Zoning up to optimize pasture production

Summary

Over 80% of New England soils are deficient in phosphorus, notwithstanding inherent and high levels of soil acidity. Coupled with variability in the levels of these elements across paddocks, the current practice of blanket rate input applications does not appear to provide the right input at the right amount in the right place.

For five properties in the New England region soil tests were conducted annually on a 1-ha grid, to determine local soil pH and phosphorus levels. Project-paddocks were ‘zoned-up’ based on their requirements for lime and phosphorus, which constitutes the Variable Rate Application (VRA) method. The cost of using the VRA method was compared to the cost of applying inputs at blanket rate, annually, for each project paddock.

In paddocks where inputs were consistently applied through the VRA method, the paddock proportion with optimal pH and phosphorus levels increased, demonstrating nutrients were applied where required. For paddocks with a consistent fertiliser history, the VRA method was more cost-effective than the blanket-rate application method, as the soil sampling cost was offset by the savings in inputs.

Consistent use of VRA targets nutrient application where required, thereby reducing input costs and avoiding the over-use of fertilisers and lime.

Objectives

By November 2025 in the New England area across five demonstration sites:

1. Validate site-specific management of fertiliser and soil amendment treatments using soil nutrient zone mapping of sub-paddock soil nutrient variability to increase pasture production in a grazing system by 20% per hectare and livestock productivity by 25% over existing fertiliser applications.

2. Demonstrate that targeted treatments by zone will achieve potential optimal pasture biomass production over at least 90% of the treated paddock or farm.

3. Prove the cost benefit of investing in spatial imagery, grid sampling and site-specific management to define variable fertiliser application zones that will lead to livestock production gains and soil treatment savings.

4. Fine tune the pasture production response curves already established for the New England region.

5. Conduct an annual field day and other extension activities to showcase the demonstration site results and encourage adoption of key practices to result in:

• 100% of core producers (5) fully implementing the practice of soil nutrient zone mapping and variable fertiliser application across their pasture and livestock operations.
• 10% of observer producers (15) fully implementing the practice of soil nutrient zone mapping and variable fertiliser application across their pasture and livestock operations.
• 100% of core producers and 80% of observer producers having greater knowledge and skills in the value of zoning paddocks for soil nutrient variation.

Key findings

Primary project results were the following:

• Bulking soil samples at paddock-level rather than analysing individual soil samples may mask soil acidity issues or areas of sub-optimal soil phosphorus levels
• Three (3) out of 5 participants adopted the VRA method for input application
• The VRA method, when used consistently, ensured nutrients were applied where needed, leading to increasing proportions of paddocks with optimal nutrient levels
• When used consistently, the VRA method of input application was cheaper than the traditional blanket-rate application method, with soil sampling costs offset by reduced input costs, leading to overall savings in input application ranging from $42/ha - $ 341/ha

Benefits to industry

The project found the combination of soil testing and using the VRA method was cheaper than the standard blanket-rate method for input application, when used consistently.

Consistent use of VRA targets nutrient application where required, reducing input costs, leading to more uniform paddocks in terms of nutrients, and avoiding environmental risks related to the over-use of fertilisers and lime.

This project is a proof of concept for the use of VRA and provided participants with a clear understanding of the principles for targeting fertiliser rates and treatments within a paddock.

MLA action

MLA continues to deliver the Producer Demonstration Site (PDS) program, supporting livestock producers working in peer-to-peer groups to pursue new skills, knowledge and management practices applicable to their own commercial livestock production systems.

Future research

For future projects, recommend by the project team were the following:

• Designing larger trial plots or conducting plot trials to assess pasture growth under different lime and phosphorus fertiliser treatments,
• Making input application (lime and phosphorus fertiliser) part of the project, to ensure inputs are consistently applied, in accordance with project objectives,
• In the negotiation stage at the beginning of a project, ensure project participants clearly recognise and understand the importance of their obligations within the project methodology.