In the last 20 years our understanding of what makes soil has grown tremendously and it is a fascinating story.
We have learnt that most soil comes from thin air.
We understood soil is made up sand, silt and clay (which relates to particle size), water, air and organic matter. We understood organic matter was made up mostly of leaves, grasses, trees etc. decaying and mixing with the mineral particles. More recently we have learnt that this makes up around 20% of the organic matter in soil – plant organic matter. The remaining 80% can be microbial organic matter if the conditions are right and this allows us to build soil much more quickly than we previously thought.
Photosynthesis involves plants taking energy from the sun, CO2 from the atmosphere (currently around 418ppm) and H20 from moisture in the air or soil and making carbohydrates, sugars to make roots, shoots and fruits. We now know that this takes around 20-40% of the carbohydrates and the remaining 60% plus is sent into the soil via the roots. Why would a plant or tree offer so much of its energy to the soil? To feed the microbes. The bacteria and fungi in the soil which in turn mine the soil to provide the nutrients the plant requires in a symbiotic relationship. Fungi have been measured to mine soils metres from the plant through the extensive hyphae network. Like a spider web under the soil, through each hollow hyphae the plant is sending out its sugars and through the same hyphae the plant is sending back nutrients. We have also recently learnt that fungi store Carbon in these hyphae.
For every 1% increase in Soil Organic Matter some soils have been measured to hold an additional 144,000 litres of water per hectare. Consider the consequences for increasing the growing season as global heating bears down on us and climate models suggest the Wairarapa, for example, will have annual droughts by 2070. Global heating is also demonstrating much more severe rainfall events as the warmer water in seas and lakes provide more energy in the weather system. By holding so much more water in the soil, we significantly reduce flooding events and the associated soil erosion with the pesticides, herbicides and fertilisers that then travel through the tributaries, streams, rivers and out into the ocean causing silting and pollution along the way. New Zealand is estimated to lose 200 million tonnes of topsoil each year. Increasing the organic matter in soils can be a very effective way of storing water compared to large earthworks for dams with many significant benefits for the farmer. Some farms in the U.K. where the focus has a been on increasing soil organic matter in the soils are now over 20% Organic Matter and the health of the farms and stock transformed. New Zealand farms are seeing the same trends.
Grasslands evolved 50 – 60 million years ago and only in conjunction with the ruminant. The Bison, Springbok, Zebra and Wildebeest etc. These mobile bio-digesters are a key component in keeping grasslands regenerative and they harvest, digest and poop and pee fertility back onto the pasture.
Increasingly growers and farmers in New Zealand are seeing the benefits of farming in harmony with nature and changing management practices to optimise the microbial community in the soil. Minimising; salt based fertilisers that lock up moisture required by the microbes; tillage that breaks up the kilometres of fungal hyphae that are used by plants to mine the rocks, sand, silt and clay for nutrients; biocides (fungicides, pesticides, herbicides) that kill more beneficial insects and soil microbes than pests and overgrazing that minimises the photosynthesis potential of plants to produce the carbohydrates that feeds the biology in the soil. At the same time, increasing diverse pasture species and leaf surface area, optimises the carbohydrates going into the soil to feed the biology which in turn maximises the diverse nutrient supply to the plant, optimising plant health and resistance to pest and disease while further reducing the requirement for inorganic fertilisers.
There are 5 generally accepted key principles to soil regeneration. Minimise soil disturbance (such as tilling), maximise living roots in the soil (to feed the biology), apply a mulch where it is not possible to have living roots (minimise soil compaction from rain and biology destruction from heat), integrating ruminants and increased biodiversity.
In addition to the many benefits of regeneration set out above, there is an even more critical consideration. By adding organic matter to the soil, we significantly increase the water holding capacity of the soil which enables a much longer growing season. When the sun beats onto bare land or dried out pastures, the heat is reflected back onto the atmosphere, creating a ‘heat island’ effect which further minimises rainfall. When there are green plants and moisture in the soil, we create a soil ‘sponge’ and when the sun shines the plants transpire and imbedded in this humid haze as it rises are hygroscopic bacteria which absorb moisture. As the humid haze rises, these bacteria continue to suck in moisture until they accumulate in the clouds. This process continues until the clouds can hold no more and it rains. This is the small water cycle which should produce around 40% of a regions water.
Water covers 95% of the planets heat dynamics. Each gram of water transpired from liquid to gas requires 590 calories, removing heat and clouds themselves also cool. Walter Jehne of Regenerate Earth teaches that all we need to do to destabilise the global temperature increase is cool it by 1% or some 3 watts/square metre of the 342 w/m2 incident solar radiation the Earth gets continually on average at the top of the troposphere. If you compare it to the mean natural global cooling effects from say evapo-transpiration i.e. 85 w/m2 or cloud albedos i.e. 120 w/m2 it puts our imperative of 3 W/m2 cooling into a practical perspective. As Walter says, this is where we have agency and our land management practices can make the biggest difference.
Through our lack of understanding, some of our traditional farming and growing practices have reduced soil organic matter leaving us ever more dependent on fertilisers, pesticides, herbicides, tilling and irrigation. The exciting new understanding means we can minimise these and there are many examples where, within 2 to 3 growing seasons of farming or growing more regeneratively, significant benefits are seen. It is a bonus that customers are increasingly looking for products that are grown this way for their own health’s sake.
Imagine growing regeneratively where we consider the biology in the soil as much as life above it. Plants are photosynthesising and sending sugars down into the soil via their roots. We get a big increase in the population of the fungi and bacteria which mine the soil for plant nutrients. As this population increases in the soil, the predators arrive, the Arthripods, Nematodes and Protozoa. As these predators feed on the fungi and bacteria they poop out the minerals and trace elements held in the fungi and bacteria in much higher concentrations than the predators can absorb and they release it in plant available form. The plants have access to practically all the macro and micro nutrients they need in real time as they require them (not only N, P and K) so become healthy to resist pest and disease and therefore maximise photosynthesis and pump more carbohydrates into the soil to feed the biology. With a diverse pasture species, each with its own specific nutrient requirements, the zoo in the soil is really humming and we are growing microbial soil.
With healthy soil we have healthy plants, healthy animals, healthy humans. We are, most importantly, building the water cycle and cooling the earth at the same time as taking CO2 from the atmosphere where it is doing so much damage and putting it into the soil where it does so much good. And enjoying a healthy planet.