Effect of level of effluent from biodigesters loaded with pig manure on the growth of mulberry (Morus alba) trees

Chiv Phiny, Khieu Borin, T R Preston* and Chhay Ty

Center for Livestock and Agriculture Development, POB 2423, Phnom Penh 3, Cambodia
chphiny@celagrid.org
TOSOLY, AA 48 Socorro, Santander, Colombia

Abstract

An agronomy trial to evaluate the effect of level of effluent from plastic biodigesters loaded with pig manure on the growth of mulberry (Morus alba) trees was conducted for one year (25 August 2004 to 25 August 2005) during both the dry and rainy seasons in the ecological farm of CelAgrid, Cambodia.  The trial included six treatments with four replications, divided into 4 blocks according to a Complete Randomized Block Design. The effluent application levels were: 0, 100, 250, 400, 550 and 700 kg N / ha / year). Effluent was applied every 7 days. Mulberry foliage was harvested (cutting height 60 cm above ground level) after 3 months and again at 2 month intervals. The foliage was separated into stem and leaf + petiole and analyzed for dry matter (DM) and nitrogen (N).

Dry matter biomass yield of mulberry foliage increased linearly with increasing amount of effluent N applied. Crude protein content of leaves increased with effluent level but there were no changes in the stems. Soil content of N and OM increased in direct relationship with the quantity of biodigester effluent.

Key words: Biomass, crude protein, fertilizer, leaves, petioles, soil, stems

Introduction

Mulberry is a traditional feed for silk worms. It was reported to have a high edible biomass yield of 8 to 12 tonnes DM/ha/year, with a range of cutting intervals from 6 to 12 weeks (Huy Sokchea et al 2008). According to Yao et al (2000) the leaves have 21% crude protein in the DM and are high in vitro organic matter digestibility. It thus has a high potential as a protein-rich forage supplement for ruminant production (Singh and Makkar 2000; Nguyen Xuan Ba et al 2004). Mulberry plants grow very well in the rainy season, especially when fertilizer is applied. However, fertilizer use in Cambodia is low because of the high cost of chemical fertilizer.

Biodigesters play a crucial role in the conversion of organic matter to methane-rich biogas, with positive impacts on the environment and on human and animal health. Soeurn Than (1994) demonstrated that plastic tube biodigesters can be a low-cost source of energy and partly reduce the problem of severe energy shortage for households in rural areas of Vietnam and Cambodia. Besides environmental preservation, Preston and Rodriguez (1996) showed that biodigesters provide a very good source of fertilizer for crops on land and water. The advantages of passing manure through a biodigester are many and include gas production for cooking, improved health through elimination of pathogens and no loss of plant nutrients in the process (Bui Xuan An et al 1997).

The present study was carried out to measure the effect on biomass yield and composition of mulberry foliage when fertilized with increasing levels of effluent from a tubular, plug-flow plastic biodigester charged with pig manure.

Materials and methods

Location

The research was carried out at the experimental farm of CelAgrid, located in Kandal village, Ro Lous commune, Khandal Steung district, Khandal Province. The center is about 25 km from Phnom Penh City. Previously the field had been used for monoculture rice production. The soil of the experimental plot was a sandy loam with a range of pH of 6.4-8.0. The range in temperature was 25-30^oC during the experimental period. The lowest (25-26^oC) occurred in November-February and the highest (30-31^oC) in April-May. There was irregular precipitation of 55-170 mm/month recorded in February-April and 105-410 mm/month in May-October. The total annual rainfall averages 1600 mm.

Design and treatments

Six (6) levels of effluent (0, 100, 250, 400, 550 and 700 kg of N/ha per year) and 4 replications were arranged in 4 blocks according to a Complete Randomized Block Design (Table 1). Application rates were made according to the N content of the effluent. Twenty four plots were prepared with a total area of 918 m². Each plot had an area of 38.25 m² (8.5m x 4.5m). The distances between plants and rows were 50 cm, giving a density of 153 seedlings per plot (40000 seedlings per ha) (see Photos 1 and 2).

Experimental procedure

Plots were prepared by hoeing to a depth of 20-25 cm and were sun-dried for a week before the final tillage. A total of 4000 stem cuttings (about 20 cm in length) from mature mulberry bushes were established in the plant nursery at the CelAgrid station and allowed to develop over a period of 1.5 months. The mulberry seedlings were transplanted at a depth of 15-20 cm into holes in the experimental plots, in the bottom of which cow manure was already applied uniformly in each plot. Irrigation was applied as judged to be necessary to provide adequate humidity. Preparation and transplanting of the mulberry seedlings was carried out from March to July 2004. Measurements were made from 25 August 2004 through 25 August 2005.

The biodigesters

Two tubular plastic biodigesters were constructed. The diameter of the plastic polyethylene tube was 100 cm and the length 10 m. Each biodigester was linked with pig pens. The total volume of each biodigester was 7860 litres with the liquid phase occupying 5890 litres. Each biodigester discharged into an effluent tank of approximately 1000 litres capacity.  Pig manure was put into the biodigesters through washing the pens 2 times per day.

Fertilizer application

During the dry season (December through May) the plots were irrigated by water pumped from underground sources. Effluent was pumped from the effluent tank and stored in 6 earthenware jars (about 500 litres capacity) close to the mulberry plots (Photos 3, 4) and was applied at weekly intervals, manually in amounts adjusted according to the results of the N analysis.

Planting and harvesting

The mulberry plants were harvested by cutting the entire plant at 60 cm above soil level. The first harvest was 4 months after planting, with subsequent harvests at 2 month intervals. Immediately after harvesting, the mulberry foliage of each treatment was weighed and then separated into leaves and stems.

Data collection

Samples of soil were taken from each plot before planting and after the last harvest. Samples of effluent were analyzed for N before application to the plots. Samples of leaves and stems from all the treatments were taken for chemical analysis.

Measurements

DM in leaves plus petioles and in stems was determined by using a microwave oven (Undersander et al 1993). The ratio of leaf and petiole to stem was calculated and approximately 100g of each plant fraction (stem, leaf and petiole) for each treatment was retained for analysis. Samples from replicates were analyzed for N and ash (AOAC 1990) and also for water soluble dry matter (WVDM) and water soluble nitrogen (WVN) (http://www.mekarn/labman/Washvalue.htm).  In each treatment and replicate plot a soil sample of 0.5 kg was taken at approximately 30cm depth and was kept for analysis of pH, N, DM and ash.

Statistical analysis

The data were analyzed using the General Linear Model option of Minitab (version 13.31) ANOVA software. The sources of variation were level of effluent, blocks and error. Regression analysis was applied to the data relating responses (Y) to the input variable (X = Level of effluent N).

Results and discussion

Composition of effluent

Data on the composition of the biodigester effluent (Table 2) indicate that most of the N (91%) was in the form of ammonium salts. 

Fresh and dry matter yields

Biomass yields of the whole plant and the component leaves and stems increased linearly with level of effluent N (Tables 3 and 4; Figure 1).  

Biomass yields of the whole plant and the component leaves and stems increased linearly with level of effluent N (Figure 1).

Figure 1.  Biomass yield response to fertilizer effluent

Forage composition

Crude protein increased in the leaves, but was unchanged in the stems, in response to effluent N application (Table 5; Figure 2). Conversely DM content increased in stems but was unchanged in leaves in response to effluent N (Figure 3).

There were no effects of level of effluent application on the contents of water soluble DM and water-soluble N (Table 6).

Chemical composition of soil

The levels of effluent N did not affect the DM content and the pH of the soil (Table 7). However,  at the end of the experiment, there were positive trends in content of OM and N according to the level of effluent N (Figures 4 and 5).

Discussion

The linear trends for increase in mulberry biomass yield with effluent N application are similar to those reported by Benavides et al (1994) using goat manure and Ramos et al (2002) who applied swine lagoon effluent, although the actual yields were much lower in our study.  According to Takahashi and Kronka (1986), mulberry biomass yield was higher when N was applied in the form of manure in comparison with chemical fertilizer.

The linear increase in crude protein content of the leaves with application of effluent N observed in this study is similar to what was observed by Rodríguez et al (1994) using chemical fertilizer. Positive effects of biodigester effluent on the crude protein content of cassava leaves and of duckweed were reported by Le Ha Chau (1998a,b).  The fact that effluent level had no effect on the content of water soluble DM and N in mulberry leaves suggests that the proportion of the nitrogenous components in the form of true protein did not change even at the highest levels of effluent application.

Conclusions

• Biomass yield of mulberry foliage, and crude protein content of leaves increased linearly with increasing application of N from biodigester effluent.

  
  

• Soil fertility, as measured by content of N and OM, was improved in direct relationship with the quantity of biodigester effluent.
   

Acknowledgments

The authors would like to express their gratitude to the personnel of the Center for Livestock and Agriculture Development, for help with the experiment. Financial support by the Cambodian Agricultural Research Fund (CARF) to CelAgrid made it possible for us to carry out this research. Thanks are given to Dr.John Schiller, consultant of the CARF project, and to Dr. John Skeritt, Deputy Director General - Research, Australian Centre for International Agricultural Research (ACIAR), for assisting in the financial management, and providing an internship.

References

AOAC 1990 Official methods of chemical Analysis. Association of Official Agricultural Chemists. Washington DC (16th edition)

Benavides J, Lachaux M y Fuentes M 1994 Efecto de la aplicación de estiércol de cabra en el suelo sobre la calidad y producción de biomasa de morera (Morus sp.). In Benavides J.E. Árboles y arbustos forrajeros en América Central. CATIE, Turrialba, Costa Rica. 2: 495-514

Bui Xuan An, Preston T 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) 2:27-35 http://www.lrrd.org/lrrd9/2/an92.htm

Huy Sokchea, Chhay Ty, Khieu Borin, Preston T R and Mech Phalla 2008 Effect of harvest interval on biomass yield and composition of mulberry (Morus alba) managed for feed and fuel..   Proceedings MEKARN Regional Conference 2007: Matching Livestock Systems with Available Resources (Editors: Reg Preston and Brian Ogle), Halong Bay, Vietnam, 25-28 November 2007 http://www.mekarn.org/prohan/sokchea.htm

Le Ha Chau 1998a Biodigester effluent versus manure from pigs or cattle as fertilizer for production of cassava foliage (Cassava esculenta) Livestock Research for Rural Development (1). http://www.lrrd.org/lrrd10/3/chau1.htm

Le Ha Chau 1998b Biodigester effluent versus manure, from pigs or cattle, as fertilizer for duckweed (Lemna spp.) Livestock Research for Rural Development (1). http://www.lrrd.org/lrrd10/3/chau2.htm

Nguyen Xuan Ba, Vu Duy Giang and Le Duc Ngoan 2004 The use of mulberry foliage for ruminants. Science and Technology Journal of Agriculture and Rural Development Volume 5

Preston T R and Rodriguez L 1996 Recent developments in the recycling of livestock excreta; an essential feature of sustainable farming systems in the tropics. http://www.fao.org/WAICENT/FAOINFO/AGRICULT/AGA/AGAP/FRG/recycle/default.htm

Ramos T O, Lara L P E, Rivera L J A and Sanginés G J R 2002 Mulberry production with swine lagoon effluent. FAO, Rome .http://www.fao.org/DOCREP/005/X9895E/x9895e0s.htm

Rodríguez C, Arias R and Quiñones J 1994 Efecto de la frecuencia de poda y el nivel de fertilización nitrogenada sobre el rendimiento y calidad de la biomasa de morera (Morus sp) en el trópico seco de Guatemala. In Benavides J E (Editor) Árboles y arbustos forrajeros en América Central. Turrialba, Costa Rica, CATIE. 2:515-529.

Soeurn Than 1994  Low cost biodigesters in Cambodia. Proc. National Seminar-workshop on sustainable livestock Production  on local feed resources. Agric. Pub. House Ho Chi Minh, pp.109-112.

Singh B and Makkar H P S 2000 The potential of mulberry foliage as feed supplement in India. FAO Animal Production and Health Paper 147, p. 139-156. 

Takahashi R and Kronka R N 1986 Efeitos dos diferentes tipos de adubacao na producao de amoanim. Nova Odessa 46: 157-164

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

Yao J, Yan B, Wang X Q and Liu J X 2000 Nutritional evaluation of mulberry leaves  as feeds for ruminants. Livestock Research for Rural Development. Volume 12, Number 2 http://www.lrrd.org/lrrd12/2/yao122.htm

Received 10 February 2009; Accepted 1 June 2009; Published 1 July 2009

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