Leaf area index (LAI) can help monitor crop growth and diagnose nitrogen (N) levels in rice. Researchers developed LAI-based N diagnostic models for irrigated lowland rice by studying N application rates and plant densities. They found a strong relationship between LAI and plant N accumulation, as well as a more accurate N nutrition index using relative LAI. The models created can conveniently diagnose the N status of rice in the field, making it easier for farmers to manage their crops effectively.