monocropping is bad for the soil and local ecology no matter which plant you are growing, which is why I try and grow a variety of plants and put a lot of effort into rejuvenating the soil in between crops by adding fresh compost and manure which can break down and provide the nutrients and minerals than the soil needs to feed the plants.
if you wanna see the negative side of monocropping just look at florida rn. They've grown a single variety of orange over countless orchards and now they're screwed because of a bug that is ruining orange harvests. If they hadn't only planted one variety of one fruit, they would have plenty of other sucsessful healthy crops right now, but because they practiced monocropping they are facing huge financial struggles right now
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After a bit of googling and looking deeper into it I think that tobacco farming does cause a lot of problems, but mainly when it's grown on a large scale. First off, there is deforestation to make way for the crops, and then there is the fact that monocropping depletes the soil of its resources, and then you have the fact that big tobacco industry uses chemical fertilisers and pesticides. Unfortunately, all three of these factors aren't only limited to tobacco but most crops that can be grown.
as I'm doing all of my cultivation on a smaller scale I'm able to avoid using any inorganic pesticides and fertilisers and only use things that come from nature to enrich the soil. This was a big motivator for me to start growing my own crops as even organic foods in the supermarket are mass produced and sprayed while growing/processing. Because I'm growing using organic methods, I don't ever need to worry about using chemicals on the plants that will hinder the soil ecology, and I already try and practice biodiversity in my garden
Yeah, at first you'd probably have to purchase a lot of compost but after a while you will start to make your own from the inedible parts of food that you normally throw away and from plant scraps when you harvest your crops
my advice would be to try and grow species of veg and fruit that are native to your country as these will have the best chance of surviving and wont cause any harm to the local ecosystem