Guideline Index

Chapter 15: Nutrient Planning

15.3 Phases of farm development

Nutrients required will depend on the stage of development of the farm. In their natural state, most Australian soils have low levels of phosphorus (P) and sulphur (S) and, to a lesser extent, potassium (K). When converting land to a dairy farm, large inputs of nutrients may be required to raise the nutrient levels to adequate levels for pasture production. This is referred to as the development phase (Figure 15.1).

Figure 15.1   Development and maintenance phases of pasture production.  Source: Adapted from Roberts A (1996) ‘Farm for Profit’ Conference Proceedings.
Figure 15.1 Development and maintenance phases of pasture production. Source: Adapted from Roberts A (1996) ‘Farm for Profit’ Conference Proceedings.

In the development phase, pasture response to nutrient applications will be high. For most dairy farmers, it is profitable to rapidly increase soil nutrient levels to the optimum, particularly P. Nutrients that are applied in excess of that required for maintenance (capital applications) raises the nutrient status of the soil.

Eventually, further increases in soil nutrient levels through capital applications will result in only very small increases in plant and animal production and the added nutrients provide no economic benefit. At this stage, optimum nutrient status has been reached and soil fertility is not limiting pasture production.

The optimum soil nutrient status on dairy farms is often regarded as being the point at which the production of existing pasture species is at 95% to 98% of potential. However, the economic optimum nutrient status may be lower on farms where pasture utilisation is low, product value is low or where seasonal production is not reliable.

When a soil reaches its optimum nutrient status, further applications of nutrients will be uneconomical and may increase risk of losses which pollute the environment (see Chapter 10.5 ). No further capital applications of fertiliser will be required. Such soils are referred to as being in the maintenance phase (see Figure 15.1). Soils that are in the maintenance phase only require fertiliser applications that replace the nutrients that are removed from the soil through the farming operation.

So, to recap:

Nutrient applications are considered either as maintenance or capital applications.

  • Maintenance applications keep the soil nutrient status at the same level while supporting pasture production.
  • Capital applications increase soil fertility to a target level. Capital applications are the nutrients that are applied in excess of the maintenance requirement for any given production system .

The concept of capital and maintenance applications is used to estimate farm nutrient requirements. If a maintenance application of nutrients is spread annually, assuming stocking rate and product removal do not alter greatly, soil fertility will remain at a similar level over time. If a capital application is made, soil fertility will increase over time.