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<aside> 🌱 Anaerobic digestion is a technology which degrades organic waste into biogas and digestate. Increasing the nutrient concentration of digestate from 1.27% to 46% (average nitrogen content of Urea) can improve the effectiveness of digestate to replace synthetic fertilizer, which would provide South African farmers with a cheap and effective fertilizer to increase yields and agricultural productivity.
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Problem: Sub Saharan Africa has the lowest fertilizer application rate in the world causing millions
The average maize yield in Sub Saharan Africa is 1.3 tons per hectare, compared to the USA at 10.79 tons per hectare. Crop yields throughout Sub Saharan Africa are on average 3 times less than the rest of the world. Sub Saharan Africa’s low crop yields are directly correlated to fertilizer application rates, which are 5X less than the rest of the world. [1]
Nth order problems: synthetic fertilizer degrades soils long term, pollutes water, releases greenhouse gases
The environmental impact of synthetic fertilizer cannot go unnoticed. 1.8% of global greenhouse gas emissions are from synthetic fertilizer, releasing 6 tons of CO2 for every ton of ammonia produced. [2] Apart from the apparent dead zones and greenhouse gases that synthetic fertilizer causes, it also compromises soil health and quality long term. It has been shown that long term, synthetic fertilizer can actually decrease yields by decreasing the organic compounds in the ground and depleting macro and micro nutrient content of the soil. [3]
Potential solution: small scale home digestors to turn on-farm agricultural waste into biogas and digestate. Processing digestate to concentrate nutrients can improve digestate effectiveness and replace synthetic fertilizer.
Anaerobic digestion is like sophisticated composting; organic waste (like manure, agriculture waste and food waste) goes into the digester, and biogas and digestate come out. The process relies on acidogenic and methanogenic bacteria to break down the waste into long chain fatty acids which form biogas. The often overlooked by product of this process is digestate, a nutrient rich slurry which can be used as fertilizer. Applying all digestate produced from a 2m3 digester can reduce the use of synthetic fertilizers by 15%. [4] Improving the nutrient concentration of digestate by processing nitrogen from urine can increase the effectiveness of digestate and make digestate an alternative to synthetic fertilizer.
Synthetic fertilizer is the single biggest determinant of crop yields. Since the creation of synthetic nitrogen fertilizer via the Haber Bosch process in 1903, yields globally have skyrocketed at a rate of 160% per year. [5] Synthetic fertilizer is arguably the most important invention of the twentieth century, directly responsible for feeding 3.5 billion people that would have otherwise starved. [6]
The relationship between fertilizer and crop yields is simple - the more fertilizer applied to crops, the higher the yield, the less fertilizer applied, the lower the yield.
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