– if we throw away, say, 1T of grass clippings every year, and grass is just the nutrients of the soil, some sunlight and water, why do we not need to add 1T of new soil to the lawn every year?
In: Biology
Most of the mass of grass and other plants actually comes from carbon dioxide absorbed from the air. The plant uses a process called photosynthesis to combine water, carbon dioxide, and the energy of the sun to produce glucose (a type of sugar) which is used as a source of energy for the plant. It also produces oxygen as a byproduct.
There are other contributing factors, but the majority of plant growth is driven from the carbon they “inhale” during photosynthesis. This carbon is primarily where the mass of plants come from.
For starter, there are a lot of nutrients in the soil acting as a buffer, but over time this buffer will get consumed if not replenished. Nutrients can come back to the soil from various sources, for example animal droppings, leaves from trees etc. that end up in the soil. These will be broken down and the nutrients in them will come back to the soil.
Now, if you want to keep your lawn nice with a lot of grass, you should not throw away the clippings. Or if you do, you should fertilize the lawn. The natural process of regaining nutrients is far too slow to keep up if you throw away all the clippings each time you mow the lawn. Over time, this will result in the soil in your lawn becoming short on nutrients and the grass can’t grow very well. Moss on the other hand, is better at growing in nutrient poor soils than grass, so if you keep throwing away the clippings and not fertilize, you will eventually have a lawn full of moss instead of grass.
Edit:
Soils running out of nutrients are not true just for grass and lawns. Crops used to have to be rotated back in the day or they would eventually fail. Not all crops need the same type of nutrients, so by rotating what crops were being grown, they could prevent the soil from running out of nutrients for the crops.
Today we fertilize the farmlands so heavily so it’s not needed, but if we stopped fertilizing, this would become a problem again.
In addition to the carbon dioxide
Your grass probably takes in 650 pounds of water throughout the year, including rain
Well I live near a beach and the topsoil is at best maybe an inch thick if lucky? I’ve been saving all the leaves and dog poop for my flower garden. Letting it compost and break down over time. Honestly the yard debris should probably stay and build layers without human interference that’s how you get really deep moist dark brown loam in a healthy forest. Ultimately animals / humans in my case my dogs, my chiweenie, scrapes at the top soil disturbing it. I’ve been battling it to prevent erosion by planting new clover grass and tried dandelion seeds.
Anywhere I put wood chips down that broke up over time has seen an increase of new grass as the wood chips give something for water and moisture to anchor into above the sand erosion.
Throw away? Adding new soil? Why do you need to do that?
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