The next generation of APSIM > APSIM Next Gen User Tutorials > Module 5: Long-term simulations

Module 5: Long-term simulations

Created 07/03/2023

IMPORTANT NOTE: It is highly recommended that you upgrade your APSIM Next Gen version to at least version 2023.2.7164.0 or later.

Long-term Simulations

Chickpea sowing rates - 40 year runs

In this exercise you will use sowing rules to plant Chickpea crops and observe yield probabilities for a 40 year period given a half full soil moisture profile at sowing. We will compare two sowing rate strategies for these conditions with the goal of maximising yield. The weather will be different each year but the soil starting conditions will be the same.

By default, in long term simulations (i.e. longer than one year), the end of one years’ simulation becomes the starting point of the next year. This is useful if you are interested in seeing the degradation or improvement of the soil over a long time period. But what if you wanted to work out what the best strategy would be for the current year using weather scenarios from the past 40 years? To do this we could create 40 different simulations all with the same starting conditions but a different weather file (which would be a lot of work), or we could run the same simulation over 40 years and just reset the starting conditions each year (much simpler).

We can then try different management strategies to see which one would have worked best under the past 10 years weather scenarios.

Start a new simulations using Wheat example.
Rename the simulation as Chickpea and save the simulation as Module5.
Change the Clock nodes’ start and end date values to: 1/01/1940 and 31/12/1980
Copy the Heavy clay soil from the Training toolbox and delete the exisiting Soil node.
Set the starting Water to 50% full - filled from top.
Set NO3 Depth to 0-1800 and initial value to 20kg/ha (right-click heading to change units).
Set NH4 Depth to 0-1800 and initial value to 0kg/ha.
Change the SurfaceOrganicMatter node’s type to sorghum (don’t forget to rename the pool name to sorghum as well), initial surface residue: 550 kg/ha, Carbon:Nitrogen ratio of 76, leave the Fraction of residue standing as is.
Right-click Field and add a Chickpea plant node.
In SowingRule1 change the values to match the following:
In addition to this, to make it work correctly with the Chickpea node, we need to modify the underlying Script.

Clear the script completely and copy and paste this script into the Script input for SowingRule1:

using Models.Interfaces;
using System.Linq;
using System;
using Models.Core;
using Models.PMF;
using Models.Soils;
using Models.Soils.Nutrients;
using Models.Utilities;
using APSIM.Shared.Utilities;
using Models.Climate;

namespace Models
{
    [Serializable]
    public class Script : Model
    {
        [Link] private Clock Clock;
        [Link] private Fertiliser Fertiliser;
        [Link] private Summary Summary;
        [Link(ByName = true)] private Plant Chickpea;
        [Link] private Soil Soil;
        private Accumulator accumulatedRain;
        [Link]
        private ISoilWater waterBalance;

        [Description("Start of sowing window (d-mmm)")]
        public string StartDate { get; set;}
        [Description("End of sowing window (d-mmm)")]
        public string EndDate { get; set;}
        [Description("Minimum extractable soil water for sowing (mm)")]
        public double MinESW { get; set;}
        [Description("Accumulated rainfall required for sowing (mm)")]
        public double MinRain { get; set;}
        [Description("Duration of rainfall accumulation (d)")]
        public int RainDays { get; set;}
        [Description("Cultivar to be sown")]
        [Display(Type=DisplayType.CultivarName, PlantName = "Chickpea")]
        public string CultivarName { get; set;}
        [Description("Sowing depth (mm)")]
        public double SowingDepth { get; set;}        
        [Description("Row spacing (mm)")]
        public double RowSpacing { get; set;}    
        [Description("Plant population (/m2)")]
        public double Population { get; set;}    


        [EventSubscribe("StartOfSimulation")]
        private void OnSimulationCommencing(object sender, EventArgs e)
        {
            accumulatedRain = new Accumulator(this, "[Weather].Rain", RainDays);
        }


        [EventSubscribe("DoManagement")]
        private void OnDoManagement(object sender, EventArgs e)
        {
            accumulatedRain.Update();

            if (DateUtilities.WithinDates(StartDate,Clock.Today,EndDate) &&
                !Chickpea.IsAlive &&
                MathUtilities.Sum(waterBalance.ESW) > MinESW &&
                accumulatedRain.Sum > MinRain)
            {
               Chickpea.Sow(population:Population, cultivar:CultivarName, depth:SowingDepth, rowSpacing:RowSpacing);    
            }

        }

    }
}

Run the simulation.
You should get an error with the message: Cannot find a soil crop parameterisation called ChickpeaSoil
- This is caused by using a soil that is missing a SoilCrop node (located under Physical) with the same name as the plant node you are using.
To fix this error, copy and paste the WheatSoil node, located under Heavy Clay > Physical. Rename WheatSoil1 to ChickpeaSoil.
Your simulation should now run successfully and you should have data in your DataStore node.
Add a management script called Reset on date to the Chickpea simulation (found in Management Toolbox under Other)
Leave all parameters as yes and change the date to reset on to 1-may.
- note: make sure this management script sits above all other management scripts in the tree as they are ran in the order they are arranged from top to bottom.

Add the below to the Report variables.

[Clock].Today
[Chickpea].Grain.Total.Wt*10 as Yield

Make report frequency as:
```
[Chickpea].Harvesting
```
Remove SowingFertiliser management node.
Rename the Chickpea simulation as Chickpea 10 plants.
Copy Chickpea 10 plants and rename it Chickpea 15 plants.
Change the Plant population(/m2) to 15 in the SowingRule1 management script.
Run the simulations.
Create a graph. Rename it Total chickpea yield time series with a series that plots [Clock].Today and Yield.
Now you have a graph showing yield when comparing differing plant density of 40 years.