Theoretical Determination of a Critical Nitrogen Dilution Curve Based on the Carrot Case Study

The objectives of the present study were to: (a) formulate a general dilution equation for a critical nitrogen percentage in a leaf (Nc); (b) monitor dilution function of carrot as a case study; (c) demonstrate applicability of digital color imaging to monitor total nitrogen (N_tot) in crops. Carrot (Daucus carota) was grown on loess soil at five N_tot application rates. N_tot weight (kg/ha) was obtained by standard laboratory analysis and by image processing. Total yield of the treatments was the sum of canopy and roots dry matter. A new logistic decay curve Nc = a/[1 + (W/W₀)^b] agreed with experimental data. Nc (g/kg) is the critical nitrogen level, a and b are coefficients, and W/W₀ is the relative dry matter biomass. Values of Nitrogen Nutrition Index (NNI) ≥ 1.0 indicated that there was no nitrogen deficiency in treatment larger than 100% application of N_tot. The weight of nitrogen in form of multiplication of the dry leaves weight (W) and N percent is suitable for the determination of nitrogen status. The availability of image-based data for N percent is faster, timely and less expensive than that of laboratory test. Applicability of digital color camera to monitor N_tot in crops instead of laboratory test was successfully demonstrated.