Effect of effluent and biochar on the growth of water spinach

Kong Saroeun

Center for Livestock and Agriculture Development (CelAgrid)

Kandal province, Cambodia

saroeunkb@celagrid.org

*UTA-TOSOLY, AA#48, Socorro, Colombia
regpreston@utafoundation.org

Abstract

An experiment was conducted in Cambodia for 20 days to study the growth of water spinach in a poor clay soil (pH 5.0) by using bidigester effluent as fertilizer and biochar as soil amendment. The design was a 2*2 factorial arrangement with 4 replications, in a completely randomized layout.  The factors were effluent application (with or without) and biochar application (with or without). The biochar was the residue after gasification of sugar cane bagasse and contained 27% carbon and 73% ash. It was applied to the soil at the level of 5% (w:w) in plastic baskets holding 20 kg of soil. The water spinach was established from seeds.

Biochar application had no effect on water spinach growth in the poor clay soil (pH  5.0). By contrast, application of biodigester effluent at 80 kg N/ha more than doubled the fresh biomass yield (from 771 to 1675 kg/ha). There was no interaction with application of biochar.

Key words:  Ash, biomass,  crude protein, height, leaf, organic matter, pH

Introduction

In Cambodia, vegetables are the pivotal source of food and income for rural families. To grow them, chemical fertilizers need be used. Recently, the price of fuel has increased dramatically and so has the price of commercial fertilizers. It is a constraint for farmers to buy them for their crops. To solve this, farmers should use low cost organic fertilizers. A new possibility is to use fine-grained charcoal (biochar) as a soil conditioner, because charcoal fertilization can permanently increase soil organic matter content and improve soil quality, persisting in soil for hundreds to thousands of years. Soils receiving charcoal produced from organic wastes were much looser, absorbed significantly more water and nutrients and produced higher crop biomass. Charcoal amendment is considered to be a revolutionary approach for long-term soil quality improvement (Marsh and Bernstein 2008). Biochar is traditionally produced in smoky kilns from biomass (wood, plants, organic residue such as tree leaves and wood chips) heated in the absence of oxygen through a process called pyrolysis (Sustainable Society Club 2008)  Biochar is also produced in the process of gasification (Miech Phalla and Preston 2005).  From recent field experiments, biochar also appears to have potential to provide further climate benefits by reducing nitrogen fertilizer requirements, as well as cropland nitrous oxide and methane emissions from soil (Swift 2001). Bio-char can therefore act as a soil conditioner enhancing plant growth by supplying and, more importantly, retaining nutrients and by providing other services such as improving soil physical and biological properties (Glaser et al 2002; Lehmann et al 2003a,b; Lehmann and Rondon 2005).

Effluent is a nutrient-rich fertilizer in the form of the liquid waste from biodigester that farmers can set up for multipurpose utilization in their family. Effluent gives higher biomass yield with increased crude protein when applied to vegetables and plants such as Chinese cabbage (San Thy and Pheng Buntha 2005), water spinach (Kean Sophea and Preston 2001; Ho Bunyeth and Preston 2004) and cassava (Le Ha Chau 1998).

Research on biochar is relatively recent and there is a need to know the effect of biochar on the growth of different crops, and especially the possible interaction with the use of effluent. 

Hypothesis

• Biochar can act as a soil conditioner enhancing the growth of water spinach .

• Effluent can increase biomass yield and quality of water spinach.

• The effect of biochar will be greater when applied together with biodigester effluent.

Materials and methods

Location

The experiment was conducted for 20 days in the experimental area of Kampong Cham National School of Agriculture (KCNSA).

Materials

The biochar (Picture 1) was brought from Columbia and had been produced as a byproduct of the gasification of sugar cane bagasse. The effluent was taken from a biodigester located in the experimental  area of KCNSA. The soil used in the experiment was a poor clay soil (Picture 2) taken from the campus of KCNSA.  Water spinach seeds were bought from the market.

Experimental design

The experiment was designed as 2*2 factorial arrangement with 4 replications, in a completely randomized design (CRD). The factors (Table 1) were:

Effluent application

-Application of effluent (BE)

-No application of effluent (NBE)

Biochar application

            -Application of biochar (BC)

-No application of biochar (NBC)

The individual treatments were:

-BC: Biochar at 5% of the soil

-BCBE: Biochar at 5% of soil + biodigester effluent at 80 kg N/ha

-BE: biodigester effluent at 80 kg N/ha

-C: Control no treatment 

Cultivation preparation

The 20 kg of soil was put into plastic baskets (size about 37*51cm) according to the experimental layout (Picture 3 and Table 2). Seeds (n=60) of dry-land water spinach species were planted in the  baskets. The distance between rows was 8 cm. The baskets were lined with a net so that excess water could drain away easily. Water was applied uniformly to all baskets every morning and evening. In the case of raining, water was not applied.

Fertilizing

The effluent was taken from a biodigester charged with pig manure. It was applied at the beginning and every 5 days for 20 days for a total of 4 times during the growing period (Table 3).  The quantity applied depended on the nitrogen content of the effluent.  

Data collection

Plant height was measured every 5 days before applying the effluent. The measurement was done on a random number of plants (5 plants/basket). The water spinach was harvested at 20 days after planting. All plants were separated into stem and leaf after weighing the two components. Samples of each were taken for chemical analysis. 

Laboratory analysis

The samples of water spinach were analyzed  to determine dry matter by microwave radiation (Undersander et al 1993), N and ash (AOAC 1990). Organic matter was calculated as 100-ash. Samples of soil were analyzed for DM, N, pH and ash (AOAC 1990). The sample of biochar was analyzed for DM, pH and ash.

Statistical analysis

The data were analyzed by Analysis of variance (ANOVA) using the General Linear Model (GLM) procedure of the Minitab software (version 14). Sources of variation were: biochar, effluent, interaction of biochar*effluent and error.

Results and discussion

Chemical composition of soil and biochar

The soil was acidic (pH 5.0) and very low in N and organic matter (Table 4). The biochar contained 26.9% of organic matter. The high ash content explains the the high pH of 9.5.

Water spinach growth

The growth in height of the water spinach was increased by application of effluent but not by the biochar (Table 5; Figures 1 and 2; Picture 4). There was no interaction between biochar and effluent application on the growth of the water spinach. 

Biomass yield

The results for biomass yield mirrored those for growth in height (Table 6; Figures 3-6); however, there was an indication (P=0.07) that DM yield of biomass was lower with application of biochar.  The results for the proportion of the water spinach as leaf were the converse of those for yield, with higher leaf proportions when yields were reduced.