Presentation Information
[O12-P100]Protect Agriculture from Water Shortages — Building Drought-Resistant Soil
*Tsutomu Kuniya1, *Yusei Tamura1, *Riwa Takeda1, *Haduki Morigaki1 (1. Toyooka High School, Hyogo Prefecture)
Keywords:
water retention capacity,water retention
Last summer, Toyooka City in Hyogo Prefecture suffered from a severe water shortage for agriculture due to low rainfall. This experience motivated me to start this research to find ways to improve the water-holding capacity of soil. Through my initial investigation, I discovered a substance called EF Polymer—a polymer compound made from fruit peels and other organic waste—which is effective in enhancing soil water retention. However, I also identified a challenge: EF Polymer is more expensive than conventional fertilizers when considering its application over vast areas of land. Therefore, I began this study to see if it could be replaced with relatively inexpensive materials available at local home improvement centers.
Preliminary Experiment As a preliminary test, I examined the relationship between particle size and water-holding capacity. I prepared three types of soil with different particle sizes: Scoria (volcanic ejecta, largest), river soil, and paddy soil (smallest). These were placed in boxes with holes at the bottom. I poured water from the top and compared the time it took for water to drain from the bottom. The results showed that water flowed through the Scoria the fastest, followed by the river soil, and then the paddy soil. A faster drainage time indicates lower water-holding capacity and faster infiltration. Thus, I confirmed that larger particle sizes result in lower water retention, while smaller particles provide higher retention.
Experiment Methodology Next, I purchased seven types of relatively low-cost materials from a home improvement center: EF Polymer, bark compost, bamboo powder, rice husk charcoal, perlite, peat moss, and leaf mold. I also collected five types of soil: Andosol (used in Kannabe Highlands), dune sand (used in Kumihama), paddy soil (used in Toyooka), field soil (used in Toyooka), and Scoria.
For the experiment, I mixed 40g of soil with 10g of each material in cups with three small holes at the bottom. Since EF Polymer has a different recommended application rate, I also tested it at a ratio of 48g of soil to 2g of polymer. As a control, I prepared cups containing only 50g of soil. I added 60g of water to each cup and measured their weights daily for 11 days to compare their water-holding capacities.
Results and Discussion Overall, the samples mixed with EF Polymer, perlite, and rice husk charcoal showed high water retention. In contrast, bark compost and peat moss showed low retention, in some cases even lower than the soil-only samples. I found that water permeability—the inability to retain water as it flows out of the bottom—was a crucial factor.
The difference in permeability was evident from the weight on the first day, immediately after water was added. For almost all samples, the weight ranking established on the first day remained consistent throughout the 11-day period. EF Polymer, perlite, and rice husk charcoal showed low permeability across all soil types, while bark compost, peat moss, and soil-only samples showed high permeability. Regarding the soil types alone, Andosol had significantly lower permeability, while dune sand had significantly higher permeability compared to the others.
From the second day onwards, the rate of weight loss (evaporation) was nearly identical across all soil and material types. This suggests that the final results were determined primarily by the initial drainage (permeability) rather than differences in evaporation from the surface.
Conclusion The results indicate that Andosol has the highest natural water-holding capacity. Furthermore, EF Polymer, perlite, and rice husk charcoal effectively improve water retention in any soil type.
While my goal was to find a material that could rival EF Polymer, the polymer ultimately showed the highest water retention. However, the difference between EF Polymer and materials like perlite or rice husk charcoal was small, providing a basis for further improvement. Additionally, while the preliminary experiment suggested that larger particles lead to lower retention, the main experiment showed that Scoria (larger particles) actually retained more water than dune sand. Consequently, the exact relationship between particle size and water-holding capacity remains a subject for further investigation.
Preliminary Experiment As a preliminary test, I examined the relationship between particle size and water-holding capacity. I prepared three types of soil with different particle sizes: Scoria (volcanic ejecta, largest), river soil, and paddy soil (smallest). These were placed in boxes with holes at the bottom. I poured water from the top and compared the time it took for water to drain from the bottom. The results showed that water flowed through the Scoria the fastest, followed by the river soil, and then the paddy soil. A faster drainage time indicates lower water-holding capacity and faster infiltration. Thus, I confirmed that larger particle sizes result in lower water retention, while smaller particles provide higher retention.
Experiment Methodology Next, I purchased seven types of relatively low-cost materials from a home improvement center: EF Polymer, bark compost, bamboo powder, rice husk charcoal, perlite, peat moss, and leaf mold. I also collected five types of soil: Andosol (used in Kannabe Highlands), dune sand (used in Kumihama), paddy soil (used in Toyooka), field soil (used in Toyooka), and Scoria.
For the experiment, I mixed 40g of soil with 10g of each material in cups with three small holes at the bottom. Since EF Polymer has a different recommended application rate, I also tested it at a ratio of 48g of soil to 2g of polymer. As a control, I prepared cups containing only 50g of soil. I added 60g of water to each cup and measured their weights daily for 11 days to compare their water-holding capacities.
Results and Discussion Overall, the samples mixed with EF Polymer, perlite, and rice husk charcoal showed high water retention. In contrast, bark compost and peat moss showed low retention, in some cases even lower than the soil-only samples. I found that water permeability—the inability to retain water as it flows out of the bottom—was a crucial factor.
The difference in permeability was evident from the weight on the first day, immediately after water was added. For almost all samples, the weight ranking established on the first day remained consistent throughout the 11-day period. EF Polymer, perlite, and rice husk charcoal showed low permeability across all soil types, while bark compost, peat moss, and soil-only samples showed high permeability. Regarding the soil types alone, Andosol had significantly lower permeability, while dune sand had significantly higher permeability compared to the others.
From the second day onwards, the rate of weight loss (evaporation) was nearly identical across all soil and material types. This suggests that the final results were determined primarily by the initial drainage (permeability) rather than differences in evaporation from the surface.
Conclusion The results indicate that Andosol has the highest natural water-holding capacity. Furthermore, EF Polymer, perlite, and rice husk charcoal effectively improve water retention in any soil type.
While my goal was to find a material that could rival EF Polymer, the polymer ultimately showed the highest water retention. However, the difference between EF Polymer and materials like perlite or rice husk charcoal was small, providing a basis for further improvement. Additionally, while the preliminary experiment suggested that larger particles lead to lower retention, the main experiment showed that Scoria (larger particles) actually retained more water than dune sand. Consequently, the exact relationship between particle size and water-holding capacity remains a subject for further investigation.