eli5 : If plants can make their food with water and carbon dioxide using photosynthesis why do they need manure and fertilisers ?
In: Biology
Imagine you’re trying to build a nice big barn. You make it out of wood. It’s entirely made out of wooden planks. But you need something to hold the planks together, mount the doors on, etc. so you use some metal nails and hinges. So the barn isn’t entirely made out of wood is it? That’s what’s happening here. All of their “food” (the energy they use) comes from the sun and photosynthesis which turns that water and CO2 into sugars, which only have oxygen, hydrogen, and carbon, and then they also use that carbon for the bulk of the structures, but some things need to be iron, phosphorous, sulfur, etc. almost the entire mass of a plant (and actually you too) is carbon, oxygen, and hydrogen. Nitrogen is next usually, and that typically comes from the atmosphere indirectly (bacteria in the root system “breathe” it), or comes from fertilizer. The rest are trace elements that come from the soil.
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