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What to consider when looking to reduce fertiliser applications

How to prioritise nutrient applications on crops and pasture

What to consider when looking to reduce fertiliser applications

For a farm to perform well on an ongoing basis, applying a range of nutrients as fertiliser is vital. Lower than average farmgate revenue, coupled with higher fertiliser prices, means many farmers are considering cutting back on applications.

If continuing to apply nutrients is not an option, it is best to cut back applications in a deliberate and well-informed manner. Consider which nutrient to reduce and which not to depending on, for example, their mobility. This may be on a block level, which is often the scale of fertiliser planning. However, part of paddocks and blocks can be avoided if they are considered higher due to stock transfer of nutrients.

On a dairy farm, this can be applying fertiliser, especially nitrogen (N) containing products, in a way that avoids the parts of the paddock where animals congregate. Farmers who must cut back on fertiliser applications want the best value from their spend. Phosphorus (P), the costliest fertiliser nutrient, is not very mobile in the soil. So, if P levels are above optimal, P applied as fertiliser can be lessened gradually. This is an option for many dairy farms if they are already operating above economically optimal Olsen P. The Olsen P targets and response curves are well-researched in New Zealand.

Sulphur is the least costly nutrient, but is very mobile in the soil, so annual applications should be continued so clover production, for example, is not limited by a deficiency.

Most sheep and beef farms, however, do not have above-optimal Olsen P levels, so withholding P impacts production. Long-term trials show both pasture and animal production – ewe live weights, lamb production, and wool weights decline by about five percent per year when P fertiliser is withheld.¹

Hill country farms can consider using variable rate technology to apply fertiliser strategically to areas that provide the best returns. In modelling reported in the last edition of Ballance Agri-Nutrients Grow publication of spring 2022, SpreadSmart variable rate application continued to provide higher returns than fixed flow rate application. Variable rate application allows fertiliser to be applied based on soil fertility or land class, for example. Dairy farms could apply fertiliser to less fertile slopes and exclude it from more nutrient-rich, flatter areas and gateways.

Another option is to prioritise which nutrients and lime to apply, focusing on the most limiting nutrients as shown in Table 1.

Your local PGG Wrightson Technical Field Representative can offer you advice and recommendations to help you form a fertiliser programme.

1 O’Connor, M.B., Smart, C.E., & Ledgard, S.L. (1990). Long term effects of withholding phosphate application on North Island hill country: Te Kuiti. Proceedings of the New Zealand Grassland Association 51: 21-24.


Table 1: Prioritising nutrient and lime applications to areas of most value if financially constrained

Land management area to apply fertiliser to (from highest to lowest priority) Nutrients/lime to apply
Crops Nitrogen, phosphorus, lime
New pasture Nitrogen, phosphorus, sulphur, potassium, lime
Hay and silage Potassium, nitrogen, phosphorus, sulphur, lime
Older pastures - ground spread Phosphorus, sulphur, lime
Older pastures - aerial spread Phosphorus, sulphur, lime