The first step when creating an analysis in OverseerFM is to define the blocks that make up the farm. Details for creating blocks is described in this article, including adding forests to a tree block to assess carbon sequestration.
OverseerFM analyses nutrient movements within similarly managed land on a farm to produce nutrient budgets that identify where nutrients are being lost from the system (as leaching, run-off or emissions) rather than being converted into product.
To do this OverseerFM defines blocks of land that are managed similarly. Soil and water added through rain or irrigation are important factors in drainage and nutrient flows and previous versions of Overseer have required setting up management blocks based on a single soil type and irrigation application.
To reduce data entry effort and align with farm practice, OverseerFM allows for up to three soils and two or more irrigation systems per management block. The model breaks these down in the background.
This article describes how to define a block, how to create a block, add soils, add forests to tree blocks, and complete the block setup.
If you import a farm file where the blocks have been divided by soil/irrigation, these will be imported as is. You have the choice of combining the blocks into management blocks (including using the simplify tool) or leaving them separated. We suggest leaving older analyses and only converting the new ones that will be used going forward.
This article assumes the reader has extensive farm systems knowledge. Decisions on creating OverseerFM analyses are dependent on working knowledge of the farm being analysed.
What is a block?
As a block may contain multiple soils and irrigation, it could be defined as land used for a common purpose and managed in a similar way. It can be made up of areas of the farm separated from each other by managed in the same way.
Larger blocks provide the model with more flexibility in averaging out the usage of the block. Due to this when deciding on blocks, try to combine paddocks and only separate on soils and irrigation where it is significant to the area being modeled.
When dividing a farm into blocks, each block should:
- Grow the same pasture/fruit or crop
- Support similar animals
- Have similar climate
- Have similar topography (for pastoral blocks)
- Have similar fertiliser applied
- Have the same drainage system
After creating a new analysis, the only option available is to create a block. This launches a map on which you can draw the outline of the block. The map location is based on the address entered when creating the farm.
The OverseerFM model does not use any of this spatial information, so the drawing of blocks is mostly cosmetic. You do not need to draw the blocks perfectly, it should simply be representative of the block so that users can understand which blocks are on the farm.
Draw the block by clicking on the map at each point of the block and then click the starting point to complete the outline. You should see the outline being creating as you click on each point.
Entering block details
Completing the block will launch the block details screen.
The effective area is populated based on the area of the drawn block. This may be an approximation depending on the drawing and topography of the land. If the actual area is known this should be changed to the actual value. The calculated area will remain in the blue box for reference.
On completion of the block details, it will be return to the map. The climate details are automatically populated based on location. The ability to enter climate date manually is no longer available (both annually or monthly).
Adding soils to the block
Up to three soils can be added to a block. Each soil is defined as representing a percentage of the block area. Only add dominant soils, such that any single soil is not too small in area.
Using SMap soils
Where available, the S-map soils that intersect the block are shown on the map. The soils (siblings) are listed in a box at the top right of the map. You can switch between viewing by sibling reference or viewing by polygon (soil outline).
The soil areas drawn on the map are called polygons. Each polygon may contain one or more soil siblings as defined by Landcare in S-map. Where there is more than one soil sibling within a polygon, each soil sibling is given a proportion (percentage of the polygon that is likely to be that sibling).
Each polygon defines a percentage of the block that it intersects. The total percentage is determined by multiplying the proportion of the polygon by the percentage that polygon intersects the block.
Currently OverseerFM does not return polygons that are less than 2% of the block. Therefore, the total intersecting percentage may not add to 100.
Select ‘+’ for the soils that you wish to add to the block.
Using soil order/group
If there is no SMap data available or it is not deemed appropriate, soils can be added manually. Selecting ‘Add new soil’ will launch the following. You can select an existing soil (one that has been used on another block), enter an SMap reference or select soil order and/or group.
Using farm soils
Soils that have already been used on the farm are also displayed in a table on the map. These can also be selected for the block from here.
Adjusting soil percentages
Adding soils will populate the block soils section (shown below). You can adjust the percentages of each soil by selecting and dragging the blue circles on the slider. No single soil can be under 10% and the total of all soils must equal 100%.
Adding forests to tree blocks
New Zealand farmers can now estimate how much carbon their tree blocks are sequestering. The carbon stock tool in OverseerFM uses data from the MPI Carbon Look-up tables to estimate the carbon sequestration for tree blocks on a farm. Forests can be added to your farm whilst creating or editing a trees and scrub block by clicking on the "Add new forest" button in the forests section of the block. Multiple forests can be created for a single tree block. The following video demonstrates how the carbon stock tool works in OverseerFM and how to add forests to your Overseer trees and scrub blocks.
Use the button “Save and Create new” to cycle through the creation of each block. When finished select save and then from the main screen select “I have completed all my blocks”.
This will show all the tabs to enter the remaining farm details for this analysis. The next step is to add soil tests, snowfall and/or drainage to each of the blocks.