Managing soil acidity in permanent pastures

Summary

Subsurface (5-20 cm) soil acidity is considered a major constraint to production systems in the medium and high rainfall zones of central and southern NSW and soil acidity was the only indicator of soil condition reported to be worsening in the latest NSW State of Environment report (SOE, 2018). The effects of falling pH in these systems is insidious, less well understood by landholders and advisors than in cropping systems, and acidification of these systems is often underestimated or overlooked.

The aim of this producer demonstration site (PDS) project is to demonstrate that improved monitoring of soil pH profiles and adapting liming application rates and methodologies to meet higher pH targets will improve pasture production and composition and therefore the profitability and sustainability of permanent pasture systems. 

Objectives

By December 2027, in the NSW Southern Slopes region of NSW, Holbrook Landcare Network will: 

1. Demonstrate the most effective top-dressed liming strategy for ameliorating soil acidity in perennial pasture systems (to increase 0-10 cm target pHCa to above 5.5) on 3 typical soil profiles across 3 demonstration sites. These sites will particularly demonstrate: 

   • the importance of using higher pH targets 

   • the value of monitoring the soil pH profile to identify the timing and rate of lime application 

   • the impact of top-dressed lime applications on the pH levels of the soil profile through time in permanent pasture situations 

   • the long-term impact on pasture production and composition  

   • Conduct a cost-benefit analysis to determine the relative economic impact on livestock enterprises as a result of these amelioration treatments, inferred/modelled from the impact on subsurface pH and pasture production.  This will be compared to current industry practice of 2.5t/ha every 10 years. 

2. Implement a series of skills and training development activities to increase the knowledge, skills and confidence of 10 core and observer producers and 50 producers at engagement events in interpreting soil tests, assessing pasture composition and feed value of pastures and arriving at a liming strategy for their farm – based on soil type, soil capability and production objectives. 

3. 75 per cent of core producers will have adopted (or intend to adopt) higher pH targets than current industry practice and 25 per cent of observers intend to. 

4. Conduct an annual field day and other activities to showcase the demonstration sites results and encourage adoption of key practices by 150 attending producers.  

5. Produce 3 case studies summarising outcomes from the demonstration sites or alternate case study site. 

Progress

Holbrook Landcare Network’s ‘Managing soil acidity in permanent pastures’ PDS is investigating top-dressed liming strategies in non-arable pasture systems where lime incorporation is not possible or preferred. Two demonstration sites at Holbrook and Mannus, NSW had different rates of topdressed lime applied in 2021, targeting 3 different pH targets. The third site at Rosewood, NSW had different rates of topdressed lime applied over multiple years by the farmer.

Fourth year soil data and pasture measurements were collected at all sites. The soil pH and exchangeable aluminium results from the demonstration sites show that the lime is continuing to impact the subsurface soil layers, 4 years post liming, and the degree of pH and exchangeable aluminum change varies between the sites.

At the Rosewood demonstration site, pasture DM, subclover composition, subclover nodulation score and subclover tissue nitrate nitrogen was highest in the 6 t/ha strip compared to the 3 t/ha and 9 t/ha strips. The cause of this will be investigated further.

At the Holbrook site, there was no statistically significant difference in dry matter production between the treatments. However, subclover composition was significantly higher (P<0.05) in all three lime treatments compared to the control (nil lime). At the Mannus site, the control plots (nil lime) appeared to have less living plant material than the limed plots throughout the year, however there wasn’t a significant difference in dry matter or composition measured in the spring.