Critical nitrogen

Two approaches are currently implemented within CropML_NL for the determination of the critical N concentration (i.e., the concentration below which the crop is stressed and above which further N uptake determines N luxury consumption), both based on the concept of critical nitrogen diluition curve.

The first approach (Greenwood et al., 1990) links critical nitrogen concentrations in the aboveground biomass (N%) and crop dry weight (W, t ha-1) for both C3 and C4 crops in the vegetative stage as:

where a and b are empirical parameters. Default values for rice are a = 3.53 and b = 0.28 for Japonica rice (Ata-Ul-Karim et al., 2013) and a = 5.35  and b = 0.5 for Indica rice (Sheehy et al., 1998).

The second approach (Confalonieri et al., 2011) reproduces the effect of leaf selfshading in remobilizing (recycling) N from senescent leaves through an inverse of the fraction of radiation being intercepted by the canopy while estimating critical N diluition curve:

Nmat (mg/g) is a parameter indicating the critical N concentration at physiological maturity, 1−e−k×LAI is the fraction of solar radiation intercepted by the canopy, k (−) is the extinction coefficient for solar radiation, and LAI (m2/m2) is the total leaf area index. Values of 10 mg/g and 0·5 were used for Nmat and k in rice simulations.

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