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Processing cattle manure with California Red worms (Eisenia foetida); effect of seeding rate (ratio of worms to substrate) on the conversion of manure to end-products 

Nop Sophary, T R Preston and Khieu Borin

 

Ministry of Environment, Royal Government of Cambodia, Phnom Penh
Phary72@hotmail.com
University of Tropical Agriculture Foundation, Chamkar Doung, Phnom Penh, Cambodia
regpreston@utafoundation.org; borin@forum.org.kh

 

Abstract  

Two experiments were carried out at the Ecological Farm of the University of Tropical Agriculture Foundation in Chamcar Daung, Phnom Penh, Cambodia.  In the first experiment (June to October 2001), the treatments were four seeding rates (0.5, 1.0, 1.5, 2.0 and 2.5% of earth worms in the fresh manure) of adult California Red worms (Eisenia foetida) added to fresh manure derived from cattle fed mainly on untreated rice straw. There were four replications of each treatment which was applied to 10 kg fresh manure in plastic baskets (39 litre capacity) lined with nylon mesh. The trial lasted 3 months and samples of the substrate were taken at monthly intervals to estimate numbers of eggs and worms. Experiment 2 was a repeat of experiment 1 done from March to June 2002 but with only four seeding rates (0.5, 1.0, 1.5 and 2.0%). 

The rate of increase in worm biomass was inversely related with the seeding rate in both experiments. The maximum population of earth worms was reached within 2 months in both experiments. In the first experiment, the highest earth worm concentrations were with seeding rates between 15 and 25 g per 1 kg of fresh manure. In the second experiment, the concentrations of earth worms at the end of the second month were similar for all seeding rates. The yield of “worm compost” after 3 months was about 65% of the original weight of manure and was not affected by the seeding rate. The concentration of organic matter in the dry matter of the substrate decreased significantly from the end of the first month to the end of the second month, but there was no further change by the end of the third month. 

It is considered that availability of substrate became a limiting factor to worm growth and reproduction in both experiments after the second month.  Future experiments should focus on rates and intervals of providing fresh substrate.

Keywords: Red earth worms, cow manure, seeding rate, compost.
 

Introduction 

One way of improving the animal production without negative effects on the environment and of increasing the efficiency of resources utilization is by integrating all the processes in the system, in the context of the sustainable use of those resources (Beteta 1996; Preston 2000).

Recently, the use of the California Red worm (Eisenia foetida) as an agent for recycling live stock manure has received increasing attention (Preston and Rodríguez 2002).  The products of this process are the worm castings (“worm compost”) and the worms themselves. The worm compost derived from manure is superior to the original manure as a fertiliser according to  Nguyen Quang Suc et al (2000) and the worms themselves can be fed to chickens as a high quality protein supplement (Rodríguez et al 1995).  

It is known that scavenging chickens search selectively for earth worms (Nguyen Kim Quang 2001). Also the worm compost can be used as a highly valuable organic, environmentally friendly fertilizer for small scale farmers throughout the country. Thus the cultivation of earth worms using local resources such as live stock manure would seem to be a potential intervention for the target group – poor and landless women – most in need of support in the rural areas of Cambodia.
 

Objectives 

The objectives of the research to be described in this study were to determine the effect of the initial proportion of worms in the substrate (cow manure) on the rate of conversion of the substrate into end-products – worms and worm compost.
 

Methods and Materials

Location and timing

The study was done in the Ecological Farm of the University of Tropical Agriculture Foundation (UTA) located on the Campus of the Royal University of Agriculture (RUA), in Dangkar district, on the outskirts of Phnom Penh.  The experiment was repeated in each of the years 2001 (July to October) and 2002 (March to June).  

Treatments and design

Experiment 1:

The treatments were four seeding rates of adult California Red worms (Eisenia foetida) added to fresh manure derived from cattle fed mainly on untreated rice straw (Seng Mom et al 2001). The worms were imported originally from Colombia.  The proportions were: 0.5, 1.0, 1.5, 2.0 and 2.5% of earth worms in the fresh manure, equivalent to: 50, 100, 150, 200 and 250 g of earth worms in 10 kg of fresh cattle manure. There were four replications of each treatment. The worms were obtained from an existing culture grown on goat manure.  The material was harvested from the upper layer of this culture, which was estimated to contain approximately 10% of worms (w/w), the remainder being worm castings. The proportions of worms were estimated by counting the number of adults in a given sample of the seed stock and converting this to weight on the basis of the average weight of the worms (0.36 g) as determined in a concurrent experiment (San Thy 2001). For the actual seeding, uniform samples of the seed stock were added to fresh cow manure as indicated in Table 1. 

 The experiment lasted for 92 days from 13 July through 14 October in 2001, which is the first half of the wet season in Cambodia.

Experiment 2:

This was essentially a repeat of experiment 1 but with greater care being taken in the seeding process by weighing the actual amounts of worms used in each treatment.  The treatments were reduced to four proportions of worms in the manure of: 0.5, 1.0, 1.5 and 2.0% (fresh basis) added to 10 kg of fresh manure (Table 2). There were four replications of each seeding rate.  

 Experiment 2 lasted from 3 March to 3 June 2002 which was the latter part of the dry season.

Housing and Management

The worm seed stock and the fresh cow manure were mixed and placed in plastic baskets lined with nylon netting and located in an open-sided shed roofed with dry Imperata grass. The baskets had an area of 0.123 m² (35*35cm) and the depth of the substrate was 30 cm, giving a volume of 36 litres and therefore a density of the substrate of 0.28 g/cm³. The baskets were placed in random order on boards suspended at approximately 50 cm above the ground. A layer of rice straw was placed on the top of each basket to create a dark environment above the substrate and to help maintain a uniform humidity. Water was sprinkled on the substrate at the rate of one litre per basket, three times per week

Measurements

A vertical core sample (10 cm diameter) extending from the top to the bottom of the substrate was taken from every basket at monthly intervals and weighed.  The numbers of eggs and earth worms were counted in each sample. In experiment 1, this was done from 13 August  until the end of the experiment 13 October 2001.  In experiment 2, the eggs and earth worms were counted and the earth worms also weighed in samples taken at monthly intervals beginning 3 April through 3 June 2002. At the end of each experiment, the contents of each basket were weighed and separated into earth worms and residual substrate (mainly worm casts). The worm eggs were counted in samples of the residual substrate. Samples of the original manure, the substrate and the earth worms, were analysed  for DM by microwave radiation (Undersander e al 1993) and for N and ash (AOAC 1990). 

Statistical analysis

The data were analysed by analysis of variance using the General Linear Model procedure of the  Minitab Software (Version 12). The model was:

Y_ij = µ + a_i + b_j + (ab)_ij + e_ij

Y  = Response parameter

µ   = Overall mean.

a   = Effect of seeding rate i

b   =  Effect of month j

e    = Error

ab  =  Interaction between seeding rate and month.

Results and discussion

The cattle manure in experiment 1 was derived from animals fed untreated rice straw supplemented with 300 g/day of a cake containing 13% urea and 3 kg daily of fresh cassava foliage (Seng Mom et al 2001).  In experiment 2 the manure was from cattle fed only un-treated rice straw.  The N content of the manure (Table 3) reflected these differences in the N content of the feeds offered.  

 

 

Worm eggs

Experiment 1

There were differences (P=0.007) among treatments in numbers of worm eggs at the end of month 3 (Table 4; Figure 1). There were no eggs in the 2.5% seeding rate and very few in the 1.5 and 2.0% rates. The interpretation of these results is that the initial population (seeding rate) was important during the first month when earth worm numbers were very low (Table 5 and Figure 3), but not in the second month, by which time the earth worm population had increased. In the third month it would appear that the availability of substrate was limiting for reproduction but not for growth (Figure 3).

Experiment 2

There were no differences in egg numbers among seeding rates in Experiment 2, irrespective of the month of sampling (Table 4 and Figure 2). There were marked differences among months, with much fewer eggs at the end of the third month compared with earlier stages. This agrees with results from Experiment 1. Limited availability of substrate could have been the reason for this.

Worm counts

Experiment 1

With seeding rates of 0.5%,  the earth worm population increased throughout the 3 month period (Figure 2) but there were few changes for the 1% rate.  For rates of 1.5, 2.0 and 2.5% the maximum earth worm development appeared to have been reached by the end of the second month, presumably because substrate became the limiting factor. This is supported by the data on the egg counts.

Experiment 2

As in Experiment 1, maximum earth worm biomass was reached at the end of the 2^nd month after which the population declined with the degree of decline being inversely related with the seeding rate (Table 5 and Figure 4). 

 

Figure 1: Worm egg counts at monthly intervals according to seeding rate (experiment 1)	Figure 2: Worm egg counts at monthly intervals according to seeding rate (experiment 2)

 

Figure 3: Development of earth  worms at monthly intervals according to seeding rate (Experiment 1)	Figure 4: Development of earth  worms at monthly intervals according to seeding rate (Experiment 2)

Rate of increase in earth worm biomass

Experiment 1

The increase in the worm biomass, expressed as a percentage of the initial biomass, decreased linearly as the seeding rate was increased (Table 6; Figure 5). At the lowest (0.5%) seeding rate the worm biomass increased by 30% per day and fell to 14% at the highest rate of seeding.  Presumably the inverse relationship between the rate of increase and the seeding rate reflects the relative availability of substrate which obviously was higher the lower the seeding rate.  

Experiment 2

The same trend was noted as in experiment 1, with the rate of increase in the worm biomass decreasing as the seeding rate was increased (Table 6; Figure 6). However, the rate of decline was much steeper with a net loss of worm biomass at the 2.0% seeding rate. 

In experiment 1, there was no further increase in worm biomass after the end of the second month for seeding rates of 1.5, 2.0 and 2.5%. This indicates that the substrate became limiting on these treatments after two months and that more manure should have been added at this point. These findings differ from those reported from Vietnam (Nguyen Quang Suc et al 2000) where there was a major increase in earth worm biomass in the 4^th month. However, these researchers started with 0.5 kg of worms in 50 kg cow manure (1% seeding rate) and added further amounts of manure at 2-day intervals. The lower ambient temperature in North Vietnam compared with Cambodia could also have been a factor contributing to the slower growth rates. 

In experiment 1,  the net yield of worm biomass was slightly more than 1 kg from 100 kg of fresh manure (Table 6; Figure 5) and was not affected by seeding rate. In experiment 2, the highest net yield of earth worms was also1 kg from 100 kg manure and was highest with the lowest seeding rate. At higher seeding rates the net yield decreased and was negative on the 2% seeding rate.  The value of 1 kg net worm increase per 100 kg fresh cow manure is at the lower end of the range reported by Rodriguez et al  (1995) of 0.9 to 2.6 kg worm biomass from 100 kg fresh cow manure; and less than the findings of Beteta (1996) who reported 2 kg of worm biomass from 100 kg cow manure. Both these reports were from experiments done in the Cauca Valley in Colombia.  In North Vietnam, the yield of earth worms from 100 kg of cow manure was 0.93 kg after 3 months (Nguyen Quang Suc et al 2000).  

Figure 5: Increase in worm population according to seeding rate in experiment 1	Figure 6: Increase in worm population according to seeding rate in experiment 2

 

Production of worm compost

The yield of “worm compost” (the residue after 92 days of transformation of the manure) was on average 67 kg from 100 kg of fresh manure and was not affected by the seeding rate (Table 7). This is higher than the range of 49 to 57 kg reported by Rodríguez et al (1995) and the value of 50 kg in the work of Beteta (1996).  

The concentration of organic matter in the dry matter of the substrate decreased significantly from the end of the first month to the end of the second month, but there was no further change by the end of the third month (Table 8). This appears to confirm the hypothesis that available substrate was limiting worm growth and reproduction after the second month.

According to Nguyen Quang Suc et al (2000), the “worm compost” produced from goat manure had a higher fertilizer value than that produced from cattle manure. It is probable that there would be similar differences in the “worm compost” resulting from the different seeding rates, but this could no be verified in the present experiment. 

 

Conclusion

From this study, it can be concluded that with fresh cow manure as the substrate, and with a seeding rate with Red worms (Eisenia foetida)  within the range of  5 to 25 g per 1 kg of fresh manure:  

• the rate of increase in worm biomass was inversely related with the seeding rate

• the time to reach maximum earth worm concentrations in the substrate was at the end of 2 months and was not affected by the seeding rate

• the yield of “worm compost” after 3 months was about 65% of the original weight of manure and was not affected by the seeding rate.

It is considered that availability of substrate became a limiting factor to worm growth and reproduction in both experiments after the second month.  Future experiments should focus on rates and intervals of providing fresh substrate.
 

References

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

Beteta T 1996 Experiences of recycling manure in Colombia. MSc Thesis. Swedish University of Agricultural Sciences. Uppsala, Sweden

Nguyen Quang Suc, Le Thi Thu Ha and Dinh Van Binh 2000 Manure from rabbits, goats, cattle and buffaloes as substrate for earthworms. In: Proceedings of Workshop-seminar "Making better  use of local feed resources" (Editors: T R Preston, B Ogle and Luu Trong Hieu), SAREC-UAF,  January , 2000, Ho Chi Minh City, Vietnam  

Nguyen Thi Kim Khang 2001 Scavenging behaviour and feed selection by local and exotic chickens. Report of Mini-project, September 2001. MEKARN-UTA, University of Tropical Agriculture Foundation, Phnom Penh Cambodia.  http://www.mekarn.org/minipro/khang.htm  
 

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Rodríguez Lylian, Salazar P and Arango M F 1995 Lombriz roja Californiana y Azolla-anabaena como sustituto de la proteina convencional en dietas para pollos de engorde. Livestock Research for Rural Development  (7) 3 http://cipav.org.co/lrrd/lrrd7/3/5.htm 

San Thy 2001 Culturing earthworm in different substrates. Mini-project as part of MSc course in “Research cooperation for livestock-based sustainable farming systems in the lower Mekong basin”. sidaSAREC. http://www.mekarn.org/minipro/SanThy.htm 

Seng Mom, Preston T R, Leng R A and Meulen U ter 2001 Response of young cattle fed rice straw to supplementation with cassava foliage and a single drench of cooking oil. Livestock Research for Rural Development  (13) 4: http://www.cipav.org.co/lrrd/lrrd13/4/seng134.htm 

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