Evaluation of five soil nutrient extraction methods for practical assessment of phosphorus and potassium availability for tomato ( Solanum lycopersicum) ) fertilization in Indonesia

Phosphorus and potassium are essential nutrients for plant growth and development. Plants will achieve optimum biomass and production if phosphorus and potassium needs are met through fertilization. Determining the availability of phosphorus and potassium in the soil is essential because it is related to decisions on phosphorus and potassium fertilizer rate recommendations. In this study, we evaluated 5 common phosphorus and potassium extraction methods by correlating the indicated soil nutrient levels to the relative biomass dry weight of tomato plants. The phosphorus and potassium extraction methods used were Mehlich-1, Bray-1, Morgan-Wolf, Ammonium acetate, and HCl-25%. Mean Root Error (MRE) and Root Mean Square Error (RMSE) were used to determine the precision of the linear regression equation model in predicting the relationship between phosphorus and potassium soil extraction methods and the relative biomass dry weight of tomato plants. The correlation of the soil extraction methods used in Andisols with the relative biomass dry weight of tomato was highly significant and very strong (r > 0.75) suggesting that Bray-1 was the best soil-phosphorus extraction method (P-r = 0.88; P-MRE = 0.10; P-RMSE = 4.44), while HCl-25% was the most suitable for soil-potassium extraction (K-r = 0.90; K-MRE = 0.05; K-RMSE = 2.95). The results of the two extraction methods will be used to determine the dosage of phosphorus and potassium fertilizers (nutrient sufficiency approach) for tomato plants grown in Andisols.