Purpose

Chemical testing of soil samples pre-planting and of plant tissue during the growing season provides an important tool for agricultural producers who wish to maximise their profitability by identifying and correcting nutrient deficiencies. By using calibrated tests, growers can determine the rate of fertiliser that needs to be applied to the crop to maximise their financial return. Biological testing of soil samples is carried out to ascertain the absence/presence and quantity of soil-borne pathogens or pests, particularly nematodes, which may affect certain crops more than others (Reuter 2001; McKenzie et al. 2002)..

Farm planning and soil testing have improved the general awareness of soil-based constraints to crop production and, in some cases, broader issues of natural resource management (McKenzie et al. 2002).

Components that may be affected:         Soil structure; Water balance.

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Some characteristics of management practices relating to soil testing 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

• 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