Biotic Nutrients

The Biotic Nutrients or Carbon Cycle Group:

Within The UM-BBD spiral periodic table the primary essential non-metal group of Hydrogen, Oxygen, Carbon,Nitrogen, Phosphorus and Sulphur are to be found. These six elements are distinguished within the 3-4-5 Dynamic Nutrient Model into the two groups of the ‘God-Elements’ and the Biotic Nutrients by the mechanisms that maintain them.

The God Elements:

the 'God' and the biotic elements

The first of these two groups contains Hydrogen, Oxygen and Carbon. These elements whilst extremely important are supplied by the Air (CO2 and O2) and water (H2O). Whilst water is perhaps the most important factor in both animal and plant nutrition; within the context of soil fertility it is the physical role in transportation rather than the Hydrogen component of waters chemistry that is significant.

Thus whilst major components of life, the mechanisms that supply Oxygen, Carbon and Hydrogen lie outside the soil environment and we need not concern ourselves further with the supply of these; the God-Elements.


The Biotic Nutrients

The Second group in the primary essential non-metal group of the UM-BBD spiral periodic table is composed of Nitrogen, Phosphorus and Sulphur. These the three biotic nutrients are maintained within the soil matrix by the organic matter reserves. This material, the remains of plants, animals and bacteria is composed of Carbon in complex with small amounts of Nitrogen, Phosphorus and Sulphur. Subsequent action by bacteria breaks this organic matter down, mineralising and releasing the biotic nutrients into solution where they become available to plants.

The process of releasing these nutrients is known as mineralisation and it is the primary means by which Nitrogen, Phosphorus and Sulphur are maintained and made available to plants. A consequence of the Carbon cycle the significance of this mechanism to maintaining natural biological processes is arguable under estimated and poorly understood.

the carbon cycle in cycling N, P & S

The Importance of the Microbial Biomass

Whilst a part of the carbon cycle the majority of the cycling of the biotic nutrients occurs exclusively within the microbial biomass itself, with plants largely relying on intercepting the excesses for their own nutrition. Thus plants rely on the microbial turnover to constant liberate the biotic nutrients transforming them into the soluble forms which only then can they capture with their roots.


microbial role in maintaining N P & S

The rate at which the microbial biomass liberate the biotic nutrients is dependent on both an ample and suitable substrate and on the right environmental conditions.

Similarly the majority of the turnover of the biotic nutrients is within the microbial biomass itself with plants relying exclusively on capturing excesses.


Under natural conditions this process is highly variable and often the period of most need for the plant and that of the most activity within the microbial biomass can and often fails to coincide.

Thus the management and maintenance of the organic matter input is a key component in managing and regulating the supply of the biotic nutrients of nitrogen, phosphorus and sulphur. However even with good and regular inputs of organic matter maintaining the optimum environmental conditions in the field is extremely difficult. This difficulty can to a large degree be overcome by the adoption of composting, a process that effectively addresses the environmental variability found in the field, replacing it with optimum conditions for microbial growth. As one one of the principal methods at our disposal to improve soil fertility, composting should be performed on all organic material that is destined for the land.

The process of mineralisation

The processes by which these elements are made soluble and insoluble is called mineralisation and immobilisation respectively. These are the two halves of microbial nutrition; nutrition that differs from plant and animal but has similarities with both.

Microbial nutrition initially mimics animal nutrition in that it is achieved through the breakdown of organic material by enzyme activity. However unlike animals, where this process takes place inside the gut, microbial digestion is external. Enzymes are produced and released into the soil solution which then seek and break down organic matter. The breakdown products are then released into the soil solution where the organism then hopes to capture the biotic nutrients released by the process.

At this point microbial nutrition begins to mimics plant. For both rely on the acquisition of the mineralised biotic nutrients through passive uptake. The process is haphazard and its effectiveness is dependent on many factors; as is the subsequent availability to plants. Both the microbial population dynamics and the carbon:nitrogen ratio are critical in determining the subsequent availability of mineralised biotic nutrients to the plant. However in the field both factors are highly variable and difficult to manipulate.

Plant Microbial Interactions

The dependency of plant nutrition on the activities of the microbial world has largely gone unnoticed. Yet the world beneath our feet is more complex, more varied and more diverse than any environment above it. Highly complex symbiotic and sympathetic relationships between plants and microbes have evolved and whilst we are still largely unaware of many we now have clear evidence that plants actively encourage microbial growth within the rhizosphere (the area of the soil in contact with the root). Research in this field has found that plants produce root exudates to encourage the proliferation of bacteria and fungi in the root zone (Harsh et al 2006). The precise reason for this is unknown but it is sufficiently important for plants to exude up to 60% of the carbon fixed through photosynthesis.

In Depth: Nitrogen Phosphorus and Sulphur

next: the basic nutrients


References and External Links

University of Minnesota BBD spiral periodic table

mineralisation University of Missouri measuring soil nitrogen mineralisation resources predicting soil mineralisation rates

Free Cultural Works (CC-BY-NC-SA)Malcolm McEwen 2011

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