Variable Rate Lime
Management of soil acidification is central to long-term agricultural productivity and efficient use of available water and nutrients. It is an essential practice to counteract the acidification of agricultural soils over time.
Liming not only represents a high capital investment but carries a GHG cost as it reacts in the soil to produce CO2. Variable rate application, therefore, has an important role in optimising the costs and GHG impact associated with liming.
Variable Rate (VR) Lime combines knowledge of paddock spatial variability with GPS technology and VR input controllers.
Profit gains arise from unlocking the yield potential by addressing acidity and improving plant water use. Multiple benefits include reduced input costs and application errors, alongside improved efficiencies, agronomic performance, and profit margins.
The spatial landscape of every enterprise is unique. Success is dependent on the level and depth of acidity, the responsiveness of the soil, the rainfall environment, and cropping system. Liming can take several years to show benefits but yield gains of 15 - 50% can be achieved.
Designing the right VR approach requires investment in time to establish and optimise prescription maps, to manage and integrate baseline data and to monitor performance for improvement.
Primary emissions benefit
- Reduced emissions from spatially optimised lime application.
Co-benefits
- Reduced input costs
- Operations efficiencies / flexibility
- Agronomic performance
- Reduced operator error/fatigue
- Improved profit
Potential barriers:
- Cost (time and investment) to establish prescription maps
- Data management and integration
- Limited connectivity and infrastructure
- Technology failure.
Considerations
The magnitude of benefit depends on:
- Enterprise size and composition,
- Severity and depth of acidity constraint to yield potential
- Underlying landscape variability
- Management and rotational practices.
To estimate avoided emissions resulting from a VR-lime activity you will need the following data for both the baselineb, and activitya scenarios:
|
L |
= |
Lime application amount (kg) |
|
P |
= |
Proportion that is limestone or dolomite |
|
EF |
= |
Emissions Factor determined by lime type (limestone = 0.12; dolomite = 0.13) |
The following calculations can be used as simple indicators of benefit based on a direct reduction in lime use. The only change to the equation is the amount of fertiliser used.
GHGbase = Lb * P * EF
GHGactivity = La * P * EF
These calculations provide a simple estimate of the annual GHG emissions (kg CO2-e) and should then be applied to the Avoided Emissions Equation (AEE) to estimate the GHG benefit from the activity.
Implementation
Successful implementation of VR-Lime requires integration of several data-streams and technologies into operations.
Development of a variable rate lime FERP should consider the following implementation steps:
- Agronomic services and soil testing to define prescription maps based on the spatial variability in soil properties, acidity and its depth, across the production landscape.
- Remote sensing and on-farm sensors to collect data on crop health and biomass production from satellite imagery, drones, or sensors mounted on equipment.
- Data analytics and agronomy services to combine multiple data sources, identify zones with different acidity levels, and develop prescription liming maps.
- Global positioning systems and variable rate controllers on farming equipment to adjust application rates based on pre-defined prescription maps.
- Calibration of equipment to ensure variable rates are accurately delivered according to the prescription maps.
- Operator education or service contracting to ensure effective implementation of variable rate liming.
- Continuous monitoring, evaluation, and learning to evaluate plant performance indicators, optimise nutrient needs, and understand lime dissolution and movement following VR-Liming.
Activities:
- Spatial positioning and guidance systems (GPS, RTK)
- Variable rate controllers
- Harvest or yield monitors
- Data connectivity solutions
Supporting services:
- Agronomic Services and Soil Testing – to define prescription maps
- Lime purchase and transport
- Data services - connectivity & analysis
Monitoring:
- Proof of eligible purchases (invoices)
- Evidence of prescription maps
- Crop/pasture performance metrics
- Enterprise emissions baseline reporting (2 year, and 5 year)
Stacking compatibility:
- Variable Rate (VR) Fertiliser
- Pasture regeneration - Legume
- Electrification and automation
The magnitude of benefit depends on enterprise size and composition, crop type, soil variability, and management practices. In general, benefits are more likely to be achieved in large farms that encompass variable soil types, and where yield variability has significant impact on management decisions and profitability.