Purpose

To ensure adequate nitrogen supply to grain crops.

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Most Australian soils are naturally infertile, requiring the addition of a range of nutrients to maximise agricultural yields. Nitrogen (N) is a major plant nutrient and constituent of all plant cells, thus playing a major role in the growth and grain development of all grain crops. Usually, nitrogen is only present at low levels in Australian soils. For this reason, nitrogen is commonly applied in the grains industry in situations where moisture availability is not the most limiting production factor. In situations of low moisture availability, application of nitrogen fertiliser may be wasteful and contribute to increased greenhouse gas emissions and nitrate leaching due to the inability of plants to utilise the nutrients on offer.

Mineral nitrogen fertiliser is highly soluble and does not build up in the upper soil profile. It is easily leached from the upper soil layers or dissolved in run-off water if not utilised by plants soon after application. This may increase soil acidity and contribute to off-site degradation of ground and surface waters. In addition, ammonium or urea fertilisers easily volatilise in dry, alkaline soils, while nitrate fertilisers undergo denitrification in waterlogged condition, leading not only to reduced nutrient availability to plants but also to increased greenhouse gas emissions (nitrous oxide). Therefore, it is important to avoid over-fertilisation, choose the fertiliser appropriate to the conditions and only supply nitrogen levels required at the right time to meet crop demands.

Components that may be affected:         Soil acidity; Soil phosphorous and Surface water nitrogen.

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Some characteristics of sustainable management practices relating to ensuring adequate plant nutrient supply were investigated by Cary et al. (2002). The results are presented in Table 1.

Table 1: Characteristics of sustainable management practices as assessed by Cary et al. (2002)

Sustainable practice	Geographic applicability	Relative advantage	Risk	Complexity	Compatibility	Trialability	Observability
(Ideal rating)	(high)	(high)	(low)	(low)	(high)	(high)	(high)
Nutrient balance accounting (soil and plant sampling)	low	low	low	high	medium	low	low
Soil and plant tissue tests to determine fertiliser needs	low	low	low	high	medium	low	low
Regular soil testing	medium	medium	low	low	medium	low	low
Fertilising of pastures	medium	high - medium (locality)	medium	low	high	high	high - medium

• Geographic applicability—refers to relative appropriateness of a practice, in terms of whether it is effective or adapted to only specific localities or, more universally, across many localities.
• Relative advantage—relates to the financial advantage or other convenience or personal advantage to the farm business or the adopter.
• Risk—refers to uncertainty about likely benefits or costs associated with a sustainable practice, the effectiveness of the practice, when the benefits might be realised and the social acceptability of the practice.
• Complexity—implies that a practice comprises more than one or two simple elements and that its elements interact with each other and, in sometimes complicated ways, with elements of the farming system into which it is to be incorporated.
• Compatibility—refers to the extent to which a practice fits in with existing farm practices, knowledge or social practice.
• Trialability—where practices can be implemented on a small or pilot scale, decisions can be more easily made about the value of a new practice without the risks associated with full implementation.
• Observability—practices where the impact or advantage is easily observable or the outcome quickly realised are more likely to be adopted.

Indicator

Application of nitrogen (tonnes per GRDC agro-ecological zone per year).

More desirable indicators would be the level of achievement of the desired nutrient balance for each farm or paddock, aggregated to regional or national level, although this is rarely  reported, or the level of application of nitrogen fertiliser per unit area.

Results

Map 1 displays the total amount of nitrogen applied to crops per GRDC agro-ecological zone in 1996, while Table 2 provides results for multiple years.

Table 2: Total amount of nitrogen fertiliser (t/year) used for crops in GRDC agro-ecological zones during 1992-96. 

^{Source- NLWRA (2001) Australian Agriculture Assessment: Farm gate nutrient balance.}

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The National Land & Water Resources Audit Australian Agriculture Assessment 2001 report made the following assessment:

• The nitrogen status of Australia's agricultural soils has been increased from their inherently infertile state, by application of fertilisers. Nitrogen balance varies from neutral (inputs = exports) through to positive (inputs > exports) in many Australian regions, suggesting that supply is now approaching near-optimal levels, and soil nutrient reserves are not being mined (NLWRA 2001). Nitrogenous fertiliser use has increased 2.5 times over the last 10 years, with most going on to crops. This has boosted production. On the other hand, nutrients from diffuse and point sources may enrich regional water bodies and coastal estuaries increasing the risk of algal blooms and lower water quality. Nitrate contamination of ground waters can occur through leaching, especially on sandier soils. This can affect the quality of domestic and stock water. Increased use of ammonium-based nitrogenous fertilisers can accelerate soil acidification. These processes may pose future problems for rural communities.
• Negative balances, signifying soil nutrient depletion, existed in major regions of Queensland (all nutrients); the Victorian Wimmera (nitrogen, phosphorus and potassium).. To gain a more precise spatial understanding of these findings, further regional scale investigations would be required.
• trends in the levels of use of fertilisers were consistently lower in more arid, low yielding environments of the cropping zone than in more reliable, higher yielding regions—decisions on fertiliser use match anticipated returns.
• Increased consumption in nitrogen fertiliser is associated with:
• deterioration in legume content of many pastures;
• a growing awareness and promotion that rates of organic nitrogen mineralisation in agricultural soils were not meeting nitrogen demands of intensively cropped rotations or zero tilled soils;
• increased plantings of nitrogen-fertilised canola crops;
• improved crop rotations and recognition of the benefit break-crops (e.g. canola) provide in cereal rotations for controlling root diseases and nematodes;
• introduction of high analysis ammonium phosphate fertilisers from the 1970s and 1980s to cropping regions of southern Australia (replacing traditional superphosphate applications) and increased use of urea in cropping regions; and
• declining protein levels in wheat (identified and widely promoted in 1989), and the introduction of premium prices for higher protein grades of wheat.

 

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Metadata:

The farm gate map for Australia was downloaded from the website of the National Land & Water Resources Audit. The dataset contains nutrient inputs from various sources, nutrient exports in harvested agricultural products and the calculated differences between nutrient inputs and exports (termed farm gate nutrient balance). The data are reported by Statistical Local Areas within the intensive agricultural zone of Australia and cover the period from 1992/93 (1989/90 for WA) to 1996/97. The nutrients were nitrogen (N), phosphorus (P) and potassium (K) for that span of years and sulfur (S), calcium (Ca) and magnesium (Mg) for 1995/96 (More information- Farm Gate Nutrient balance metadata summary). Fertiliser sales data for each SLA were mapped to GRDC agro-ecological zones (More information- GRDC zone metadata summary).

References

Cary, J. Webb, T. and Barr, N. (2002) Understanding landholders capacity to change to sustainable practices: Insights about practice adoption and social capacity for change. Bureau of Rural Sciences, Canberra, p. 17.

NLWRA (2001) Australian Natural Resources Atlas: Australian Agriculture assessment 2001. National Land & Water Resources Audit, Canberra. Website- http://www.anra.gov.au/topics/agriculture/index.html. Accessed 16/07/2008.