Weeds taking back abandoned farm
About 500 million years ago, terrestrial lands converted from a barren desert into a rich, green biosphere. This living biosphere now regulates water cycles, surface temperature, and to a large extend the global carbon cycle and climate.
When the first plants conquered the barren and dry land, this happened in partnership or symbiosis with fungi. Early plants did not have root systems – they “plugged into” a network of fungal hyphae, which had the biochemical apparatus to dissolve minerals, bind nutrients, and transport these nutrients through vast networks. The fungi also worked in collaboration with nitrogen-fixing bacteria, thus providing a complete diet to their early plant partners. In exchange, plants provided something different: sugars from photosynthesis fed the fungal networks; evapotranspiration from plants brought cooling. Only over time, plants started building root systems – probably first for stability reasons, later as “docking stations” with mycorrhizal fungi, and even later to soak up nutrients directly. Even today, about 95% of all plants still rely mainly on symbiotic networks of soil mycorrhiza to access these nutrients.
Now weeds kick in. Weeds are the latest evolution of plant biology: they have emancipated themselves from their dependence of mycorrhiza. Weeds can live on dead minerals without living soil! After you dig up a hole on a construction site, weeds will be the earliest colonizers. If you kill living soil (with pesticides, salt in the form of fertilizer, or tillage), this dead soil offers perfect growing conditions for weeds. Weeds are unique that way – they can live “individualistically” without larger symbiosis. Kind of the homesteaders among the plants! But weeds cannot compete once complex living soils have formed, because they are not on good terms with its fungi!
From a biosphere perspective, weeds have a tremendous task: they convert dead land into living soil. As specialists that survive without the ancient fungal partners, weeds had to learn to retrieve nutrients from soil water. This is especially difficult because plant roots are unable to separate ‘good’ and ‘bad’ nutrients – they take up whatever is dissolved in the soil water. This is vastly inferior to living with fungal partners, who selectively provide exactly those nutrients that plants request. Weeds do it anyway!
Industrial agriculture has perfected in creating optimal growing conditions for weeds. Farmers were advised to plow, till, fertilize with salts, until the soil biology was devastated. Living soil degraded and left was only the mineral matrix – sand, silt and clay. Soil carbon content dropped from 6-8% in natural soils down to a little more than 1% in most agricultural soils in Ontario. Weeds thrive in these conditions, attempting to fulfill their ecological role of healing the soil.
The best way to manage weeds is by creating healthy soils – soil with high carbon content and lots of fungal life. As soon as plant life returns, root system sweat out sugars and other chemicals that kickstart the return of fungal networks. This is the natural way how plants retrieve micro-nutrients, mobilize phosphorus from the mineral matrix, and provide habitat for nitrogen-fixing bacteria. The specialized weeds are in disadvantage in these healthy soils and soon parish.
Watch this 5-min video by Elaine Ingham, on how you ensure that your compost is dominated by fungi.
