3.1 Nutrient Planning Strategies for Pastures

Factors that influence your nutrient decisions

Many interacting factors need to be considered when making a decision to manage your crop's nutrition. The following information has been put together to help your consideration of each factor in making a nutrient decision.

Soil Factors

• Soil type

• Structure and depth

• pH

• Nutrient status

Paddock Factors

• Previous crops and fertiliser use

• Crop residue level and plant type

• Rainfall total and frequency

• Disease and weed levels

Crop Factors

• Crop choice

• Production objectives, potential yield and quality

• Growth stage

Other factors

• Application method

• Fertiliser source/product

• Price and marginal returns

• Herbicide use

Using Soil Tests for Nutrient Decisions

Soil tests provide a good starting point when making a nutrient decision. The results are just one tool and they must be considered together with the other factors listed above.

Soil Testing:

• Does not define what rate of fertiliser should be used

• Does not tell you what product to use

• Does not define trace element response potential

• Does give a snap shot of the levels of available macro and micro nutrients on the day of the test

• Can give soil pH, organic carbon and salinity status which helps monitor sustainability

• Helps monitor current fertiliser practices and long term nutrient trends

• Provides a basis for informed budgeting and problem solving.

Critical success factors for useful soil test results:

• Robust sample collection methods

• Reliable laboratory analysis

• Interpretation in relation to other nutrient information

Soil testing should be adopted as a routine part of your nutrient management program.

• Sample a minimum of three paddocks across your property each year

• Record areas sampled

• Sample at the same time each year between December and March

• Clearly label samples

• Maintain good paddock records

When submitting a soil sample for testing you need to know:

• Which paddock it came from

• Last years crop

• Soil type

• Rainfall

Macro Nutrients

There are 10 major or macro nutrients required by plants. Under legume dominant pasture in South Australia phosphorus, potassium and sulphur are often deficient and need to be manipulated to improve soil productivity.

Micro nutrients/ trace elements

There are 7 micro nutrients or trace elements that plants required for growth . These are only required in small amounts but a deficiency of any trace element in the soil can limit plant growth even when all other essential elements are present in adequate amounts. In South Australian soil zinc, manganese and copper are often deficient or insufficiently available. In acid soils molybdenum availability is reduced often resulting in pasture deficiency.

Total soil content does not necessarily indicate the level of nutrient available for plant growth.

Figure 1:

Nitrogen returns. Estimated annual N fixation by legume plants (temperate climates)

Figure 2:

Micro nutrients, range of soil contents and optimum pH range for availability

Figure 3:

Nutrients removed by 1 tonne of

Data from Tisdale et al except data marked * Peoples et al. (Aus. J. Ag. Res. (1998) 49:459-474

na - not available or not applicable

Figure 4:

Macro nutrients, requirement and source

3.1 Nutrient Planning Strategies for Pastures

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