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| Photo 1: HOTBIN Lid Thermometer & Vent (23/3/23) |
In an earlier post on winterizing your hot compost bin, I discussed using supplements, such as urea and animal manure, to boost nitrogen levels in the hot compost bin when 'green' waste was in short supply during the winter months. I also mentioned that urea, as it is currently manufactured, comes with baggage such as its carbon footprint. While evaluating Google's new AI Chatbot (Bard), I entered into a discussion about the relative merits of urea and animal manure in terms of their carbon intensity.
I asked Bard (Google's AI Chatbot) the following question:
What is the carbon footprint of urea manufacture? And its answer was ...
The carbon footprint of urea manufacture is significant. The process requires the use of fossil fuels, which release carbon dioxide into the atmosphere when they are burned. In addition, the process produces other pollutants, such as nitrogen oxides and sulfur dioxide, which can also contribute to climate change.
The carbon footprint of urea manufacture can be reduced by using renewable energy sources, such as solar and wind power, and by improving the efficiency of the process. However, even with these improvements, the carbon footprint of urea manufacture will still be significant.
The carbon footprint of urea manufacture is an important factor to consider when making decisions about fertilizer use. Farmers can reduce the environmental impact of their operations by using less fertilizer and by choosing fertilizers with a lower carbon footprint.
The follow-up question was:
Is the carbon footprint of urea worse than animal manure? And its answer was ...
The carbon footprint of urea is worse than that of animal manure. The production of urea requires the use of fossil fuels, which release carbon dioxide into the atmosphere when they are burned. In addition, the process produces other pollutants, such as nitrogen oxides and sulfur dioxide, which can also contribute to climate change.
Animal manure, on the other hand, is a natural fertilizer that does not require the use of fossil fuels. The carbon footprint of animal manure is also reduced by the fact that it is recycled back into the soil, where it helps to sequester carbon dioxide.
Therefore, the carbon footprint of urea is worse than that of animal manure. Farmers can reduce the environmental impact of their operations by using less fertilizer and by choosing fertilizers with a lower carbon footprint, such as animal manure.
However, it is important to note that the carbon footprint of animal manure varies depending on the type of animal, the way the manure is managed, and the climate. For example, the carbon footprint of cattle manure is higher than that of pig manure, because cattle produce more methane, a greenhouse gas. The carbon footprint of manure is also higher if it is stored in lagoons, which can leak methane into the atmosphere. Finally, the carbon footprint of manure is lower in warmer climates, because bacteria in the soil break down manure more quickly and release carbon dioxide into the soil.
Overall, the carbon footprint of urea is worse than that of animal manure, but the carbon footprint of animal manure can be reduced by using best management practices.
Then came the follow-up follow-up question:
Do you have any quantitative data? And its answer was ...
Yes, I do. According to the Food and Agriculture Organization of the United Nations, the carbon footprint of urea production is 1.2 kg CO2 per kg of urea, while the carbon footprint of animal manure is 0.6 kg CO2 per kg of manure. This means that the production of urea releases 2 times more carbon dioxide into the atmosphere than the production of animal manure.
It is important to note that these numbers are estimates, and the actual carbon footprint of urea and animal manure may vary depending on the specific conditions of production.
We are warned that Bard is not always correct but these data look about right. There is also a reference you can follow up. One of the good things about these AI-driven Chatbots, is the way it remembers your previous question; indeed, it is like you are in a conversation. My (follow-up)³ question was:
But isn't the nitrogen content of urea much higher than manure? And its answer was ...
Yes, the nitrogen content of urea is much higher than that of manure. Urea is a synthetic fertilizer that contains 46% nitrogen, while manure is a natural fertilizer that contains 2-3% nitrogen. This means that urea is much more concentrated than manure, and it can provide plants with a much higher level of nitrogen.
However, it is important to note that nitrogen is not the only nutrient that plants need. They also need phosphorus, potassium, and other nutrients. Manure contains a wider range of nutrients than urea, and it can also provide plants with beneficial microorganisms.
Therefore, both urea and manure can be effective fertilizers. The best fertilizer for a particular plant will depend on the specific needs of the plant and the soil.
I know the nitrogen content of urea is 46% and the reported content for manure is about what I would expect. Intuitively, one would think, urea is the preferred option as a nitrogen fertilizer because it has about 20 times the nitrogen but is only twice as carbon intensive as manure. Bard reminds us that nitrogen is only one of the nutrients required by plants and manure comes with other advantages. However, intuitively you would think that obtaining the other nutrients, such as potassium and phosphorus, might have a similar carbon intensity to urea manufacture so that a balanced artificial fertilizer might still be less carbon intensive than manure.
On to the next question:
Does that mean urea has a lower carbon footprint than manure when used as a nitrogen fertilizer?
No, it does not mean that urea has a lower carbon footprint than manure when used as a nitrogen fertilizer. When urea is used as a fertilizer, it releases nitrogen into the atmosphere as ammonia. Ammonia is a greenhouse gas that contributes to climate change.
Manure, on the other hand, does not release ammonia into the atmosphere. Instead, it releases nitrogen into the soil as organic matter. Organic matter helps to sequester carbon dioxide in the soil, which helps to reduce the amount of greenhouse gases in the atmosphere.
Therefore, the carbon footprint of urea is higher than the carbon footprint of manure when used as a nitrogen fertilizer.
Here Bard seems to be winging it. Manure most definitely does give off ammonia with upto 90% lost by the time it is applied as fertilizer. Urea, on the other hand, only loses about 16% of its nitrogen content as ammonia when applied as a fertilizer. Manure adds organic matter (humus) to soil which is definitely beneficial to soil health; however, some studies suggest that the soil does not hang onto the carbon long-term so may not be a viable carbon sink for the excess carbon dioxide in our atmosphere.
When questioned on this error of fact, Bard was contrite and admitted to its error ...
I'm sorry but animal manure most definitely releases ammonia into the atmosphere.
Yes, I apologize for the error in my previous response. You are correct that animal manure releases ammonia into the atmosphere. Ammonia is a byproduct of the breakdown of nitrogenous wastes in animal manure. When manure is stored in a liquid state, ammonia can escape into the atmosphere as a gas. Ammonia can also be released from manure when it is applied to soil.
The amount of ammonia released from manure depends on a number of factors, including the type of animal, the amount of manure produced, the way the manure is stored, and the weather conditions. For example, pigs produce more ammonia than cattle, and manure stored in lagoons releases more ammonia than manure stored in solid form.
Ammonia is a greenhouse gas that contributes to climate change. When ammonia reacts with other chemicals in the atmosphere, it forms particulate matter, which can cause respiratory problems. Ammonia can also damage crops and other plants.
There are a number of ways to reduce the amount of ammonia released from manure. These include:
* Using best management practices when storing and applying manure
* Using anaerobic digestion to convert manure into a gas that does not contain ammonia
* Using nitrification inhibitors to slow the breakdown of nitrogenous wastes in manure
* Using technologies to capture ammonia emissions from manure
By taking these steps, farmers can help to reduce the environmental impact of animal manure.
I then posed the following question:
Based on this new information, is animal manure still better than urea as a nitrogen fertilizer?
The environmental impact of animal manure and urea as nitrogen fertilizers is a complex issue with no easy answers. Both have their own advantages and disadvantages.
Animal manure is a natural fertilizer that does not require the use of fossil fuels. However, it can release ammonia into the atmosphere, which is a greenhouse gas. Urea is a synthetic fertilizer that requires the use of fossil fuels. However, it does not release ammonia into the atmosphere.
The best fertilizer for a particular plant will depend on the specific needs of the plant and the soil. If you are concerned about the environmental impact of your fertilizer, you should talk to a local agricultural extension agent or a certified organic farmer.
A somewhat anodyne response with Bard sitting uncomfortably on the fence! As with many questions like this, it is almost certainly more complex than you think. Personally, I would rather use natural fertilizers though that would be garden compost (with added biochar) rather than animal manure. Urea is demonised because it is made in an industrial process that uses fossil fuels. Technically, its manufacture could be very green, and much greener than using animal manures, but it might still be demonised for being part of the industrial complex. On the other hand, those of us who adopt a more pragmatic approach to life might still want to use urea in a minimal and efficient way while, at the same time, encouraging a more environmentally sustainable means of production.
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