Improving Sugarcane ( <i>Saccharum Officinarum</i> L.) Nitrogen, Phosphorus and Potassium Fertilization: Evaluation of Soil and Foliar Diagnoses

Effective fertilization management is crucial to balancing agricultural productivity with environmental and economic sustainability. Adjusting fertilizer doses based on field fertility is crucial, but reliable methods remain limited in tropical regions, including for sugarcane (Saccharum officinarum L.). This study evaluated the relevance of soil and foliar diagnoses in determining nitrogen (N), phosphorus (P), and potassium (K) fertility levels in sugarcane fields to improve fertilizer recommendations. We conducted four long-term field trials (6 to 9 years) in contrasting volcanic soils, with annual applications of mineral and organic fertilizers. Soil and foliar diagnoses were performed each year, using standard laboratory soil properties and nutrient concentrations in leaves sampled at 5 to 8 months of growth. We compared these diagnoses to sugarcane nutrition indexes at harvest. Results show that available element stocks were generally better indicators of fertility than raw element concentrations. Across all sites, soil fertility levels corresponded well with nutrition indexes for P and K, and moderately for N. Foliar diagnosis reflected well on nutrition indexes for N and P but was less reliable for K. These findings suggest that soil diagnosis is especially effective for P and K, while foliar diagnosis is better suited for N and P. Adapting fertilizer doses based on these diagnoses could significantly enhance recommendations for growers.