Comparison of Slow-Release Nitrogen and Water-Insoluble Nitrogen Methods for Fertilizers

Abstract

A collaborative study was made to compare AOAC method 2.057 for determination of water-insoluble organic nitrogen (WIN) with the slow-release nitrogen method adopted as official, first action in 1965. Both methods showed improvement in precision over the 1964 study. The betweenlaboratory standard deviation of the WIN method was 6.16 in the 1964 study and 1.03 in 1966; the slow-release method was 4.42 in 1964 and 0.65 in 1966. With the improved precision, the two methods will give significantly different results on some types of fertilizers. This difference will affect the calculation of the activity index of urea formaldehyde. It is recommended that both methods be retained in Official Methods of Analysis.

Fertilizers

“…The AOAC collaboratively compared a slow-release nitrogen method and a water-insoluble nitrogen method (4, 28). Precision of the water-insoluble nitrogen results was improved over an earlier collaborative study from an among laboratory standard deviation of 6.16 to 1.03%.…”