MINERALIZATION POTENTIAL OF ORGANIC NITROGEN AND MEASUREMENT OF ITS AVAILABILITY IN CULTIVATED SOILS OF MYZEQE (ALBANIA)

Nitrogen mineralization potentials (No) from the organic fraction present in the Ap horizon of 8 various cultivated soils were quantified using STANFORD and SMITH'S method slightly modified at 28 +/- 2-degrees-C, instead of 35-degrees-C, under optimum soil water conditions. The results of No calculated after a 33 - week incubation according to the first-oder equation N = No (1 - e(-Kt)) showed different values of No and rate constants of mineralization (K). Alluvial soils: the rate constant of mineralization was low (K = 0,046 +/- 0,005 week-1). The No was high and represented about 11,7% of the total organic N. Loam clayey soils: the K value in these soils was slightly higher (0,051 +/- 0,008 week-1) than that in the alluvial soils. The No was moderate and corresponded to about 6,2% of the total organic nitrogen. Hydromorphous soils: these soils presented a lower K (0,039 week-1); this fact indicates that the mineralization was very steadly over time. Since the amount of total nitrogen in these soils is important (2,25 parts per thousand) the percentage of No reached only about 6,5%. Acid clayey soils: the rate constant K was high (0,057 week-1) but the No was relatively low. Expressed as percentage to the total organic N, the No value represented 9,5%. Salt clayey soils: these soils present a high rate constant of mineralization (0,073 week-1) but a very low percentage of potentially mineralizable nitrogen (4,5%). A pot experiment carried out on the same soils under the same conditions of temperature and humidity showed a significant correlation between No and N taken up by the rye-grass after a 9 - week experiment.