Mineralization of nitrogen compounds in a soil under an oxalis birch forest

The total mineralization of nitrogen in the AO-A1 (0–6 cm), A1 (6–11 cm), and A2 (11–21 cm) horizons of a soddy pale-podzolic soil under an oxalis birch forest in Yaroslavl oblast was measured from May to November in 2009 and 2010 and comprised 6.7 ± 0.9, 3.0 ± 0.4, and 5.5 ± 0.6 g of N/m2 in 2009 and 5.6 ± 0.5, 2.5 ± 0.2, and 2.1 ± 0.5 g of N/m2 in 2010, respectively. The total nitrification reached 0.4 ± 0.1, 1.1 ± 0.2, and 1.4 ±0.1 g of N/m2 in 2009 and 1.0, 0.6, and 0.7 g of N/m2 in 2010. Overall, the amount of mineralized nitrogen in the 21-cm-deep soil layer in 2009 and 2010 constituted 15.2 ± 1.1 and 10.2 ± 0.7 g of N/m2, respectively. The contribution of nitrification to the nitrogen mineralization amounted to 20%. The seasonal variations in the soil temperature and moistening affected the concentrations of ammonium in the upper horizons and the accumulation of ammonium in the AO-A1 and A1 horizons. The combined effect of the temperature and moisture controlled the ammonification in the AO-A1 horizon (R = 0.83 at p = 0.16 in 2010), the nitrification in all the studied horizons (R = 0.86 at p= 0.13 in 2009), and the ammonia emission from the soil surface (R = 0.92 at p = 0.06 in 2010). A correlation between the seasonal dynamics of the ammonification and the CO2 emission was found for the AO-A1 horizon (r = 0.64 at p = 0.16 in 2010) and was absent in the deeper layers of the soil profile. The nitrogen losses from the soil surface due to the ammonia emission in the investigated periods reached 95 ± 31 g of N/ha (2009) and 33 ± 30 g of N/ha (2010).