Nitrogen mineralisation in the soil of indigenous oak and pine plantation forests in a Mediterranean environment

Nitrogen mineralisation in soils of various forest sites (pine plantation, natural and thinned oak) at Uludağ University campus in Bursa, Turkey was investigated continuously over a year by the field incubation method. Net nitrogen mineralisation and nitrification rates varied depending on sampling dates. Although nitrogen mineralisation and nitrification rates increased in the spring and summer months, there was no seasonal variation in the soils of the examined forests. Annual net nitrate (NO3−–N) accumulation in the upper soil layer (0–5 cm) was higher in Oak I and Oak II (14 kg ha y−1 and 12 kg ha y−1) than in the pine plantation (8 kg ha y−1). While annual net NO3−–N accumulation (0–5 cm) varied between the oak forests (possibly due to forest management practices), annual net Nmin values were similar in these forests. No significant correlation was found between the examined soil parameters and net nitrification and mineralisation rates in the soils (P > 0.05). These results indicate that tree species and forest management practices play important roles in N cycling in forest ecosystems.