Main content area

The application of a modified procedure in nitrogen transformation studies in forest soils

Lunt, H.A.
Agronomy journal 1935 v.27 no.5 pp. 346-355
forest soils, nitrification, incubation, temperature, sampling, environmental factors
A modification in the procedure for sampling and incubating soils is proposed for use primarily in forest soil studies. The essential features of this new procedure are (a) sampling about May 1 with a soil cylinder or tube which cuts out a core of the upper 6 or 8 inches with very little disturbance and (b) incubating this sample out of doors subject to the natural temperature changes but not exposed to the direct sunlight. Glass containers were the most satisfactory. Cardboard, whether paraffined or not, greatly interfered with the accumulation of soluble nitrogen and should not be used. The results of studies carried on with samples from a rather wide range of forest conditions may be generalized as follows: 1. The mull types found in fast-growing hardwood stands nitrify to a considerable degree with the formation of only a relatively small amount of ammonia. 2. The greatest ammonia accumulation occurred in the thick duff found in mature hemlock-hardwood and mature white pine stands. 3. Lime stimulated nitrification in the soil from a white pine plantation but had little effect in a red pine plantation. 4. Soil from a locust stand nitrified to a marked degree and was in extreme contrast in this respect to a young red pine plantation adjoining. Growth of the red pine trees is directly correlated with the nitrifying capacity of the soil. 5. In general, there is an inverse relation between ammonia accumulation and initial acidity and a direct relation between nitrate accumulation and initial acidity. The change in reaction during the incubation period was toward a lesser acidity where ammonification was greatest and toward a stronger acidity where nitrification was greatest. 6. There was no correlation between nitrogen transformation and the amount of other soil constituents as determined by the spot plate method. 7. The procedure followed has proved satisfactory and the results obtained are believed to be more nearly in keeping with nitrogen changes in the natural forest soil than are those obtained under artificial optimum conditions.