Accuracy of compositional nutrient diagnosis for nitrogen and phosphorus in HLB-affected sweet orange across three Florida soil environments

Abstract

Compositional Nutrient Diagnosis (CND) relies on multinutrient gradients associated with crop yield, but its agronomic efficiency is rarely validated through actual yield response to fertilization, particularly in citrus orchards affected by Huanglongbing (HLB), where physiological variability is high. This study evaluated the diagnostic accuracy and agronomic efficiency of CND for nitrogen (N) and phosphorus (P) in ‘Hamlin’ and ‘Valencia’ sweet orange orchards grown in three Florida soil environments (Alaquods, Glossaqualfs, and Quartzipsamments) over three growing seasons. True nutritional status was defined from yield response to fertilization, and CND performance was assessed using diagnostic accuracy metrics and Net Yield Productivity (NYP). Nitrogen exhibited more consistent nutrient–yield relationships and more frequent positive productivity gains across soils, whereas P responses were more variable and strongly influenced by soil characteristics. Quartzipsamments showed the most consistent agronomic gains for N, whereas Alaquods presented the lowest diagnostic efficiency for both nutrients. ‘Valencia’ exhibited more stable performance across soils, while ‘Hamlin’ showed greater variability and stronger responses for N than for P. These results indicate that, under the evaluated HLB-affected citrus production conditions, the agronomic efficiency of CND varied according to nutrient type, Florida soil environment, and variety. Generalized norms provided a useful alternative when local nutrient–yield relationships were weak, whereas environment-specific norms provided greater agronomic benefit when these relationships were consistently expressed. Overall, the agronomic usefulness of CND for N and P is not fixed, but depends on how consistently nutrient–yield relationships are expressed across soils, varieties, and nutrients.