Evaluation of fertilizer of fresh solid manure, composted manure or biodigester effluent for growing Chinese cabbage (Brassica pekinensis)

San Thy and Pheng Buntha

Center for Livestock and Agriculture Development (UTA-Cambodia),
POB 2423, Phnom Penh 3, Cambodia
santhysimon@yahoo.com

Abstract

The research was carried out at the ecological farm of CelAgrid/UTA-Cambodia over the period May through August 2004 to evaluate the response of Chinese cabbage (Brassica pekinensis) to different forms of organic fertilizer. There were two consecutive trials each of 2 months including soil preparation, nursery seeding, transplanting and measurements (from May to June for Trial 1, and from July to August for Trial 2). Plots were prepared on the same surface with 3 m² area (3m x 1m) using raised beds to reduce wet conditions when there was high rainfall. The four treatments (each replicated four times) were: raw cattle manure solids, composted cattle manure solids (in piles of 0.5 or 1.0m³ volume) and the effluent from a mixing biodigester (20 day retention time) charged with the liquid and small particles from raw cattle manure. The fertilizers were applied at the same level of nitrogen (150 kg N/ha) at 7 day intervals with increasing quantities equivalent to 10, 20, 30, and 40 % of the total amount over the first 28 days. The experimental design was a Randomized Complete Block Design (RCBD). A basal fertilization of 2 kg per m² of fresh cattle manure was applied to all plots one week before starting the trials.

In Trial 2, when seeding was directly in the field and the plots were protected with plastic sheet against the rain, biomass yield of the cabbage showed a 100% increase for use of biodigester effluent (34 tonnes/ha) compared with composted manure (14 to 17 tonnes/ha), with lowest results for fresh manure solids (9 tonnes/ha). Yields and responses to fertilizer were much lower in Trial 1, apparently due to the effects of heavy rain and poor root development caused by the practice of transplanting the seedlings. In Trial 2, the cabbage fertilized with biodigester effluent was higher in moisture and in crude protein compared with plants fertilized with raw manure solids. Soil N and organic matter tended to be higher after than before the trials.

Key words: Biodigester effluent, Chinese cabbage, composted manure, cow manure, fertilizer, yield

Introduction

Cambodian agricultural activities are based on rice, horticulture, livestock and fruit trees grown at the homestead or in the farm field. Usually the system is monoculture on the same plots of land. The overall result has been a decline of fertility, imbalance in soil nutrients and low crop yields. For these reasons, most farmers like to use chemical fertilizers because they are easy to transport, are used efficiently for growth of the plants and give high yields, but it has been observed that with succeeding crops, the quantity of chemical fertilizer has to be increased apparently because of declining soil fertility.

In contrast, organic fertilizers have beneficial effects on soil structure and nutrient availability, help to maintain yield and quality of the product and are less costly than chemical fertilizers. Traditional practice in Cambodia is to use manure from cattle but the quantity is not usually enough for the available crop areas. Alternative ways to improve the availability of organic manure are: making compost from wastes and residues from vegetable crops and fruit trees; and processing the manure through anaerobic biodigesters ,which has been shown to result in an effluent which has higher fertilizer value than the raw manure with improved yields being demonstrated for cassava and duckweed (Le Ha Chau 1998a,b) and for fish (Pich Sophin and Preston 2001).

Vegetables are an important component in the diet of rural families in Cambodia as they provide essential vitamins and minerals. In a benchmark survey by FAO (2003), it was estimated that the average per caput daily food consumption included rice 500g, vegetables and fruit 160 to 500g, fish 110g and meat 30g. Vegetable production would thus seem to be the logical target for studies to demonstrate the advantages of the different kinds of organic fertilizers.

Objectives

The overall aim is to promote the sustainable use of natural resources by using recycling systems based on the biodigester, as a means to improve the fertilizer value of animal wastes. This research is part of a series of activities directed towards the sustainable use of natural resources and to increase biodiversity in farming systems. The objective of this study  was to compare the yields of Chinese cabbage when fertilized with different kinds of organic manure.

Hypothesis

It was expected that yields of Chinese cabbage would be higher when they are fertilized with effluent from biodigesters as compared with compost and raw cattle manure.

Materials and Methods

Location

The research was carried out at the ecological farm of CelAgrid-UTA Cambodia, located in Kandal village, Ro Lous commune, Khandal Steung district, Khandal Province. The land chosen for the experiment was in a low-lying area, subject to flooding in the rainy season. Previously the field had been used for monoculture rice production.

Experimental period

There were two trials each lasting 2 months including soil preparation, nursery seeding, transplanting and measurements. The experimental period for trial 1 was from May to June, and from July to August, 2004 for the second one (Table 2).

Plot size

Plots were prepared with an area of 3 m² (3m x 1m) in the form of raised beds to avoid excessive moisture affecting the crop when there was too much rainfall.

Experimental design

The experimental materials were taken from an anaerobic biodigester (Photo 1) charged with the liquid and small particles after pumping the raw manure (from cattle and buffaloes) through a screen which retained the solid materials (Photo 2). These solids were used directly or after composting.

Photo 1: The mixing biodigester		Photo 2: The pump used to separate the solid manure from the liquid and small particles

 The individual treatments were:

• ERM: residual solids from cattle manure after extraction of the liquid and small particles
• ERMC₁: compost made from residual solids from cattle manure which was stacked in a volume of 1 m³
• ERMC_0.5 : compost made from residual solids from cattle manure which was stacked in a volume of 0.5 m³

• EFFC: effluent from biodigester that was charged with the liquid and small particles from cattle manure

The experimental design was a Randomized Complete Block Design (RCBD) with 4 blocks (replications) arranged in two rows (Photo 3). The application of the fertilizers was at the same level of nitrogen (150 kg N/ha), equal to 15g N/m² or 46g N per plot per harvest. .

Photo 3: Plot arrangement according to the experimental design and biodigester system

The two trials differed slightly in the management of the plant material

Trial 1:

Chinese cabbage was germinated in a nursery bed and transplanted in the field beds20 days  after germination.

Trial 2:

The seed was planted directly on the beds in the field with distance between rows and between plants of 20cm. 3 to 4 seeds were put in each hole and then, after 20 days, one seedling was selected and the others removed, leaving one plant in each location.

The practice used in Trial 2 was based on farmer tradition in Kandal Province whereby the seed is sown directly in rows 30 cm apart and seedlings are thinned to 30-50 cm between plants within the row. This practice is also reported in the USA (http://oregonstate.edu/dept/NWREC/vegindex.html) and by Tomkins and Daly (1998).

Fertilizer application and management

Fertilizer application

The fertilizer was applied at 150 kg N/ha equal to 45 g N per plot of effective area of 3 m². The nitrogen was applied in increasing quantities of 10, 20, 30, and 40 % at intervals of 7 days over the first 28 days. This application of fertilizer is within the range recommended by Hochmuth and Hanlon (2000) that the maximum N fertilizer to be applied should not exceed 196 kg /ha. A level of N of 168 to 196 kg/ha was reported in the Commercial Vegetable Production Guide (2002).

A basal application of raw cow manure was applied to each plot at 2kg /m² (fresh basis) one week before the trial and was put in the furrow between the rows. The experimental fertilizers were applied at the same time for each treatment, at about 4.00 pm in the afternoon because at this time the evaporation rate is low. The solid fertilizer was applied 5cm around the root of the plants taking care not to touch the leaves of the Chinese cabbage. The liquid effluent was applied in the furrow between two rows for similar reasons. After application of the fertilizer the plots were watered.

Management

The growth trial was carried out in an open field with a covering of black plastic net for the first trial for one week after transplanting. The second trial was also covered with plastic net and plastic sheet for protection against excessive rain. For irrigation, sprinklers were used to spray the plots, with hand watering on the edges of the plots not reached by the sprinklers.

Weed control

The plants were kept free of weeds during the early growth stage, until the crop had reasonably good ground cover. Chinese cabbage appears to be more susceptible to post-emergent herbicides than other cabbages, so it is preferable to plant into a weed-free seed bed (Waters et al 1992).

Harvesting

Chinese cabbage is fairly quick maturing. It requires about 40 days from sowing to harvest for some cultivars with up to 75 days for the longer maturing ones (Stephens 1994). According to Palada and Crossman (1999), Chinese cabbage is a quick maturing plant which can be harvested 30 to 45 days after planting. For this experiment it was harvested 42 days from the time of germination. It was harvested by cutting the entire plant just above the soil line. Old, ragged, and decayed outside leaves were removed.

Data collection and analyses

Soil:

Samples of soil were taken from each plot before planting, and after harvesting, for analysis of DM, OM, pH and nitrogen.

Fertilizers:

Samples of all types of fertilizers were analyzed before application in order to quantify the amounts of N actually applied.

Chinese cabbage:

The height of the cabbage was measured every week before applying the fertilizers. At harvest after 40 days, the green biomass was weighed and analyzed for DM, OM and Nitrogen.

Statistical analyses

The data were subjected to analysis of variance (ANOVA) using the General Linear Model (GLM) of the MINITAB software Release 13.31 (2000). The model was:

Y_{ij k} = µ + T_i +P_j + e_ij

Where:

Y_{ij k}: Dependent variable

µ: Overall mean

T_i: Treatment effect

P_j : Block effect

e_ij : Random error

Results and discussion

Compost

In both piles of composted manure the temperature rose to a maximum of 58 to 59ºC by day 7 then falling to a range of 43 to 51 by day 36 (Table 2 and Figure 1). These trends are similar to those reported by Solomon (1993).

Figure 1: The average of temperature from different piles of compost with 0.5 and 1m³ volume

Fertilization characteristics and quantity

The nitrogen content in each fertilizer is shown in Tables 3 and 5. The amount applied at each of the times is shown in Tables 4 and 6 for Trials 1 and 2, respectively.

Growth in height

Trial 1:

There was a tendency for the growth in height of the cabbage to be highest when fertilized with biodigester effluent and lowest when the fertilizer was raw manure (P=0.09) (Table 7 and Figures 2 and 3). 

Trial 2:

The trends for growth in height in Trial 2 were similar to those in Trial 1 but the differences were more pronounced (P=0.001) in favour of biodigester effluent (Table 8 and Figures 4 and 5).

Biomass yield

Trial 1

There were no differences in biomass yield due to the type of fertilizer (Table 10 and Figure 6).

Figure 6: Effect of different fertilizers on yield of Chinese cabbage (Trial 1)

Trial 2

The results for biomass yield in Trial 2 showed a 100% increase for use of biodigester effluent compared with composted manure solids (Table 10 and Figure 7), with lowest results for fresh manure solids.

Figure 7: Effect of different fertilizers on yield of Chinese cabbage (Trial 2)

Overall growth rates and differential responses to fertilizers were much higher in Trial 2 than in Trial 1. The explanation could be the better root system and stronger seedlings when planting was directly in the field and there was protection against excessive rain in the case of Trial 2. In Trial 1, heavy rain at 30 days resulted in the death of some plants and washing away of the fertilizers. Negative effects of high temperature and wet conditions on the growth of Chinese cabbage were reported by Fu I-M et al (1993), Kuo and Tsay (1981) and Fritz and Honma (1987).

The marked improvement in growth rate when biodigester effluent was used can be seen clearly in Photo 4. The superior results from use of biodigester effluent compared with raw manure agree with the findings of Le Ha Chau (1998a,b) for effects of these fertilizers on growth of cassava and duckweed.

The maximum yield recorded in this experiment (35 tonnes/ha) was slightly less than has been reported in Japan, where yields steadily increased up to 46.5 tonnes/ha from 1970 to 1996 (MAFF 1999). In Taiwan, yields at the Asian Vegetable Research and Development Centre were 64 tonnes per ha (Pan 1995); however, the national average in 1991 was 36.9 tones per ha (Waters et al 1992). Yields of 8 to 11 kg/m² (80 to 110 tonnes per ha) were reported for intensive management in glass house conditions (Vogel et al 1989).

Photo 4: View of the green biomass of Chinese cabbage showing the superior growth on the biodigester effluent (EFFC)

Chinese cabbage composition

In Trial 2, the cabbage fertilized with biodigester effluent was higher in moisture and in crude protein compared with plants fertilized with raw manure (Table 11; Figure 8).

Soil properties

Soil pH and organic matter content tended to be higher at the end of the trials with no apparent relation with the kind of fertilizer (Table 12).

Conclusions

• The biomass yield, and content of moisture and crude protein, of Chinese cabbage was highest when fertilized with biodigester effluent and lowest when fresh residual solids from manure were used.

Acknowledgements

The authors would like to thank the Meiden Plant Engineering and Construction Co., Ltd for funding this research project. Special thanks are given to KIRIHARA KOGYO CO., LTD for assisting in the financial management, and providing an internship for a student to participate in the research.

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Received 20 September 2004; Accepted 11 November 2004; Published 1 March 2005

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