Biochar potential for improvement of soil properties and plant growth

Various claims have been made for the use of biochar (the carbon-rich product derived from pyrolysis of biomass) to improve soil fertility and crop yield and for C sequestration. In this thesis, the impact of a biochar produced at 550 oC from woody waste to loamy sand, a red loam and a coarse sand was assessed at a rate of 2% w/w. Coarse (particle size >1.5 mm) biochar significantly increased infiltration rate of both soil types, but only for 15 months, while fine biochar reduced infiltration rate of coarse sand by 19% at 18 months. The field capacity, plant available water and permanent wilting point of sand were increased by 37, 41 and 15% respectively with addition of fine biochar compared to the control. Plant growth was improved accordingly in well watered conditions, but not in a severe water stress treatment (maintained at 20% of field capacity). Soil rhizobial activity (measured by soil respiration) increased with the addition of biochar at low and high water potentials (- 1.0 and -1.5 MPa), however, biochar on its own had low microbial activity at both water potentials. Rhizobia number (log CFU) also increased in biochar-amended soil compared to the un-amended soil at both water potentials. The little increased water content at permanent wilting point (-1.5 MPa) may have provided micro-habitats for rhizobia to survive and remain active. The apparent effective cation exchange capacity of soil increased after 3 years of biochar application in loamy sand, but the change was of little practical significance (4.87 meq/100g bichar amended soil, compared to 4.41 for the soil). An observed decrease in nutrient leaching in pot and field trials was associated with increased plant nutrient uptake and growth. Improved plant growth and reduced nutrient leaching are ascribed to changes in soil infiltration rate, microbial growth and water availability in biochar amended soil lead. Further long term field studies are required to find its expanded role in broad scale agriculture.