Spring! It’s the time of year for planting and tending the soil. Lawn care keeps suburbanites busy. Immaculate vistas of leveled grass grace the dreams of many. One of the first duties is to feed the hungry bits of red fescue and Kentucky blue. For landowners know that these grasses aren’t natural and requires a lot of care.
Typically a lawn needs feeding about four times a year. Fertilizer comes with feeding instructions that are typically in the range of 6 kilograms for 400 square metres. To make fertilizers, producers use vast quantities of energy to fix the nutrients onto a neutral substrate. Nitrogen fixation requires about 6 Gigajoules per tonne. Phosphate is about 6.5 Gigajoules per tonne. Hence, to make fertilizer, both nutrients and energy are necessary.
Assume fertilizer with a ratio of 29-3-4 is applied four times over the course of a year on a 230 square metre plot of land. This is a typical urban yard size. The resulting annual energy cost for producing the fertilizer is 26 600 000 joules. Or, in other words, keeping a luxurious suburban lawn of rich green requires as much energy as feeding a person for two days. This isn’t a large amount of energy for one lawn but it is energy going for luxury rather than a necessity.
More alarming is that fertilizer is a necessity for food production. After hundreds of years of growing crops, soil has almost no nutrients remaining and crops grow only by continually spreading fertilizer. Globally, 2% of primary energy consumption is for fertilizer, for nutrient fixing. This is 2% of the total being 4e20 joules. The share used to make fertilizer is 8e18 joules or 8 exajoules. This is a huge quantity that keeps our lawns green and lush and farmer’s fields vibrant and plentiful.
Equally alarming is that natural gas is the source for almost all energy used in fertilizer production. Is there another source of such a vast amount of energy to keep plants growing once natural gas supplies run out?
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