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Graph: Above, you can see how different amounts of biochar affect the soil's ability to hold water. The Y-axis shows the percentage of water the soil can hold, and the X-axis shows how much biochar was added. The standard value is the average water-holding capacity for clay soil, based on previous studies. We have also included error bars, which show how much measurements can vary.

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At MASH Makes, we want to discover where biochar offers the most significant benefits, so we can support the right agricultural communities in the right way. While biochar's ability to improve water retention is well-documented, research is limited when it comes to how different soil types react to it. To address this, we began by analysing soil from our field trials at our research lab in India.

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An analysis of our field trial’s red clay soil revealed a 30% increase in water-holding capacity (WHC) with biochar application. This aligns with previous research, though with different application rates. For instance, one study achieved similar increases using 1.8% biochar¹, whereas we used 25% biochar to see a 30% improvement.

These variations are due to the soil's clay content, the source of biochar used, and the production process implemented. Other research indicates that adding 5% biochar to sandy soil can boost water holding capacity by 50%², compared to only a 6% increase in clay soil with the same amount of biochar. Based on this research, we hypothesise that biochar is more effective at retaining water in sandy soil than in clay soil.

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What does this mean for farmers?

While these results might lead one to conclude that biochar should only be used in deserts and coastal areas, they shouldn’t be interpreted that way. Biochar’s other benefits, including reduced bulk density, better microbial growth, and resistance to heat stress, have not yet been shown to be dependent on soil type.

In fact, farmers are already seeing the results of using our biochar. In Ambajogai, India, which often suffers from drought and reduced groundwater, farmers and researchers note that applying MASH Makes biochar with organic fertiliser helps soil retain water better, boosting crop yields even in dry conditions. Farmers apply biochar once at the start of the season and continue using organic fertiliser for each crop. Even during severe droughts, this combination has kept crop yields much higher compared to using only fertiliser – even after the second season.

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Overall, our analysis shows that incorporating biochar into soil can significantly enhance water holding capacity, improve soil structure, and promote healthier plant growth. While these insights are promising, further research is needed to explore long-term effects and applicability across soil types.

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Technical details and limitations

Our analysis is based on an experiment at our research lab in India using red clay soil and 1-3 mm biochar particles. We measured the water-holding capacity (WHC) by seeing how much water was added compared to how much was collected afterward.

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Despite biochar's high water holding capacity (WHC) of 181%, the moderate increase in soil WHC observed in our study might be due to limitations in how we conducted the experiment:

• Preferential pathways: Biochar’s porous structure acts like a drain, allowing water to flow efficiently. While traditionally used in soil, it's important to explore different methods of applying biochar, such as mixing it extensively instead of just adding water on top. Different application methods yield varying results depending on soil type. Testing and adjusting techniques can optimise biochar's effectiveness.
• Modified funnel method: We used a simple method where soil samples were placed in a funnel with filter paper, then water was added and allowed to drain for 24 hours. This low-cost method might not be as accurate as alternatives.
• Manual water pouring: Adding water by hand can cause uneven distribution, leading to some areas getting more water while others get less.
• Water application rate: If water was added too quickly, it might have run off or bypassed the soil-biochar mix before being absorbed.
• Small sample sizes: Using small samples might not accurately reflect changes in WHC that would occur in larger, more representative soil samples.
• Insufficient replicates: Not having enough repeated tests could have caused variability in results.
• Collecting filtered water: The method of collecting water that drained through the soil might have led to errors.

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¹Yu, OY., Raichle, B. & Sink, S. Impact of biochar on the water holding capacity of loamy sand soil. Int J Energy Environ Eng 4, 44 (2013). https://doi.org/10.1186/2251-6832-4-44

²Santos, J. A., Gonzaga, M. I. S., Santos, W. M., & Silva, A. J. (2022). Water retention and availability in tropical soils of different textures amended with biochar. Catena, 216, 106616. https://doi.org/10.1016/j.catena.2022.106616

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