Livestock Research for Rural Development 16 (10) 2004

Citation of this paper

Biodigester effluent as fertilizer for water spinach established from seed or from cuttings

Ho Bunyeth and T R Preston*

Heifer Project International PO Box 2447, Phnom Penh, Cambodia
bunyeth@online.com.kh
UTA-TOSOLY, AA#48, Socorro, Colombia
regpreston@utafoundation.org


Abstract

A split-plot design was used to study growth of water spinach (Ipomoea aquatica)  as affected by the type of planting material (seeds or stems) and by biodigester effluent  (0, 50, 100, 150 and 200 kg N/ha) used as fertilizer.

Fresh biomass yields after 24 days were higher (15 tonnes/ha) when water spinach was established from seed than from stem cuttings (9.18 tonnes/ha). Biomass yield of water spinach increased linearly with effluent N level when planted from stem cuttings and logarithmically when planted from seed. The N content of water spinach leaves increased from 3.08 to 5.56% in DM (19.3 to 34.8% crude protein)  by application of 200 kg N/ha as biodigester effluent. Stems were much lower in N (1.2 to 2.0% in DM) and this index tended to decrease with increasing application of effluent N. Water extractable N tended to be higher in leaves than in stems but the converse was true for the water extractable DM. Water extractable DM in leaves and stems increased with level of effluent N up to 100 kg/ha but then declined. Effluent N level had no effect on  water extractable N.

It is recommended to establish water spinach from seed rather than from stem cuttings.

Key words: Biodigester, effluent, fertilizer, Ipomoea aquatica, nitrogen, water spinach


Introduction

Cambodia is one of many countries in Asia South Pacific bordered by Thailand, Lao, Vietnam and the gulf of Thailand. The country has a sub-tropical climate with monsoon rains. The population is concentrated in the central basin, where rice, the mainstay of the diet, is grown. Rice production is a key factor in household food security in the rural areas which are occupied and farmed by approximately 80% of the population.

Unfortunately, many disasters particularly the long time of civil war have caused many problems in Cambodia, resulting in poverty and hunger. The land has became less fertile and many parts are still affected by land mines. Land use patterns are also distorted in many areas.  Loss of biodiversity, land degradation and deforestation are identified as major problems. Many households are still not self-sufficient in rice. About 50% of all children  aged under 5 years are either stunted or underweight, which appears to be due to long term chronic under-nutrition rather than wasting from short-term, severe food shortages (Heifer-Cambodia 2002). Malnutrition is broadly recognized as a main problem for both human well-being and also animal production in the world, especially developing countries like Cambodia. Lack of information on technical systems relating to sustainable agriculture makes the farmers with a small land area feel less confident,  or they pay less attention to production, resulting in an increase in  landless families or loss of land among the poor farmer families.

Using water spinach (Ipomoea aquatica) as vegetable for family consumption and animal feeding is very common in Asian countries, as it takes a short time to grow and is highly resistant to common insect pests, and is rich in protein. However, most farmers cultivate water spinach by using urea as fertilizer.  The introduction of low-cost biodigesters in Southeast Asia (Bui Xuan An et al 1997) has made it possible for small-scale farmers to convert manure into biogas and nutrient rich effluent. Kean Sophea and Preston (2001) showed that water spinach responded dramatically to fertilization with biodigester effluent. This concept is based on processing the raw manure in a biodigester to produce gas for cooking and at the same time reducing environmental pollution (Preston and Leng 1989).  An advantage of water spinach is that it grows in soil or water and can be planted from vegetative cuttings or from seed. However, there is no information about the productivity of  water spinach when established from seed or stems.

Hypothesis
Objective

To study growth of water spinach planted as seed or stems and with fertilizer recycled in the form of biodigester effluent.


Materials and methods

Treatments and design

Two main treatments were compared in a split-plot arrangement with two replications (Table 1):

Table 1. Layout of the experiment (S is seed; P stem cuttings)

               Level of effluent N, kg/ha

Block

Replicate

200

0

100

150

50

1

 

1

S

P

S

P

S

1

P

S

P

S

P

2

2

P

P

S

S

S

2

S

S

P

P

P

Procedure
Land preparation

 PVC baskets, lined with polyethylene (capacity about 50 litres, area 0.16 m) were filled with soil to a depth of 20 cm. The soil contained 0.097% of N and had a pH of 7.46.

Planting the water spinach

The  dry-land water spinach species was chosen for both seed and stem planting, which was done on August 3, 2003. The seeds were kept in water at ambient temperature for 12 hours before planting in rows across the basket at a spacing of 3-4 cm and at 1-2 cm depth. The distance between rows was 10cm, and the overall seeding density was 62.5g/m2. The stems for planting were each 5 cm long and were taken from a section starting 4-5 cm from the main root. They were planted at spacing of 5cm x 5cm, equivalent to an average of  30 plants per basket (equal to 200 plants/m) (Photos 1 and 2).

Photo 1: Planting the stem cuttings Photo 2: Fertilising the water spinach after 14 days
Fertilizing

The biodigester effluent was applied every 4 days for a total of 6 times during the growing period. It contained 410 mg N/litre, thus the total amounts used were 0,  1.95, 3.9, 5.85 and 7.8 kg in each basket over the 24 day period, divided in 6 equal applications. The effluent was from a biodigester charged with cow manure managed with a 20 day retention time and a charging rate of 4 kg solids per 1 m of liquid volume (Bui Phan Thu Hang 2003).  

Irrigation

The plants were irrigated  twice a day (morning and afternoon) at the rate of 3 to 4 litres/m). On rainy days no additional water was applied.

Measurements

Plant height was measured every 4 days before applying the effluent. The measurement was done on a  random number of plants (10 plants/basket). The water spinach was harvested at 24 days after planting. All plants were separated into stem and leaf, and after weighing the two components, samples were analysed immediately to determine dry matter by microwave radiation (Undersander et al 1993), N (AOAC 1990) and water extractable DM and N (Ly and Preston 1997).

Statistical analysis

The data were analysed by ANOVA using the General Linear Model (GML) software of Minitab (Version Release 13.2). Sources of variation were: planting materials (S, P), effluent N level, the interaction of plant material*level N, blocks and error.
 

Results and discussion

Water spinach growth

The height of the water spinach increased linearly with level of effluent up to 150 kg N/ha (Table 2 and Figure 1) with no further increase for 200 kg N/ha. The water spinach planted from seed had faster growth in the first 4 days (P=0.023) but there was no difference in the rate of growth in height between the two plant materials (Table 3).  There were differences between the two blocks in rate of growth in height (P=0.008) with the highest value for block 2, situated close to a wall which perhaps shielded the plants from excessive wind and rain, which occurred at intervals during the experiment.

Table 2. Least square means for height (cm) due to effluent level effect

N level

4days

8days

12days

16days

20days

24days

Increase, cm/day

0

4.94

8.39

12.8

14.8

18.0

20.6

0.78

50

4.03

7.66

14.4

19.2

25.3

28.5

1.29

100

4.74

8.73

14.9

21.8

29.9

35.4

1.60

150

4.58

8.03

15.5

23.8

32.5

38.4

1.79

200

4.46

8.34

16.7

24.8

33.7

39.4

1.85

SEM

0.278

0.494

0.68

0.86

1.02

1.02

0.054

Prob

 0.270

 0.634

 0.032

0.001

0.001

0.001

0.001

 

Table 3.  Least square means for height due to planting material effect

 

4days

8days

12days

16days

20days

24days

Increase, cm/day

      Stem

4.21

8.00

13.2

19.6

26.9

28.8

1.45

Seed

4.89

8.46

16.5

22.1

28.8

32.7

1.47

SEM

0.176

0.313

0.428

0.547

0.645

0.647

0.034

Prob

0.023

0.325

0.000

0.009

0.069

0.567

0.72

The growth in height of the water spinach was similar to the findings of  Ngo Tien Dung (2001) (42 cm with 40 kg N/ha over 28 days) and  San Thy and Preston (2001) (47 cm with 140 kg N/ha in 28 days), taking account of the shorter growth period (24 days) in the present experiment.


Figure 1.  Mean values for height of water spinach after 24 days according to effluent N levels
and source of planting material

Biomass yield

The hypothesis that biomass yield would be higher by planting from seed was verified by the results (Table 4). Response to effluent N level was curvilinear for planting from seed and linear for planting with stem cuttings (Figure 2). Maximum yield for seed planting (15,000 kg/ha) was  lower than was reported in Cambodia (23,600 kg/ha with 140 kg N from effluent) by Kean Sophea and Preston (2001).  Differences in soil and climate could be the reason for the differences. There appears to be no information in the literature on yield responses to fertilizer with stem cuttings as plant material.

The proportion of leaf in the fresh biomass was higher for stem planting, presumably because the plants were less mature,  but there was no consistent trend for effect of effluent N level (Table 3).

Table 4. Least square means for fresh biomass yield and proportion of leaf material according to effluent N level and source of planting material

 

Stem

Seed

Treat

Yield, kg/ha

% leaf

Yield, kg/ha

% leaf

0

2000

51.2

4219

38.8

50

4531

45.7

7656

39.6

100

6094

43.2

11563

36.6

150

7187

42.4

13500

36.8

200

9219

43.7

15000

39.9

Mean

5820

45.3

10380

38.3

Yield: SEM/Prob plant material effect 403/0.001
% leaf: SEM/Prob plant material effect 0.62/0.001



Figure 2: Response in biomass yield to effluent N level with two sources of plant material


Dry matter and Nitrogen content, N recovery of the water spinach

The DM content of the leaves and stems decreased as effluent fertilizer level was increased; and leaves had higher DM content than stems (Table 5; Figure 3). Nitrogen (and therefore crude protein) in leaves increased with effluent N level as far as 150 kg N/ha, but then leveled off (Figure 4). Crude protein in the stems was much lower than in the leaves, and appeared to decrease with increasing effluent N level, but the trend was not uniform (Figure 4).

Table 5. Least square means for DM and N in stems and leaves of water spinach according to level of effluent N in kg/ha

 

0

50

100

150

200

SEM

Prob.

Dry matter content, %

Leaf

10.2

10.3

9.42

9.20

9.37

0.194

0.007

Stem

8.09

7.30

6.43

6.13

6.33

0.194

0.001

N content in DM, %

Leaf

3.08

3.74

4.33

5.66

5.56

0.156

0.001

Stem

2.01

1.10

1.26

1.40

1.19

0.191

0.121



Figure 3: DM content of leaves and stems of water spinach according to level of effluent N



Figure 4: Mean values for content of crude protein in leaf and stem of water spinach according
to effluent N level


Water extractable DM and N

There was no effect of planting materials, and no interaction between planting materials and N level of effluent on the water extractable DM and N, therefore the data in Table 6 and Figure 5 are from the average of the sources of the planting material.

Table 6. Least square means for water extractable DM and N according to N levels of effluent

 

Water extractable DM

Water extractable N

Level N

Leaves

Stems

Leaves

Stems

0

24.6

34.8

60.8

52.9

50

36.8

43.3

65.1

64.4

100

46.3

50.3

52.6

51.3

150

41.9

53.4

55.4

62.2

200

39.6

44.6

61.4

56.3

There was an indication that the water-extractable DM was higher in the stems than in the leaves (Figure 5) but there were no differences between leaves and stems for water-extractable N (Figure 6). Water-extractable DM increased in both leaves and stems as effluent N level was increased up 100 kg N/ha, but thereafter there was no further response, and in fact a decrease with 200 kg N/ha. Values for both indices were relatively high and this is in agreement with in vitro measurements of the nutritive value of water spinach (Ly and Preston 2001).


Figure 5. Water extractable DM in leaves and stems according to level of effluent N



Figure 6. Water extractable N in leaves and stems according to level of effluent N


N recovery

The recovery of the N applied in the effluent, calculated as [(N in plant biomass/Total N applied)*100], decreased with increasing levels of application of N in the effluent (Figure 7), and was higher in the water spinach planted from seed. Higher values than these were reported by Kean Sophea and Preston (2001), but they planted the water spinach on raised beds of soil, and obtained higher yields, probably because of better utilization of soil nutrients.


Figure 7. Recovery of N by water spinach fertilized with increasing levels of effluent N


Conclusions


Acknowledgements

This experiment was carried out as part of the MSc (2003-05) course, supported by the MEKARN project financed by sida-SAREC. The authors expresses their  gratitude to all the personnel of the Agriculture and Natural Resources faculty of An Giang University, for assistance with the experiment. Grateful thanks are given to colleagues (Dr J Ly, Mr Chhay Ty and Mr San Thy) for advice and supervision during the conduct of the present study.


References

AOAC 1990 Official Methods of Analysis. Association of Official Analytical Chemists. 15th edition (K Helrick, editor). Arlington pp 1230

Bui Xuan An, PrestonT R and Dolberg F 1997 The introduction of low-cost polyethylene tube biodigesters on small scale farms in Vietnam. Livestock Research for Rural Development (9) 2: http://www.cipav.org.co/lrrd/lrrd9/2/an92.htm

Bui Phan Thu Hang 2003: Effect of dimensions of plastic biodigester (width:length ratio) on gas production and composition of effluent, from MEKARN Mini-projects. http://www.mekarn.org/msc003-05/miniprojects/hangctu.htm

Heifer Project International-Cambodia 2002 Country strategic plan regarding livestock development project with the poor farmer families at the rural communities in Cambodia. Heifer Project International-Cambodia, Phnom Penh

Kean Sophea and Preston T R 2001 Comparison of biodigester effluent and urea as fertilizer for water spinach vegetable. Livestock Research for Rural Development (13)6:  http://www.cipav.org.co/lrrd/lrrd13/6/kean136.htm.

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Ly J and Preston T R 2001 In vitro estimates of nitrogen digestibility for pigs and water-soluble nitrogen are correlated in tropical forages feeds. Livestock Research for Rural Development 13(1): http://cipav.org.co.lrrd/lrrd13/1/ly131.htm

Ngo Tien Dung 2001 Response of water spinach (Ipomoea aquatica) to fertilization with increasing concentrations of the rubber tree latex wash water and biodigester effluent. http://www.mekarn.org/minipro/dung.htm

Preston T R and Leng R A 1989 The greenhouse effects and its implications for world agriculture. The need for environmentally friendly development. Livestock Research for Rural Development (1). http://www.cipav.org.co/lrrd/lrrd1/1/preston.htm

San Thy and  Preston T R 2003 Evaluation of the effluent from different retention times as fertilizer for growing water spinach (Ipomoea aquatica).  http://www.mekarn.org/msc2001-03/theses03/santexp2.htm

Undersander D, Mertens D R and Theix N 1993 Forage analysis procedures. National Forage Testing Association. Omaha pp 154.


Received 5 June 2004; Accepted 10 August 2004

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