Guideline Index

Chapter 15: Nutrient Planning

15.4. Key tools for nutrient planning

There are a number of key tools that are considered essential to the nutrient planning process. Soil testing has been discussed in Chapter 8 and Chapter 9 and will assess the nutrient status of the soil in order to develop target levels, as well as to monitor the effect of previous nutrient applications. Nutrient mapping and farm management zones are relatively new key tools that are also necessary for effective nutrient planning.

15.4.1 Farm Management Zones

There are a large number of paddocks on a dairy farm and therefore it is often more practical to soil test in farm management zones (FMZ) than to soil test in every paddock. Ideally, when soil testing the farm, a representative soil sample would be taken from each FMZ.

Areas on the farm that could form separate FMZs include:

  • Different soil types

– Different soil types will likely have different phosphorus buffering indexes, resulting in different amounts of phosphorous necessary for maintenance and capital applications, may also have different baseline K and S and different leaching potential which may affect soil nutrient status

  • Within those different soil types, different nutrient status

– For example areas of low phosphorus or potassium versus high phosphorus or potassium

  • Different management

– Day or night paddocks; areas where fodder is regularly cut or fed out; where effluent has been spread; run-off blocks; problem paddocks.

  • New and old irrigation areas

Initially a farm should be divided into six to seven FMZs. After soil testing it may be that two to three FMZs have quite similar results and can therefore be grouped together resulting in only four to five FMZs on the farm. Refer to Figure 15.2 for an example of an Australian dairy farm divided into management zones.

Figure 15.2   A map of an Australian dairy farm showing management areas. Red lines show were soil samples were taken, blue lines show the boundary, and the yellow line show the management areas.
Figure 15.2 A map of an Australian dairy farm showing management areas. Red lines show were soil samples were taken, blue lines show the boundary, and the yellow line show the management areas.

The farm in figure 15.2 has been divided into four FMZs (North End, Central, Silage and Church). These areas correspond to different management areas and have been confirmed over a number of years with the aid of soil tests in other paddocks within the FMZs. Representative soil sampling is now used to monitor these areas. As you can see, the silage FMZ has a much lower P level than other areas of the farm and this will be a priority for fertiliser application. There is also high K and S levels in the Church FMZ, indicating potential to reduce or halt applications of these nutrients on these areas.

15.4.2 Nutrient Mapping

Nutrient mapping allows translation of soil tests into a visual representation of fertility across the farm. This assists with assessing variability across the paddocks on the farm. Colours are assigned to areas or paddocks depending on whether the nutrient level is low, marginal, good or excessive. Using nutrient mapping will allow quick visualisation of the variability within the farm and areas that have excessive nutrient levels, where consideration must be given to reducing inputs.

Nutrient maps can be as simple as using a farm map and highlighter pens to shade in different areas of fertility. Different colours are used to correspond to soil fertility guidelines and targets. Advisors may also assist in developing nutrient maps for the farm using different mapping programs.

Nutrient maps can also help with grazing decisions on the farm. Areas with a lower nutrient status may not produce as much pasture dry matter as areas with good nutrient levels and this may influence how long and/or when these areas are grazed. This information can also aid in fodder conservation decisions; for example areas high in potassium should be identified and treated with caution as they can increase K levels in feed and therefore the risk of metabolic problems in livestock. Metabolic problems are discussed more in Chapter 3 .

Nutrient maps are generally produced for phosphorus, potassium and sulphur. Some farms also produce maps for pH and salinity, as these can influence nutrient application decisions. Refer to Figure 15.3 for an example of a nutrient map on an Australian dairy farm.

 

Figure 15.3   A nutrient map on an Australian dairy farm for Olsen P (left) and Colwell K (right). Red suggests very high, blue is high, green is adequate, orange is marginal and yellow is deficient nutrient P or K levels.  Source: Gourley et al (2007).
Figure 15.3 A nutrient map on an Australian dairy farm for Olsen P (left) and Colwell K (right). Red suggests very high, blue is high, green is adequate, orange is marginal and yellow is deficient nutrient P or K levels. Source: Gourley et al (2007).

Figure 15.3 illustrates how nutrient mapping can assist with nutrient decisions. P fertiliser will be a priority in the paddocks that are shaded yellow and orange and K fertiliser will be cut right back in the areas shaded red. The black dot in the figure is the dairy and as is often the case, K levels have built up close to the dairy where animals spend more time.