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Nitrogen Mineralization Potential of Arid and Semiarid Soils of Morocco

INRA-MIAC Project B.P. 290, Settat, Morocco

R. L. Westerman^*

Dep. of Agronomy, Oklahoma State Univ., Stillwater, OK 74078

P. N. Soltanpour

Dep. of Agronomy, Colorado State Univ., Ft. Collins, CO 80523

* Corresponding author.

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 (N_o) 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 N_o 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 N_o and 0.06 to 0.274 week^–1 for k. The values ranged from 164 to 391 mg N kg^–1 of soil for N_o and 0.024 to 0.212 week^–1 for k, using the hyperbolic model. The lowest average N_o 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 N_o and k values in soils if a nonlinear least-squares fitting technique is used.

Joint contribution from INRA-MIAC and the Oklahoma Agric. Exp. Stn. Journal no. 5289.

Received for publication June 16, 1988.