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Detrimental effects of nitrogen

This material addresses aspects of the following syllabus outcomes:

A student:

H1.1 explains the influence of the physical, biological, social, historical and economic factors on sustainable agricultural production
H2.1 describes the inputs, processes and interactions of plant production systems.

The work presented in the following section contributes towards understanding the following syllabus content areas:

• the role of soil nutrient cycles in Australian agricultural systems
• the role of microbes and invertebrates in the decomposition of organic matter and the fixing of atmospheric nitrogen via their association with legumes.

Source: Board of Studies NSW (1999) Stage 6 Agriculture Syllabus.

While nitrogen is a major essential element it can be a problem in some circumstances. This is particularly the case when nitrogen is leached into waterways. Nitrogen becomes a concern to drinking water quality when nitrogen in the soil is converted to the nitrate (NO3-) form. It is a concern because nitrate is very mobile and easily moves with water in the soil. The concern of nitrates and water quality is generally directed at groundwater. However, nitrates can also enter surface waters such as ponds, streams and rivers and eventually the ocean, stimulating excessive plant growth (algae, periphyton attached algae, and nuisance plants weeds). This is know as eutrophication.

You can investigate eutrophication further at the following links:

• US Geological Survey
• OzCoast and OzEstuaries
• Water Quality: HSC Chemistry .

The presence of nitrates in the soil is mostly the result of natural biological processes related to the decomposition of organic matter such as plant residues and animal wastes. Nitrates can also come from rainfall and nitrogen fertilisers.

Whether or not nitrates actually enter groundwater depends on underlying soil and/or bedrock conditions, as well as the depth to groundwater. If groundwater is near the surface and the soil is sandy, the potential for nitrates to enter groundwater is high. High levels of nitrates can be toxic to newborn humans and animals, causing anoxia, or internal suffocation. The most common symptom of nitrate poisoning in babies is a bluish colour to the skin, particularly around the baby's eyes and mouth. These symptoms of nitrate toxicity are commonly referred to as the ‘blue-baby’ syndrome.

Back to the tutorial Role of nitrogen in agricultural production systems.