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

Nitrogen mineralization potentials (No) from the organic fraction pres ent in the Ap horizon of 8 various cultivated soils were quantified us ing STANFORD and SMITH'S method slightly modified at 28 +/- 2-degrees- C, instead of 35-degrees-C, under optimum soil water conditions. The r esults 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 con stant of mineralization was low (K = 0,046 +/- 0,005 week-1). The No w as high and represented about 11,7% of the total organic N. Loam claye y soils: the K value in these soils was slightly higher (0,051 +/- 0,0 08 week-1) than that in the alluvial soils. The No was moderate and co rresponded to about 6,2% of the total organic nitrogen. Hydromorphous soils: these soils presented a lower K (0,039 week-1); this fact indic ates that the mineralization was very steadly over time. Since the amo unt of total nitrogen in these soils is important (2,25 parts per thou sand) 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 rep resented 9,5%. Salt clayey soils: these soils present a high rate cons tant of mineralization (0,073 week-1) but a very low percentage of pot entially mineralizable nitrogen (4,5%). A pot experiment carried out o n 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.