Are you monitoring your soils?

02 Aug 2022

Tablelands Telegraph - August 2022

Clare Edwards, Senior Land Services Officer - Pastures

I often get asked to help landholders in making decisions about soil health and, in particular, soil nutrition. A default we use to monitor our soil nutrition health is by using soil tests. Soil nutrition or soil fertility is just one of three interrelated components of soil health. The physical nature of the soil and the soil biology are the other two factors. All three can have positive and negative impacts on each other. For example, a too acid soil can impact on soil biology. Too acid can also reduce the amount/size of nodules found on our legumes (particularly sub-clover), the amount and type of rhizobia found and, in turn, reduce the potential amount of nitrogen fixed.

I recently summarised 641 paddocks that have been soil tested through the Soil and Pasture health workshops (2015 – 2022) held across the Mudgee, Bathurst, Trunkey Creek, Oberon, Lithgow and Capertee areas. I found these results interesting:

• 86.4% of the paddocks sampled had a pH (Ca) less than 5.5
• Almost 20% had Aluminium percentage greater than 15%
• 68% of samples were responsive to sulphur
• 74% were responsive to phosphorus
• 14% had an organic carbon less than 1.5%

If you are interested in seeing a more comprehensive paper on some of these results, page 93 of this paper written for the National Soils Conference in 2018 contains more detail.

When 29 landholders went through a soil testing masterclass we ran back in 2019 (unpublished), soil depth and acidity were looked at closely. The 0 – 10cm depth average pH was 4.61, with 93% of samples recording less than pH 5.5. Likewise, the 10 – 20cm depth pH average was 4.41 and over 93% of samples recorded less than pH 5.5.

Similarly, when we look at the intensive sampling that was undertaken in the collative project across several Local Land Services regions (including Central Tablelands) investigating soil pH and other soil factors at depth in pasture and cropping paddocks, you can see that soil acidity is widespread problem.

When we talk about the management of soil acidity on the tablelands, we are limited to a few options.

Option one is to do nothing. I always mention this as an option, as many pastures and landscapes are very stable. For example, this might be acceptable management for some paddocks with large areas of microlaena and carrying few stock. Limitations such as slope, rocks, and access may mean that other higher priority land is considered. Some soil types on the tablelands should not be disturbed, especially those which have sodic subsoils. Soil decisions should not be taken in isolation from the context of pasture species, livestock enterprise, financial considerations and farm planning.

Option two is to consider using tolerant species. Pasture species such as tall fescue and cocksfoot can tolerate acid soils and high aluminium percentages. There are also new breeding lines available for some introduced species that are worth investigating. However, this option does not necessarily address the problem and potentially reduce the problem in the future.

Option three involves the use of soil ameliorants that change the pH, such as lime, dolomite and other types of products. Once again, consider the landscapes, terrain and economic return of these products. It is always worth investigating the soil texture, the amount, the neutralizing value and how you apply these products. Note: Gypsum does not change pH.

Option four is that soil acidity is just one aspect of soil health. It is worth checking other aspects of soil health to find out if they might be the most limiting factor.

Do you want to know more about soil fertility, soil testing and linkages with soil health?

There are two soil and pasture health workshops planned for September in the Bathurst and Mudgee areas. The workshops are two half-days over 5 – 6 weeks. The first workshop is about soils, soil health and some simple soil tests. At this day participants are given equipment to take soil samples from their own properties. On the second day (5 – 6 weeks later), we go through soil testing, explain what the numbers mean and link some of the numbers to pasture health.

Bathurst - Friday 2 September 1.00pm – 4.00pm

Mudgee - Monday 5 September 10.30am – 1.00pm

While these days and the workshop are free, numbers are limited so RSVP now.