Assessment of Soil Nutrient Status and Fertiliser Recommendation Systems for Rubber Plantations in Edo State, South South Nigeria

This study assesses the soil nutrient status of rubber plantations in Edo State, located in Nigeria's South South geopolitical zone, and evaluates the suitability of existing fertiliser recommendation systems for rubber cultivation. Rubber is a major industrial crop in Edo State, with significant employment and export earnings contributions, yet systematic soil fertility data underpinning fertiliser recommendations for rubber in the state are outdated, and practitioners rely on generic recommendations not calibrated to current Edo State soil conditions. Using a professional agronomic advisory design, composite soil samples were collected from 0 to 20 cm and 20 to 40 cm Soil Sciencehs across 50 rubber blocks in Ovia North-East, Orhionmwon, and Akoko-Edo local government areas, representing plantation ages from establishment to 25 years. Samples were analysed for pH, organic carbon, total nitrogen, available phosphorus, exchangeable cations, cation exchange capacity, and micronutrients (B, Zn, Mn, and Cu). Findings were compared against the International Rubber Research Development Board critical thresholds for rubber soils. Findings revealed boron deficiency on 64 percent of sampled plots and zinc deficiency on 51 percent, while macronutrient levels were generally adequate in plantations receiving standard NPK inputs. Long-established plantations (greater than 15 years) showed progressive pH decline and calcium depletion not addressed by current NPK recommendations. The study delivers updated fertiliser and micronutrient recommendations for Edo State rubber plantations by plantation age class, and recommends adoption of leaf analysis as a routine complementary monitoring tool. Keywords: soil nutrients, rubber plantation, fertiliser recommendation, Edo State, micronutrients.