2: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on CP content of foliage of Flemingia in each of the two years

Figure 3: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on DM content of foliage of cassava in each of the two years
Figure 4: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on CP content of foliage of cassava in each of the two years
Biomass yield

In the first year, biomass yield of Flemingia was low but increased in the second year (Table 2; Figures 5 and 6). In both years the maximum yield of biomass DM and crude protein was recorded for the treatment of 2 rows Flemingia; 2 rows cassava (Figures 7 and 8). In the second year, yield of DM and crude protein decreased linearly as the ratio of cassava to Flemingia increased (Figures 7 and 8). In the optimum treatment (2 rows Flemingia: 2 rows cassava) total biomass yield was higher in the second year. A similar finding was reported by Nguyen Phuc Tien et al (2003).

Table 2: Mean values for yield (tonnes/ha) of DM and crude protein in foliages of cassava and Flemingia in each of the two years

 

2FM-1CF

2FM-2CF

2FM-3CF

2FM-4CF

2FM-5CF

SEM/P

Year 2003

 

 

 

 

 

 

DM

8.14a

10.31b

11.03c

11.16cd

11.72d

0.15/

Flemingia

3.50a

3.40a

2.85b

2.21c

1.67d

0.075/

Cassava

4.63a

6.91b

8.18c

8.95d

10.06e

0.113/

Crude protein

1.31a

1.66b

1.78c

1.81cd

1.89d

0.025

Flemingia

0.52a

0.52a

0.47b

0.38c

0.29d

0.012

Cassava

0.79a

1.14b

1.31c

1.43d

1.60e

0.018

Year 2004

 

 

 

 

 

 

DM

11.32a

11.99b

11.06a

10.15c

10.00c

0.164

Flemingia

7.62a

6.72b

5.30c

4.12d

3.43e

0.115

Cassava

3.69a

5.26b

5.76c

6.03c

6.56d

0.090

Crude protein

2.04a

2.17b

1.95a

1.72c

1.69c

0.029

Flemingia

1.34a

1.18b

0.92c

0.67d

0.56e

0.019

Cassava

0.69a

0.98b

1.03b

1.05b

1.13c

0.016

Two years

 

 

 

 

 

 

DM

19.46a

22.31b

22.10b

21.32b

21.72b

0.308

Crude protein

3.35a

3.83b

3.73bc

3.54ac

3.58c

0.052

a bc Means within rows,  within years,  without common  superscripts differ at P<0.05


Figure 5: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on DM yield of foliage of Flemingia and cassava in 2003
Figure 6: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on DM yield of foliage of Flemingia and cassava in 2004

Figure 7: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on DM yield of foliage (combined Flemingia and cassava) in 2003, 2004 and for both years
Figure 8: Effect of treatment (rows of cassava relative to 2 rows of Flemingia)
on crude protein yield of foliage (combined Flemingia and cassava) in 2003, 2004 and both years

Soil fertility

Soil fertility as measured by the maize "bio-test" increased with time over 24 months for treatments 2FM:1CF and 2FM:2CF but declined for the treatments with 4 or 5 rows of cassava per 2 rows of Flemingia (Table 3 and Figure 9). Other measures of soil fertility (organic matter and N content) also showed a linear decline as the ratio of cassava to Flemingia increased (Figures 10 and 11).

Table 3: Least square means for weight of root and green biomass of maize plants grown in soil from the experimental plots (g/pot)

 

2 FM-1CF

2FM-2CF

2FM-3CF

2FM-4CF

2FM-5CF

SE

Beginning

32.8

34.7

33.7

32.9

33.2

2.20

6 months

36.5

35.1

34.9

33.4

33.6

1.50

12 months

37.25a

36.81a

34.0ab

31.7b

29.6b

1.32

18 months

39.9a

37.1ab

33.9b

30.7b

30.6b

1.56

24 months

40.1a

38.1a

34.8ab

31.6b

28.7b

1.47

a, b Means within rows without common superscript differ at P<0.05



Figure 9: Changes in soil fertility with time according to ratio of Flemingia to cassava


Figure 10. Changes in organic matter in soil according
to ratio of Flemingia to cassava
Figure 11. Changes in N content of soil according
to ratio of Flemingia to cassava


The protein content of the cassava foliage was positively related with soil fertility (Figure 12).


Figure 12: Relationship between relative soil fertility (according to maize biotest)
and crude protein content of foliage of cassava (end year 2004)


In the first year, soil erosion varied inversely with the ratio of Flemingia to cassava as growth of the Flemingia was slower than that of the cassava leading to reduced soil cover in plots with highest proportion of Flemingia (Table 4 and Figure 13). The opposite effect was observed in the second year when soil loss was lower in all plots compared with the first year and increased linearly as the proportion of cassava in the plots increased.

Table 4: Least square means for parameters of soil fertility

 

2FM-1CF

2FM-2CF

2FM-3CF

2FM-4CF

2FM-5CF

SE

Beginning

 

 

 

 

 

 

pHKCl

4.30

4.26

4.22

4.30

4.24

0.032

OM, %

4.69

4.10

4.76

4.39

4.75

0.259

N %

0.16

0.17

0.165

0.155

0.162

0.015

P2O5, %

0.055

0.041

0.051

0.036

0.090

0.015

K2O, %

0.58

0.47

0.45

0.40

0.48

0.039

After 2 years

 

 

 

 

 

 

pHKCl

4.37

4.22

4.28

4.30

4.28

0.05

OM, %

5.10

4.42

4.56

4.21

4.08

0.121

N %

0.24

0.187

0.15

0.142

0.132

0.015

P2O5, %

0.105

0.081

0.104

0.078

0.085

0.007

K2O, %

0.63

0.515

0.565

0.30

0.28

0.055

Beginning compared to after 2 years

pHKCl

NS

NS

NS

NS

NS

 

OM, %

*

*

NS

NS

*

 

N %

*

NS

NS

NS

**

 

P2O5, %

**

**

**

NS

NS

 

K2O, %

NS

NS

*

*

*

 

Soil erosion (tonnes/ha)#

Year 1

50.0

46.7

43.0

42.4

39.1

2.25

Year 2

12.8a

18.7a

22.1ab

23.9b

29.5b

2.25

2 years

63.2

65.4

65.1

66.3

68.7

6.7

a, b Means within rows without common superscript differ at P<0.05
# The slope of the plots ranged from 17.3 to 17.7%




Figure 13: Soil erosion in plots with varying ratios of Flemingia to cassava in the two years

Soil cover is an important factor in control of erosion by water through interception and absorbing the kinetic energy in the rain. The soil cover reduces the direct impact of the rain drops and prevents the surface from becoming sealed as well as preserving the soil structure. Andersson (2002) compared plots with monoculture of cassava or Flemingia and reported that in the second year, soil loss in the former was 34 tonnes compared with only 5.4 tonnes/ha for the Flemingia. Nguyen Phuc Tien  et al (2003) also found that soil fertility was maintained over two years in plots inter-cropped with Flemingia and cassava in equal proportions.


Conclusions


Acknowledgements

The Senior Author acknowledges the support of the International Foundation of Science (IFS) for financing this research (Grant No. B/3085-1).


References

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Received 1 June 2006; Accepted 12 December 2006; Published 8 February 2007

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