Long-term N Mineralization
Sampling Frequency: Annually
N mineralization and nitrification are measured by estimated changes in accumulated and in situ nitrogen pool sizes, the difference equaling the assumed net mineralization potential. Two methods of estimating mineralization and nitrification rates are used: a short-term buried bag (in field) incubation that accounts for the daily and seasonal temperature fluctuations and a long-term incubation that assesses soil organic matter quality with respect to mineralizable N.
Triplicate 10 g fresh weight sub samples for each of 10 extraction intervals (thirty 10g subsamples) are taken from the composite soil sample of selected plots. The composite soil samples (T0) are immediately brought to the laboratory and subsampled for inorganic N analysis and soil moisture. The subsamples are weighed into flasks, adjusted to soil field capacity (22%), loosely capped, and placed into a darkened incubation chamber at 25 degrees C. At each extraction interval (1, 2, 4, 6, 9, 12, 15, 20, 28 and 36 weeks), appropriate flasks are removed and extracted with 1 M KCl. Analyze extract for inorganic-N. Periodically check a subset of flasks for moisture loss and adjust as needed.