Soil versus Dirt
At Jingeri we see soils as the fundamental building block of our production enterprises. But it is important to recognise that soils are separate to dirt. Dirt is a combination of non-living (abiotic) minerals and particles which act as a substrate. Similar to the growing mediums used in hydroponics dirt is merely a place where plants can anchor themselves. Soils on the other hand are a living medium and to be highly productive they need to contain millions (possibly billions) of organisms working in symbiosis, so that the minerals, nutrients and trace elements are bioavailable to the plants that rely on this medium for growth. The diagram below is a representation of how we at Jingeri see living soils to be structured. We believe that the transition zone between the topsoil and the subsoil is one of the most important components of soil structure. It is in this zone that the processes of nutrient cycling and mineral cycling meet and where living soils are formed, however if there is reduced biodiversity within the topsoil layer then the process of building topsoil is reduced as well.
Figure 1: Conceptual Model of living soils (T. Finnegan 2014)
The importance of humus
Living soils are critically dependant on a healthy humus layer or ‘O horizon’. The term humus actually refers to the non-living organic material which is produced from the decomposition of dead plant and animal matter. Simply put it is the zone where water cycling, nutrient cycling, carbon cycling and terrestrial ecosystems meet and interact. It is the zone where dead matter is recycled and made available to living organisms and in my view is where life begins.
Figure 2: The nexus of natural cycles (T. Finnegan 2014)
Humus can generally be broken down as follows: around 60% pure carbon (C) and 6% nitrogen (N), the other 34% is made up of other trace elements such as phosphorus (P), magnesium (Mg), Calcium (Ca) and Sulphur (S) as well as course particulates such as sand and clays. Depending on the climatic zone and rainfall levels humus will also contain a huge diversity of organisms such as worms, beetles, fungi and bacteria. The levels of biodiversity are dependent on temperature, pH and moisture content of the humus layer and soil ecosystems can differ greatly at both the local and landscape scales. Biological activity by soil animals, fungi and bacteria will determine the rate of topsoil creation as well as the depth of the topsoil profile. The formula is a simple one, the higher the soil biodiversity, the deeper and more nutrient rich the topsoil profile and the greater the capacity for terrestrial plant diversity and growth.
Fungi: a bridge for nutrient uptake by plants
Fungi is a critical component of topsoil acting as a nutrient bridge for plants. Soils can be high in both micro and macro nutrients but still have low productivity in terms of plant health and yields. Fungi, specifically mycorrhizal fungi, have long filaments (hyphae) which extend great distances within the topsoil profile. These filaments act as a bridge between the nutrients and the plant allowing the plant to assimilate nutrients and utilise them for growth. Essentially the fungi act to increase the root surface area by around 100-1000 times (healthy soils can contain as much as several kilometres of hyphae within a spoonful of soil) and release enzymes that act on the hard to access soil nutrients such as nitrogen, phosphorus, iron and potassium making them more absorbable by the plant root system. Disturbance is the greatest threat to soil fungi diversity, eg: tillage, erosion and mechanical excavation. Mycorrhizal fungi populations are reportedly slow to recolonise following disturbance events, meaning that gradually over time our soils have essentially lost much of this important biological activity.
The problem with modern farming
In modern agriculture we apply the term ‘soil’ to the growing medium in which we grow our crops, unfortunately industrial farming methods over the past 200 years or so have reduced agricultural soils to something that is more like the abiotic growing mediums used in hydroponics. Agricultural soils today are either lifeless or have such reduced biodiversity within them that farmers are constantly faced with the problem of ever increasing inputs to production in order to maintain yields and profitability. The problem with industrial farming methods is the use of chemical fertilizers, herbicides and pesticides. All of these things act to reduce the biological diversity within the topsoil and are especially toxic to mycorrhizal fungi. Modern agricultural methods also tend to reduce or remove the critical humus layer, though moves toward minimal or better still zero tillage has reduced this problem in more recent times.