I am clearing an acre of land that contains very established grasses as well as several broad-leaf plants. I will be using a moldboard plow to till everything under, but I first wish to eradicate this foliage. The area will be a forest garden. I will be using the existing soil.
The soil requires amendment in nitrogen, phosphorous, potash, and boron. I have organic sources for all but the boron. The forest garden will be on soil that has never seen Glyphosate (a rarity these days), pesticides, or herbicides. I will keep it pristine, but also want to make the project realistic.
Fire won't kill the root systems, so that's not much help. I can tarp/cover the land to limit moisture and cook the roots; that option is a bit tedious but possible. What I've been considering of late is dousing the soil with an overabundant supply of nitrogen and then tarping it to maintain high concentration where the foliage and roots exist. Materials could be metered so tilling the soil will result in the right nitrogen mix for planting, after which I would go entirely organic. I'm not fond of the fact this would involve fertilizing using a non-organic source, but I know of no better way. The goal of first year planting would be to convert this non-organic nitrogen source into biomaterial by planting cover crops that would be tilled under in the following year. I'd also plant fruittrees and other forest garden foliage that takes time to establish, accepting that it will introduce some challenges with respect to tilling cover crops.
I'm very open to better suggestions, given an understanding that I will not use poisons. Enduring chemical treatments are out, as are solutions that require exceptional volumes of labor.
I realize and accept that grasses will eventually creep back into the area, and that some seed will sprout to provide future challenges. My goal is to give the forest garden time to effectively establish.