There are three phases to the mineral cycle, which in turn is part of the larger carbon cycle—the process of Birth, Growth, Reproduction, Death, and Decay. When they are all working together the cycle is ‘effective’. The three phases of the mineral cycle are:
1. Moving minerals from below the soil surface to above the soil surface
During this phase plants take minerals from below the soil surface, transport them upwards and as part of the photosynthetic process they become part of the leaves and branches that wave around in the breeze. It’s worth noting as well that the more effective the water cycle is, the more effective the mineral cycle is—and the more quickly are more minerals made more available for more plant growth.
2. Placing the minerals back down onto the soil surface
Depending on location, this phase operates slightly (but crucially) differently.
Once atmospheric humidity declines and plant death or dormancy is initiated, the environment becomes too harsh for microbes, and small vertebrates and invertebrates, to survive in the open. It is simply too dry for them. In the absence of some other form of intervention the plants begin the decay process by slowly oxidising, They turn a grey colour and over years, the decay process is completed. Plants that are allowed to decay this way become over-rested.
- In non-brittle tending or humid environments dropping plant material from above the soil surface onto the soil surface is often a biological or living process. This is because there is always enough atmospheric humidity for microbes, small vertebrates and invertebrates to live above ground and actively consume or decompose standing plant material, as well as any bulky material that might be lying on the soil surface. It is common for the decay process to occur from the ground up, and you will often see old material such as tree leaf drop (and even entire fallen tree trunks) rapidly incorporated back into the soil. In humid environments it is also difficult to find over-rested grass plants, as the old material is actively consumed by these living organisms.
Unfortunately, no more than 40% of the earth’s surface is sufficiently non-brittle tending to allow this to happen, and in Australia it is probably no more than 5%. So, what then happens about decay in the remaining 60% to 95%?
- For much of the year in brittle-tending or seasonal environments, there is insufficient atmospheric humidity to sustain year round plant growth, and for prolonged periods the vegetation is brown, being either dead or dormant. If the vegetation is predominantly annual grasses, every year there is a massive die-off of plants at the end of their growing season, which is the humid phase of the year. If the vegetation is substantially perennial, there is a massive dry down of billions of tonnes of plants at the end of the growing or wet season, and the plants remain dormant for the entire non-growing season.
Prior to human intervention, around the world the natural function under these seasonal conditions was the presence of vast herds of herbivores, who were in turn are predated upon by pack hunting critters—often but not exclusively members of the dog and/or cat families. In Australia it seems there were a great number of species of megafauna, filling most (if not all) of the ecological niches occupied by different species on other continents. The most intact large-scale remnant of natural function today that can readily be observed is the Serengeti of Tanzania, in Africa.
Because there are many predators nearby, the large herbivores seek safety by mobbing together. In a mob situation their behavior is changed from that of an individual to that of a herd, and a herd is much less careful than an individual animal about where it treads. The greater the herd density the greater the amount of standing plant material that is trampled onto the soil surface by the herd, thus completing the second part of the cycle.
- There, vast herds of large herbivores eat the standing vegetation, which for much of the year is almost exclusively the dry, brown dormant or dead material referred to above. These herds play several major roles in returning material to the soil surface.
- In their moist, humid, microbe rich gut they reduce the volume of plant material to dung and urine which they deposit on the soil surface. This is the first way of completing the second phase of the mineral cycle.
The photo below shows well trampled grass material that is covering the soil surface, retaining moisture and facilitating new growth, more than six months after the last rainfall.
In summary: In managed seasonal or brittle-tending environments where grazing is the predominant tool, the only manner in which the mineral cycle can rapidly be completed is by correctly using managed livestock movements. The core components of this are utilisation of the microbes that are safely contained in the gut of animals whose purpose and design is the recycling of vast quantities of lignous plant material, and/or the trampling of that material onto the soil surface as the animals move around.
3. Moving the minerals from the soil surface to below the soil surface
This stage is great aided by the presence of an effective water cycle. An effective water cycle means the soil retains moisture for long periods, maintaining a suitable long term environment for microbes and some small organisms whose function is to pull dung pats and trampled plant material from the soil surface into the soil, a nd in the process, to convert it to humus, the form of organic matter that holds the minerals ready for immediate re-use by plant roots.
In a fully effective mineral cycle minerals will complete a full cycle in twelve months or less.
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