Agronomic properties and characterization of rice husk and wood biochars and their effect on the growth of water spinach in a field test

    In a study made by Hossain et al. (2011) concerning the influence of pyrolysis temperature on production and the nutrient properties of biochar, researchers concluded that pyrolysis temperature has a significant effect on the chemical properties of the biochar produced. There are important implications regarding the suitability of biochar as a soil amendment. In our study, all biochars tested were produced at relatively low temperatures (250oC -300oC) and were slightly alkaline.

Source: http://biochar.pbworks.com/w/page/9748043/FrontPage

Biochar preparation and characterization

    Production of rice husk biochar (RHB) was carried out by the Industrial Technology Research Institute (ITRI), located in Hsinchu, Taiwan. RHB was pyrolized using a small-scale reactor at 300ºC -350ºC with a residence time of 1 hour. These temperatures may be applicable for small scale farmers who lack access to credit and cannot afford high-scale pyrolysis plants. In order to observe the performance of both biochars in their original shapes, we avoided the use of grinders or sieves to reduce the particle size in the soil applications. Wood biochar (WB) was purchased in an agricultural shop near the experimental site and WB was prepared by open-burn (the proposed temperature was 250ºC -300ºC).

Production of rice husk biochar (RHB)  by the Industrial Technology Research Institute (ITRI).

    Several analyses, including use of scanning electron microscopy (SEM) equipped with an energy dispersion X-ray spectroscopy (EDX), elemental analysis of biochars (EA), Fourier transform infrared spectroscopy (FT-IR), volatile matter (VM), surface area analysis (BET), electrical conductivity (EC), total dissolved solids (TDS) analysis, water-holding capacity (WHC), and heavy metal analysis (ICP), were used to characterize the properties of the biochars.

Scanning electron microscopy (SEM)

    By using an SEM S-3000N HITACHI production microscope, the morphology of both WB and RHB samples was examined. The sample powder was sprinkled as a thin layer on an adhesive tape placed on the brass sample holder. Excess amounts of the sample were removed with a small manual air blower. The adhered sample was then coated with gold powder using a sputtering device, the Ion Sputter E-1010 HITACHI, and then transferred into the JEOL sample chamber for analysis. The accelerating voltage was set at 15- 40 kV; 200, 300 and 600 times magnification were selected. A Perkins-Elmer EA analyzer determined the elemental composition of the biochar, such as the biomass that would be ideal for application as biochar for carbon sequestration.

Brass sample holder for SEM analysis.

    A Bruker Vector-22 FT-IR spectrometer identified the sample to determine the organic functional groups present for each biomass, especially carbons. Volatile matter in biochar was determined following the ASTM D 3175 -07 standard test method. In order to determine the surface area of each biochar, samples were ground and sieved using a No. 60 mesh. A Beckman Coulter SA 3100 BET analyzer containing approximately 0.1000 g to 0.2000 g of each biochar sample was then used at a temperature of 50Cº for 60 min.

Fourier transform infrared spectroscopy (FT-IR)

    Electrical conductivity and total dissolved solid analysis are theoretically the best measure of salinity to indicate the actual salinity level experienced by the plant root (Corwin and Lesch, 2003). Hence, electrical conductivity and total dissolved solids were measured using a SUNTEX SC-110 portable conductivity-meter. Samples were prepared at a ratio of 1:10 (sample: distilled water), mixed in a HMS-212 stirrer for 30 min, and then left to stand for 4 hours.

HMS-212 stirrer.

    To evaluate the heavy metals present in the biochars, we used a leaching extraction procedure, which follows the USA EPA method No.1311 with minor modifications; 5 g of ground and weighted biochar were added into a volumetric flask together with 1000 ml of distilled water and 5.7 mL of acetic acid. After samples were left for 18 h in a toxicity characteristics leaching procedure (TCLP) rotator, they were filtered and poured into 100 mL containers. The trace metals analysis in the samples was realized by using a Perkin-Elmer 3000-XL inductively coupled plasma (ICP-AES) spectrometer.

Overview of a Basic Inductively Coupled Plasma—Atomic Emission Spectrometry (ICP-AES)
Source: http://people.whitman.edu/~dunnivfm/FAASICPMS_Ebook/CH3/3_3_1.html


Field trial

Water spinach plants were germinated for two weeks and later transplanted into plots.

     Each plot was 1.94 m x 1.10 m. Five different treatments were assigned to each of the biochars and to one control group. RHB and WB were weighted and added to each plot. Every plot was mixed with the assigned quantity of biochar using a top soil mixing technique (Major, 2009). Before transplanting, each plot was irrigated for 20 min. Plants were transplanted 15 cm apart, with 22 plants per plot.  A perforated pipe system was used to water the plants every 2 days for 10 min. Soluble N-P-K fertilizer 20-20-20 was applied to the crops; 1 g of the fertilizer was dissolved in 2 liters of water and the procedure was repeated for each of the plots. The application was made only one time during the growth of the plants during the second week.

   After eight weeks of growth, the plants were harvested. Plant morphological characteristics measured included: leaf number, leaf length, leaf width, stem number, stem size, fresh plant weight, root growth and the chlorophyll content of the leaves.

    The effect of biochar on root growth was measured to compare the effects of the different types and quantities of rice husk and wood biochars used. Ten water spinach plants were randomly selected from each treatment; their roots were washed to avoid loose soil and blotted to remove any free surface moisture.

                                   Rice Husk Biochar                                               Wood Biochar

     After plants were harvested and their roots measured, each was weighed; plants were collected and grouped by treatment in order to obtain their total fresh weight. Relative chlorophyll content (Soil Plant Analysis Development (SPAD)) was measured every two days using a Minolta chlorophyll meter (model SPAD 502).

Soil characteristics evaluation

    There were eleven treatments for rice husk biochar and wood biochar, along with one control group. Four soil samples from each treatment were dried in a precision oven at 35ºC, homogenously mixed, ground and passed through a 2mm sieve. A 20:20 (soil: distilled water) solution ration was prepared for the determination of pH. Organic carbon (OC) and organic matter (OM) were determined using the Walkley-Black method (Walkley and Black, 1934). Soil texture and characteristics were also obtained using the hydrometer method (Milford, 1997).

 Rice Husk Biochar in Soil

Wood Biochar in Soil

    The water-holding capacity (WHC) of biochars was measured, following procedures for soil analysis as outlined in a manual (Lee, 2007).  Soil samples where oven dried for 24 h at 105ºC; then 5 g of each sample were poured into a 100mL beaker and distilled water was added until the saturation point was reached and the weight loss could be counted for the water-holding capacity of the sample.

Water-holding capacity (WHC) of biochars