Effect of biochar and charcoal with staggered application of biodigester effluent on growth of water spinach (Ipomoea aquatica)

Sisomphone Southavong, T R Preston* and Ngo Van Man**

Champasack University
Champasack province, Lao PDR
spdeuk@yahoo.com
* Finca Ecológica, TOSOLY, UTA (Colombia)
AA #48, Socorro, Santander, Colombia
** Nong Lam University, Ho Chi Minh City, Vietnam

Abstract

The hypothesis that was tested in the present study was that there would be a synergistic response in growth of water spinach when biodigester effluent with staggered application was combined with biochar derived from rice husk in an updraft TLUD stove. The experiment was carried out at the research centre of Champasack University, Lao PDR to measure changes in soil fertility as a function of the growth of water spinach plants over a 28 day period following seeding. A completely randomized design was used with 3 replications of fifteen treatments in a 3*5 factorial arrangement. The factors were: soil amender (biochar or charcoal or none) at 40 tonnes/ha and level of effluent (0, 25, 50, 75 or 100 kg N/ha). The treatments were applied to samples of soil held in fifteen litre capacity plastic baskets. Effluent was applied at 7 day intervals (total 4 times) and the application was staggered with 10, 20, 30 and 40% respectively at each successive application. 

Green biomass yield of the water spinach was increased by biochar but not by charcoal. The application of biodigester effluent increased linearly the green biomass yield of the water spinach. Soil pH and water-holding capacity was increased by biochar but was not affected by level of effluent.

Key words: biotest, rice husk, soil pH, TLUP gasifier stove, water holding capacity

Introduction

Soils are one of the Earth's essential natural resources, yet they are often taken for granted. They are the medium in which plants grow to feed and clothe the world. Soils and the functions they play within an ecosystem vary greatly from one location to another as a result of many factors, including differences in climate, the animal and plant life living on them, soil's parent material, the position of the soil on the landscape, and the age of soil. To understand soil fertility is to understand a basic need of agricultural production (Jhonson 2009; Glendinning 2000).

Biochar, a charcoal-like substance made from biomass and used as a soil amendment, has been credited with multiple benefits, including the ability to improve soil fertility, protect water quality, and generate carbon neutral energy (Brick 2010).

In recent years, producing and using biochar as a soil amender and climate mitigation strategy has generated considerable interest (Lehmann et al 2006; Lehmann 2007). It is believed that biochar acts as a soil conditioner enhancing plant growth by retaining nutrients and by providing other services such as improving soil physical and biological properties (Glaser et al 2002; Lehmann and Glaser 2003; Lehmann and Rondon 2005). Many researches have been done and reported on the use of biochar in combination with biodigester effluent for improving plant growth and yield as well as physical properties of the soil (Southavong and Preston 2011; Sokchea and Preston 2011; Rodríguez et al 2011; Sisomphone et al 2012). Moreover, Rodríguez et al (2009) showed that there were synergistic effects on growth of maize from combining biochar (the residue from the gasification of sugar cane bagasse) with biodigester effluent, as additives to an acid sub-soil (pH 4.5). In a previous study in our laboratory (Sisomphone et al 2012), the biodigester effluent was applied in equal amounts at 7 day intervals in the growth of the plant. In the present study, it was hypothesized that adding biochar and applying biodigester effluent in a staggered (increasing) pattern would enhance the impact of both the biochar and the effluent on plant growth. 

Materials and methods

Location 

The study was conducted between June and Aug 2010 in the integrated farming demonstration center of Champasack University, located in the village of Huay Leusy, about 13 km from Pakse district, Champasack province, Lao PDR (15° N, 105° 2' E, 175 m above sea level). The mean air temperature in the region is 28.2°C and average annual rainfall 2000mm.

Treatments and design 

A completely randomized design was used with 3 replications of the treatments applied to samples of soil held in fifteen litre capacity plastic baskets. Fifteen treatments were compared in a 3*5 factorial arrangement. The trial covered a period of 28 days from 06 May to 03 Jun 2011. 

The factors were: 

• Soil amender: biochar, charcoal at 40 tonnes/ha or none
• Biodigester effluent: 0, 25, 50, 75 and 100 kg N/ha with staggered (increasing) rates of application over 21 days

The layout of the experiment is shown in Tables 1 and 2 and Photo 1.

Materials

The biochar was derived from rice husk (Photo 2), produced locally in an updraft (TLUD) gasifier stove (Olivier 2010; Photo 4). Charcoal was bought locally from an adjacent farmer. The effluent was taken from a “plug-flow” biodigester made of tubular polyethylene with UV filter of 5 m³ liquid volume (Photo 5) charged daily with washings (1 m³) from pig pens holding on average 21 pigs of 50 kg mean live weight. Water spinach seeds were bought locally from the market.

Procedure and data collection 

Plastic baskets (35*48cm; capacity 20 kg) were filled with 15 kg of acid soil (pH 4.86) to which had been added 4% (by weight) of biochar (Photo 6). Seeds of dry-land species of water spinach (n=60) were planted in each basket. After germination some plants were eliminated leaving only 40 plants as the experimental unit. The distance between rows was 8cm and 2-3 cm between seeds. The baskets were lined with a plastic net so that the excess water could drain away easily (Photo 6). The water was applied uniformly to all baskets every morning and evening. In raining day additional water will not be applied.

The height of the plants was measured every 7 days over a total period of 28 days. At the end of the trial, the green biomass (leaf + stem) was harvested and weighed, then analysed for dry matter (DM) content. Samples of soil were analysed at the beginning and end of the trial for pH, OM, water holding capacity, and N. Biochar and charcoal were analysed for DM, pH and ash content.

Fertilizing 

The fertilizer (biodigester effluent) was applied at the beginning and then at 7 day intervals (total of 4 times) during the growing period. The quantities were calculated according to the N content of the effluent based on the experimental layout (Table 2). The staggered application was 10, 20, 30 and 40% of the total specified quantity applied at days 1, 7, 14, and 21 respectively (Table 3).

Chemical analysis

The DM content of the water spinach, biochar, charcoal and soil samples was determined using the micro-wave radiation method of Undersander et al (1993). Organic matter (OM) of soil and N effluent were determined by AOAC (1990) methods. The pH of soil, biochar, charcoal and effluent was determined using a digital pH meter. For measurement of the pH of the solid samples, 5g of grounded samples (DM basis) were put in a beaker and 25 ml of distilled water were added. The suspension was stirred and kept over night. In the next morning before measuring the pH the sample was stirred again for 5- 10 minutes, then kept for another 5 - 10 minutes to let the solid part sink down and then the measurement was taken in the liquid part by using a digital pH meter. 

Statistical analysis

The data were analyzed according to the General Linear Model option in the ANOVA programme of the Minitab (2000) software. Sources of variation were effluent, soil amender, interaction effluent*soil amender and error. The Tukey test in the Minitab software was used to separate mean values that differed when the F-test was significant at P<0.05.

Results and discussion

Chemical composition of experimental materials 

The biochar contained more ash [less organic matter] and the pH was higher (Table 3) in this study than was reported for biochar derived from gasification of sugar cane bagasse for which the organic matter was 65% and pH was 9.0 (Rodriguez et al 2009). This presumably reflects the much higher content of ash in rice husk compared with sugar cane bagasse. The N content of the biodigester effluent was much lower compared to the value reported by Rodriguez et al (2009) which was 700 mg N/litre. This was probably due to the newly installed biodigester and the feed of the pigs which was only taro silage and rice bran.

Water-holding capacity and pH of the soil

Biochar improved the soil water holding capacity by 50% (Table 5 and Figure 1), with charcoal having a smaller effect. The level of improvement with biochar was similar to the value reported by Sisomphone et al (2012) when 4% (by weight) biochar was added to the soil. Soil pH was increased by biochar but not by charcoal (Figure 2). There was no apparent effect of level of effluent on soil pH. A positive effect of biochar in improving soil pH was observed by Rodríguez et al (2009), where the pH of an acid soil increased from 4.6 to 6.3 with addition of 5% biochar to the soil and Southavong and Preston (2011) where the soil pH increased from 4.5 to 5.13 and 5.40 when biochar was added to soil at 2 to 8% with the higher value for biochar from the stove than from the down draft gasifier. Agusalim Masulili et al (2010) also reported that application of biochar from rice husk at 10 tonnes/ha in a very acid soil increased pH from 3.75 to 4.40.

Effect of biochar and effluent on water spinach biomass yield

The increase in growth of the water spinach brought about by the biochar (Table 6; Figures 3 and 4) is in agreement with the majority of reports in the literature (rice [Sisomphone Southavong and Preston 2011]; maize [Rodriguez et al 2009; Sokchea and Preston 2011]; water spinach [Sisomphone et al 2012]). The staggered application of biodigester effluent resulted in a linear increase in height and green biomass yield of the water spinach. This response (equivalent to 18.3 tonnes/ha) is similar to the 20.7 tonnes/ha yield of water spinach reported in Cambodia by Kean Sophea and Preston (2001) with the same application of 100 kg N/ha of biodigester effluent.

Conclusions

• Biochar increased foliage yield of water spinach but there was no apparent effect on foliage growth from application of charcoal.
  
  
• Soil pH was increased from 4.86 to 6.17, and water holding capacity from 25.9 to 38.6%, due to addition of biochar.
  
  
• The staggered application of effluent gave a linear increase in biomass yield with the increasing level of effluent up to 100 kg N/ha.

Acknowledgement

This paper is part of the requirements by the Senior Author for the MSc degree at Cantho University in "Animal Production; Specialized in Response to Climate Change and Depletion of Non-renewable resources". The authors are grateful to the MEKARN program funded by sida SAREC project for financial support, and staff and students from Champasack University for their help with the experiment. Special thanks to Dr. Phetsamay Vyraphet for useful advice during the experiment.

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Received 24 December 2011; Accepted 29 January 2012; Published 7 February 2012

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