Table 6.

Coefficients of determination (R²) of regressions between integrated SPAD (SPADi) values and integrated nitrogen nutrition index (NNIi) for each phenological stage in each of the three sweet pepper (Capsicum annuum) crops independently, and for the three crops together. Each crop was subjected to five different N treatments with four repetitions. According to the Akaike information criterion, the best-fit regression model (exponential, linear, power, quadratic, and natural logarithm) is shown. Also, the fitted equation and standard error of the estimate (SEE) are presented. All regressions were highly significant at p-value <0.001. N is the number of data points of regressions.

Crop	Phenological Stage	Regression	Equation	R 2	SEE (±NNIi)	N
2014	Vegetative	Quadratic	NNIi = −0.004∙SPADi2 + 0.4324∙SPADi − 10.5	0.89	0.04	20
	Flowering	Linear	NNIi = 0.047 SPADi − 1.6315	0.95	0.05	20
	Early fruit growth	Exponential	NNIi = 0.087e0.038∙SPADi	0.92	0.05	20
	Harvest	Exponential	NNIi = 0.082e0.0362∙SPADi	0.97	0.04	20
2016	Vegetative	Natural Logarithm	NNIi = 2.127∙log(SPADi) − 7.319	0.80	0.07	20
	Flowering	Linear	NNIi = 0.043∙SPADi − 1.5753	0.88	0.07	20
	Early fruit growth	Natural Logarithm	NNIi = 3.079∙log(SPADi) − 11.741	0.88	0.07	20
	Harvest	Natural Logarithm	NNIi = 1.981∙log(SPADi) − 7.1744	0.86	0.05	20
2017	Vegetative	Natural Logarithm	NNIi = 1.517∙log(SPADi) − 4.9752	0.86	0.07	20
	Flowering	Natural Logarithm	NNIi = 2.379∙log(SPADi) − 8.5002	0.92	0.06	20
	Early fruit growth	Exponential	NNIi = 0.064∙e0.0453∙SPADi	0.96	0.06	20
	Harvest	Natural Logarithm	NNIi = 1.349∙log(SPADi) − 4.523	0.87	0.08	20
2014 + 2016 + 2017	Vegetative	Quadratic	NNIi = −0.002∙SPADi2 + 0.1935∙SPADi − 4.57	0.82	0.07	60
	Flowering	Quadratic	NNIi = −0.002∙SPADi2 + 0.2031∙SPADi − 5.5115	0.73	0.11	60
	Early fruit growth	Power	NNIi = 0.00007∙SPADi2.3116	0.85	0.08	60
	Harvest	Natural Logarithm	NNIi = 1.125∙log(SPADi) − 3.6978	0.64	0.11	60