Fertilizers are needed to increase the productivity of pastures or meadows. But as humans aren’t ‘statin deficient’ when they have a heart attack, grasslands aren’t ‘fertilizer deficient’ if their performance is poor.
All soils in the world have the potential to grow plants because of the minerals they contain. Minerals come from rocks that are weathered into soluble forms. These minerals are absorbed directly by plants through their roots and are recycled back into soil during the decay process. This is the ‘soluble pool’ that shows up in a soil analysis test. But how do we access the limitless ‘total pool’ available in the crystalline structures of the rock that can provide the full range of the forty-two essential nutrients that plants need to be healthy and disease resistant?
Figure 1: The soil profile in a grassland.
This is where the underground army is required. Every spoonful of healthy soil contains a billion or more microorganisms. In healthy grasslands, there is approximately the same weight in earthworm biomass as the weight of the cattle grazing above ground, not to mention the thousands of other tiny critters all shredding, digesting, dissolving, and excreting to gradually improve the soils.
But to understand this vital process, we should start – as the earth did – with bare rock and some bacteria, fungi, and algae. These microorganisms use enzymes and acids to break down the rock and access the nutrients. With no soil in which to reside, the bacteria, fungi and algae form symbiotic relationships to create a plant-like species called lichens. These communities can then offer a home to mosses and lower ‘successional’ species. Gradually the cycle of growth, death and decay builds enough soil for whole plant communities to thrive.
The more complex the plant community, the better the overall access to the minerals in the soil will be. Different species have different root depths, soil preferences and water tolerance. The plant will grow deep roots if the foliage can develop mature leaf; this will help it access a higher concentration and wider range of the soluble nutrients. Minerals tend to leach downwards as rain passes through the soil layers; deep roots help transport minerals back upwards.
Dead plants, excretions from grazing animals and other organic matter pass some of these recycled minerals in a plant-available form back into the top layers of the soil again. But the real potential to make free fertilizer forever is in the so-called ‘microbial bridge.
Figure 2: The microbial bridge of white mycelia in the rhizosphere of a small pine tree.
References
S. A. Kulasooriya, W. K. Hirimburegama, S. W. Abeysekera, Azolla as a bio fertilizer for rice in Sri Lanka
Matton, D. P., Nass, N., Clarke, A. E., & Newbigin, E. (1994). Self-incompatibility: How plants avoid illegitimate offspring. Proceedings of the National Academy of Sciences of the United States of America, 91(6), 1992–1997. https://doi.org/10.1073/pnas.91.6.1992
Image Curtesy
https://www.theatlantic.com/health/archive/2013/06/healthy-soil-microbes-healthy-people/276710/