The most important organism on earth (isn’t you)

One cannot seriously discuss the nitrogen crisis without understanding the natural nitrogen cycle(s), and we cannot understand the nitrogen cycles without pausing for a moment by the most important single natural biological process, and that is the fixation of Nitrogen.

The most important organism on earth

You see, Nitrogen is very abundant in the atmosphere. Moreover, Nitrogen is also critical to DNA, RNA and proteins, the building blocks of everything alive on earth. However, as strange as it sounds, none of the animals and plants on earth can consume the Nitrogen in the air, because the Nitrogen gas molecule N? is too strongly bound. There is however a very small family of organisms, the Rhizobium bacteria family, who are indeed capable of doing just that. They live in the soil under our feet, in and around the roots of plants, and they serve as the basis for the entire food chain. Without them providing reactive Nitrogen molecules, there will be no plants and no animals.

The first link in the food chain

This unsung family of bacteria is the only capable of producing the Nitrogenase protein, which allows taking Nitrogen gas from the atmosphere, along with Hydrogen atoms and creating Ammonia (NH? ), the first form of Nitrogen that can be assimilated (consumed) by a plant, and the first chain in the entire land food chain. This unique and so important protein is very sensitive to oxygen, and thus the protein and the bacteria cannot exist in a too-well-aerated soil. This is in contrast to the roots of plants that need some oxygen. You can imagine what a fine balancing act is required for a healthy soil to exist, such that allows both bacteria and plant roots to flourish. You can also imagine what happens when we plow the soil.

Stress, infection and symbiosis

Some of those bacterial species evolved to find shelter from this highly toxic oxygenated soil. They did it by infecting the roots of some plants, finding a safe environment, protected from oxygen, and also one that offers access to the products of the plant’s photosynthesis. For some plants, this infection did not necessarily turn out to be so bad. A direct supply of reactive Nitrogen could actually be very useful for a plant. And so a symbiotic relationship came into existence between some bacteria and a family of plants, named the Legumes. These plants, including some beans, peanuts and Alfalfa, grow some very unhealthy looking nodules around their roots, hosting huge numbers of bacteria, providing the plant with a fresh and constant flow of Ammonia. This is a very healthy combination because virtually all of the Ammonia produced by the bacteria goes into the plant, without any going to waste or polluting ground water. It is considered good practice to include these plants in soils of low Nitrogen contents, also as a support system for other plants

More bacteria, better nutrients

The work of bacteria does not end here. Ammonia can indeed be consumed (assimilated) by plants, however it still requires a large amount of energy from the plant to assimilate. In comes a second family of bacteria, the Nitrifying bacteria. These bacteria, in what can be considered a second cycle, convert the Ammonia to Nitrite (NO?-) and then to Nitrate (NO?-), the latter being much more convenient for plants, and requiring much less energy from the plant to assimilate. This allows for a healthier plant with energy spares that translate to biomass.

The operation succeeded, the patient died

Soil bacteria and fungi are easy to ignore, especially when easy-to-use Nitrogen fertilizers are at hand and the farmer struggles to sell as much biomass as possible. However the benefits of external Nitrogen sources are short-term, as their introduction steadily creates a less hospitable environment for the soil biology, ending up with dead soils and plants that are completely dependent on external injection of nutrients, and the loss of micro-nutrients and trace minerals that are also in their own way dependent on the culture of the soil, and without them plants are fragile and susceptible to disease and pests.

Measure and diagnose

If we want to have healthy food, we need healthy plants, and for that we need a healthy soil. We cannot afford to disregard the hidden biology of the soil. We need to be aware of the condition of the soil as a whole. Aardvark sensing envisions an ecosystem in which we regularly measure the vital signs of our soils, to give them better treatment, in line with the European healthy soil initiative.

This is part of a series of short articles about the #nitrogencrisis (with focus on the Netherlands), the physics and biology behind it, measurement techniques, politics and solutions.

Also read about

the invention of industrialized fertilizers

and the dangers of excess Nitrogen