The Potential of Biochar produced from Eichhornia crassipes and Prosopis juliflora to Enhance Soil Water Holding Capacity of Drylands Soils

Environmental degradation, agricultural productivity, food security, fresh water scarcity, and the adaptation to and mitigation of climate change are all significant concerns of the 21st century. Biochar is a highly porous, carbon rich material which is a natural soil amendment being investigated to address these current issues. Expanding agricultural production into dryland environments where sandy soils dominate is highly likely to be of great importance for ensuring future global food security, as population and food demands continue to increase. Sandy soils have little ability to store water, making food production difficult and crop yields an unreliable source of food and income for inhabitants living in these environments. This study looked at the water holding capacity (WHC) and hydrophobicity of Eichhornia crassipes and Prosopis juliflora for use as biochar, to potentially enhance soil moisture storage and thus agricultural productivity, with a particular focus on arid and semi-arid lands (ASALs) and northern Kenya. Both are invasive species found in Kenya which was the reason for their selection for use in this study. Biochar was produced at 350°C, 450°C, and 550°C in a Carbolite furnace and also in a Sampada gasification stove, to mimic traditional kiln char production. Biochar WHC was examined at mixtures of 2%, 5%, and 7%, corresponding to a field application rate of roughly 20 t ha-1, 50 t ha-1, and 70 t ha-1, respectively. Results demonstrated that both biochars increase soil WHC the greatest at a 7% application rate. The greatest hydrophobicity values were apparent at 350°C, with E. crassipes the more hydrophobic of the two. Mercury porosimetry analysis, which compares various characteristics of the pore space in relation to physical properties of the biochar, is consistent with the WHC data, revealing that as the total intruded volume increases the water holding capacity increases. Overall E. crassipes and P. juliflora show potential for use as biochar, but P. juliflora with its greater lignin content, is likely the better choice.