When to topdress your pastures?

Clare Edwards, Pastures Officer
June 2015

Over the last few weeks, I have had a number of enquiries about the most appropriate time to fertilise. In particular, the timing for topdressing pastures with phosphorus and sulphur. The answer is complex.

It depends on individual circumstances and, to some degree, product.

Many enquiries are inspired by taxation issues. However, producers must also ask themselves important questions such as what does El Nino mean to your spring pasture production?

Most areas received some good falls of rain this week, with some around Mudgee experiencing long awaited runoff rain. This top up of soil moisture was critical for getting through the next few months. Even though evaporation and overall pasture growth is lower at this time of year, pastures are set up for when soil temperature rises and pastures start to increase their growth rate. As always, follow up rain is critical, and spring rains will be important after the temperatures rise.

Some other points on timing include not to fertilise when there is potential for storms or when groundcover is low.
Low soil temperatures and waterlogged soils may also have an effect on applied phosphorus. I often ask producers if they are intending to add clover seed to their fertiliser application.

Adding sub clover in autumn is a common practice, but may not always be ideal after about mid June. Sub clover is an annual legume which germinates in the autumn, growing through the winter months and sets seed in spring-early summer. This set seed is important to establish a seed bank for next year.

Unfortunately, sub clover needs time between germination and setting seed; applications with fertiliser after mid – late June will often leave insufficient time and so affect the clover's persistence and performance. On the other hand, some varieties will have a proportion of hard seed and this might persist in the seed bank until the next year. Overall, sub clover copes well with top dressed fertiliser applications if the timing is right. In contrast, grasses don't tend to perform so well with this method of application.

The other reason to top dress in autumn is the potential to increase pasture growth before winter.

Therefore, applications of fertiliser at this point in time may not be ideal if the pastures are not actively growing. Some producers will now wait until Spring, however predictions of potential low soil moisture and rainfall may influence this decision.

Lastly, the question of plant species and population is important. For example, summer native pastures that might have been frosted off can have a large amount of vulpia underneath. By fertilising at this time of year, this less desirable species may increase. 

Ideally, soil tests would inform you about choice of product and application rates, particularly when critical nutrient levels are likely to be met or exceeded.

Fertiliser efficiency is about matching the application to the plant's needs. There are other considerations regarding application, such as:

• the availability of product,
• prioritising paddocks and
• avoiding certain areas.

In addition, I haven't mentioned the strategic use of nitrogen in spring and its implications for pasture growth and quality. However, there is another set of rules for using this nutrient and products on pastures.

We are hoping to run another series of Soil and Pasture health workshops in August/September this year. Let Phil Cranney or myself know if you are interested in learning more about your soils, especially soil fertility.

Download the information sheet (PDF, 66KB)

More information

Phil Cranney, Pastures Officer | Phone: 6363 7888 | Email: phil.cranney@lls.nsw.gov.au

Clare Edwards, Pastures Officer | Phone: 63781709 | Email: clare.edwards@lls.nsw.gov.au