Guideline Index

Chapter 15: Nutrient Planning

15.9. Prioritising nutrient applications on farm

Whether the nutrient requirements of the farm will be fulfilled depends largely on the availability of money and the cost of nutrients. Sometimes these constraints mean that only part of the ideal nutrient plan can be implemented.

In that case, choices have to be made as to which part to implement now and which to implement later. Similarly, the choice may be between fertilising only part of the farm at the desired nutrient application rate and allowing the remainder to be unfertilised, or fertilising the entire farm at a lower rate.

If areas of the farm have recently been renovated, it is important to maintain nutrient application to these paddocks to ensure they do not become run down, as considerable dollars have already been invested in them.

Areas of the farm that have been cut for hay or silage also need special consideration. These paddocks will quickly deplete their stores of potassium in particular and may become infested with low producing grasses and flat weeds if potassium is not applied.

Part of the farms effluent management may be to pump out the ponds onto several paddocks throughout the year. These paddocks may not need additional applications of nutrients due to the high loads that may be being applied via the effluent.

It is up to the farm owner to decide on the nutrient level targets for the different Farm Management Zones on the farm. Once targets are reached, capital applications are no longer required and maintenance rates will be the most economic rate to apply. Soils with lower P levels should, under good management, reap larger economic benefits per unit of phosphorus applied compared to farms with higher P levels (see Figure 15.9).

Figure 15.9   Relationship between soil Olsen P level and milk fat and protein responses to capital P applications
Figure 15.9 Relationship between soil Olsen P level and milk fat and protein responses to capital P applications

Figure 15.9 illustrates the principle of diminishing returns. This shows that fertiliser applied to increase the soil Olsen P level by one unit when the soil Olsen P levels are low will give a greater increase in production and financial return than fertiliser applied when the soil Olsen P levels are high. This same principle applies to all the nutrients required by plants.

In years where milk returns are high, capital applications may be applied to the paddocks with low P levels to prepare them for the sowing of improved pasture species or to improve the growth of existing improved species.

Factors affecting the nutrient requirements are constantly changing, and the soil fertility levels should be regularly monitored to make more informed, cost effective nutrient decisions.

Ideally, every paddock on the farm would be soil tested to determine the spatial distribution of each nutrient over the entire farm. This is very expensive, but research has shown that the cost is several times less than the savings that can be made.