Three estimation approaches are combined:
1. **IPCC root:shoot ratio** (IPCC 2019 Refinement, Vol.4, Ch.11): `Root_DM = Aerial_DM * RS_ratio`, where RS_ratio is adjusted for N input and irrigation from the `IPCC_root_coefs` table.
2. **Reference root biomass** (Biomass_coefs `BG_Biomass_kgDM_ha`): A fixed per-hectare root biomass value, independent of yield. `Root_ref = BG_Biomass_kgDM_ha / 1000 * Area_ha`
3. **Biomass_coefs RS fallback**: When IPCC coefficients are not available, uses the `Root_Shoot_ratio` from Biomass_coefs.
The final estimate averages the RS-based and reference-based approaches, capped at 3x the default RS ratio to prevent unrealistic values.
Arguments
- Dataset
Data frame with above-ground biomass already calculated. Required columns:
- Name_biomass
Crop name matching Biomass_coefs.
- Prod_MgDM
Product dry matter (Mg).
- Residue_MgDM
Residue dry matter (Mg).
- Area_ygpit_ha
Harvested area in hectares.
- Water_regime
"Irrigated", "Rainfed", or "Mixed".
- N_input_kgha
Nitrogen application rate (kg N/ha/yr).
- w_ref
Numeric weight for the reference root biomass approach in the ensemble (0-1). Default 0.5. The RS-based approach gets weight `1 - w_ref`.
- simple
Logical. If `TRUE`, bypasses all context-dependent RS corrections (N-input, crop-group N-sensitivity, irrigation), setting all adjustment factors to 1. No `Water_regime` or `N_input_kgha` columns required. Default `FALSE`.
Details
Estimates root biomass dry matter from above-ground biomass using an ensemble of IPCC root:shoot ratios, reference root biomass values, and adjustments for N input and irrigation regime.
**N-input adjustment**: Higher nitrogen availability decreases root allocation due to functional equilibrium (Poorter & Nagel 2000). The `N_input_RS_adj` table classifies N rates into 5 classes with multiplicative RS factors (0.80 for >200 kg N/ha to 1.20 for <20 kg N/ha). This generic factor is then scaled by the crop-group-specific `RS_N_sensitivity` from `Crop_RS_N_response` (e.g., legumes respond minimally to soil N because they fix their own).
**Irrigation adjustment**: Irrigated crops develop shallower root systems (Benjamin et al. 2014). Factor from `Irrigation_adj` table (default 0.85 for irrigated).
**RS selection priority**: IPCC_root_coefs > Biomass_coefs fallback. When irrigation or N-input columns are present, the IPCC table provides context-specific RS values; otherwise the default `RS_default` is used.
**Ensemble and cap**: Final root = weighted average of RS-based and reference-based estimates, capped at 3x the default RS ratio times aerial biomass.
Requires from `load_general_data()`: - `Biomass_coefs` (Root_Shoot_ratio, BG_Biomass_kgDM_ha) - `IPCC_root_coefs`, `IPCC_crop_mapping` (with `crop_group` column) - `N_input_RS_adj`, `Irrigation_adj`, `Crop_RS_N_response`
References
IPCC (2019) 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, Volume 4, Chapter 11.
Bolinder, M.A. et al. (2007) Root biomass and shoot to root ratios as related to above ground biomass. J Agric Sci 145:127-137.
Poorter, H. & Nagel, O. (2000) The role of biomass allocation in the growth response of plants to different levels of light, CO2, nutrients and water. New Phytologist 147:135-147.
Benjamin, J.G. et al. (2014) Water deficit effects on root distribution of soybean, field pea and chickpea. Agronomy Journal 106:2033-2040.
Examples
if (FALSE) { # \dontrun{
load_general_data()
crop_data |>
calculate_crop_residues() |>
calculate_crop_roots(w_ref = 0.5)
} # }