Polyculture chemicals into the environment such as eutrophication of fresh water or the presence of excess atmospheric nitrogen are greatly reduced in polycultures. Other negative impacts of modern agriculture are similarly reduced. Excessive tillage occurs in most modern agricultural practices, but removes essential microbes and nutrients from the soil that are conserved in polycultures, especially permacultures. Agricultural machinery not only uses fossil fuels and creates waste, but is more costly to farmers. Because polyculture relies on natural systems of crop maintenance these costs can be eliminated as well. Modern agriculture is also dependent on a very limited number of plant species.
Eutrophication those levels, so they can be overgrown by faster growing and more competitive species. In meadows, tall grasses that can take advantage of higher nitrogen levels may change the area so that natural species may be lost. Species-rich fens can be overtaken by reed or reedgrass species. Forest undergrowth affected by run-off from a nearby fertilized field can be turned into a nettle and bramble thicket. Chemical forms of nitrogen are most often of concern with regard to eutrophication, because plants have high nitrogen requirements so that additions of nitrogen compounds will stimulate plant growth. Nitrogen is not readily available