A Chemical Index of Soil Nitrogen Availability

Abstract

MANY laboratory methods of obtaining an index of the availability of soil nitrogen to plants have been proposed, but biological procedures involving estimation of the amount of nitrogen mineralized when soil is incubated under aerobic conditions at 28°-35° C for 1–4 weeks have been generally preferred¹. However, recent work has shown that the results of these incubation procedures are greatly affected by the method and duration of storage of the soil sample before analysis. This has led to a renewal of interest in chemical methods, because it seems likely that the results of chemical methods will be less affected by preliminary handling and storage of the soil sample than the results of incubation methods. A chemical approach to the problem of obtaining an index of soil nitrogen availability is also encouraged by the experience that chemical methods of analysis are usually simpler and more rapid and precise than biological techniques. Studies in our laboratory of chemical methods of obtaining an index of the availability of soil nitrogen to plants have led to development of the following procedure which appears suitable for routine analysis of soils.