Abstract. Regularly monitoring the variations in soil composition is an essential part of proper cultivation management. Some conventional soil characterization methods are often costly and require experienced labor. The spectroscopic method is a simpler procedure that minimizes experimental steps and is faster and more economical than conventional methods. Wide-ranging analytical methods have been developed to determine soil phosphorus concentrations in the field; however, no method has been commercialized. Analytical methods based on colorimetric Mehlich-3 and Lancaster soil tests, developed to reduce measurement time in laboratories in the U.S. and South Korea, have been efficient. However, due to laboratory procedures, the soil was pretreated and not verified with field soil. We tested the rapid colorimetric method, which is for on-site plant-available soil phosphorus tests in the field and allows reduced analysis time. The target accuracy of the field tests was >70% correlation with laboratory test results. This method consists of three steps: fast extraction, fast filtration, and fast color development. In a comparison of the rapid colorimetric method and the standard laboratory procedure, the R2 values were 0.78, 0.71, 0.72, and 0.74, respectively, for field soils collected in four regions of South Korea. However, the results showed significant differences in some areas. When the moisture content and electrical conductivity of soil from each region were included in the multiple regression analysis, the cross-validation results showed superior output with no significant difference (p > 0.05). Keywords: Colorimetry, Phosphorus, Precision agriculture, Sensor, Soil.

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