EFFECTS OF FERTILIZATION ON NET NITROGEN MINERALIZATION AND NITRIFICATION RATES AT DIFFERENT LAND-USE TYPES: A LABORATORY INCUBATION

Abstract

This study was carried out in order to determine the net nitrogen mineralization and nitrification rates occurring at different land-use types in laboratory incubation of 020 cm upper soil layer using the 28 days aerobic within different fertilization applications and 7 days anaerobic incubations. Three sampling points were observed for monthly and weekly mineralization and nitrification rates consisting from one old abandoned agricultural land (AAL) (no application for 20 years), one shrub-land (SL) and one oak forest land (OFL). The samplings were executed on June 06, 2009. The fertilizers were applied as follows: 390 and 600 kg NH(4)(+)-N addition/ha, 420 and 770 kg NO(3)(-)-N addition/ha, as well as 260 and 520 kg urea N addition/ha. Following the fertilizers gravimetrically, 60% water were added to soil samples to make fertilization available. To better understand the effects of fertilizer addition, we incubated control samples with and without water addition both without fertilizer addition. Land-use type had higher impacts on net nitrogen mineralization, net nitrification than urea N addition or NH(4)(+)-N + NO(3)(-)-N fertilizer addition. After fertilizer addition, the net nitrogen mineralization was highest for all fertilizer applications at OFL but lowest for AAL. The net nitrification was seen at OFL for each type of fertilizer applications with the highest net nitrification at U2 (0.342 mg NO(3)(-)-N kg(-1)) and lowest at AN1 (0.110 mg NO(3)(-)-N kg(-1)) while both SL and AAL could produce no nitrate-N, with the exception of AAL AN 1 applications. There is no significant difference between nitrification rates of OFL for any type of fertilizer applications according to Dunnett T3 test (p<0.05). Ammonium-N production under waterlogged conditions provided variation for both pre and post incubation with lowest NH(4)(+)-N production at OFL (3.711 mg NH(4)(+)-N kg(-1)) and highest at AAL (14.682 mg NH(4)(+)-N kg(-1)). In conclusion, we found that fertilization type and amount had a lower effect than land-use type. Anaerobic laboratory incubations could give controversial results with dry laboratory incubations, especially when the water content of soils was low as in summer (dry soil) conditions. The results revealed that land-use type creates significant differences at the nitrogen transformation rates.