Simple pasture model

[HamishBrownPFR]

Most people probably think this is not needed but I build it because it was useful for a job I was doing and I think it will be useful for others.

Justification: Sometimes we just want an approximate pasture model to produce at specified levels and use water and nitrogen with a sensible seasonal pattern without having to go to the effort of getting a full blown pasture model and associated management set up. The Simple Crop Resource Uptake Model (SCRUM) was written to fill this role for crops and now the Simple Pasture Resource Model (SPRUM) has been written to fill this role for pasture:

Key features:

• Follows similar philosophy to SCRUM with a product (consumed or removed at grazing), stover (post grazing residue) nodule and root organ.
• Two phenological stages (Canopy expanding and Full Canopy) which have set thermal time durations. When the end of the Full canopy phase is reached a "GrazeAndRewind" phase is entered which returns the phenogy to the start of the canopy expanding phase. This give a pasture that will grow up to full cover and be grazed without any manager scripts required to do so.
• the "GrazeAndRewind" phase triggers a Grazing event each time it is reached and default biomass parameters have all of product removed, 50% of stover added to surface OM and 20% of root added to soil OM.
• Photosynthesis is calculated as the product of daily thermal time, a daily growth rate (g DM /oCd) and a water stress factor.
• daily growth rate can be set hither or lower values to give pastures of differing productivity.
• N fixation is calculated as the product of a fixation constant (0.03 g N / g photosynthesis) daily Photosynthesis and a LegumePropn constant. Thus the amount of fixiation will vary through the season depending on pasture growth rate (temperature, radiation interception and water stress) and can be turned up or down depending on legume content of simulated pasture by changing the LegumePropn value.

[lie112]

I'd be really interested in learning more about using this pasture (and crop) model as to date I have developed CLEM but not really used APSIM. I'd like to add grazing of SPRUM from the CLEM herd, and discuss the model limits of this pasture (e.g. suitability for tropical or temperate pastures, ability to allow basal area to change with grazing pressure, how to include species composition and handle annual vs perennial grasses) and whether it is possible to modify the soil profile by loss/gain of a macroinvertebrate community and associated macropores that increase infiltration 10+ fold. SPRUM could benefit from some of the functionality of GRASP to be quite a nice little pasture model.

[HamishBrownPFR]

Hi @lie112. I would be happy to discuss this with you at some stage to see what the potential is here. SPRUM is an early prototype so good time to look at how else it might be used and what changes would be needed to achieve this.