Harmonization of the determination of phosphorus and potassium in soil according to national and international methods

Abstract

Goal. To harmonize national and international methodical approaches to determining the level of phosphorus and potassium in soils. Methods. Statistical-mathematical analysis of agrochemical research data, parallel tests in various laboratories, and literary and stock data on soil nutrient availability. Results. Regression equations were developed to convert the results of determining the content of mobile phosphorus and potassium in the soil according to the standardized methods of Chyrikov and Machyghin into predicted data according to the Mehlich 3 (for RK) and Olsen (for P) methods. It was established that such conversion has certain exceptions, so it is better to use it only for a qualitative assessment of the level of soil supply with these nutrients. The following levels of phosphorus (P) and potassium (K) content according to Mehlich 3 are proposed for a qualitative assessment of soil in Ukraine: low — less than 6 mg/kg and 110, medium — 6–24 and 111–155, high — 25–42 and 156–200 mg/kg, high — 43–60 and 201–245, very high — over 60 and 245 mg/kg, respectively. According to Olsen, it is recommended to evaluate the availability of mobile phosphorus in the soil according to the following levels: low — less than 8 mg/kg, medium — 8–15, high — 16–22, high — 23–30, very high — over 30 mg/kg. Conclusions. The results of measurements of the content of mobile phosphorus and potassium according to the Machyghin (DSTU 4114) and Chyrikov (DSTU 4115) methods can be converted into results according to the Mehlich 3 or Olsen methods (only for P) for a qualitative assessment of the level of soil supply with these nutrients. Recalculation of the results from the Machyghin method gives a better result than from the Chyrikov method.