You can navigate to other sections of the report by folllowing these links:

  1. What Overseer is
  2. The Overseer farm file
  3. What Overseer produces
  4. How the Overseer engine works
  5. Uncertainty in model results
  6. Overseer Glossary

This page includes:

Overseer predicts how much each nutrient moves within the farm, where to and when. To do this, users need to create a farm analysis for the Overseer engine to model. The farm analysis is a detailed description of the farm with a specific purpose.

Creating a Farm analysis

One of the key principles of OVERSEER is that it uses information that is readily available to farmers and where information may not be readily available, suitable defaults are built-in. Because specific information is required to generate a nutrient budget, the software lets a user know if the data required is compulsory or optional, and if default values are available.

Management blocks are areas within the farm managed the same way (e.g. irrigated, cropped, effluent applied) and have the same bio-physical attributes (e.g. soil type, topography). Data required to describe each block varies, depending on the farm type.

Type of information required in a Farm File includes:

Farm location

Types of blocks and block areas
Types of enterprises (pastoral, cropping)

  • Stock numbers, breed
  • Production
  • Placement (grazing off, wintering pads)

Types of structures

  • Effluent management of structure
  • Stock management on structure

Type of effluent management system

Supplements imported and where they are fed


Soil type
Soil fertility tests
Pasture type
Supplements made on the block
Fertiliser applied
Irrigation applied
Effluent applied
Animals (type, timing) grazing the block

Crop rotation*; crops grown – yield, fertiliser applied, harvesting method

* As Overseer models crop rotations over a two-year time period, information required for crop blocks can be significant.

Management blocks

The creation of management blocks is critical to setting up the farm file to produce meaningful results. The fate of nutrients within a block (and the farm as a whole), plus the transfers between blocks and structures is the focus of most of the modeling carried out in the Overseer engine. For example, where and when animals excrete and deposit nutrients in paddocks, laneways and feed pads.

Management blocks don’t need to be next to each other. For example, Overseer can model a farm with a separate runoff block in a different catchment.

Overseer models seven management block types 

Click on the block icon to see more details about the block type.

Includes both pastoral and cut and carry. Pastoral grows pasture (i.e. non-effluent or effluent pasture block) which animals graze, and a proportion can be removed as supplements. Key feature is pasture and grazing animals. Cut and carry grows a perennial pasture where all forage is removed (i.e. grass or lucerne). Key feature is that all growth is removed as supplements, and no animal grazing occurs.


Grows an arable or vegetable crop (i.e. wheat or potatoes) (and fodder crop rotations when the return to pasture is >12 months). Can include grazing animals, depending on crop. Key feature is the crop rotation over a 2-year period.

Grows a permanent fruit crop (peaches, apples, kiwifruit, grapes and avocados). Can include grazing animals. Key feature is the management of the fruit crop.

Area of land within a farm that contains a house and surrounding gardens, no animal grazing occurs. Note this doesn’t apply to urban properties. 

Area of land covered in trees, scrub or native bush. 


Area of land fenced off to all grazing where there is a wetland. Key defining feature is the description of the wetland. 

Area of land fenced off on either side of streams or rivers where animals are excluded. Key feature is the description of the riparian strip.


The definition of ‘farm’ and the arrangement of the management blocks depend on the total area being modelled - and how easy it is to separate the management of the blocks. For example, a farm’s runoff block can be included in the modelling of the whole farm system, or individually as part of a catchment area (provided the management of that block can be separated from the farm system).

Overseer built-in databases

Overseer has a range of built-in databases that store location or product specific information to populate the farm file. 

Click on the icons in the diagram below to get more detail on the different built-in databases.

Click on each
type of database
to find out more

Database: Climate

Why we use this database

Provides long-term estimates of annual and monthly rainfall, PET (potential evapotranspiration) and temperature based on a 30 year dataset (currently 1980-2010). This allows users to enter climate data for each block through entering longitude and latitude, or choosing the nearest town or region.


NIWA (National Institute of Water and Atmospheric Research) virtual climate network for New Zealand interpolated at 5km grid scale.
* This is an online database so is only available when the user is connected to the internet.

Database: Fertiliser and Lime product composition data

Why we use this database

Provides the nutrient compositions for a range of common fertilisers to allow users to auto-populate these products into their farm file.

For more information, see the Overseer Technical Manual Chapter “The Characteristics of Fertilisers”.


Based on data supplied by the product owner – currently Ballance Agri-Nutrients, Ravensdown and Viafos. 

Database: Supplementary Feed

Why we use this database

Provides the nutrient and dry matter (DM) content and the metabolic energy (ME) supplied by a range of common feed supplements imported onto a farm (such as grains, silage and processed products, like molasses and palm kernel meal).

For more information, see the Overseer Technical Manual Chapter “Supplements”.


Compositions are derived from typical (not necessarily average) values of feeds measured by the commercial feed testing company FeedTech. Data for corn grits/hominy came from the Nutritional Requirements of Dairy Cattle (1989).

Database: Salt Blocks

Why we use this database

Provides the nutrient content for a range of salt blocks or licks as part of health supplements fed to animals.

For more information, see the Overseer Technical Manual Chapter “Supplements”.


Summit (Dominion Salt Ltd).

Database: Soil Data

Why we use this database

Provides a range of soil properties values.

For more information, see the Overseer Technical Manual Chapter “Characteristics of Soils”.


National Soils Database (Wilde R H and Ross C W 1996 New Zealand Reference Soil Collection and the National Soils Database. New Zealand Soil News 44: 224-227.) and AgResearch Limited.

Database: Crop Data

Why we use this database

Provides the parameters that define the growth, uptake and nutrient content of crops.


Plant and Food Research Limited.

Data input quality and file type

Overseer can be operated by nearly anyone. However, the description of the farm (creation of the farm file) and interpretation of the results should be done by formally trained users who understand farm systems.

So that Overseer nutrient budgets are good quality, when users are creating Overseer farm files they should ensure:

  1. They have the best quality farm data to create the farm file
  2. They know what type of farm file is required and are consistent about how they create it.

Understanding what type of input data has been used to create the farm file is also important in interpreting Overseer results. Farm files can be created to generate different budgets in three ways:

  1. “Predictive”
  2. “Year End”
  3. “Scenario”

A Predictive analysis is based on the known biophysical characteristics of the farm and the expected farm system for the coming year(s).

A Year End analysis is based on the actual farm inputs and outputs from how the farm is currently managed.

A Scenario analysis is based on a hypothetical farm system. This budget requires a very good understanding of the proposed system to make reasonable predictions of nutrient flows.

Go to next section: What Overseer produces

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