Dig up a cost-effective fertiliser strategy

For WA producer, Don McNab soil testing has enabled him to refine his fertiliser strategy and save costs while maintaining pasture productivity.

Fertiliser savings represent around 7-8% of his business turnover – “a substantial saving” according to Don.

Don. his wife Amanda and their three children took over the family business, ‘Glencoe’ three years ago in Thomson Brook in south-west WA.

On their 194ha property, of which 130ha is grazable, they run 90 Angus cattle and 230 Merino ewes plus followers. They aim to maintain a self-sufficient feedbase, made up of annual ryegrass and clover-based pastures which they cut for hay in spring.

Their combined soil, pasture and grazing management has enabled them to maintain a relatively high stocking rate for the region and their soil type (sandy loams with some lighter quartz soil).

Whole farm nutrient mapping

Don’s father first participated in a Catchment Council-supported whole farm nutrient mapping program in 2014 and Don has used follow up testing to keep track of soil pH and nutrient levels since.

“We first participated in the soil program because we saw it as a good opportunity to understand the requirements we needed to achieve optimal pasture production,” Don said.

“We tested sporadically in the past but have tested the whole farm twice since 2014 and anticipate we will test the whole farm again after the 2021 growing season. We have tested three paddocks over this summer to give us an indication of how we are travelling to and see the results from liming since the last round of testing.

“We are aiming to get a representative sample from each paddock, taking a 0–10cm topsoil sample. The contractor that completes the sampling uses GPS coordinates to collect samples along the same transects each time to ensure some consistency in the method.

Don also uses plant tissue testing to check macro nutrient levels in hay paddocks. “We can use this information to back up our decisions, it verifies that the nutrients are there,” he said.

Cutting back and saving more

Initial soil testing revealed high levels of nutrients such as phosphorus (P), potassium (K) and sulphur (S) present in the soils on Don’s property – almost three times the amount required for optimal plant production.

With agronomic advice based on these results and the help of a fertility index that outlined the nutrient requirements for his production system, Don felt confident to cut down on the use of fertilisers.

“The most beneficial part of the program was the agronomic advice which gave me the confidence to cut out P application and focus more on getting the soil pH corrected to allow optimal use of the nutrients already present,” Don said.

“With the application of lime, soil pH levels have shifted from around 4.5-4.6 to 5.2-5.4.

“Cutting back on fertilisers and seeing no loss in production – that really validated the information we were getting.

“In the past we had been applying P at a rate of 18kg/ha/yr based on a stocking rate calculation of approximately 18 DSE/ha. We also applied extra K and N to hay paddocks.

“We were essentially throwing out about $9,000 of fertiliser that we didn’t need. That equates to around 7–8% of our turnover which is a pretty good saving,” he said.

Future soil testing

Don intends to continue soil testing into the future.

“We have realised that we can make significant savings on inputs by paying closer attention to what is available in our soils and the return on soil testing is quite good. Instead of just applying a blanket approach to the whole farm we have been more targeted in the application of nutrients,” he said.  

“It’s definitely going to be a benefit to continue. We will probably keep doing what we’ve been doing – we’ll test select paddocks I’ve got questions about or we’ve applied amelioration to each year and we’ll test the whole farm every two to three years.”