Food miles (https://www.carbonbrief.org/food-miles-have-larger-climate-impact-than-thought-study-suggests/)

Biogeochemistry page 161: “Agricultural lands account for up to 10% of global net plant productivity (Imhoff et al., 2014, 2004b), but only about 1% of the NPP from croplands is fed to humans or livestock (Wolf et al., 2015), and the rest is left in the field as crop residues or lost to spoilage during shipping and marketing.”

Grand Transitions page 71: time it takes to produce 1kg wheat 1800-2000. Number of US farms and crops produced throughout 20th century (https://www.ers.usda.gov/publications/pub-details/?pubid=44198)

Energy per crop: https://pure.au.dk/portal/en/publications/energy-inputs-and-ghg-emissions-of-tillage-systems . Grand Transitions page 74

Fertilizer efficiency: “The single most effective way to reduce fertiliser-associated emissions, however, would be to reduce the amount of fertilisers that we use. “We’re incredibly inefficient in our use of fertilisers,” said Serrenho. “We’re using far more than we need, which is economically inefficient and that’s down to farming practices. If we used fertiliser more efficiently, we would need substantially less fertiliser, which would reduce emissions without affecting crop productivity.”” (https://www.sciencedaily.com/releases/2023/02/230209114736.htm)

Food system isn’t efficient (https://www.sciencedirect.com/science/article/abs/pii/S026087741500309X)

Optimal N fertility doesn’t correlate to yield (https://link.springer.com/article/10.1007/s13593-024-00955-7)

Vaclav Smil How to feed the world chapter 3 (pg 55-75) Energy efficiencies

• 1720 Thomas Newcomen’ first coal-burning steam engine- less than 0.5% chemical to mechanical energy
• 1780’s James Watt improvements- 2%
• 1900 coal-burning steam engine – greater than 15%
• 1900 best steam locomotive engine – more than 6%
• Gasoline ICE- more than 10% in 1890s to more than 20% by 1930s. Diesel efficiency was greater than 30% then.
• Recent diesel engines- more than 50%.
• Recent best natural gas-fired combined-cycle gas turbines (combines gas and steam engines) are the most efficient ICE – up to 65%.
• Modern jet-liner lighter kerosene-fueled gas turbines – more than 40%.
• Early oil-fired furnaces for house heating – around 50% to useful heat. Now, the best natural gas-fired furnaces- around 97%.
• Recent resistance electric heaters- 100%.
• Electricity followed a similar pattern. 1882 Edison bulbs- 0.2% electricity to visible radiation. 1900 – 0.5%.
• 1930s Fluorescent lightbulbs- 15%.
• Today’s LED- 80-90% of all electricity to visible light.
• Max theoretical efficiency of traditional single-junction photovoltaic (Shockley Queisser limit) is 33.16%. Modern crystalline- 20%. Amorphous silicon – 6%.
• Human body- Well trained athletes turn chemical food energy into mechanical energy at 16-21% efficiency.
• Photosynthesis efficiency resembles Newcomen’s or at best Watt’s 18th century steam engines. Manitoba spring wheat output:input – 0.27% of solar energy that reached a hectare of 90 day spring wheat was converted into chemical energy of harvested grain.
  • 99% of sun’s emitted radiation is in the UV, visible light and IR regions. Plant pigments only absorb in the visible region, leaving 48.7% for photosynthesis. Green is reflected, leaving 44% blue and red. Blue photons carry 75% more energy and plants can’t use or store a lot of it, so some is lost, leaving 37% left. It takes 25% of incoming solar energy to create and regenerate compounds used to turn CO2 into glucose, leaving the value at 12.6% available. Photorespiration- cuts this remaining in half to 6.5%. Respiration losses- Increases with plant/ecosystem age, reducing net photosynthesis by 75-85% in some aged ecosystems. Claims about 30% of what is left after carb synthesis and photorespiration losses in short maturing crops, making the final max efficiency at 30C and today’s co2 to a measly 4.6% (for C3). 6% for C4).
  • Edible to inedible mass index: Traditional wheat, rye, oats, barley had long stalks, making the ration smaller compared to today’s shorter cultivars. Wheat was 0.25-0.3 (3-4x more inedible). Now, 0.45-0.5 for semidwarf wheat. Rice was usually less than 0.35. Now, 0.6 for paddy rice. “This redistribution – rather than any improvement in the overall efficiency of photosynthesis – has, with fertilization, been a principal cause of improved harvests.”
  • Photosynthetic conversion efficiency: Entire canola seed- 0.33% (oil is 45% of seed, so 0.15% in terms of edible oil. Nutritious cake used to feed livestock a high protein feed adds to food contribution. Manitoba potatoes – 0.6%. Whole grain Jjiangsu rice kernel – 0.4% (white rice contains only 60-65% of the whole grain’s mass, so white rice is 0.25%.) Optimally fertilized 2020 Iowa corn averaging 178 bu/acre – 0.7%. 99% is not directly consumed by humans. Washington sweetcorn- 0.35%. Sugarcane edible energy- 0.28%. “More water supply and/or better drainage, fertilization and varieties bred to use these conditions took better advantage to redistribute part of the newly synthesized phytomass from a plant’s inedible to digestible parts.” (Smil pg. 69 how to feed the world). No improvement in the efficiency of photosynthesis, but an improvement by redesigning photosynthesis would be significant.
  • Water- Transpiration results in a grossly lopsided exchange of water for carbon. C3 crops need between 400 and 1,600 grams of water to incorporate one gram of carbon into new phytomass. C4 is 160-250 grams for one gram C. Crop production uses the most freshwater for human use with about 80% of all freshwater used. 1,600 tons water/ton carbon for staple crops, wheat is 1,800, corn is 1,200. Legumes average 4,000. Vegetable oils from soybean (4,200), peanut (7,500), olive (nearly 15,000), nuts (9,000) and coffee (18,000). Sugar crops (less than 200), fruits and veg below 300 (pineapple, watermelon, plums) to 800 (bananas, apples, pears, peaches) to above 2,000 (grapes, dates, figs). Beer is around 300, wine nearly 900, orange and apple juices around 1,000-1,100. WUE is almost directly proportional to the atmospheric concentration of CO2. At about 700 ppm Co2, most C3 species would yield nearly 30% more.
  • Nitrogen- NUE. Grain corn has the highest among staple crops at 33% globally. 66% does not reach the plant. Rice is lowest at just above 20%. 2000 global review found about 35% of available N was taken up by harvested crops and 20% by their residues, the remainder lost to leaching (16%), erosion (15%) and gaseous emissions (14%). “In 2013, a study tracing global and regional trends in nitrogen efficiency between the 1960s and 2007 found the overall recovery of N by harvested crops was “about the same at the beginning of the time series as it was a the end”, averaging about 40%. Highest in high income countries and variable in low incomes ones. Brazil, India, USSR/Russia recorded increased recoveries. Chinese mean declined from 37% to 29%. 2014 evaluation found global NUE 69% in the 1960s, 45% in 1980, 47% stabilized later.