Effect of effluent-treated biochar and biodigester effluent on growth of maize (Zea mays) and on soil physical properties

Sisomphone Southavong, Khamphisay Khammingsavath, Phetsamay Vyraphet and T R Preston*

Champasack University
Champasack province, Lao PDR
spdeuk@yahoo.com
* Finca Ecológica, TOSOLY, UTA (Colombia)
AA #48, Socorro, Santander, Colombia

Abstract

A bio-test experiment was conducted at the Integrated Farming Demonstration Centre, Champasack University, Lao PDR to investigate the effect of effluent-treated biochar on growth of maize and on soil fertility. The treatments were arranged in a completely randomized design (CRD) as a 2*5 factorial with 4 replications. The factors were: (i) suspension of the biochar in the effluent for 0, 24, 48, 72 and 96 hours; and (ii) application of biodigester effluent (with or without) at 50 kg N/ha.

With fertilization of biodigester effluent, the biomass of aerial part (leaf + stem) and root weight of maize were increased due to application of treated biochar with maximum values for the treatment time of 72h. Suspension of the biochar in effluent had no effect on biomass yield in the absence of fertilization with effluent. The treatments had no apparent effect on root length of maize. The effluent treated biochar had no effect on soil pH.

Key words: rice husk, root weight, soil pH, TLUP gasifier stove

Introduction

Soil amendment with biochar is evaluated globally as a means to improve soil fertility and to mitigate climate change. Biochar is the product of thermal degradation of organic materials in the absence of air (pyrolysis), and is distinguished from charcoal by its use as a soil amendment (Lehmann and Joseph 2009). Biochar has been described as a possible means to improve soil fertility as well as other ecosystem services and sequester carbon (C) to mitigate climate change (Lehmann et al 2006; Lehmann 2007; Laird 2008; Sohi et al 2010). The observed effects on soil fertility have been explained mainly by a pH increase in acid soils (Van Zwieten et al 2010) and water holding capacity (Southavong and Preston 2011; Southavong et al 2012a; Southavong et al 2012b; Southavong et al 2012c) or improved nutrient retention through cation adsorption (Liang et al 2010) and the increasing in crop yields (e.g. rice [Asai 2009; Southavong and Preston 2011]; water spinach [Southavong et al 2012a; Southavong et al 2012b; Southavong et al 2012c]; maize [Rodríguez et al 2009; Sokchea and Preston 2011]).

Previous biotest experiments conducted in our laboratory (Southavong et al 2012a; Southavong et al 2012b) showed that there were positive effects on growth of water spinach from combining biochar (the residue from the gasification of rice husks) with biodigester effluent, as additives to an acid soil (pH 4.6). Similar effects of biochar on growth of maize were earlier reported by Rodríguez et al (2009) and Sokchea and Preston (2011).

Biochar is repoorted to remove nutrients such as phosphorus (http://news.ifas.ufl.edu/2011/05/12/uf-researchers-develop-method-to-remove-phosphate-from-water-using-biochar/) and ammonia from waste water. However, there appear to be no reports on the effects on plant growth of biochar after it has been used to absorb nutrients from biodigester effluent.

It was therefore hypothesized that the combination of effluent-treated biochar with  biodigester effluent would have synergistic effects on  fertility of acid soils and on growth of maize.

Materials and methods

Location

The experiment was carried out between Oct 2011 and Mar 2012 in the integrated farming demonstration centre of Champasack University located in the Huay Leusy village, about 13 km from Pakse district, Champasack province, Lao PDR. The mean air temperature in the area is 28.2°C and the average annual rainfall of 2000mm.

Experimental design

Ten treatments were arranged in a completely randomized design (CRD) as a 2*5 factorial with 4 replications.

The factors were:

• Treatment time of biochar (soaked in biodigester effluent at 100 g/liter): 0, 24, 48, 72 and 96 h
• Application of biodigester effluent: with or without at 50 kg N/ha

Materials

The biochar (Photo 2) was derived from rice husk (Photo 3), produced locally in an updraft (TLUD) gasifier stove (Olivier 2010; Photo 5). Before applying to the soil, the biochar was treated with biodigester effluent (Photo 6) at the rate of 100 g of biochar per one liter effluent with different soaking time according to the experimental layout (Tables 1 and 2). The effluent used in the experiment was taken from a “plug-flow” biodigester made of tubular polyethylene with UV filter (Southavong et al 2012a). Maize seeds were bought locally from the market.

Procedure and data collection 

Plastic bags (15*20cm; 3 kg capacity) were filled with 3 kg of acid soil (pH 4.86) to which had been added 4% (by weight) of effluent treated biochar. Seeds of maize (n=5) were planted in each bag. After germination some plants were eliminated leaving only 1 plant as the experimental unit.

The height of the plants was measured every 10 days over a total period of 50 days. At the end of the trial, the whole plants were removed from the bags, washed free of soil, and weighed for fresh biomass. The root length was also measured. The green aerial parts (leaves and stems) and the roots were separated and analyzed immediately for DM content. Samples of soil were analysed at the beginning and end of the trial for pH, OM, and N. Biochar was analysed for DM, pH and ash content.

Fertilizing and irrigation

Samples of the effluent were analyzed for N before applying to the treatments. Biodigester effluent was applied to the treatments at the beginning of planting and then at 10 day intervals (total 4 times). The quantities were calculated according to the N content of the effluent to give the equivalent of 50 kg N/ha. Water was applied uniformly to all plots every morning and evening.

Chemical analysis

The DM content of the maize (aerial part and root), biochar and soil samples were determined using the micro-wave radiation method of Undersander et al (1993). Organic matter (OM) of biochar and soil and N content of effluent were determined by AOAC (1990) methods. The pH of soil was determined using digital pH meter (Southavong et al 2012b).

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, treatment time, interaction effluent* treated time, 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

Effect of biochar and effluent on maize biomass yield and on soil pH

Maize biomass yield was increased from 2 to 6 times by addition of biodigester effluent. The response to the biochar treatment time was curvilinear (Figure 1, Table 4) with increases in yield as the time was increased from 0 to 72 hours, followed by a decline with longer periods. Lehmann et al (2011) has reported on the major benefits that biochar combined with biodigester effluent can confer on poor soils with little or no organic matter and low nutrient status. Similar synergistic effects on plant growth by combining charcoal with chicken manure were observed by Steiner et al (2007).

There was no apparent effect on soil pH due to addition of effluent-treated biochar, either in presence or absence of biodigester effluent (Table 3; Figure 2).

The increase in root weight of maize was noticeable with a similar response as for growth of the aerial biomass with the highest values for the treatment time of 72 h (Table 3; Figure 3). Rodríguez et al (2009) observed a similar increase in root weight of maize with the application of biochar at 50 g/kg soil, in fertile or subsoil and with or without biodigester effluent. Effects on growth of the roots mirrored those on the green biomass except in the case of the sub-soil without effluent when the biochar markedly increased root growth. Similar findings for effects of biochar in increasing root weight were also reported by Sokchea and Preston (2011). Makoto et al (2010) showed not only a significant increase in root biomass (47%) but also in root tip number (64%) within a layer of char from a forest fire with larch twigs, birch twigs, and shoots of dwarf bamboo buried in a dystric Cam-bisol. The number of storage roots of asparagus increased with coconut biochar additions to a tropical soil (Matsubara et al 2002). In rice, the length of the roots was shown to increase with biochar additions (Noguera et al 2010).

The reasons for changes in root growth are rarely well identified in existing studies, and will likely vary depending on biochar properties and the conditions that restrict/promote root and shoot growth in different soil environments. Biochar with properties that improve the chemical and physical characteristics of a given soil such as nutrient or water availability, pH, or aeration will likely improve root growth.

Conclusions

• Biochar soaked in biodigester effluent for 72h increased foliage yield of maize by 300% in presence of effluent but there was no response in absence of effluent.
  
  
• When the biochar had been soaked for 72h in biodigester effluent, application of biodigester effluent at 50 kg N/ha increased the maize yield by 400%, compared with no effluent.

Acknowledgement

The authors are very grateful for the financial support received from the MEKARN program funded by Sida, Sweden. Staff from the Faculty of Agriculture and Forestry made valuable contributions to the research, especially Ms. Pany Chanthany final year student for data collection and taking care of the experiment. Champasack University is acknowledged for provision of research facilities.

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Received 20 May 2012; Accepted 28 May 2012; Published 1 June 2012

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