A Study on Temperature and Time Conditions of Colorimetric Method in Measuring Soil Available Phosphorus

Abstract

Molybdenum blue colorimetric method is one of the standard methods of detecting soil available phosphorus and is crucial to guide variable fertilization. In practice, however, we find that color-developing temperature and stable time could affect test results. To ensure precision, in this paper we conducted a comprehensive experiment under the temperature range from 10°C to 40°C and time range from 0 to 80 minutes after color reaction and compared the test results in single calibration mode with that in repetitive calibration mode. Eventually we optimized temperature and testing time conditions in the two different calibration modes respectively. Under the optimum conditions we conducted a verification test using 55 soil samples which were collected from main crop-growing regions of China. The test results had a better linear correlation with standard results (R 2 = 0.97) and a small mean relative error (MRE = 0.047), which could meet the accuracy requirement of variable fertilization.