Diversity in pastoral agriculture.
Pastoral agriculture done well is based on species diversity.
Diversity of species in pasture increases soil organic carbon (SOC). In the face of increasing atmospheric CO2 concentrations and resulting climate change, the accumulation of SOC in land based ecosystems is an important ecosystem service as in this process atmospheric carbon is sequestered in the soil.
In simple terms, this is as a result of increased soil carbon input from higher root biomass production. There could be reduced decomposition rates of carbon as well, although the science is mixed on this aspect and it could also be that with increased stimulation of soil biology, decomposition rates actually increase.
Even in the absence of legumes, plant species diversity promotes soil carbon and nitrogen via increased plant productivity. The enhanced soil carbon and nitrogen in turn support plant productivity via enhanced nitrogen mineralisation which accelerates soil carbon and nitrogen storage in the long-term.
There is a significant amount of research which indicates that this diversity-productivity relationship strengthens over time.
The key to productivity in non-legume based diverse pasture is soil carbon input and nitrogen retention rather than nitrogen input.
Legumes are however an important, indeed vital, component in regenerative pastoral systems.
Legumes live in a symbiosis with rhizobium bacteria, which fixes atmospheric nitrogen, and allocate it to the plant in exchange for carbohydrates. Most grassland ecosystems are nitrogen limited. The inclusion of legumes strongly enhances the input of nitrogen into these ecosystems. This will follow on to improve plant productivity which in turn will lead to increased carbon sequestration.
Increased soil fertility is created as a result of increased nitrogen mineralisation.
In highly diverse pastures, annual nitrogen removal is at least balanced by nitrogen inputs whereas nitrogen inputs tend to exceed nitrogen removal in monocultures, resulting in leaching
Species richness/diversity has been identified in a number of scientific studies as decreasing nitrogen leaching.
The key understanding to take away is that soil fertility increases with a diverse species pasture even without legumes. Furthermore this relationship strengthens over time, i.e. production/fertility will get better.
Organic systems maximise the use of pastures that can fix their own nitrogen fertiliser which gets shared amongst all the pasture components. In addition, there is an increasing amount of international research that shows that a greater diversity of species makes for healthier and more productive stock, improves soil biology and health due to an increased amount and diversity of plant matter returns, and further reduces leaching due to deep rooting species which can take up nitrates from deep in the soil.
Diverse pasture delivers:
− increased soil organic carbon (SOC) which involves carbon sequestration with benefits for climate change;
− improved plant productivity – even without legumes; and
− increased nitrogen mineralisation which in turn increases soil fertility.