Scaling understanding of biochar aging impacts on soil water and crop yields

Finding solutions to food-water-energy nexus challenges requires a systems approach and integration across scales to address issues of food production, environmental degradation, and energy use. Biochar, the co-product of thermochemical conversion of biomass to bioenergy, is a soil amendment that has the potential to improve soil quality, water retention, and crop productivity, while sequestering atmospheric C. Most of the positive benefits of biochar applications are based on evidence from short-term studies using freshly produced biochars, however, the effect of fresh and aged biochars over longer time periods remains inconclusive. This dissertation presents a series of integrated studies across the laboratory, greenhouse, field, and modeling scales to advance understanding of the impacts of biochar type and biochar aging on soil physical and chemical properties, soil water dynamics, and crop productivity. In the first study (Chapter 2), we developed a modified proximate analysis method that accounted for biochar diversity and found that volatile matter/fixed carbon ratios were a useful measure of biochar C stability. Using soil cores collected from a long-term bioenergy cropping system experiment we showed that crop rotations increased soil C and N, soil C/N ratio, pH and gravity drained water content, and decreased bulk density for soils with biochar relative to no-biochar controls (Chapter 3). A greenhouse soil column study (Chapter 4) showed that aged biochars impacted soil water relations differently than the equivalent fresh biochars. Biochar applications must be made strategically and take into account biochar type, soil type, and biochar age. The final two studies utilized the biochar model within the APSIM cropping systems model. In Chapter 5, we provided experimental verification of the pedotransfer functions currently used in APSIM for biochar amended soils and determined that current quality modifiers that estimate biochars impact on soil water estimates were site-specific. Lastly, model simulations revealed that over 32-years, biochar applications could eliminate negative effects associated with residue harvesting, as evaluated by reduced NO3 leaching and increased SOC levels, while not impacting corn yields (Chapter 6). Overall, biochar applications can contribute to enhancing the long-term sustainability of agro-ecosystems, but biochar age and soil type are important variables to consider

Long term biochar effects on corn yield, soil quality and profitability in the US Midwest

Corn production in the US Midwest has the potential to generate a large amount of crop residue for bioenergy production. However, unconstrained harvesting of crop residues is associated with a long-term decline in soil quality. Biochar applications can mitigate many of the negative effects of residue removal but data and economic analyses to support decision making are lacking. To explore sustainable and profitable practices for residue harvesting in central Iowa we used 11 years of soil, crop yield, and management data to calibrate the Agricultural Production Systems sIMulator (APSIM) biochar model. We then used the model to evaluate how different biochar types and application rates impact productivity and environmental performance of conventional corn and corn-soybean cropping systems in Iowa under different N fertilizer application rates and residue harvesting scenarios. A cost-benefit analysis was also employed to identify the economically optimal biochar application rate from both producer and societal perspectives. Modeling results showed for both continuous corn and corn-soybean rotations that as biochar application rate increased (from 0 to 90 Mg ha-1) nitrate leaching decreased (from 2.5 to 20 %) and soil carbon levels increased (from 8 to 115 %), but there was only a small impact on corn yields (from –2.6 to 0.6 %). The cost-benefit analysis revealed that public benefits, evaluated from decreased nitrate leaching and increased soil carbon levels, significantly outweighed the private revenue accrued from crop yield gains, and that a biochar application rate of 22 Mg ha-1 was more cost-effective (per ton) compared to higher biochar rates. Overall, this study found that applying biochar once at a rate of 22 Mg ha-1 allows for the sustainable annual removal of 50% of corn residue for 32 years, is profitable for farmers even with minimal impact on grain yield, and beneficial to society through reduced nitrate leaching and increased soil organic carbon levels

Scaling understanding of biochar aging impacts on soil water and crop yields

Finding solutions to food-water-energy nexus challenges requires a systems approach and integration across scales to address issues of food production, environmental degradation, and energy use. Biochar, the co-product of thermochemical conversion of biomass to bioenergy, is a soil amendment that has the potential to improve soil quality, water retention, and crop productivity, while sequestering atmospheric C. Most of the positive benefits of biochar applications are based on evidence from short-term studies using freshly produced biochars, however, the effect of fresh and aged biochars over longer time periods remains inconclusive. This dissertation presents a series of integrated studies across the laboratory, greenhouse, field, and modeling scales to advance understanding of the impacts of biochar type and biochar aging on soil physical and chemical properties, soil water dynamics, and crop productivity. In the first study (Chapter 2), we developed a modified proximate analysis method that accounted for biochar diversity and found that volatile matter/fixed carbon ratios were a useful measure of biochar C stability. Using soil cores collected from a long-term bioenergy cropping system experiment we showed that crop rotations increased soil C and N, soil C/N ratio, pH and gravity drained water content, and decreased bulk density for soils with biochar relative to no-biochar controls (Chapter 3). A greenhouse soil column study (Chapter 4) showed that aged biochars impacted soil water relations differently than the equivalent fresh biochars. Biochar applications must be made strategically and take into account biochar type, soil type, and biochar age. The final two studies utilized the biochar model within the APSIM cropping systems model. In Chapter 5, we provided experimental verification of the pedotransfer functions currently used in APSIM for biochar amended soils and determined that current quality modifiers that estimate biochars impact on soil water estimates were site-specific. Lastly, model simulations revealed that over 32-years, biochar applications could eliminate negative effects associated with residue harvesting, as evaluated by reduced NO3 leaching and increased SOC levels, while not impacting corn yields (Chapter 6). Overall, biochar applications can contribute to enhancing the long-term sustainability of agro-ecosystems, but biochar age and soil type are important variables to consider.</p

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

Long term biochar effects on corn yield, soil quality and profitability in the US Midwest

Corn production in the US Midwest has the potential to generate a large amount of crop residue for bioenergy production. However, unconstrained harvesting of crop residues is associated with a long-term decline in soil quality. Biochar applications can mitigate many of the negative effects of residue removal but data and economic analyses to support decision making are lacking. To explore sustainable and profitable practices for residue harvesting in central Iowa we used 11 years of soil, crop yield, and management data to calibrate the Agricultural Production Systems sIMulator (APSIM) biochar model. We then used the model to evaluate how different biochar types and application rates impact productivity and environmental performance of conventional corn and corn-soybean cropping systems in Iowa under different N fertilizer application rates and residue harvesting scenarios. A cost-benefit analysis was also employed to identify the economically optimal biochar application rate from both producer and societal perspectives. Modeling results showed for both continuous corn and corn-soybean rotations that as biochar application rate increased (from 0 to 90 Mg ha-1) nitrate leaching decreased (from 2.5 to 20 %) and soil carbon levels increased (from 8 to 115 %), but there was only a small impact on corn yields (from –2.6 to 0.6 %). The cost-benefit analysis revealed that public benefits, evaluated from decreased nitrate leaching and increased soil carbon levels, significantly outweighed the private revenue accrued from crop yield gains, and that a biochar application rate of 22 Mg ha-1 was more cost-effective (per ton) compared to higher biochar rates. Overall, this study found that applying biochar once at a rate of 22 Mg ha-1 allows for the sustainable annual removal of 50% of corn residue for 32 years, is profitable for farmers even with minimal impact on grain yield, and beneficial to society through reduced nitrate leaching and increased soil organic carbon levels.This is a manuscript of an article published as Aller, Deborah M., Sotirios V. Archontoulis, Wendong Zhang, Wendiam Sawadgo, David A. Laird, and Kenneth Moore. "Long term biochar effects on corn yield, soil quality and profitability in the US Midwest." Field crops research 227 (2018): 30-40. doi: 10.1016/j.fcr.2018.07.012. Posted with permission.</p