The Results Are In!

Last week we harvested our 19 finger millet test plots, each grown using varying amounts of biochar combined with different nutrient inputs: a 15% human urine solution, compost, and inorganic fertilizer (di-ammonium phosphate – DAP) in both half and full applications. After a week of drying and processing, the results are in.

As we expected, increased biochar application resulted in yield improvements for nearly every plot. In fact, the heaviest application of biochar (with no additional nutrients added) resulted in a 150% yield improvement over simply planting in pure Kenyan soil. This is, unfortunately, an appropriate baseline for a number of low-income western Kenyan farmers. Even for those fortunate enough to use the recommended applications of available inorganic fertilizer, heavy applications of biochar combined with organic nutrient additives (urine and compost) met or exceeded inorganic fertilizer yields.

Our test plots were planted in 4m x 4m squares, each with seven evenly space lines of finger millet. The following yield and input application amounts are per acre extrapolations.

While there is inevitably a small amount of noise in our data, the higher level trend indicates a positive causal relationship between biochar application and yield.

One of the most exciting findings from these test plots is that organic, carbon negative growing options can produce up to 300% yield improvements over planting in un-amended Kenyan soil. This was the case for a per acre application equivalent of 5,000L of 15% human urine solution combined with 6,000kg of biochar. This growing method even resulted in a 27% yield improvement over the recommended 50kg per acre application of inorganic fertilizer. In fact, there were three organic, carbon negative growing methods that resulted in yield improvements over the inorganic fertilizer baseline:

• 5,000L 15% human urine solution + 6,000kg biochar
• 6,000kg compost + 6,000kg biochar
• 6,000kg compost + 2,000kg biochar

For each of our finger millet test plots, the following graph shows the per acre yield as well as the % yield improvement over un-amended pure Kenyan soil.

Working with farmers on a daily basis, we certainly recognize the stark practical difference between applying a single 50kg bag of di-ammonium phosphate per acre versus literally tons of biochar, compost, and urine. That being said, all of our customers, and a majority of western Kenyan farmers that we have encountered, believe in the idea that being a “serious farmer” means dedicating significant amounts of time and effort to properly maintaining soil and growing food. Nearly everyone aspires to be this admirable “serious farmer” archetype, but many lack the training and technology to do so. This is the gap that we at re:char work to fill every day.

A more realistic step toward becoming a “serious farmer” may be cutting inorganic fertilizer application in half and supplementing this half application with a moderate biochar amendment. Our data indicates that the yield from a 25kg per acre application of inorganic fertilizer, when coupled with as little biochar as 400kg per acre, can produce comparable results to a full 50kg application. Not only does the reduced dependence on DAP result in substantial per season savings, it also prevents the rapid soil acidification caused by continuous DAP use.

Our on-site test plots have locally verified what the published academic community has made increasingly clear: biochar application is an effective way to organically improve crop yields.

As our prior post indicated, we are in the midst of harvest and approaching the short-rains planting season. This means that more current and future customers will soon be reaping the benefits we have seen on our own farm.


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