Gross rates of N turnover were investigated during wet season (May 2011), dry season (February 2012), and during the transition from dry to wet season (October 2011), thus accounting for the main seasons of tropical ecosystems in the Mt. Kilimanjaro region.Gross ammonification and nitrification rates were measured with the 15N soil pool dilution method (Davidson and others 1991; Dannenmann and others 2006). We used composite sieved-soil samples which were incubated on site after 15N labeling. At every site (100 m 9 100 m), samples from 3 replicated subplots were extracted at t1 = 0.5 h and t2 = 24 h after labeling and single rates were used to calculate mean turnover rates for a given site and sampling date.

Investigation of gross rates is acomplished to get information about N turnover in the mineral soil.