Pasture production maps (historical weather)

Description

Spatial distribution of estimated annual pasture production across New Zealand.

A summary of APSIM simulations of a ryegrass/white clover pasture under five different scenarios, defined by water and fertiliser management:

• No irrigation and no fertiliser;
• No irrigation and adding fertiliser following defoliations at low soil N status, but capped at 200kgN/ha/year;
• Applying irrigation as needed without fertiliser additions;
• Applying irrigation and N fertiliser as required, but limited to 200kgN/ha/year;
• Applying irrigation and adding fertiliser N without restrictions;

 

Date: July 2023 Version: v1

Owner: Plant and Food Research

Contact: Rogerio Cichota, Plant and Food Research

 

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Dataset attributes

Spatial extent	National. Large lakes and rivers and conservation areas have been excluded
Spatial resolution	Productivity surface developed at 25m resolution, based on simulations using 5km climate grid and soil map with a 1:50000 nominal scale
Temporal extent	Annual average from 30 years simulations, from 1980 to 2010
Temporal resolution	Annual averages from simulations at daily time steps
Evaluation method (Validation)	Pasture production at several sites where data is available were compared against predictions. These were divided into two groups: one where there was enough information about the local conditions (soil, weather, actual management), which constitute part of the validation set in APSIM, and a second bigger group where only general information about the location and/or actual management is available. Expert assessment regarding the general production trends shown in the maps were also used during development.
Evaluation result (Numeric)	The validation dataset in APSIM has an R2 of 0.91 for biomass accumulation and RMSE of 1795 kgDM/ha (data per cut or grazing). Comparison of annual average production for the more general dataset yields an R2 of 0.57 and RMSE of 3159 kgDM/ha.
Evaluation result (Categorical)
Uncertainty method
Uncertainty data format (Numeric)
Uncertainty data format (Categorical)

 

Methodology

The pasture production surfaces were derived from biomass accumulation data simulated using the Agricultural Production Systems Simulator (APSIM) model. Simulations were set up in APSIM to describe a continuous ryegrass/white clover mixed pasture under rotational defoliation. The simulation setup included the possibility of applying irrigation, driven by soil moisture status, and nitrogen fertiliser, applied as urea following defoliations depending on soil N status. Defoliations were set to occur whenever pasture biomass reached 2500 kgDM/ha, with further constraints to avoid defoliating in intervals less than 15 days or greater than 60 days. Biomass harvested was accumulated over the year (from July to June) and then averaged across 30 years.
Important to note that these simulations assumed that the management was unimpeded by external factors such as access to machinery, holidays, weather, etc., and there were no restrictions to access water for the irrigated scenarios. The model also assumed no inefficiencies on the application of water and N to the field. These were applied homogeneously to the soil, which was also the case for the return of residues and excreta after each defoliation. Moreover, the simulations did not account for pests and diseases nor for nutrient limitations (other than nitrogen).

Daily weather data was sourced from the Virtual Climate Station Network (VCSN, provided by NIWA and soil parameters from S-map, provided by Manaaki Whenua (with proxies used over the Fundamental Soil Layer map for areas not covered by S-map). Note that the soil and weather data were employed 'as given', with no adjusts for factors such as slope, or high water table.

 

Fitness for purpose / limitations

This table indicates whether the dataset is suitable for different types of questions at different scales.

Note: Users should carefully consider their purpose as this dataset may not be suitable.

	Operational	Absolute	Relative	Screening/scoping
Block/farm	No	No	No	Maybe
Multi-farms(5+)	No	No	Maybe	Yes
Catchment	No	Maybe	Yes	Yes
National/regional	No	Maybe	Yes	Yes
Caveat(s)	The production surfaces show the general variation pattern for a ryegrass/white clover pasture across environmental conditions and under general idealised management. The simulations considered no soil limitations other than water and nitrogen and excluded pests and diseases. It also assumed no restrictions to management or access to resources (e.g. water for irrigation).