We recently watched a presentation by Dr Christine Jones called Quorum Sensing in the Soil Microbiome, and strongly recommend it, however, in short:
The “Ah-ha” for us was photos of an agricultural experimental area where a paddock had been sown to crop in bare ground; no mulch, no cover crop. The area was currently in drought, and it looked very poorly. Adjacent was a paddock with the same crop and a 6-species cover crop looking somewhat better, but definitely stressed. In a corner of that field was a small area, about 100square m, where the cover crop mix had been expanded to 27 with the addition of a bunch of leftover seeds. This area was vibrant with crop and cover crop species growing vigorously and showing no stress whatever.
Back to the beginning: On this planet there are 550 Gigatonnes of carbon life forms (a GT is a billion tons) of which 450 GT is plants, 93 GT microbes various, and 7 GT of lifeforms we can see; insects, fish, birds, moluscs, animals and us. Of the total biomass of life on Earth humans total .01% by weight!
(Remember there are more microbes in a teaspoon of real soil than there are people on the Planet) We are embedded in a microbial world and they are embedded within us … there is no such thing as an independent life form.
It has been shown that animals which graze in a pasture rich in secondary plant compounds; tree leaves, forbs, weeds etc; have increased microbial diversity in the gut, increased ability to digest a wide variety of feeds, improved feed conversion efficiency and improved immune function. Likewise with us, people who consume 30 or more different plant foods per week* have healthier gut microbiomes and fewer health issues. The standard American Diet (& SAD is a very appropriate acronym) has been simplified to 5 basic foods and ours isn’t much better in some quarters. In the soil, plant pests and disease, low nutrient density and poor plant productivity are linked to to a low diversity in the soil microbiome.
This totally validates Permaculture’s long-held conviction that diversity in all things is of paramount importance!
A diversity of plants gives a diversity of root system profiles which give diversity in the soil microbiome. Thus it is for cover crops; diversity is paramount.
The Jena Biodiversity Experiment (Germany 2008) showed that diversified crops/covers support each other in times of stress (ie drought). More is better and there is NO competition. A diversity of cover crop plants can replace fertilizer with greater productivity. Soil carbon also increased with species richness and more plant species = more soil Carbon. In monocultures it declined over time. As well as more carbon and more nutrient availability in the soil, cover crop diversity created deeper soil. There is an 8 minute video on the Jena Biodiversity Experiment on YouTube.
A more local example recently was the Smith’s Wilith Farm in Atiamuri, NZ. They had ash soil with high sulpur content and extremely low fertility. Every known nutrient was required and they spent a fortune on chemicals to support their dairy. Three years ago after a workshop they changed their approch adding biostimulants then plant diversity and have created 6 inches of soil since. Outcomes included CEC increased 50%; all nutrients including nitrogen and phosphorous increased although none were added; Total Organic Carbon level in the top 8” tripled; milk production increased by 300 liters; cow fertility increased by 80% and somatic cell count (which relates to mastitis and the price, if anything, that the milk company pays you) halved.
Plant diversity improves animal nutrition, growth rates, milk production & conception rates while reducing dependence on vets and building soil.
All the above is due to Quorum Sensing (QS)! In the microbial world QS refers to density dependent coordinated behaviour that regulates gene expression in the microbe population and/or the host plant or animal. It depends on the numbers and diversity of the microbe population and it occurs in bacteria, archaea, fungi and viruses. If we carefully exhume a plant from healthy soil and it has a mass of soil and glomalin (the rhizosheath, which forms around the rhizosphere or root zone) attached, this is QS in action.
Similarly microbiota in our gut can switch our genes on or off and many of the autoimmune diseases we (now) have are due to the genes we need for immunity having been switched off due to our oversimplified diet. Without diversity in our gut biome these genes cannot be activated.
30+ plant based foods each week example:
LEAVES (young) of Sweet Potato, Pumpkin, Dandelion, Moringa, Chicory, Broadleaf Plantain, Amaranth
Spinach leaves – Sambung, Brazil, Lagos, Surinam, Okinawa, Tahitian
Olives, olive oil