Evaluation of tissue phosphorus concentrations as diagnostic tool for phosphorus nutrition in corn

Phosphorus (P) management in corn (Zea mays L.) traditionally relies on soil testing, but other diagnostic tools, such as tissue analysis, can be used to assess nutrient management. This study aimed to evaluate plant tissue analysis, Normalized Difference Vegetation Index (NDVI), and Soil Plant Analysis Development (SPAD) readings as diagnostic tools and identify the critical P tissue concentration (CPTC) in two different growth stages of corn in relation to response to P fertilizer. Field experiments were conducted at 30 site-years in Kansas. Fertilizer treatments included four different phosphorus rates and a control. Whole plant tissue samples and NDVI were collected at the V6 growth stage, and ear leaf samples and SPAD were collected at the R1 growth stage. The CPTC was determined using linear plateau and quadratic plateau models, and model averaging was performed for final estimation. Results indicated that the average CPTC in the whole plant at V6 and the ear leaf at R1 were 5.5 and 3.3 g kg⁻¹, respectively. Regression analysis revealed that as the P tissue concentration increases, the optimum fertilizer recommendation rate decreases with R² of 0.26 and 0.25 for V6 and R1, respectively. Correlation analysis highlighted that NDVI and SPAD correlation displayed some potential for assessing P in corn. Correlation and regression analysis showed a moderate correlation between plant P tissue concentration at V6 and leaf P tissue concentration at R1 (r = 0.50 and R² = 0.25). This study contributes valuable insights for phosphorus management in corn, providing CPTC and fertilizer calibration and highlighting diagnostic tools’ shortcomings and potential.