The sequestration of carbon into soils is hotly debated. Whether planting trees, maintaining perennial grasslands, grazing cows on grass etc is best would likely depend on factors unique to each location.
With this in mind, the information on this page is a very basic introduction to the role that cows and other ruminants play in sequestering carbon in soil, which in turn increases both fertility and water holding capacities of soils.
Lower down on this page are videos, articles and websites that explain these concepts in greater detail than on this page.
Please note - We are not arguing that everyone should have cows. They make sense in our circumstances (minimising fire risk in a subtropical climate which can alternate between very wet and very dry periods) but not necessarily in yours.
Furthermore, while we are rotating the grazing of cows on our place for various broad ecosystem benefits, which are outlined below, our system is pretty basic. While we are confident that we are sequesting carbon and improving ecosystem function through our combined strategies, we do not really know to what extent as there has been no scientific evaluation in this regard.
Basic Overview of Rotational Grazing and Soil
Some decades back, Alan Savory, a Zimbabwean ecologist, observed how grassland herbivores (cows, antelope, buffalo, etc.) behave in nature, and realised that wherever they wandered, the grasslands flourished. He found that these grazing wild animals had the following shared qualities:
- Wandering animals on the finges of herds are vulnerable to predators and so they bunch together for safety from predators.
- These animals intensely graze sections at a time but do not pull grass out from its roots, and instead trim it. This, in turn, invigorates grass growth and prevents it from growing too long.
- As they graze, the manure, urine, grass and soil are crushed and trampled which, in turn, improves conditions for seed germination and plant growth.
- Furthermore, divots are created in the soil and these collect rainfall and this is absorbed into the soil.
- The basic result of all this is that the grass and other vegetation pump carbon and nutrients into the soil (sequestering carbon from the atmosphere), which has a number of functions including the feeding of fungi and bacteria. At the same time, the plants draw nutrients up from the soil which, in turn, feed the grazing animals.
- This continues in an ongoing cycle building soil fertility, creating humus and sequesting carbon in the soil.
If grazing animals are not bunched and/or the soil is tilled, this cycle is broken. Instead, the grazing animals selectively graze. In this instance the following occurs:
- Grass is no longer trimmed and becomes too long. It falls over as it dies preventing sunlight from nurturing younger grass.
- This gradually kills much of the grass leading to increasingly bare soil with associated desertification of the land.
- This bare earth leads to a drastic loss of soil biodiversity, which leaves the soil hard and unable to retain nutrients and water. Much less water enters the soil profile and more runs off. The amount of water retained in the soil declines.
- Carbon is lost from the soil and fertility declines.
- The land in this scenario becomes increasingly desertificated or degraded.
According to Savory, we can imitate what the wild animals are doing through rotational grazing where:
- Cattle are kept in smaller areas using mobile fencing which keeps them bunched up as in the wild. This prevents the cattle from selectively grazing and the grass species in the paddock are trimmed uniformly with the ensuing benefits outlined above. In addition, the divots are concentrated with the associated benefits to the soil in relation to water, urine and manure.
- The cattle are continually cycled through the smaller paddocks with each paddock allowed sufficient time to rest and recover before being grazed again.
This approach to grazing livestock builds soil fertility and pumps carbon into soil storage. And, as the carbon cycle and water cycle are intertwinned, the soil's capacity to store water is enhanced. With the very dry periods we experience, more water stored in the soil from rain events leads to greater ecosystem resilience during those times.