Quantifying the Effect of Temperature on Ammonium Bicarbonate Diethylene Triamine Penta‐acetic Acid Extractable Potassium and Developing a Novel Correction Factor to Express the Data

Abstract

Soil testing is an important diagnostic tool in determining nutrient imbalances and providing a basis for fertilizer application. The reliability and reproducibility of nutrient determination in soils is affected by the temperature of the extracting solution. We carried out laboratory investigations to account for the effect of temperature of the extractant on ammonium bicarbonate diethylene triamine penta‐acetic acid (ABDTPA)–extractable potassium (K), and developed a correction factor to standardize the results to a standard temperature. Forty soil samples with a wide range of characteristics were analyzed for ABDTPA‐extractable K at five laboratory temperatures, ranging from 15 to 35 °C. The soils represented soil textures varying from loamy sand to heavy clays. The electrical conductivity (EC) ranged from 0.14 to 47.8 dS m⁻¹ (average 2.78 dS m⁻¹), pH from 7.2 to 8.4 (average 8.0), lime from 3.7 to 22.4% (average 12.9%), organic matter from 0.25 to 1.43% (average 0.72%), and ABDTPA‐extractable K at 25 °C from 42 to 489 mg kg⁻¹ (average 167 mg kg⁻¹). The ABDTPA‐extractable K was positively correlated with temperature. Average values increased from 129 mg kg⁻¹ at 15 °C to 225 mg kg⁻¹ at 35 °C with R² ranging from 0.63 to 0.997, and regression coefficient “b” ranged from 2.14 to 8.94. From the data, a temperature correction factor, Y  =  2.85 + 0.01X (R²  =  0.46), was developed to convert ABDTPA‐extractable K determined at room temperature to a standard temperature of 25 °C.

Keywords:

• ABDTPA‐extractable K
• temperature correction factor

ACKNOWLEDGMENTS

Thanks are due to Dr. Malcolm E. Sumner, agricultural and environmental consultant, for his technical guidance in improving this manuscript.