The accuracy of the app mostly depends on the accuracy of the test strips. Test strips typically just give a rough indication of the actual concentration. The graph below gives the results from tests at two temperatures (20 and 4 degrees Celsius or 68 and 41 Fahrenheit). testing results from the TReNDS project by SEGES (agricultural cooperation in Denmark) and Arhus University. The graph shows Nitrate App NO3-N readings after 30 sec and 60 sec at temperatures of 2oC, 10oC and 20oC using lab standard samples. The 60 s Nitrate App readings gave good results, while after 30 s the Nitrate test strips underestimate the nitrate concentations at low temperatures.
From these result, we advise to scan the test strips after 60s (especially in cold weather) and estimated the accuracy of the Nitrate App measurements at ca.+/-From these result, we estimated the accuracy at 30%. The accuracy of conventional lab measurements is ca. +/- 10%.
A known issue with testing strips in general is that the color reaction has a slight temperature dependency. At low temperatures, this leads to an underestimation of the higher nitrate concentrations for which a correction is possible. Note that the app is designed for outdoor use in good light conditions. See also the Tips and Tricks for getting the most accurate readings!
