Soil nitrogen transformation rates (potential net N transformation, mineralization, ammonification, nitrification and depolymerisation) (Schimel & Bennett, 2004) are measured by determination of the total K2SO4 or KCl extractable nitrogen (TAN), the available mineral N (NH4+-N and NO3--N) and the dissolved organic N (DON) forms before and after a soil incubation in the laboratory at 80% of water holding capacity (WHC) and 30°C for 14 days (Allen, Grimshaw & Rowland 1986), and extracted with K2SO4 0.5M or KCl 1M in a 1:10 ratio. The incubation, extraction and the colorimetric analyses of DON, NH4+-N and NO3-N in the soil´s extract are made following the procedure describe below. The amount of N forms in the soils is calculated using a linear calibration curve with standards and expressed as mgr N kg-1 soil and rates are expressed as mgr N kg-1 soil day-1.