Nitrogen Mineralization Potential of Arid and Semiarid Soils of Morocco

Abstract

An accurate estimate of N mineralized from soil organic matter during the growing season is required to make correct N fertilizer recommendations for crops. In Morocco, very little information regarding the N-supplying power of soils is available. These studies were conducted to determine N-mineralization potential (No) and rate constant (k) values, N flux, and instantaneous rate of reaction for soils of the Chaouia region of Morocco. Fourteen soils were selected and net mineralizable N during 16 wk of incubation at optimum moisture and temperature was determined for each soil. Exponential and hyperbolic models were used to describe net mineralization, and No and k values for each soil were determined using nonlinear least-squares regression. Values using the exponential model ranged from 120 to 241 mg N kg−1 of soil for No and 0.06 to 0.274 week−1 for k. The values ranged from 164 to 391 mg N kg−1 of soil for No and 0.024 to 0.212 week−1 for k, using the hyperbolic model. The lowest average No values for different soils were shown to occur in Palexerolls, which are shallow soils approximately 35 cm deep that have received very low N input. Calculations using the exponential and hyperbolic models indicated the active fraction of total N in these soils varied from 7 to 22% and 10 to 36%, respectively. This study supported earlier reports that a single exponential model as well as a hyperbolic model can be used to estimate reliable No and k values in soils if a nonlinear least-squares fitting technique is used.