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Manipulating the nitrogen cycle to maximise production

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.

Manipulating the nitrogen cycle

If we understand the cycling of nitrogen we can investigate methods that may manipulate the cycle to benefit production and minimise detrimental effects associated with nitrogen in agriculture production systems.

Management techniques that relate to this include those that influence the various processes of the cycle that introduce nitrogen, convert it to useable forms and minimise the various losses from the cycle. Examples may include:

cultivation of legumes (crop rotation, pasture mixes, green manuring etc)
legume inoculation to ensure active nitrogen fixation
maintenance of soil environments to favour beneficial microbes (structure, pH etc)
addition/increased incorporation of organic matter (OM)
addition of inorganic fertilisers
water management to reduce water-logging/denitrification and leaching.

Activity 1

Research as many of these management techniques as possible. Construct a table (similar to the one included below) to summarise an evaluation of these techniques in relation to their potential to improve production through the manipulation of the cycling of nitrogen. An example is done for you as a guide.

You may choose techniques other than those listed to include in your table.

Technique	Outline	Advantages	Disadvantages	Judgement
Green manuring	Growing a legume crop and ploughing it back into the ground.	The growing legume increases N through the symbiotic relationship with rhizobia bacteria fixing atmospheric N into a useable for plants. N rich OM increases when the crop is ploughed into the soil.	Farmer forgoes the financial return of the crop not harvested but ploughed in instead. N is not immediately available from the OM incorporated as it must first undergo decomposition.	This technique is highly beneficial as it has the double action of increasing N through legume growing and incorporation of N rich OM that releases N in a less leachable form than chemical fertilisers. Short term costs are more than offset by reduced expenditure on fertilisers and long term soil sustainability.
Crop rotation
Adding N fertiliser
Legume inoculation
Liming/pH
Planting deep-rooted plant species

Answers

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