Two estimation methods are calculated simultaneously:
1. **NPP method** (`CropBNF`): Based on total crop nitrogen from NPP estimation: $$CropBNF = Crop\_NPP\_MgN \times Ndfa_{adj} \times Leg\_share$$
2. **Anglade method** (`CropBNF2`): Based on product nitrogen, below-ground N (BGN), and nitrogen harvest index (NHI) following Anglade et al. (2015) and Lassaletta et al. (2014): $$CropBNF2 = Prod\_MgN \times Leg\_share \times Ndfa_{adj} \times BGN / NHI$$
When environmental columns are available, the reference Ndfa is adjusted: $$Ndfa_{adj} = Ndfa_{ref} \times f_N \times f_T \times f_W$$
Arguments
- x
Data frame with crop NPP data. Required columns:
- Name_biomass
Crop name matching Names_BNF classification.
- Crop_NPP_MgN
Crop NPP in Mg N.
- Prod_MgN
Product nitrogen in Mg.
Optional environmental columns (if absent, no adjustment applied):
- N_synth_kgha
Synthetic N fertilizer (kg N/ha).
- N_org_kgha
Organic N inputs (kg N/ha).
- TMP
Mean temperature (degrees C).
- WaterInput_mm
Precipitation + irrigation (mm). Computed from precip_mm + irrig_mm if absent.
- precip_mm
Precipitation (mm).
- irrig_mm
Irrigation water applied (mm).
- PET_mm
Potential evapotranspiration (mm).
- k_n_synth
Numeric. Rate constant for N inhibition by synthetic N (default 0.0035). At 200 kg synthetic N/ha, Ndfa reduces to ~50 percent of reference.
- k_n_org
Numeric. Rate constant for N inhibition by organic N (default 0.0018). Weaker than synthetic because organic N mineralizes slowly (Peoples et al. 2009).
- t_opt
Numeric. Optimal temperature for nitrogenase (default 25 degrees C).
- t_sigma
Numeric. Width of temperature Gaussian (default 8).
Value
Data frame with added columns:
- Ndfa, NHI, BGN, Leguminous_share
BNF parameters.
- N_total_kgha
Total N input (synthetic + organic).
- f_N_symb
N inhibition factor (0-1).
- f_temp_symb
Temperature factor (0-1).
- f_water_symb
Water availability factor (0-1).
- f_env_symb
Combined environmental factor.
- Ndfa_adj
Adjusted Ndfa after environmental correction.
- CropBNF
Crop BNF via NPP method (Mg N).
- CropBNF2
Crop BNF via Anglade method (Mg N).
- Alpha1, Alpha2
BNF per unit product N.
Details
Estimates symbiotic biological nitrogen fixation by crop legumes using two complementary methods, with optional environmental adjustments for nitrogen fertilization, temperature, and water availability.
**N fertilizer inhibition**: Mineral N inhibits nitrogenase and nodule formation (Salvagiotti et al. 2008; Streeter & Wong 1988). Synthetic N inhibits more strongly than organic N: $$f_N = \exp(-k_{synth} \times N_{synth} - k_{org} \times N_{org})$$
**Temperature**: Gaussian centred at T_opt, reflecting thermal sensitivity of nitrogenase (Hungria & Vargas 2000): $$f_T = \exp\left(-\frac{(T - T_{opt})^2}{2 \sigma^2}\right)$$
**Water stress**: BNF declines under drought via carbon and oxygen effects on nodules (Serraj et al. 1999). Modelled via aridity index: $$f_W = \min(1, \text{AI} / 0.65)$$
Requires `Names_BNF` and `BNF` objects from `load_general_data()`.
References
Anglade J et al. (2015) Nutrient Cycling in Agroecosystems 103:37-56.
Hungria M, Vargas MAT (2000) Field Crops Research 65:151-164.
Lassaletta L et al. (2014) Biogeosciences 11:2889-2907.
Salvagiotti F et al. (2008) Field Crops Research 108:1-13.
Serraj R et al. (1999) Plant Physiology 120:577-586.
Examples
if (FALSE) { # \dontrun{
load_general_data()
# Basic usage (no environmental adjustment):
crop_data |> calc_crop_bnf()
# With environmental data:
crop_data |>
dplyr::mutate(
N_synth_kgha = 80, TMP = 18,
precip_mm = 600, PET_mm = 900
) |>
calc_crop_bnf()
} # }