Soil and Plant Molybdenum Status in Coconut Palms of the Southern Coastal Plain (AEU 1), Kerala, India

Abstract

Aims:  To assess plant molybdenum concentrations in coconut palms across the Southern Coastal Plain (Agro Ecological Unit 1 of Kerala) and evaluate nutritional status against established sufficiency standards for tree crops. Study Design:  Survey-based field study with spatial sampling. Place and Duration of Study: Forty-seven panchayats across blocks of Agro-Ecological Unit 1 (Southern Coastal Plain), Kerala, India, during the year 2024-25. Methodology: Soil samples at two depths (0-15 cm and 15-30 cm) and corresponding mature leaf samples were collected from 141 geo-referenced locations across 47 panchayats across blocks of Southern Coastal Plain. Available molybdenum in soil was determined using acid ammonium oxalate extraction followed by AAS analysis. Plant tissue samples were digested using di-acid mixture and analyzed for Mo concentration. Spatial variability was assessed through descriptive statistics, and plant nutritional status was evaluated by comparing observed concentrations with established sufficiency ranges for other crops. Results: Soil available Mo showed considerable variation with mean concentration of 0.04 mg kg⁻¹ in both surface (range 0.02-0.07 mg kg⁻¹) and subsurface (range 0.02-0.07 mg kg⁻¹) layers, with majority of soils below critical level. Plant Mo concentrations exhibited considerable spatial variability (CV = 38.34%) with mean of 0.22 mg kg⁻¹ (range 0.15-0.44 mg kg⁻¹). Approximately 89% of sampled locations exhibited plant Mo concentrations below 0.25 mg kg⁻¹, substantially lower than sufficiency ranges for rice (0.4-1.0 mg kg⁻¹) and fruit trees (0.10-2.00 mg kg⁻¹), indicating widespread deficiency directly attributable to inadequate soil Mo availability in sandy soils. Conclusion: Molybdenum deficiency is widespread in both soil and coconut palms across the Southern Coastal Plain, likely constraining Mo-dependent enzyme activities. Strategic interventions including adequate Mo application and soil pH management are essential to elevate Mo availability and plant uptake for improved productivity.