Crop Residue Parameters

This section describes the JSON properties used to configure crop residue parameters in MONICA.

Crop residue parameters determine how plant material is divided between added organic matter (AOM) pools, how those pools decompose, and how residue carbon and nitrogen enter the soil organic matter (SOM) model.

The parameters are used for material returned after harvest, cutting, root turnover, or incorporation of an entire crop.

JSON conventions

Number means a JSON number and may contain an integer or decimal value.
Fractions are expressed on a scale from 0 to 1.
Numeric parameters may be written directly:
```
"AOM_DryMatterContent": 1
```

They may also include unit and description metadata:

"AOM_DryMatterContent": [1.0, "kg DM kg FM-1", "Dry matter content of added organic matter"]

MONICA reads the first numeric element. Unit and description strings are not validated, intepreted, or converted. Values must therefore already use the units documented below.
Missing numeric parameters generally retain their default value of zero. A zero value is not necessarily meaningful or safe for every parameter.

General parameters

Parameter Name	Type	Description	Example
`type`	String	Serialization metadata identifying the object as crop residue parameters	`"type": "CropResidueParameters"`
`species`	String	Crop species associated with the residue parameter set	`"species": "wheat"`
`residueType`	String	Optional identifier for the residue type or parameter variant, such as straw or roots.	`"residueType": ""`

Residue composition

Parameter Name	Type	Unit	Description	Example
`AOM_DryMatterContent`	Number	kg DM kg-1 FM	Residue dry-matter fraction relative to fresh mass. A value of `1` represents completely dry material.	`"AOM_DryMatterContent": 1`
`CorgContent`	Number	kg C kg-1 DM	Organic carbon content per unit residue dry matter. If the value is missing, zero, or negative, MONICA uses `0.45 kg C kg-1 DM`.	`"CorgContent": 0.46`
`NConcentration`	Number	kg N kg-1 DM	Nitrogen concentration used to derive the organic-pool C:N balance. When residues originate from a simulated crop, MONICA normally supplies the crop's dynamically calculated residue N concentration instead of this static value.	`"NConcentration": 0.005`
`AOM_NH4Content`	Number	kg N kg-1 DM	Ammonium nitrogen content per unit residue dry matter. This nitrogen is added directly to the soil ammonium pool.	`"AOM_NH4Content": 0.0002`
`AOM_NO3Content`	Number	kg N kg-1 DM	Nitrate nitrogen content per unit residue dry matter. This nitrogen is added directly to the soil nitrate pool.	`"AOM_NO3Content": 0.0001`
`AOM_CarbamidContent`	Number	kg N kg-1 DM	Carbamide/urea nitrogen content per unit residue dry matter. This is normally zero for crop residues.	`"AOM_CarbamidContent": 0`

AOM pool allocation

Residue organic carbon is divided between a rapidly decomposing AOM pool and a slowly decomposing AOM pool.

Parameter Name	Type	Unit	Description	Example
`PartAOM_to_AOM_Fast`	Number	kg kg-1	Fraction of the residue organic matter assigned to the rapidly decomposing AOM pool	`"PartAOM_to_AOM_Fast": 0.12`
`PartAOM_to_AOM_Slow`	Number	kg kg-1	Fraction of the residue organic matter assigned to the slowly decomposing AOM pool	`"PartAOM_to_AOM_Slow": 0.88`

These two fractions should normally sum to 1:

PartAOM_to_AOM_Fast + PartAOM_to_AOM_Slow = 1

Decomposition coefficients

Parameter Name	Type	Unit	Description	Example
`AOM_FastDecCoeffStandard`	Number	d-1	Decomposition rate coefficient of the rapidly decomposing AOM pool under standard conditions	`"AOM_FastDecCoeffStandard": 0.012`
`AOM_SlowDecCoeffStandard`	Number	d-1	Decomposition rate coefficient of the slowly decomposing AOM pool under standard conditions	`"AOM_SlowDecCoeffStandard": 0.0012`

Actual decomposition is additionally affected by environmental conditions and soil organic matter model parameters.

AOM carbon-to-nitrogen ratios

Parameter Name	Type	Unit	Description	Example
`CN_Ratio_AOM_Fast`	Number		Carbon to nitrogen ratio of the rapidly decomposing AOM pool. For crop residues, set this to `0`. MONICA then calculates the fast-pool C:N ratio dynamically from the residue carbon and supplied residue nitrogen concentration.	`"CN_Ratio_AOM_Fast": 0`
`CN_Ratio_AOM_Slow`	Number		Carbon to nitrogen ratio of the slowly decomposing AOM pool. This value must be greater than zero when `PartAOM_to_AOM_Slow` is greater than zero.	`"CN_Ratio_AOM_Slow": 80`

`CN_Ratio_AOM_Fast = 0`

MONICA uses a fast-pool C:N ratio of zero as a marker that the material is a crop residue.

For crop residues, MONICA calculates the fast-pool C:N ratio dynamically from:

residue organic-carbon content
residue dry-matter content
the supplied residue nitrogen concentration
the fast and slow AOM allocation fractions
CN_Ratio_AOM_Slow
the configured maximum C:N ratio of the fast AOM pool

A nonzero CN_Ratio_AOM_Fast causes the material to follow the fixed C:N organic fertilizer pathway instead. Therefore, crop residue files should normally use:

"CN_Ratio_AOM_Fast": [0, "", "Calculated dynamically for crop residues"]

Transfer to soil microbial biomass

Parameter Name	Type	Unit	Description	Example
`PartAOM_Slow_to_SMB_Fast`	Number	kg kg-1	Fraction of decomposed slow-ppol AOM routed to the fast soil microbial biomass pool	`"PartAOM_Slow_to_SMB_Fast": 0.5`
`PartAOM_Slow_to_SMB_Slow`	Number	kg kg-1	Fraction of decomposed slow-pool AOM routed to the slow soil microbial biomass pool	`"PartAOM_Slow_to_SMB_Slow": 0.5`

These fractions should normally sum to 1:

PartAOM_Slow_to_SMB_Fast + PartAOM_Slow_to_SMB_Slow = 1

Dynamically calculated residue nitrogen

When MONICA returns material from a simulated crop to the soil, the residue nitrogen concentration is normally calculated from the crop's current biomass and nitrogen state.

This applies to operations such as:

harvesting and returning residues
cutting and leaving cut material on the field
incorporating the current crop
transferring dead root biomass to soil organic matter

In these cases, the calculated crop-residue N concentration is passed to the soil organic matter model, and the static NConcentration property in the residue file does not determine the residue N concentration.

NConcentration can still be relevant when the parameter object is applied through a generic organic matter or organic fertilizer workflow.

Default organic carbon content

If CorgContent is missing or not greater than zero, MONICA uses:

CorgContent = 0.45 kg C kg⁻¹ DM

A positive value explicitly supplied in the JSON overrides this fallback.

Available crop residue files

The crop-residues directory in the monica-parameters repository contains residue parameter sets for wheat, maize, rye, potato, clover-grass ley, and many other crops.

Example: wheat residue parameters

{
    "AOM_DryMatterContent": [1, "kg DM kg FM-1", "Dry matter content of added organic matter"],
    "AOM_FastDecCoeffStandard": [0.012, "d-1", "Decomposition rate coefficient of fast AOM at standard conditions"],
    "AOM_NH4Content": [0.0002, "kg N kg DM-1", "Ammonium content in added organic matter"],
    "AOM_NO3Content": [0.0001, "kg N kg DM-1", "Nitrate content in added organic matter"],
    "AOM_SlowDecCoeffStandard": [0.0012, "d-1", "Decomposition rate coefficient of slow AOM at standard conditions"],
    "CN_Ratio_AOM_Fast": [0, "", "C to N ratio of the rapidly decomposing AOM pool"],
    "CN_Ratio_AOM_Slow": [80, "", "C to N ratio of the slowly decomposing AOM pool"],
    "NConcentration": [0.005, "kg N kg DM-1", "Nitrogen content in added organic matter"],
    "CorgContent": [0.46, "kg C kg DM-1", "Carbon content in added organic matter"],
    "PartAOM_Slow_to_SMB_Fast": [0.5, "kg kg-1", "Part of AOM slow consumed by fast soil microbial biomass"],
    "PartAOM_Slow_to_SMB_Slow": [0.5, "kg kg-1", "Part of AOM slow consumed by slow soil microbial biomass"],
    "PartAOM_to_AOM_Fast": [0.12, "kg kg-1", "Part of AOM that is assigned to the rapidly decomposing pool"],
    "PartAOM_to_AOM_Slow": [0.88, "kg kg-1", "Part of AOM that is assigned to the slowly decomposing pool"],
    "residueType": "",
    "species": "wheat",
    "type": "CropResidueParameters"
}

Consistency requirements

Before using a crop residue parameter object, verify that:

AOM_DryMatterContent lies between 0 and 1.
CorgContent lies between 0 and 1, or is omitted to use the 0.45 fallback.
NConcentration, AOM_NH4Content, AOM_NO3Content, and AOM_CarbamidContent are non-negative.
PartAOM_to_AOM_Fast and PartAOM_to_AOM_Slow lie between 0 and 1.
PartAOM_to_AOM_Fast + PartAOM_to_AOM_Slow normally equals 1.
AOM_FastDecCoeffStandard and AOM_SlowDecCoeffStandard are non-negative.
CN_Ratio_AOM_Fast is 0 for crop residues.
CN_Ratio_AOM_Slow is greater than zero when the slow-pool fraction is greater than zero.
PartAOM_Slow_to_SMB_Fast and PartAOM_Slow_to_SMB_Slow lie between 0 and 1.
PartAOM_Slow_to_SMB_Fast + PartAOM_Slow_to_SMB_Slow normally equals 1.
All values already use the documented units because unit strings are not interpreted or converted.

Current implementation limitations

CorgContent is read from JSON and used during normal execution, but it is not currently included in the Cap'n Proto organic matter parameter schema. Reconstructing residue parameters through that schema can therefore lose the configured value and cause MONICA to use the 0.45 fallback.
AOM_CarbamidContent is accepted as JSON input and used by the soil organic matter model. However, the current JSON serializer mistakenly emits a duplicate AOM_NO3Content property instead of emitting AOM_CarbamidContent.
For simulated crop residues, the crop's calculated residue N concentration normally overrides the static NConcentration value.