Modeling the Leaf Area Dynamics of Sweet Potatoes under Varying Nitrogen Conditions

Understanding the leaf area index (LAI) dynamics of sweet potatoes grown under different nitrogen conditions is helpful for accurate yield estimation and management of nitrogen stress and fertilization. Therefore, the aim of this study was to clarify: 1) the effects of the nitrogen application rate (NiAR) on the LAI dynamics of sweet potatoes using logistic curves including the effective cumulative temperature and 2) the validity of the developed LAI estimation model considering the effects of NiAR. The results revealed that a higher NiAR resulted in a significantly higher maximum LAI and leaf expansion rate than a lower NiAR. The effects of NiAR on the thermal times of leaf expansion start and leaf senescence start differed among sweet potato cultivars. These differences may be related to the growth characteristics of the sweet potatoes grown under varying NiAR conditions. These results demonstrate that the LAI estimation model should be used separately, depending on the NiAR for each cultivar. Then, the applicability of the developed model was verified. The results showed that the accuracy of the LAI estimation was conditionally improved by using different model parameter configurations for NiAR. The reason for the improved accuracy could be that nitrogen is one of the dominant factors influencing the shoot growth dynamics of sweet potatoes. These results demonstrated the effectiveness of the developed model for LAI estimation using different NiAR configurations; however, further research is required to improve the estimation accuracy, robustness, and its applicability in various situations.