Simulation of pepper (Capsicum annuum L.) growth stages under different nitrogen fertiliser levels based on three models

The pepper variety 'Sanying' was treated with different nitrogen levels (0.36, 0.72, 1.08, 1.44, 1.80, 2.16, 2.52, 2.88 g/basin) in 2022. The onset, end dates, and the meteorological data of the environment of each growth period were recorded. Simulation models of the effect of nitrogen levels on the growth period of pepper were constructed with physiological development time (PDT), product of thermal effectiveness and photosynthetically active radiation (PAR) (TEP), and growing degree days (GDD) as indices using experimental data from March to September. The models were fitted and verified with experimental data from April to October. The results showed that with the increase of the amount of nitrogen fertiliser, the growth process of pepper showed a significantly delayed trend. The root mean squared errors of the fitting values and observed values during the flowering stage, fruit setting stage, and harvesting stage of peppers were 1.02 days, 1.05 days, and 1.27 days, respectively. The relative errors were 0.71%, 0.88%, and 0.95%, and the coefficients of determination (R-2) were 0.97, 0.96, and 0.94, respectively. Therefore, the PDT model is the optimal model with the highest simulation accuracy to simulate the pepper phenological stage under different nitrogen levels.